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Post by swamprat on Feb 2, 2016 18:09:08 GMT -6
About The LIGO Gravitational-Wave Rumor. . .By: Shannon Hall | January 13, 2016
The physics and astronomy world is all agossip: has LIGO heard its first black-hole merger?
Artist's concept of gravitational waves produced by closely orbiting black holes embedded in a 2-dimensional sheet. K. Thorne (Caltech) / T. Carnahan (NASA GSFC)
Rumors are swarming on social media that the newly upgraded LIGO, the Advanced Laser Interferometer Gravitational-Wave Observatory or aLIGO, has finally seen the gravitational-wave signature of two stellar-mass black holes spiraling together and merging. Maybe even two such events since September. Or not.
Such an observation would confirm one of the most elusive predictions of Einstein’s general theory of relativity, and it would also open a new field of cosmic observation: gravitational-wave astronomy.
- See more at: www.skyandtelescope.com/astronomy-news/about-this-weeks-gravitational-wave-rumor/#sthash.lWap566k.dpuf
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Post by Deleted on Feb 2, 2016 18:49:54 GMT -6
The current excitement could easily be a false alarm. Even if LIGO has a promising signal, it may be a false test signal planted as a drill. It's been done before, in 2010 near the end of LIGO's last pre-upgrade run. Three members of the LIGO team are empowered to move the mirrored blocks by just the right traces in just the right way. Only they know the truth, and the test protocol is that they not reveal a planted signal until the collaboration has finished analyzing it and is ready to publish a paper and hold a press conference. “Blind tests” like this are the gold standard in all branches of science. - See more at: www.skyandtelescope.com/astronomy-news/about-this-weeks-gravitational-wave-rumor/#sthash.lWap566k.aYpc84tx.dpuf____________________________________________________________ but, 2 drills since September? Makes you wonder how (and why) this type of "gossip" gets started great stuff, swampster!
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Post by swamprat on Feb 8, 2016 19:03:21 GMT -6
Scientists to Provide Update on the Search for Gravitational Waves on Feb. 11FOR IMMEDIATE RELEASE February 8, 2016
BATON ROUGE and LIVINGSTON, LA – Journalists are invited to join members of LIGO Livingston and LSU for a live viewing event as the National Science Foundation brings together scientists from Caltech, MIT and the LIGO Scientific Collaboration this Thursday, Feb. 11, at 9:30 a.m. CST at the National Press Club, or NPC, for a status report on the effort to detect gravitational waves – or ripples in the fabric of spacetime – using the Laser Interferometer Gravitational-wave Observatory, or LIGO.
The LIGO Livingston Observatory will host a press conference at that time, and will show the main half-hour network-streamed NPC conference to the press, LIGO scientists and engineers, representatives from regional collaborating universities, community partners and political offices. Immediately afterwards, a local program focusing on Louisiana’s role in LIGO and LIGO’s contributions locally will be presented. Scientists will be on hand to answer questions, provide guided tours and interviews.
A simultaneous screening event will be held on campus at LSU’s 130 Nicholson Hall in Baton Rouge. LSU Physics & Astronomy faculty will be on hand to answer questions.
Members of the media are invited to all of the events. Please RSVP to the contact listed below the event location: WHEN: Thursday, Feb. 11 9:30 a.m. CST Doors open 9 a.m. for media to setup Directions: ligo.caltech.edu/LA/page/Directions-for-public
Directions | LIGO | Livingston ligo.caltech.edu Directions to LIGO. Take I-12 towardsLivingston/Frost (East from Baton Rouge, West from New Orleans). Take exit 22. Proceed North on Highway 63 (left from Baton Rouge ...
WHERE: LIGO Livingston Science Education Center Auditorium 19100 LIGO Lane Livingston, La. 70754 RSVP to Dawn Jenkins at djenkins1@lsu.edu, office 225-578-2935 or cell 225-571-3617 LSU Dept. of Physics & Astronomy 130 Nicholson Hall Baton Rouge Campus Tower Drive Baton Rouge, La. 70803 RSVP to Michael Cherry at cherry@phys.lsu.edu, 225-892-2262 or cell 225-892-1101
LIGO, a system of two identical detectors carefully constructed to detect incredibly tiny vibrations from passing gravitational waves, was conceived and originally built by MIT and Caltech researchers and funded by the National Science Foundation, with significant contributions from other U.S. and international partners including LSU. The twin detectors are located 1,865 miles apart in Livingston, La., and Hanford, Wash.
LSU is a major participant in the LIGO experiment. LSU Physics & Astronomy Department Professor Joseph Giaime is LIGO Livingston Observatory Head, and LSU Professor Gabriela González is spokesperson and leads the 15-nation international LIGO Science Collaboration with more than 1,000 scientists working on the project. González will be a featured speaker describing the science results at the Washington, D.C., press conference. The LIGO lab in Livingston is also located on LSU property.
For those unable to travel to the observatory, the LSU Physics & Astronomy Department will also show a live stream of the announcement on campus in Nicholson Hall room 130, including a panel discussion with LSU research faculty.
This year marks the 100th anniversary of the first publication of Albert Einstein’s prediction of the existence of gravitational waves. With interest in this topic piqued by the centennial, the group will discuss their ongoing efforts to observe and measure cosmic gravitational waves for scientific research.
Additional links: LIGO Livingston: ligo.caltech.edu/LA LIGO Scientific Collaboration: www.ligo.org/ LSU Department of Physics & Astronomy: www.phys.lsu.edu/newwebsite/research/relativity.html Contact Ernie Ballard LSU Media Relations 225-578-5685 eballa1@lsu.edu
Dawn Jenkins LSU College of Science 225-578-2935, c. 225-571-3617 djenkins1@lsu.edu
Mimi LaValle LSU Department of Physics & Astronomy c. 225-439-5633 mlavalle@lsu.edu
Alison Satake LSU Media Relations c. 510-816-8161 asatake@lsu.edu
Kathy Svitil Caltech 626-395-8022 ksvitil@caltech.edu
Kimberly Allen MIT 617-253-2702 allenkc@mit.edu
Ivy Kupec NSF 703-292-8796 ikupec@nsf.gov More news and information can be found on LSU’s media center, www.lsu.edu/mediacenter
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Post by swamprat on Feb 8, 2016 19:28:18 GMT -6
Beginning to sound like they may have some developments of some importance. They certainly are inviting a lot of folks, including the National Press Club.....
From: Joseph A Giaime Date: Monday, February 8, 2016 Subject: LIGO event
Dear Colleagues,
I expect that it won't be a surprise to anyone that LIGO Livingston is having a press conference at 9:30 am CST this Thursday, Feb 11; doors open at 9AM. You are all invited!
Our first observational run with the Advanced LIGO detector upgrade ended Jan 12, and we will tell what we've learned on Feb 11. For those in DC, there is a 'main' press conference at the National Press Club at the same time (10:30 EST there); our own Gabriela González, as the collaboration's elected spokesperson, will be there, joined by a small number of other prominent contributors, to make the statement to the gathered science press in town for the AAAS meeting.
Closer to home, the LIGO Livingston press conference will offer fine weather, laboratory ambiance, wide open spaces, and good company. I expect the press, bloggers, various community partners (both outreach and science), as well as delegations from regional universities (LSU, Southern, and Ole' Miss). In addition, LIGO Science Education Center docents will be there to assist visitors with the LIGO SEC exhibits. Staff and students will give tours of the site, and we will accommodate Q/A and interviews from journalists and guests.
