LIGO detects gravitational waves for third time

June 1, 2017
An international team of researchers has made a third detection of gravitational waves, ripples in space and time, in a discovery that provides new insights into the mysterious nature of black holes and, potentially, dark matter. Credit: LSC/OzGrav

The Laser Interferometer Gravitational-wave Observatory (LIGO) has made a third detection of gravitational waves, ripples in space and time, demonstrating that a new window in astronomy has been firmly opened. As was the case with the first two detections, the waves were generated when two black holes collided to form a larger black hole.

The newfound black hole, formed by the merger, has a mass about 49 times that of our sun. This fills in a gap between the masses of the two merged black holes detected previously by LIGO, with solar masses of 62 (first detection) and 21 (second detection).

"We have further confirmation of the existence of stellar-mass black holes that are larger than 20 solar masses—these are objects we didn't know existed before LIGO detected them," says MIT's David Shoemaker, the newly elected spokesperson for the LIGO Scientific Collaboration (LSC), a body of more than 1,000 international scientists who perform LIGO research together with the European-based Virgo Collaboration. "It is remarkable that humans can put together a story, and test it, for such strange and extreme events that took place billions of years ago and billions of light-years distant from us. The entire LIGO and Virgo scientific collaborations worked to put all these pieces together."

The new detection occurred during LIGO's current observing run, which began November 30, 2016, and will continue through the summer. LIGO is an international collaboration with members around the globe. Its observations are carried out by twin detectors—one in Hanford, Washington, and the other in Livingston, Louisiana—operated by Caltech and MIT with funding from the National Science Foundation (NSF).

LIGO made the first-ever direct observation of gravitational waves in September 2015 during its first observing run since undergoing major upgrades in a program called Advanced LIGO. The second detection was made in December 2015. The third detection, called GW170104 and made on January 4, 2017, is described in a new paper accepted for publication in the journal Physical Review Letters.

In all three cases, each of the twin detectors of LIGO detected gravitational waves from the tremendously energetic mergers of black hole pairs. These are collisions that produce more power than is radiated as light by all the stars and galaxies in the universe at any given time. The recent detection appears to be the farthest yet, with the black holes located about 3 billion light-years away. (The black holes in the first and second detections are located 1.3 and 1.4 billion light-years away, respectively.)

The newest observation also provides clues about the directions in which the black holes are spinning. As pairs of black holes spiral around each other, they also spin on their own axes—like a pair of ice skaters spinning individually while also circling around each other. Sometimes black holes spin in the same overall orbital direction as the pair is moving—what astronomers refer to as aligned spins—and sometimes they spin in the opposite direction of the orbital motion. What's more, black holes can also be tilted away from the orbital plane. Essentially, black holes can spin in any direction.

The new LIGO data cannot determine if the recently observed black holes were tilted but they imply that at least one of the black holes may have been non-aligned compared to the overall orbital motion. More observations with LIGO are needed to say anything definitive about the spins of binary black holes, but these early data offer clues about how these pairs may form.

This image shows a numerical simulation of a binary black hole merger with masses and spins consistent with the third and most recent LIGO observation, named GW170104. The strength of the gravitational wave is indicated by elevation as well as color, with blue indicating weak fields and yellow indicating strong fields. The sizes of the black holes are doubled to improve visibility. Credit: Image Credit: Numerical-relativistic Simulation: S. Ossokine, A. Buonanno (Max Planck Institute for Gravitational Physics) and the Simulating eXtreme Spacetime project Scientific Visualization: T. Dietrich (Max Planck Institute for Gravitational Physics), R. Haas (NCSA)

"This is the first time that we have evidence that the black holes may not be aligned, giving us just a tiny hint that binary black holes may form in dense stellar clusters," says Bangalore Sathyaprakash of Penn State and Cardiff University, one of the editors of the new paper, which is authored by the entire LSC and Virgo Collaborations.

There are two primary models to explain how binary pairs of black holes can be formed. The first model proposes that the black holes are born together: they form when each star in a pair of stars explodes, and then, because the original stars were spinning in alignment, the black holes likely remain aligned.

In the other model, the black holes come together later in life within crowded stellar clusters. The black holes pair up after they sink to the center of a star cluster. In this scenario, the black holes can spin in any direction relative to their orbital motion. Because LIGO sees some evidence that the GW170104 black holes are non-aligned, the data slightly favor this dense stellar cluster theory.

"We're starting to gather real statistics on binary black hole systems," says Keita Kawabe of Caltech, also an editor of the paper, who is based at the LIGO Hanford Observatory. "That's interesting because some models of black hole binary formation are somewhat favored over the others even now and, in the future, we can further narrow this down."

The study also once again puts Albert Einstein's theories to the test. For example, the researchers looked for an effect called dispersion, which occurs when light waves in a physical medium such as glass travel at different speeds depending on their wavelength; this is how a prism creates a rainbow. Einstein's general theory of relativity forbids dispersion from happening in gravitational waves as they propagate from their source to Earth. LIGO did not find evidence for this effect.

"It looks like Einstein was right—even for this new event, which is about two times farther away than our first detection," says Laura Cadonati of Georgia Tech and the Deputy Spokesperson of the LSC. "We can see no deviation from the predictions of general relativity, and this greater distance helps us to make that statement with more confidence."

"The LIGO instruments have reached impressive sensitivities," notes Jo van den Brand, the Virgo Collaboration spokesperson, a physicist at the Dutch National Institute for Subatomic Physics (Nikhef) and professor at VU University in Amsterdam. "We expect that by this summer Virgo, the European interferometer, will expand the network of detectors, helping us to better localize the signals."

The LIGO-Virgo team is continuing to search the latest LIGO data for signs of space-time ripples from the far reaches of the cosmos. They are also working on technical upgrades for LIGO's next run, scheduled to begin in late 2018, during which the detectors' sensitivity will be improved.

"With the third confirmed detection of gravitational waves from the collision of two black holes, LIGO is establishing itself as a powerful observatory for revealing the dark side of the universe," says David Reitze of Caltech, executive director of the LIGO Laboratory. "While LIGO is uniquely suited to observing these types of events, we hope to see other types of astrophysical events soon, such as the violent collision of two neutron stars."

Explore further: Gravitational waves data suggest Goldilocks black holes are rare

More information: Physical Review Letters (2017). DOI: 10.1103/PhysRevLett.118.221101

Related Stories

LIGO expected to detect more binary black hole mergers

January 9, 2017

The Laser Interferometer Gravitational-wave Observatory (LIGO) broke the news almost one year ago about the first-ever direct observation of gravitational waves. Now, LIGO scientists hope that this year could yield even more ...

LIGO discovery named Science's 2016 Breakthrough of the Year

December 23, 2016

The scientific journal, Science, has chosen as its 2016 Breakthrough of the Year the discovery of tiny ripples in spacetime called gravitational waves – a finding that confirmed a century-old prediction by Albert Einstein. ...

Recommended for you

New eruptions detected in two luminous blue variables

December 12, 2017

(Phys.org)—Astronomers report the detection of new eruptions in two luminous blue variables, known as R 40 and R 110, located in the Magellanic Clouds. The finding, presented December 5 in a paper published on the arXiv ...

Juno probes the depths of Jupiter's great red spot

December 12, 2017

Data collected by NASA's Juno spacecraft during its first pass over Jupiter's Great Red Spot in July 2017 indicate that this iconic feature penetrates well below the clouds. Other revelations from the mission include that ...

Telescopes team up to study giant galaxy

December 12, 2017

Astronomers have used two Australian radio telescopes and several optical telescopes to study complex mechanisms that are fuelling jets of material blasting away from a black hole 55 million times more massive than the Sun.

77 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Tuxford
1.7 / 5 (17) Jun 01, 2017
So how do they KNOW that these core stars are actually black? Might they be gray??
physman
4.1 / 5 (24) Jun 01, 2017
@Tuxford If you were in a black hole we wouldn't be able to hear your bullshit
Lischyn
2 / 5 (3) Jun 01, 2017
Looking at the x-section graph, why do they call it a neutron star when it is made of layers of electrons, neutrons and protons ( including others). The outer most major layer is electrons. Shouldn't it be called an electron star?
joel in oakland
2.7 / 5 (7) Jun 01, 2017
Given that the wave impacted/impacted us shortly before the inauguration of the current U.S. admin, it may be that bullshit is the only thing that can escape BH's, and we just got flooded by an extra large wave of the stuff.
Dingbone
Jun 01, 2017
This comment has been removed by a moderator.
Chris_Reeve
1.4 / 5 (10) Jun 01, 2017
The article states ...