We will begin with a live viewing of the main press conference from Washington DC, and then move to the local program, which will focus on LIGO's history in Louisiana, in local universities, education and public outreach, etc. There will be Q&A about the science and these things. One important thread is the public stewardship of this multi-decade effort.
If you are are interested in this but can't make the trip, Mike has set up a viewing of the NPC presentation in Nicholson 130. I wish I could be both places...
When there are links available to the support materials, I'll sent them along.
Best Regards, Joe
Joseph A. Giaime Professor of Physics & Astronomy (LSU), Observatory Head, LIGO Livingston (Caltech)
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Post by swamprat on Feb 11, 2016 9:22:49 GMT -6
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Post by swamprat on Feb 11, 2016 10:05:17 GMT -6
My notes:
LIGO Press Conference
2/11/16 10:30am EST
David Reitze opened the conference: "On Sept. 14, 2015, the two LIGO locations detected a signal simultaneously. The frequency of the signal went up as time moved forward."
They have concluded that this was indeed a gravitational wave. The source was a binary black hole merger. Two black holes, each about 30 times the mass of our sun, collided at about half the speed of light! These objects subsequently became one larger black hole. It has taken 1.3 billion years for this signal to reach Earth.
400 years ago, Galileo started the age of astronomy. On September 14, we started a new phase in astronomy. We will hear more signals, perhaps including those from phenomena we have never heard of.
Just a comment on the abilities of the LIGO instrumentation located in Washington and in Louisiana: Our nearest neighboring star is roughly 3.25 light years away. LIGO has the capability of measuring that distance accurate within the width of a human hair!
In that brief moment of collision, the power generated that created the gravitational wave phenomenon was 50 times the power output of all of the stars in the universe combined!
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Post by swamprat on Feb 11, 2016 11:28:31 GMT -6
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Post by Deleted on Feb 12, 2016 10:33:18 GMT -6
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Post by swamprat on Feb 12, 2016 10:42:05 GMT -6
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Post by auntym on Feb 13, 2016 14:06:58 GMT -6
EINSTEIN'S ORIGINAL HISTORICAL DOCUMENT ON GRAVITATIONAL WAVESThe original historical documents related to Albert Einstein's prediction of the existence of gravitational waves are seen at the Hebrew University in Jerusalem, Thursday, Feb. 11, 2016. In a blockbuster announcement, scientists said Thursday that after decades of trying they have detected gravitational waves, the ripples in the fabric of space-time that #Einstein predicted a century ago. #APPhoto by Sebastian Scheiner AP news story: apne.ws/1PFIF6X CLICK TO SEE ORIGINAL HISTORICAL DOCUMENT: www.facebook.com/APImages/photos/a.10150155125758865.285772.70610223864/10153493271023865/?type=3&theater
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Post by auntym on Feb 13, 2016 14:18:54 GMT -6
President Obama ✔ @potus
Einstein was right! Congrats to @nsf and @ligo on detecting gravitational waves - a huge breakthrough in how we understand the universe.
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Post by lois on Feb 13, 2016 17:13:01 GMT -6
EINSTEIN'S ORIGINAL HISTORICAL DOCUMENT ON GRAVITATIONAL WAVESThe original historical documents related to Albert Einstein's prediction of the existence of gravitational waves are seen at the Hebrew University in Jerusalem, Thursday, Feb. 11, 2016. In a blockbuster announcement, scientists said Thursday that after decades of trying they have detected gravitational waves, the ripples in the fabric of space-time that #Einstein predicted a century ago. #APPhoto by Sebastian Scheiner AP news story: apne.ws/1PFIF6X CLICK TO SEE ORIGINAL HISTORICAL DOCUMENT: www.facebook.com/APImages/photos/a.10150155125758865.285772.70610223864/10153493271023865/?type=3&theaterThis makes me think of timetravel being possible. Not that I don't already believe it.
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Post by patsbox7 on Feb 13, 2016 18:53:23 GMT -6
Centuries ago? Would've been exactly one century last year that General Relativity was theorized... :S Did I get trapped in one of those dang time loops again. God, those pesky black holes. And I swear, if was the Berenstein bears, I don't care WHAT they say, it WAS NOT the BerenSTAIN bears. Wtf is going on here??!!
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Post by swamprat on Feb 17, 2016 19:57:56 GMT -6
Black Holes, Too! Gravitational Wave Find Had Other SurprisesBy Calla Cofield, Space.com Staff Writer February 17, 2016
For the first time in history, scientists have physical proof that pairs of black holes will sometimes circle around each other, collide and mush together to form a single, bigger black hole.
This news of binary-pair detection is extremely significant for astrophysicists, but it was somewhat eclipsed by the simple fact that the Large Interferometer Gravitational Wave Observatory (LIGO) had detected gravitational waves at all. It was the first instance of a direct detection of these ripples through space-time, and it marks the dawn of a new subfield of astronomy.
Vicky Kalogera, a black hole scientist at Northwestern University in Illinois and a member of the LIGO team, said it was appropriate that gravitational waves took center stage last week. But she took some time to talk to Space.com about why the pair of black holes that LIGO detected is particularly strange and exciting, too.
Another first There are two things that make the pair of black holes detected by LIGO interesting to astrophysicists like Kalogera.
One of the ways that black holes are thought to form in the universe is via star death. The hypothesis goes that when massive stars stop burning fuel, all their mass collapses down into a very small area, and creates an object with such a massive gravitational pull that not even light can escape. The gravity is so intense that the laws of physics, as humans understand them, break down.
Individual black holes have been observed in various ways, but until last week, there was no physical proof that black holes can exist as binary pairs that circle around each other and eventually collide.
"We see binary stars all the time," Kalogera told Space.com. It should follow that those star pairs should one day die and form black-hole pairs. And yet, "up until now, we had zero experimental evidence, even indirect, that binary black holes exist. … So, the significance of this discovery from an astrophysics point of view is that it confirms all the theoretical predictions that binary black holes exist."
Without a gravitational-wave detector like LIGO, scientists would never have been able to study binary black holes. Researchers can spot individual black holes in distant locations because material around those objects gets accelerated and radiates light.
But Kalogera said scientists don't expect to see any kind of light radiated from around two black holes spinning toward each other and colliding, because the dynamics of the system would be very chaotic, and not very conducive to material accumulating and staying nearby. So detecting them with light-based telescopes may be impossible.
The fact that the recently upgraded LIGO detector spotted a binary black hole merger so early in the instrument's observation period means there's a chance that scientists will have a lot of black hole data to study in the coming years.
Watch video explaining how colliding black holes make gravity waves: www.space.com/31945-gravitational-wave-detection-black-holes-science.html
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Post by swamprat on Feb 18, 2016 11:00:48 GMT -6
Hawking: Gravitational Waves Could Revolutionize AstronomyBy Ian O'Neill, Discovery News February 17, 2016
In the wake of last week's historic announcement of the discovery of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO), British physicist and black hole theorist Stephen Hawking was quick to congratulate the US-led collaboration, sharing his excitement for the historic news.
"These results confirm several very important predictions of Einstein's theory of general relativity," Hawking said in a BBC interview. "It confirms the existence of gravitational waves directly."
As is becoming clear, the direct detection of these ripples in spacetime not only confirm Einstein's famous theory of general relativity, they open our eyes to a previously "dark" universe. Astronomy uses the electromagnetic spectrum (such as visible light, X-rays, infrared) to study the universe, but objects that do not radiate in the electromagnetic spectrum will go unnoticed. But now we know how to detect gravitational waves, there could be a paradigm shift in how we detect and study some of the most energetic cosmic phenomena.