"While LIGO is uniquely suited to observing these types of events, we hope to see other types of astrophysical events soon, such as the violent collision of two neutron stars."

It sounds like they are hoping to invest the public in further conjecture without any requirement to FIRST definitively localize the sources.
jonesdave
4.5 / 5 (15) Jun 01, 2017
The article states ...

"While LIGO is uniquely suited to observing these types of events, we hope to see other types of astrophysical events soon, such as the violent collision of two neutron stars."

It sounds like they are hoping to invest the public in further conjecture without any requirement to FIRST definitively localize the sources.


OK genius, how would you do that? Armed with your degree in BS and obfuscation? Please, do explain for us mere mortals.
Tuxford
1.5 / 5 (8) Jun 01, 2017
@Physman: LOL - https://www.seeke...098.html - does he say bullshit after then?

LOL. Perhaps the maniac got the idea from me! Imagine. See my early comment thereunder referencing gray holes. Any other earlier use of the term? Perhaps LaViolette, who predicts ejections therefrom.

https://phys.org/...ole.html
cantdrive85
1.7 / 5 (6) Jun 01, 2017
And in other news, a GRB accompanied this GW as well...
barakn
4.5 / 5 (8) Jun 01, 2017
Why would there be a GRB from two black holes colliding? May you're just clueless?
vacuumforce
1.1 / 5 (9) Jun 01, 2017
As it turns out, gravitational undulation is a key component in physical attraction.

If space has an atomic structure, then why not a chemical, or even organic one?
JongDan
4.3 / 5 (6) Jun 01, 2017
As it turns out, gravitational undulation is a key component in physical attraction.

If space has an atomic structure, then why not a chemical, or even organic one?

DUDE WEED LMAO
Da Schneib
4.6 / 5 (10) Jun 01, 2017
This is getting to be like people arguing those bright dots you see in telescopes aren't stars.
Chris_Reeve
2 / 5 (8) Jun 01, 2017
Re: "OK genius, how would you do that [localize the signals]? Armed with your degree in BS and obfuscation?"

Yeah, you might want to think about the trouble with localization as an important aspect for why this claim is difficult to falsify. If it proves impossible to actually localize the signal, then what do we really have here? Yet another non-falsifiable claim embedded within mainstream astrophysics and cosmology.
cantdrive85
2.5 / 5 (8) Jun 01, 2017
Why would there be a GRB from two black holes colliding? May you're just clueless?

We're more likely to observe two unicorns horn fighting than two fanciful mathematical entities. These "GW's" may very well originate from electromagnetic events.
https://phys.org/...ity.html
RealityCheck
2.3 / 5 (6) Jun 01, 2017
@Da Schneib.
This is getting to be like people arguing those bright dots you see in telescopes aren't stars.
DS, instead of posting trolling insults, how about calculating the likelyhood of receiving 'here' the signal claimed? Take into account:

- the alleged grav-waves were emitted by a 'source' 3 BILLION LIGHTYEARS away;

- how much would the alleged grav-waves spread/weaken in physically effective terms during that 3 billion lightyear transit that...

- ALSO according to BB 'model' has spacetime EXPANDING while that space transit of 3 billion lightyears is underway.

Can you or anyone actually support this claim to have 'detected' a signal of 'grav-waves' from a BH merger 3 billion lightyears distant at time of merger/emission from alleged source 'there'?

I would be very interested to see your/anyone's calculations in support of this claim that they can differentiate such alleged emissions from so far away over closer random grav-wave 'signals'. Thanks.
SlartiBartfast
4.1 / 5 (14) Jun 01, 2017

I would be very interested to see your/anyone's calculations in support of this claim that they can differentiate such alleged emissions from so far away over closer random grav-wave 'signals'.