"Gravitational waves provide a completely new way of looking at the universe," said Hawking. "The ability to detect them has the potential to revolutionize astronomy."
Using LIGO's twin observing stations located in Louisiana and Washington, physicists not only detected gravitational waves; the gravitational waves they detected had a very clear signal that closely matched theoretical models of a black hole merger some 1.3 billion light-years away. Already, from initial analysis of the black hole merger signal, Hawking has realized that the system seems to align itself with theories he developed in the 1970's.
"This discovery is the first detection of a black hole binary system and the first observation of black holes merging," he said. "The observed properties of this system is consistent with predictions about black holes that I made in 1970 here in Cambridge."
Hawking is perhaps most renowned for his work on melding quantum theory with black hole physics, realizing that black holes evaporate over time, leading to his involvement in the fascinating "Firewall Paradox" that is continuing to rumble throughout the theoretical physics community. But here he refers to his black hole area theorem, which forms the basis of the "second law" of black hole mechanics. This law states that entropy, or the level of disorganization of information, cannot decrease within a black hole system over time. A consequence of this theorem is that should two black holes merge, like the Sept. 14 event, the combined event horizon area "is greater than the sum of the areas of the initial black holes." Also, Hawking points out that this gravitational wave signal appears to be in agreement with predictions based on the "no-hair theorem" of black holes, basically meaning a black hole can be simply described by its spin, mass and charge.
The details behind how this first gravitational wave signal of a black hole merger agrees with theory are complex, but it is interesting to know that this first detection has already allowed physicists to confirm decades-old theories that have, until now, had little to no observational evidence.
"This discovery also presents a puzzle for astrophysicists," said Hawking. "The mass of each of the black holes are larger than expected for those formed by the gravitational collapse of a star — so how did both of these black holes become so massive?"
This question touches on one of the biggest mysteries surrounding black hole evolution. Currently, astronomers are having a hard time understanding how black holes grow to be so massive. On the one end of the scale, there are "stellar mass" black holes that form immediately after a massive star goes supernova and we also have an abundance of evidence for the existence of the supermassive behemoths that live in the centers of most galaxies. There is a disconnect, however.
If black holes grow by merging and consuming stellar matter, there should be evidence of black holes of all sizes. But "intermediate mass" black holes and black holes of a few dozen solar masses are astonishingly rare, throwing some black hole evolution theories into doubt.
With the detection of gravitational waves on Sept. 14 came the realization that a black hole binary merger caused it. Two black holes, "weighing in" at 29 and 36 solar masses, collided and merged as one, generating a very clear gravitational wave signal. But, as pointed out by Hawking, how black holes of this specific mass came to being could provide some clues as to how black holes grow.
One thing is clear, however: This is the first time that we've acquired direct evidence of a black hole merger — a key mechanism that underlies black hole evolution theories — so it's good to know we're on the right track.
Watch Hawking's interview video:
- See more at: www.space.com/31960-hawking-gravitational-waves-could-revolutionize-astronomy.html#sthash.jp6kvKgf.dpuf
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Post by plutronus on Feb 19, 2016 3:10:33 GMT -6
I was surprised by the fact that there was virtually no mention about the detection in the local news. However, I did watch Kip Thorne on Aljazeera America (best news channel in the US in my opinion) on the day of the detection. In the theme of JCurio's letter regarding a 'test', Kip Thorne was flat out stating that a gravity wave had been detected. This science news is as big a breakthrough as a cure for cancer will be, if the drug companies ever release it...they are making soooooooooooo much money selling non-cure therapies.
Einstein was correct again and so was Mdm Blavatsky.
plutronus
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Post by swamprat on May 5, 2016 13:01:25 GMT -6
Colliding Black Holes May Sing Different Gravitational SongsBy Calla Cofield, Space.com Staff Writer May 5, 2016
What is the sound of two black holes colliding? Some of them chirp. But a truly massive, fast-spinning black hole — such as the one featured in the movie "Interstellar" — might create a more dynamic song.
Colliding black holes don't actually create sound waves, but they do create gravitational waves — distortions to space-time, the fabric of reality itself. In February, scientists with the Laser Interferometer Gravitational-Wave Observatory (LIGO) collaboration announced the first-ever direct detection of gravitational waves.
To help the general public understand the signal that LIGO detected, the researchers transformed the data into sound waves. As the black holes circle each other faster and faster, the sound climbs in pitch, like a slide whistle. The final collision produces a high-pitched chirp (listen to it here), and then the sound is abruptly cut off — the song stops because the two black holes have become one. This simple cosmic song may not be the only music these gravitational-wave emitters are capable of producing. At the American Physical Society April Meeting, held April 16 to 19 in Salt Lake City, Niels Warburton, a postdoctoral fellow at the MIT Kavli Institute, discussed simulations showing what kind of gravitational-wave "song" should be produced by collisions involving black holes that spin faster and are significantly larger than those that have been detected by LIGO.
Extreme collisions To illustrate the new research, Warburton used the black hole Gargantua from the movie "Interstellar" as an example. In the film, a planet orbiting closer to this monster experiences extreme time dilation, so that one hour on the surface of the planet is equal to seven years on a spaceship nearby.
Astrophysicist Kip Thorne (who is also a founding member of LIGO) was deeply involved with the film and the science therein. He wrote in his book "The Science of Interstellar" that in order to cause the level of time dilation portrayed in the movie, the black hole would have to spin at nearly the fastest possible speed that scientists believe is possible for a black hole. More specifically, "1 part in 100 trillion less than maximum rate allowable," Warburton said.
(While it has not been demonstrably proven, it is thought that if a black hole were to spin faster than this maximum, its event horizon would shrink so far back as to leave a naked singularity, Warburton said — a result that has defied physical models until now.)
For their study, Warburton and his colleagues looked at very massive black holes spinning a little slower than Gargantua — only about 99.99 percent of the maximum theoretical speed.
Before black holes collide, they spiral around one another, getting closer and closer together. One black hole will circle the other until it reaches a point known as the lowest stable orbit, after which it "falls in" to its companion, Warburton explained.
But the faster a black hole spins, the closer that lowest stable orbit gets to its event horizon, or the point beyond which nothing (not even light) can escape, he said. And what their research shows is that when the companion black hole can get extremely close to its companion, the gravitational waves emitted by the pair are very different from what had been expected.
The two black holes that LIGO observed merged together and produced a "chirp" — that is, the frequency of the signal rose steadily, then was cut off abruptly when the two objects combined. But Warburton and his colleagues showed that fast-spinning black holes create a signal that reaches a peak frequency, and then starts to lower in frequency, before fading out.
"Instead of chirping, you get this kind of singing sound from the black hole," Warburton said. "It'll rise, it won't get cut off, it'll sing, and then it's quiet at the end."
"[It's] a completely different gravitational-wave signature … than what was detected [by LIGO]," he said. If a gravitational-wave detector picked up a signal that looked like the one the researchers' model describes, "you would know you were looking at a gargantuan system, something that is rotating extremely close to the maximum," he said.
This runs contrary to what scientists expected from a merger involving a very fast-spinning black hole, according to Jolyon Bloomfield, a lecturer at MIT, who presented research at the same press conference.
"It was certainly very unexpected to see something that didn't chirp," Bloomfield said, when asked during the press conference what he thought of the results. "Every template that we've seen so far … has had this beautiful, chirping feature, and we just assumed that [if we] make [the spin of the black hole] bigger … it chirps bigger. But this is quite interesting work that says no, the chirp actually goes away. Something else is happening here."
Hunting for gravitational songs The work Warburton presented focuses mainly on a scenario involving a black hole millions of times more massive than the sun, spinning very fast, and colliding with a much smaller companion black hole — something on the order of tens of times the mass of the sun. To detect these signals would require a very large gravitational wave detector like the European Space Agency's eLISA mission, which is scheduled for launch in the 2030s. However, Warburton said that some of these strange gravitational-wave songs could also be created by two midsize black holes, and those signals could potentially be detected by LIGO.
Will gravitational-wave detectors pick up signals created by these superfast-spinning black holes? Warburton said that such a scenario depends on how common these objects are in the universe.
"There are theoretical arguments that suggest that 99.8 percent is the most maximal speed you will find," Warburton said. "But until the detection of gravitational waves recently, people thought that the biggest black holes you would see would only be 15 solar masses. And the [black holes that LIGO] saw were double that: 30 solar masses."
"So these things might not be that common in the universe," he said. "But when you're doing gravitational-wave data analysis, you need to kind of know what you're looking for in advance … And so we've shown what to look for in the data stream in order to detect these particularly exotic objects."
The new work could also help explain how very massive black holes form, Warburton said, because an object's spin can indicate how it acquired its mass. If a massive black hole formed from smaller black holes merging together, it shouldn't have an extremely high spin rate, he said.
A paper describing this research is available on the open-access website arXive.org, and the paper has been submitted for publication, according to Warburton.
www.space.com/32723-colliding-black-holes-sing-different-songs.html
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Post by swamprat on Jun 20, 2016 10:34:37 GMT -6
'New Era' of Astrophysics: Why Gravitational Waves Are So ImportantBy Calla Cofield, Space.com Staff Writer June 20, 2016
Two black holes collided in space, 1.4 billion light years from Earth. The ripples in space-time created by this collision were detected by the Laser Interferometer Gravitational Wave Observatory (LIGO). Credit: LIGO
There was big news in astrophysics this week: An experiment detected ripples in space-time, known as gravitational waves, created by two black holes colliding in space 1.4 billion light-years from Earth.
What's so cool about gravitational waves? The first significant thing about LIGO's direct detection of gravitational waves is that it happened at all.
But first, let's back up a bit and talk about Albert Einstein. He was a smart guy — he figured out a lot of really subtle stuff about the universe, including that space is not a fixed, rigid backdrop, like a stage on which cosmic events play out. Instead, Einstein showed that space is flexible and influenced by the objects and events within it. Very massive objects create curves in space, kind of like the way a bowling ball curves a mattress when placed on top of it.
(Einstein also showed that space and time are intimately linked — both are threads in the universal fabric that he called space-time. We'll gloss over this relationship for the sake of brevity.)
So what does this have to do with gravitational waves? If a massive object can curve space-time, then moving a massive object can create ripples in space-time. Think of a canoe moving across a lake, sending ripples across the surface of the water; or a mallet striking a drum, creating vibrations on the surface.
The Laser Interferometer Gravitational-Wave Observatory, better known as LIGO, was the first experiment ever to directly detect these ripples in space-time, so it's the first direct physical evidence that they actually exist. Its first detection came in September 2015, 100 years after Einstein first predicted their existence. It's also been 40 years since people started working on the early incantations of the technology that LIGO uses to detect gravitational waves.
So these ripples in space-time confirm Einstein's theory (although it had already been shown to be fairly airtight). Gravitational waves are an extreme illustration of general relativity; in the past, those extreme examples existed only on paper, in the theoretical world. Data can always help scientists learn more about the universe, and if Einstein's theory needs to be adjusted (to make it compatible with quantum mechanics, for example), it's possible LIGO could find where. (LIGO's executive director said he's doubtful that LIGO will find these kinds of cracks or lose ends in Einstein's theory, but it is a possibility.)
But wait — there's more. The LIGO discoveries have "launched a new era in astronomy," according to a statement from Northwestern University, where scientists are studying the gravitational waves to try to understand the black holes that created them. Other sources with LIGO have also talked about a "new era" or "new field of astrophysics," or have noted that LIGO is opening "a new window" to the universe.
That's a big claim. So how is LIGO driving this revolution? Think of it this way: If every observatory and telescope in the history of humanity allowed people to "see" the universe, LIGO is now allowing us to "hear" it. And no one has ever heard the universe in this way before. Imagine what it would be like to suddenly gain not just a new view of the world around you, but the ability to detect an entirely different kind of information.
Black holes are called black holes because they have such a strong gravitational pull that even light can't get away from them. As a result, they're typically represented in images and illustrations as big, black spheres in space — they don't emit light, and they don't radiate light.
There are other ways to "see" black holes. For example, sometimes material around the black hole radiates light, and that can at least reveal the silhouette of one of these monsters. It's also possible to detect a black hole via its gravitational influence on stuff around it. (This is also how scientists detect dark matter, more mysterious stuff that makes up a big part of the universe.)
But for the black holes detected by LIGO, and most black holes between 10 and 100 times the mass of the sun, scientists with LIGO say it's unlikely that these techniques will work. That's because there's no material around these black holes; it gets flung away as the black holes circle around each other. That means these black holes are invisible — except to a gravitational-wave detector.
Plus, a purist will tell you that all of those above methods are indirect. If someone wants information created directly by the black hole, then gravitational waves are it.
So LIGO can see things that no other observatory can, and that's a big reason why people are calling this the beginning of a new era of astrophysics. LIGO will spot many other objects, including exploding stars (supernovas) and mergers between neutron stars, or the nuggets of leftover star explosions that are just slightly not dense enough to become black holes.
LIGO's black holes To get a taste of what kind of information gravitational waves can provide, take a look at LIGO's two detections. The first signal, detected in September 2015, was created by two black holes that had masses 29 and 36 times that of the sun, respectively. They created a new black hole with a mass just shy of their combined masses. (Some of the mass was lost as energy in the merger.) The second detection was also created by two black holes that had masses 7.5 and 14 times that of the sun, respectively.
The mass of a black hole provides some insight into how it formed. All four of these black holes were likely born from single, massive stars. Those stars burned brightly, but then ran out of fuel and collapsed on themselves, crunching matter into such an incredibly small space that the density of the remaining object cannot be clearly described by modern physics.
Just the beginning LIGO detected two confirmed black hole mergers in its first science run, which lasted about six months. Currently, LIGO is operating at only about 40 percent of the sensitivity it was designed to achieve. Gradual improvements by the LIGO team will slowly drive that percentage up, and with each bump in sensitivity, LIGO is expected to detect more and more objects. According to David Reitze, executive director of the LIGO Laboratory, if the detector is 25 percent more sensitive in its next run (which starts in September), the LIGO Collaboration can expect six to eight detections, instead of two.
Meanwhile, a companion gravitational-wave detector is scheduled to go online in Italy in January, and there are plans to have detectors in Japan and India in the future. A space-based experiment is laying the groundwork for space-based gravitational-wave detectors. And a collaboration of scientists is working on measuring gravitational waves by studying pulsars, or neutron stars that radiate beams of radio waves.