It's already in the literature. If you were really that interested, you'd just go read it yourself. But something tells me your real interest is simply in trolling.
RealityCheck
3 / 5 (8) Jun 01, 2017
@SlartiBartFast.
It's already in the literature. If you were really that interested, you'd just go read it yourself. But something tells me your real interest is simply in trolling.
No, mate; you are incorrect to assume such a thing. I am genuine, as always. I have been reading the LIGO literature since the first claimed 'detection'. I only find their interpretative-model-dependent 'analysis/fitting' of 'signals' to expected signal shapes' etc. I must have missed any actual calculations which actually prove the quadrupolar grav-wave components would retain sufficient physical effect strength after such long distance travel, even across a NON-expanding space, let alone after alleged BB/INFLATION theory space EXPANSION that said waves traversed in THREE BILLION LIGHTYEARS.

Anyhow, if "it's there" as you claim, Slarti, can you/anyone actually point a link to what I asked about (not just the 'model fitting' data-massaging/interpreting 'math techniques')? Thanks, Slarti.
Da Schneib
3.7 / 5 (9) Jun 01, 2017
Looking at the x-section graph, why do they call it a neutron star when it is made of layers of electrons, neutrons and protons ( including others). The outer most major layer is electrons. Shouldn't it be called an electron star?
Because it's *mostly* neutrons. Note that the density ramps very, very fast meaning that most of the mass is inside, overwhelmingly so. The thickest part is the outer core which is almost completely neutrons.
Da Schneib
4.3 / 5 (12) Jun 01, 2017
The article states ...

"While LIGO is uniquely suited to observing these types of events, we hope to see other types of astrophysical events soon, such as the violent collision of two neutron stars."

It sounds like they are hoping to invest the public in further conjecture without any requirement to FIRST definitively localize the sources.


OK genius, how would you do that? Armed with your degree in BS and obfuscation? Please, do explain for us mere mortals.
I don't know which one of the nutjobs wrote that, but apparently they haven't noticed VIRGO (operational and collaborating with LIGO), not to mention GEO600 (operational and collaborating with LIGO) and KAGRA (currently in the final phase of construction and tuning). Then there are LISA and DECIGO, but those are a ways out, as is the Indian LIGO.
Da Schneib
3.5 / 5 (13) Jun 01, 2017
I can't for the life of me imagine how the #gravitydeniers explain simultaneous detection at no less than four gravitational observatories spread across two continents if there aren't any gravity waves. What else could this possibly be? I mean, really, if you're going to rip down relativity, what have you got in your back pocket that you claim is better? Bueller?

C'mon, people, let's at least try to stick to something with a general resemblance to reality, shall we?
krzychu01230
2.2 / 5 (5) Jun 02, 2017
How solar systems is stable if gravity possess c speeds delay? Slingshot effect should disrupt obits.
Osiris1
1.4 / 5 (5) Jun 02, 2017
Is it not odd that so many supermassive black holse are colliding, or could it be that gravitational waves really DO move at >c, and those that disagree are thje real reality 'deniers'.
Osiris1
1 / 5 (4) Jun 02, 2017
It cannot be proven untrue the conjecture that black holes are truly a rip in the fabric of spacetime at one, and the outward evidence of the creation of a higher dimnensional object within that rip. We also cannot prove that time is not dimensional as well, with timelines having six degrees of freedom, three instantaneousely temporal-linear and three instantaneousely temporal-angular. Our universe appears to select a subset of the eleven or more available dimensions, three spacelike and three others timelike. This universe is not only strange, but stranger than we can imagine lightly. The only stricture is that we can not go back in time on a timeline congruent to our past, however convoluted that is. There is no such thing as causality otherwise, so everyone's 'grandfather' is safe.
Osiris1
1 / 5 (4) Jun 02, 2017
It cannot be proven untrue the conjecture that black holes are truly a rip in the fabric of spacetime at one, and the outward evidence of the creation of a higher dimnensional object within that rip. We also cannot prove that time is not dimensional as well, with timelines having six degrees of freedom, three instantaneousely temporal-linear and three instantaneousely temporal-angular. Our universe appears to select a subset of the eleven or more available dimensions, three spacelike and three others timelike. This universe is not only strange, but stranger than we can imagine lightly. The only stricture is that we can not go back in time on a timeline congruent to our past, however convoluted that is. There is no such thing as causality otherwise, so everyone's 'grandfather' is safe.
antialias_physorg
4.4 / 5 (7) Jun 02, 2017
How solar systems is stable if gravity possess c speeds delay? Slingshot effect should disrupt obits.

it would only be an issue if (huge) masses were suddenly accelerating or decelerating - which isn't happening in the solar system.
You *can* look at planets in orbit as being accelerated towards the center. But this is not sudden (or huge masses). Still, this acceleration does cause each of these systems to emit gravitational waves. But if you do the math then the power ogf these gravitational waves emitted e.g. by the Earth-Sun system is very low (about 200 Watts).
This would move Earth closer to the sun (at a very sloooow rate), however there are so many other factors affecting Earth orbit that this one is pretty negligible.

For a simple explainer why gravitational delay isn't a problem read this:
http://math.ucr.e...eed.html
devier_n
1 / 5 (1) Jun 02, 2017
"There are two primary models to explain how binary pairs of black holes can be formed. The first model proposes that the black holes are born together: they form when each star in a pair of stars explodes, and then, because the original stars were spinning in alignment, the black holes likely remain aligned."

So from two stars, we get two black holes. But the two stars didn't collapsed at the same time, it was one after an other. So by collapsing the first star's size reduces and it's gravitational field forces increases, making it able to capture the light.
How could the two bodies continue rotating just like when they were two stars, if one's gravitational acceleration is stronger than before?
SlartiBartfast
4 / 5 (8) Jun 02, 2017
Is it not odd that so many supermassive black holse are colliding, or could it be that gravitational waves really DO move at >c, and those that disagree are thje real reality 'deniers'.


It might be odd if we were actually detecting them. But all the detections so far are from stellar-mass black holes.

And your second point is a complete non sequitir. How would faster-than-light propagation of gravitational waves cause more detection events? How would it change the nature of those events? Why do you think gravitational waves travel faster than light? If you haven't even presented an argument (and I'd bet dollars to doughnuts you don't even have a coherent one), you can't suggest that people who disagree with you are "deniers".
tttito
4.2 / 5 (5) Jun 02, 2017
Uhm, "what else could this possibly be?" is hardly a scientific argument. I am looking forward to detection of gravitational waves from an otherwise observable event. LIGO is picking up a signal, but whether it's a gravitational wave or a measurement snafu is not entirely obvious to me. "A posteriori" data fitting works wonders. I'd find detection associated with a gamma-ray burst (à la GRB 070201, which however did not trigger detection) far more convincing.
antialias_physorg
4.6 / 5 (9) Jun 02, 2017
So by collapsing the first star's size reduces and it's gravitational field forces increases, making it able to capture the light.

The collapse of a star does not increase its (far) gravitational field. Gravity is a function of mass (not density) and that doesn't change.

If you were to replace the sun with a 1-solar-mass black hole we would orbit it just the way we orbit the sun now. No difference whatsoever (OK, it would be a little darker).

If you had a seriously heat resistant craft and dove towards the sun gravity would increase. Once you pass the surface of the sun and start diving down towards its center gravity would decrease (as all the mass above you now pulls in the opposite direction). But if it were converted to a black hole and you take the same journey the gravity increase would be *exactly* the same until you hit the distance of the former sun's surface. After that gravity would still increase. Only in this region is there any difference.
antialias_physorg
4.3 / 5 (6) Jun 02, 2017
It might be odd if we were actually detecting them. But all the detections so far are from stellar-mass black holes.