LIGO's discovery means a lot of things to the astrophysics community; it might actually be the beginning of a new era.
www.space.com/33199-why-are-gravitational-waves-important.html
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Post by swamprat on Nov 10, 2016 10:55:00 GMT -6
Even Bill agrees!Bill Nye on Gravitational Waves: There's Nothing "Basic" About Basic Research Bill Nye Television Host and Science Educator
At 4am on September 14, 2015, a team of over 1,000 scientists who form the Laser Interferometer Gravitational-Wave Observatory (LIGO) confirmed an aspect of Albert Einstein's general theory of relativity.
They monitored an energy vibration just four one-thousandths of a diameter of a proton, and it set the world ablaze with celebration. Well, more than a year later, Bill Nye is still celebrating. He never stopped. These kinds of events are rare and epochal – scientists have been looking for proof of this since 1916, when Einstein published his landmark papers.
What the observation of the gravitational wave confirmed is that space and time are really one unit — space-time — that exist as part of a gravitational grid. When that grid is disturbed by massive events in space, the space-time continuum itself is altered. In this case, the event was truly epic: two black holes (one 36 times as massive as the Sun, the other 29 times) collided almost at the speed of light and formed a single black hole, during which they released 50 times the amount of energy released by all the stars in the known universe at that same moment. We’re still feeling the effects of it at a quantum level, and in many ways the ripple is only set to amplify in terms of the discoveries and technology this insight will lead to, eventually changing our daily existence in a very tangible way.
Considering that Einstein’s discovery of relativity led to things like GPS, the internet, and precision agriculture, we can only imagine what existence-altering innovations the proof of gravitational waves will bring down the line. Nye expects that it will lead “to a new understanding of another aspect of physics” and insight into energy sources that will steer us down one course of energy production.
bigthink.com/videos/bill-nye-on-the-gravity-wave-discovery?utm_source=Bill+Nye+Newsletter&utm_campaign=c14ee7fa18-BillNyeNewsletter_111016&utm_medium=email&utm_term=0_71c6d7ef14-c14ee7fa18-40548401
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Post by swamprat on Dec 1, 2016 10:37:32 GMT -6
LIGO back online, ready for more discoveriesUpgrades make detectors more sensitive to gravitational waves.
Jennifer Chu | MIT News Office November 30, 2016
Gravitational-wave Observatory. The Livingston detector site, located near Livingston, Louisiana, is pictured here. Photo: Caltech/MIT/LIGO Lab
Today, scientists restarted the twin detectors of LIGO, the Laser Interferometer Gravitational-wave Observatory, after making several improvements to the system. Over the last year, they have made enhancements to LIGO’s lasers, electronics, and optics that have increased the observatory’s sensitivity by 10 to 25 percent. The detectors, scientists hope, will now be able to tune in to gravitational waves — and the extreme events from which they arise — that emanate from farther out in the universe.
On Sept. 14, 2015, LIGO’s detectors made the very first direct detection of gravitational waves, just two days after scientists restarted the observatory as Advanced LIGO — an upgraded version of LIGO’s two large interferometers, one located at Hanford, Washington, and the other 3,000 kilometers away in Livingston, Lousiana. After analyzing the signal, scientists determined that it was indeed a gravitational wave, which arose from the merger of two massive black holes 1.3 billion light years away.
Three months later, on Dec. 26, 2015, the detectors picked up another signal, which scientists decoded as a second gravitational wave, rippling out from yet another black hole merger, slightly farther out in the universe, 1.4 billion light years away.
Now with LIGO’s latest upgrades, members of the LIGO Scientific Collaboration are hoping to detect more frequent signals of gravitational waves, arising from colliding black holes and other extreme cosmic phenomena. MIT News spoke with Peter Fritschel, the associate director for LIGO at MIT, and LIGO’s chief detector scientist, about LIGO’s new view.
Q: What sort of changes have been made to the detectors since they went offline?
A: There were different sorts of activities at the two observatories. With the detector in Livingston, Louisiana, we did a lot of work inside the vacuum system, replacing or adding new components. As an example, each detector contains four test masses that respond to a passing gravitational wave. These test masses are mounted in complex suspension systems that isolate them from the local environment. Previous testing had shown that two of the vibrational modes of these suspensions could oscillate to a degree that would prevent the detector from operating with its best sensitivity. So, we designed and installed some tuned, passive dampers to reduce the oscillation amplitude of these modes. This will help the Livingston detector operate at its peak sensitivity for a greater fraction of the data run duration.
On the Hanford, Washington, detector, most of the effort was geared toward increasing the laser power stored in the interferometer. During the first observing run, we had about 100 kilowatts of laser power in each long arm of the interferometer. Since then we worked on increasing this by a factor of two, to achieve 200 kilowatts of power in each arm. This can be quite difficult because there are thermal effects and optical-mechanical interactions that occur as the power is increased, and some of these can produce instabilities that must be tamed. We actually succeeded in solving these types of problems and were able to operate the detector with 200 kilowatts in the arms. However, there were other problems that cost sensitivity, and we didn’t have time to solve these, so we are now operating with 20 to 30 percent higher power than we had in the first observing run. This modest power increase gives a small but noticeable increase in sensitivity to gravitational wave frequencies higher than about 100 hertz.
We also gathered a lot of important information that will be used to plan out the next detector commissioning period, which will commence at the end of this six-month observation period. We still have a lot of challenging work ahead of us to get to our final design sensitivity.
Q: How sensitive is LIGO with these new improvements?
A: The metric we most commonly use is the sensitivity to gravitational waves produced by the merger of two neutron stars, because we can easily calculate what we should see from such a system — but note we have not yet detected gravitational waves from a neutron star-neutron star merger. The Livingston detector is now sensitive enough to detect a merger from as far away as 200 million parsecs (660 million light years). This is about 25 percent farther than it could “see” in the first observing run. For the Hanford detector the corresponding sensitivity range is pretty much on par with what it was during the first run and is about 15 percent lower than these figures.
Of course in the first observing run we detected the merger of two black holes, not neutron stars. The sensitivity comparison for black hole mergers is nonetheless about the same: Compared to last year’s observing run, the Livingston detector is around 25 percent more sensitive and the Hanford detector is about the same. But even small improvements in sensitivity can help, since the volume of space being probed, and thus the rate of gravitational-wave detections, grows as the cube of these distances.
Q: What do you hope to “hear” and detect, now that LIGO is back online?
A: We definitely expect to detect more black hole mergers, which is still a very exciting prospect. Recall that in the first run we detected two such black hole binary mergers and saw strong evidence for a third merger. With the modest improvement in sensitivity and the plan to collect more data than we did before, we should add to our knowledge of the black hole population in the universe.
We would also love to detect gravitational waves from the merger of two neutron stars. We know these systems exist, but we don’t know how prevalent they are, so we can’t be sure how sensitivity we need to start seeing them. Binary neutron star mergers are interesting because (among other things) they are thought to be the producers and distributors of the heavy elements, such as the precious metals, that exist in our galaxy.
news.mit.edu/2016/ligo-upgrades-gravitational-waves-1130
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Post by swamprat on Oct 3, 2017 20:25:22 GMT -6
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Post by swamprat on Oct 11, 2017 20:25:30 GMT -6
Not sure what they saw this time. If I had to guess, maybe the merger of two neutron stars?MYSTERY SPACE ANNOUNCEMENT: SCIENTISTS TO REVEAL ASTRONOMICAL PHENOMENON ’NEVER WITNESSED BEFORE’BY HANNAH OSBORNE ON 10/11/17
Scientists are set to make a major announcement about “groundbreaking observations” relating to “an astronomical phenomenon that has never been witnessed before,” the European Southern Observatory said.
THE DISCOVERY, WHICH IS BEING KEPT SECRET UNTIL PRESS CONFERENCES ARE HELD ON OCTOBER 16, RELATES TO GRAVITATIONAL WAVES. IT INVOLVES SCIENTISTS FROM THE LASER INTERFEROMETER GRAVITATIONAL-WAVE OBSERVATORY (LIGO) AND THE VIRGO COLLABORATION, ALONG WITH TEAMS FROM 70 DIFFERENT OBSERVATORIES ACROSS THE GLOBE.
Events announcing the finding will be taking place in the U.S., the U.K. and Germany. All will start at 10 a.m. ET and will begin with an overview of the latest findings from LIGO and the other observatories, followed by questions from journalists.
One event, to be held at the ESO’s headquarters in Germany, is to be introduced by Xavier Barcons, director general of the space agency. Another, run by the U.S. National Science Foundation, will take place in Washington, D.C., and the third will be held by the Royal Society in London.
Speakers at the U.S. conference will include David Reitze, executive director at LIGO Laboratory/Caltech, Julie McEnery, Fermi Project Scientist at NASA’s Goddard Space Flight Center, and Jo van den Brand, spokesperson for the Virgo Collaboration.
Gravitational waves caused by cataclysmic cosmic events result in ripples that propagate through spacetime—similar to a how stone thrown into a pond would create a ripple effect.
Scientists announced they had detected gravitational waves in February 2016. The discovery marked a major breakthrough in astronomy and physics—Einstein first predicted the existence of gravitational waves 100 years earlier, but scientists did not have instruments sensitive enough to find these tiny ripples in spacetime until the LIGO detectors were up and running.
Three other confirmed detections have been announced since then, with the last resulting from the use of both LIGO and Virgo detectors—and by combining the two instruments, scientists say the number of gravitational waves found should increase significantly in the future. This would allow researchers to probe some of the biggest questions in the universe, including the nature of dark energy and what happened just after the Big Bang.
www.newsweek.com/gravitational-waves-mystery-announcement-astronomical-phenomenon-682561?utm_source=yahoo&utm_medium=yahoo_news&utm_campaign=rss&utm_content=/rss/yahoous/news&yptr=yahoo
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Post by swamprat on Oct 12, 2017 18:50:35 GMT -6
MONDAY: New Gravitational-wave Discovery to be Announced 10/11/2017
BATON ROUGE – Scientists directly involved with the discovery will be in Baton Rouge to participate in an inaugural gravitational wave conference hosted by the LSU Department of Physics & Astronomy. WHAT: The Gravitational Wave Astrophysics conference sponsored by the International Astronomical Union will livestream the LIGO Laboratory, LIGO Scientific Collaboration, National Science Foundation and Virgo Collaboration press conference. Journalists are invited to watch the livestream of the press conference on Monday, Oct. 16, at 9 a.m. (CDT) from the National Press Club in Washington, D.C.
The livestreamed press conference will begin with an overview of new findings from LIGO, Virgo and partners that span the globe, followed by details from telescopes that work with the LIGO and Virgo Collaboration to study extreme events in the cosmos.
The first detection of gravitational waves, made on Sept. 14, 2015 and announced on Feb. 11, 2016, was a milestone in physics and astronomy. It confirmed a major prediction of Albert Einstein’s 1915 general theory of relativity and marked the beginning of the new field of gravitational-wave astronomy. Since then, there have been three more confirmed detections, one of which (and the most recently announced) was the first confirmed detection seen jointly by both the LIGO and Virgo detectors.
WHEN: Monday, Oct. 16 9 a.m. (CDT)
WHERE: Crowne Plaza Hotel (Premier Room 1) 4728 Constitution Ave. Baton Rouge, La. 70808
WHO: LSU College of Science Dean Cynthia Peterson and LSU Department of Physics & Astronomy Chair John DiTusa will provide opening remarks. LSU Department of Physics & Astronomy Professor and former LIGO Scientific Collaboration spokesperson Gabriela Gonzalez will be on hand to answer questions.
www.lsu.edu/mediacenter/news/2017/10/11physastro_gonzalez_gwadvisory.php
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Post by swamprat on Oct 16, 2017 9:18:53 GMT -6
First Detection of Gravitational Waves from Neutron-Star Crash Marks New Era of AstronomyBy Mike Wall, Space.com Senior Writer October 16, 2017 10:00am ET
A new era of astronomy has begun. For the first time ever, scientists have spotted both gravitational waves and light coming from the same cosmic event — in this case, the cataclysmic merger of two superdense stellar corpses known as neutron stars.
The landmark discovery initiates the field of "multimessenger astrophysics," which promises to reveal exciting new insights about the cosmos, researchers said. The find also provides the first solid evidence that neutron-star smashups are the source of much of the universe's gold, platinum and other heavy elements.
How do researchers describe the finding? "Superlatives fail," said Richard O'Shaughnessy, a scientist with the Laser Interferometer Gravitational-wave Observatory (LIGO) project.
"This is a transformation in the way that we're going to do astronomy," O'Shaughnessy, who's based at the Rochester Institute of Technology's Center for Computational Relativity and Gravitation, told Space.com. "It's fantastic."
A new type of detection Gravitational waves are ripples in the fabric of space-time generated by the acceleration of massive cosmic objects. These ripples move at the speed of light, but they're much more penetrating; they don't get scattered or absorbed the way light does.
Albert Einstein first predicted the existence of gravitational waves in his theory of general relativity, which was published in 1916. But it took a century for astronomers to detect them directly. That milestone came in September 2015, when LIGO saw gravitational waves emitted by two merging black holes.
That initial find won three project co-founders the 2017 Nobel Prize in physics. The LIGO team soon followed it up with three other discoveries, all of which also traced back to colliding black holes.
The fifth gravitational-wave detection — which was announced today (Oct. 16) at news conferences around the world, and in a raft of papers in multiple scientific journals — is something altogether new. On Aug. 17, 2017, LIGO's two detectors, which are located in Louisiana and Washington state, picked up a signal that lasted about 100 seconds — far longer than the fraction-of-a-second "chirps" spawned by merging black holes. "It immediately appeared to us the source was likely to be neutron stars, the other coveted source we were hoping to see — and promising the world we would see," David Shoemaker, a spokesman for the LIGO Scientific Collaboration and a senior research scientist at the Massachusetts Institute of Technology's Kavli Institute for Astrophysics and Space Research, said in a statement.
Indeed, calculations by the LIGO team suggest that each of the colliding objects harbors between 1.1 and 1.6 times the mass of the sun, putting both objects in neutron-star territory in terms of mass. (Each of the merging black holes responsible for the other detected signals contained dozens of solar masses.)
Neutron stars, the collapsed remnants of massive stars that have died in supernova explosions, are some of the most exotic objects in the universe.
"They are as close as you can get to a black hole without actually being a black hole," theoretical astrophysicist Tony Piro, of the Observatories of the Carnegie Institution for Science in Pasadena, California, said in a different statement. "Just one teaspoon of a neutron star weighs as much as all the people on Earth combined."
A team effort The Virgo gravitational-wave detector near Pisa, Italy, also picked up a signal from the Aug. 17 event, which was dubbed GW170817 (for the date of its occurrence). And NASA's Fermi Gamma-ray Space Telescope spotted a burst of gamma-rays — the highest-energy form of light — at about the same time, coming from the same general location. All of this information allowed researchers to trace the signal's source to a small patch of the southern sky. Discovery team members passed this information on to colleagues around the world, asking them to search that patch with ground- and space-based telescopes.
This teamwork soon bore fruit. Just hours after the gravitational-wave detection, Piro and his colleagues spotted a matching optical light source about 130 million light-years from Earth, using a telescope at Las Campanas Observatory in Chile.
"We saw a bright-blue source of light in a nearby galaxy — the first time the glowing debris from a neutron star merger had ever been observed," team member Josh Simon, also of the Carnegie Observatories, said in a statement. "It was definitely a thrilling moment." Then, about an hour later, researchers using the Gemini South telescope, also in Chile, spotted that same source in infrared light. Other teams using a variety of instruments soon studied the source across the electromagnetic spectrum, from radio to X-ray wavelengths.
This work revealed that some of the observed light was the radioactive glow of heavy elements such as gold and uranium, which were produced when the two neutron stars collided. That's a big deal. Scientists already knew the provenance of lighter elements — most hydrogen and helium was generated during the Big Bang, and other elements all the way up to iron are created by nuclear fusion processes inside stars — but the origin of the heavy stuff was not well understood.
"We've shown that the heaviest elements in the periodic table, whose origin was shrouded in mystery until today, are made in the mergers of neutron stars," Edo Berger, of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, said in a statement. Berger leads a team that studied the event using the Dark Energy Camera at the Cerro Tololo Inter-American Observatory in Chile.
"Each merger can produce more than an Earth's mass of precious metals like gold and platinum and many of the rare elements found in our cellphones," Berger said in a statement.
Indeed, GW170817 likely produced about 10 Earth masses' worth of gold and uranium, researchers said. Much more to come The in-depth investigation of GW170817 has revealed other important insights.
For example, this work demonstrated that gravitational waves do indeed move at the speed of light, as theory predicts. (The Fermi space telescope detected the gamma-ray burst just 2 seconds after the gravitational-wave signal ended.) And astronomers now know a little more about neutron stars.
"There are some types of things that neutron stars could be made of that we're sure they're not made of, because they didn't squish that much" during the merger, O'Shaughnessy said.
But GW170817 is just the beginning. For instance, such "multimessenger" observations provide another way to calibrate distances to celestial objects, said the CfA's Avi Loeb, who also chairs Harvard University's astronomy department.
Such measurements could, in theory, help scientists finally nail down the rate of the universe's expansion. Estimates of this value, known as the Hubble Constant, vary depending on whether they were calculated using observations of supernova explosions or the cosmic microwave background (the ancient light left over from the Big Bang), said Loeb, who was not involved in the newly announced discovery.
"Here's another path that is open that was not available before," he told Space.com. Many other such paths are likely to open, O'Shaughnessy stressed, and where they may lead is anyone's guess.
"I think probably the most exciting thing of all is really that it's the beginning," O'Shaughnessy said of the new discovery. "It resets the board for what astronomy is going to look like in the years to come, now that we have multiple ways of simultaneously probing a transient and violent universe."
www.space.com/38469-gravitational-waves-from-neutron-stars-discovery-ligo.html
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Post by swamprat on Oct 16, 2017 9:52:38 GMT -6
I've been watching the press conferences all morning on this discovery. Imagine these points:
The collision was observed in August; it actually happened over a million years ago.
When first observed, the two neutron stars were about 200 miles apart. Each one was about 10 miles in diameter, yet, each one had about the same mass as our sun.
In just seconds, the 200 mile gap closed and they collided. This type of collision is thought to be the source of much of the heavy metal we find in the universe--including the gold in that watch band on your wrist.....
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Post by auntym on Oct 16, 2017 13:18:48 GMT -6
nasa.tumblr.com/post/166466378849/when-dead-stars-collide NASA When Dead Stars Collide!Gravity has been making waves - literally. Earlier this month, the Nobel Prize in Physics was awarded for the first direct detection of gravitational waves two years ago. But astronomers just announced another huge advance in the field of gravitational waves - for the first time, we’ve observed light and gravitational waves from the same source. There was a pair of orbiting neutron stars in a galaxy (called NGC 4993). Neutron stars are the crushed leftover cores of massive stars (stars more than 8 times the mass of our sun) that long ago exploded as supernovas. There are many such pairs of binaries in this galaxy, and in all the galaxies we can see, but something special was about to happen to this particular pair. Each time these neutron stars orbited, they would lose a teeny bit of gravitational energy to gravitational waves. Gravitational waves are disturbances in space-time - the very fabric of the universe - that travel at the speed of light. The waves are emitted by any mass that is changing speed or direction, like this pair of orbiting neutron stars. However, the gravitational waves are very faint unless the neutron stars are very close and orbiting around each other very fast. As luck would have it, the teeny energy loss caused the two neutron stars to get a teeny bit closer to each other and orbit a teeny bit faster. After hundreds of millions of years, all those teeny bits added up, and the neutron stars were *very* close. So close that … BOOM! … they collided. And we witnessed it on Earth on August 17, 2017. Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet A couple of very cool things happened in that collision - and we expect they happen in all such neutron star collisions. Just before the neutron stars collided, the gravitational waves were strong enough and at just the right frequency that the National Science Foundation (NSF)’s Laser Interferometer Gravitational-Wave Observatory (LIGO) and European Gravitational Observatory’s Virgo could detect them. Just after the collision, those waves quickly faded out because there are no longer two things orbiting around each other! LIGO is a ground-based detector waiting for gravitational waves to pass through its facilities on Earth. When it is active, it can detect them from almost anywhere in space.
CONTINUE READING: nasa.tumblr.com/post/166466378849/when-dead-stars-collide
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Post by swamprat on Oct 26, 2017 20:00:05 GMT -6
Colliding Neutron Stars Could Settle Cosmology’s Biggest ControversyNewly discovered “standard sirens” provide an independent, clean way to measure how fast the universe is expanding.
Natalie Wolchover, Senior Writer October 25, 2017
To many cosmologists, the best thing about neutron-star mergers is that these events scream into space an otherwise close-kept secret of the universe. Scientists combined the gravitational and electromagnetic signals from the recently detected collision of two of these stars to determine, in a cleaner way than with other approaches, how fast the fabric of the universe is expanding — a much-contested number called the Hubble constant.
In the days since the neutron-star collision was announced, Hubble experts have been surprised to find themselves discussing not whether events like it could settle the controversy, but how soon they might do so.
Scientists have hotly debated the cosmic expansion rate ever since 1929, when the American astronomer Edwin Hubble first established that the universe is expanding — and that it therefore had a beginning. How fast it expands reflects what’s in it (since matter, dark energy and radiation push and pull in different ways) and how old it is, making the value of the Hubble constant crucial for understanding the rest of cosmology.
And yet the two most precise ways of measuring it result in different answers, with a curious 8 percent discrepancy that “is currently the biggest tension in cosmology,” said Dan Scolnic of the University of Chicago’s Kavli Institute for Cosmological Physics. The mismatch could be a clue that cosmologists aren’t taking into account important details that have affected the universe’s evolution. But to see if that’s the case, they need an independent check on the measurements.
Neutron-star collisions — newly detectable by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo detectors — seem to be just the thing.
“This first [collision] gives us a seat at the cosmology table,” Daniel Holz, an astrophysicist with the University of Chicago and LIGO who was centrally involved in the new Hubble measurement, said in an email. “And as we get more, we can expect to play a major role in the field.”
Adapted from DOI:10.1038/nature24471
In an expanding universe, the farther away an astronomical object is, the faster it recedes. The Hubble constant says how much faster. Edwin Hubble himself estimated that galaxies move away from us 500 kilometers per second faster for each additional megaparsec of distance between us and them (a megaparsec is about 3.3 million light-years). This was a gross overestimate; by the 1970s, astrophysicists favored values for the Hubble constant around either 50 or 100 kilometers per second per megaparsec, depending on their methods. As errors were eliminated, these camps met near the middle. However, in the past year and a half, the Hubble trouble has reheated. This time, 67 stands off against 73.
The higher estimate of 73 comes from observing lots of astronomical objects and estimating both distance and velocity for each one. It’s relatively easy to see how fast a star or galaxy is receding by looking at its “redshift” — a reddening in color that happens for the same reason the sound of a receding ambulance’s siren drops in pitch. Correct for an object’s “peculiar velocity,” caused by the gravitational pull of other objects in its neighborhood, and you’re left with its recessional velocity due to cosmic expansion.
Historically, however, it has proven much, much harder to measure the distance to an object — the other data point needed to calculate the Hubble constant.
To gauge how far away things are, astronomers build up rungs on a “cosmic distance ladder” in which each rung calibrates more-distant rungs. They start by deducing the distances to stars in the Milky Way using parallax — the stars’ apparent motion across the sky over the course of the year. With this information, astronomers can deduce the brightness of so-called Cepheid stars, which can be used as so-called “standard candles” because they all shine with a known intrinsic brightness. They then spot these Cepheid stars in nearby galaxies and use them to calculate how far away the galaxies must be. Next, the Cepheids are used to calibrate the distances to Type Ia supernovas — even brighter (though rarer) standard candles that can be seen in faraway galaxies.
Each jump from one rung to the next risks miscalculation. And yet, in 2016, a team known as SH0ES used the cosmic distance ladder approach to peg the Hubble constant at 73.2 with an accuracy of 2.4 percent.
However, in a paper published the same year, a team used the Planck telescope’s observations of the early universe to obtain a value of 67.8 for the current expansion rate — supposedly with 1 percent accuracy.
The Planck team started from the faint drizzle of ancient light called the cosmic microwave background (CMB), which reveals the universe as it looked at a critical moment 380,000 years after the Big Bang. The CMB snapshot depicts a simple, nearly smooth, plasma-filled young universe. Pressure waves of all different wavelengths rippled through the plasma, squeezing and stretching it and creating subtle density variations on different length scales.
At the moment recorded in the CMB, pressure waves with particular wavelengths would have undergone just the right fraction of an undulation since the Big Bang to all reach zero amplitude, momentarily disappearing and creating smooth plasma densities at their associated length scale. Meanwhile, pressure waves with other wavelengths undulated just the right amount to exactly peak in amplitude at the critical moment, stretching and squeezing the plasma to the full extent possible and creating maximum density variations at their associated scales.
These peaks and troughs in density variations at different scales, which can be picked up by telescopes like Planck and plotted as the “CMB power spectrum,” encode virtually everything about the young universe. The Hubble constant, in particular, can be reconstructed by measuring the distances between the peaks. “It’s a geometric effect,” explained Leo Stein, a theoretical physicist at the California Institute of Technology: The more the universe has expanded, the more the light from the CMB has curved through expanding space-time, and the closer together the peaks ought to appear to us.
Adapted from ESA and the Planck Collaboration
Other properties of nature also affect how the peaks end up looking, such as the behavior of the invisible “dark energy” that infuses the fabric of the cosmos. The Planck scientists therefore had to make assumptions about all the other cosmological parameters in order to arrive at their estimate of 67 for the Hubble constant.
The similarity of the two Hubble measurements “is amazing” considering the vastly different approaches used to determine them, said Wendy Freedman, an astrophysicist at the University of Chicago and a pioneer of the cosmic distance ladder approach. And yet their margins of error don’t overlap. “The universe looks like it’s expanding about eight percent faster than you would have expected based on how it looked in its youth and how we expect it to evolve,” Adam Riess of Johns Hopkins University, who led the SH0ES team, told Scientific American last year. “We have to take this pretty darn seriously.”
The 67-versus-73 discrepancy could come down to an unknown error on one side or both. Or it might be real and significant — an indication that the Planck team’s extrapolation from the early universe to the present is missing a cosmic ingredient, one that changed the course of history and led to a faster expansion rate than otherwise expected. If a hypothesized fourth type of neutrino populated the infant universe, for instance, this would have increased the radiation pressure and affected the CMB peak widths. Or dark energy, whose repulsive pressure accelerates the universe’s expansion, might be getting denser over time. Suddenly, neutron-star collisions have materialized to cast the deciding vote.
The crashing stars serve as “standard sirens,” as Holz and Scott Hughes of the Massachusetts Institute of Technology dubbed them in a 2005 paper, building on the work of Bernard Schutz 20 years earlier. They send rushes of ripples outward through space-time that are not dimmed by gas or dust. Because of this, the gravitational waves transmit a clean record of the strength of the collision, which allows scientists to “directly infer the distance to the source,” Holz explained. “There is no distance ladder, and no poorly understood astronomical calibrations. You listen to how loud the [collision] is, and how the sound changes with time, and you directly infer how far away it is.” Because astronomers can also detect electromagnetic light from neutron-star collisions, they can use redshift to determine how fast the merged stars are receding. Recessional velocity divided by distance gives the Hubble constant.
From the first neutron-star collision alone, Holz and hundreds of coauthors calculated the Hubble constant to be 70 kilometers per second per megaparsec, give or take 10. (The major source of uncertainty is the unknown angular orientation of the merging neutron stars relative to the LIGO detectors, which affects the measured amplitude of the signal.) Holz said, “I think it’s just pure luck that we’re smack in the middle,” between the cosmic-distance-ladder and cosmic-microwave-background Hubble estimates. “We could easily shift to one side or the other.”
The measurement’s accuracy will steadily improve as more standard sirens are heard over the next few years, especially as LIGO continues to ramp up in sensitivity. According to Holz, “With roughly 10 more events like this one, we’ll get to 1 percent [of error],” though he stresses that this is a preliminary and debatable estimate. Riess thinks it will take more like 30 standard sirens to reach that level. It all depends on how lucky LIGO and Virgo got with their first detection. “I do think the method has the potential to be a game changer,” said Freedman. “How fast this will occur [or] what the rate of these objects will be … we don’t yet know.”
Scolnic, who was part of SH0ES, said his team’s tension with Planck’s measurement is so large that “the standard siren approach doesn’t need to get to 1 percent to be interesting.”
As more standard sirens resound, they’ll gradually home in on the Hubble constant once and for all and determine whether or not the expansion rate agrees with expectations based on the young universe. Holz, for one, is exhilarated. “I’ve dedicated the last decade of my life in the hopes of making one plot: a standard siren measurement of the Hubble. I got to make my Hubble plot, and it is beautiful.”
www.quantamagazine.org/colliding-neutron-stars-could-settle-cosmologys-biggest-controversy-20171025/
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whatwouldyousuggest
Junior Member
I once was...I am again..I always will be....all hail the personal opinion
Posts: 121
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Post by whatwouldyousuggest on Oct 29, 2017 10:47:37 GMT -6
amazing that all of this is going on out there...wonder what worlds might have been impacted by those stars...did some civilization suffer...or die as a result...
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