Which is not surprising, since the detectors we have are only sensitive in the frequency range of stellar size BHs (which is roughly the range of 5 to several tens of solar mass).
(Secondly - even when we get appropriate detectors - there are probably a lot less supermassive black holes than others...so we should expect to detect many more small mergers than those involving supermassive BHs)

Big black holes would produce, at first glance surprisingly, lower frequency signals which are harder to detect. At second glance this makes sense because the event horizons of these are bigger and thus the angular momentum some inspiralling other black hole has before the actual merger takes place is lower.

and I'd bet dollars to doughnuts

Doughnuts costing more than a dollar now I think that phrase needs to be retired.
Chris_Reeve
2 / 5 (4) Jun 02, 2017
Re: "I can't for the life of me imagine how the #gravitydeniers explain simultaneous detection at no less than four gravitational observatories spread across two continents if there aren't any gravity waves. What else could this possibly be?"

Cosmology and astrophysics are NOT an episode of Sherlock Holmes.

http://theness.co...fallacy/

"Sherlock Holmes was working within a specific framework – a materialist, rational, scientific view of the world. Within that framework this process of elimination works well ...

In practice this process does not always work because our knowledge is incomplete ...

There is also a very practical consideration in applying this principle – how complete is your set of alternate explanations?"
antialias_physorg
4.5 / 5 (8) Jun 02, 2017
LIGO is picking up a signal, but whether it's a gravitational wave or a measurement snafu is not entirely obvious to me

It's not just a random fluke.
1) The signal has a very characteristic (and predicted) signature: a rising 'chirp' followed by a ringdown signal.
2) The signal is detected at several locations with a time lag that is consistent with the speed of light of such a wave

You can actually go ahead and calculate the likelyhood of a random fluctuation causing such a signal in both detectors so that it would be mistaken for a gravitational wave (this is called a 'false positive'). They crunched the numbers for this during the run up to experiments (characterizing the noise during detector setup and calibration)

The chance for the signal having been a false positive comes out to 1 in 4.6 million. With several detections that is now even lower. This is beyond the thershold needed to claim a discovery.
Da Schneib
4.9 / 5 (7) Jun 02, 2017
Uhm, "what else could this possibly be?" is hardly a scientific argument. I am looking forward to detection of gravitational waves from an otherwise observable event. LIGO is picking up a signal, but whether it's a gravitational wave or a measurement snafu is not entirely obvious to me. "A posteriori" data fitting works wonders. I'd find detection associated with a gamma-ray burst (à la GRB 070201, which however did not trigger detection) far more convincing.
@tittio, this is a very specific signal called a "ringdown." It has a highly distinctive changing envelope and form. This precise signal was predicted by relativity. This signal is not detected at a single site, but (for the most recent one) four separate sites around the world, nearly simultaneously (speed-of-light delay between the four sites), and nothing like it for a year or so of watching.
[contd]
Da Schneib
4.5 / 5 (8) Jun 02, 2017
[contd]
This is as distinctive as the signature of iron in a spectrum. If you see that spectral signature, there was iron there; if you see this one, there was a merger of black holes there. It's really just that simple.
tttito
3 / 5 (2) Jun 02, 2017
"It's not just a random fluke. "

I does not need to be a random fluctuation, Complex systems may have complex, highly structured, yet "a priori" unpredictable behaviour. There may be an interference affecting the apparatus, caused by a signal that has nothing to do with gravitational waves. Errors are smart.
"The chance for the signal having been a false positive comes out to 1 in 4.6 million."

Sure, under the assumptions that you are building into your error model.
As long as the detection of gravitational waves is predicated on the technical accuracy of LIGO, of the theoretical assumptions underlying it, of the the largely untested black hole merger models used and on back-fitting of the data to otherwise completely hypothetical distant black holes (mind, not distant black holes in general, but the black holes supposedly triggering the signal) , without a shred of external evidence, I believe there is reason to remain cautious. More below.
antialias_physorg
5 / 5 (4) Jun 02, 2017
I does not need to be a random fluctuation, Complex systems may have complex, highly structured, yet "a priori" unpredictable behaviour.

That's why you go through the entire "set up and characterize noise" rigmarole - each part separately and parts in combination with each - before you turn it on for actual measurements. The science behind this kind of approach is solid and has been used for many decades on all kinds of systems. This is not just calculation. This is based on actual measurements performed on the real hardware.
tttito
5 / 5 (3) Jun 02, 2017
My point is that you have to show first that the signal corresponds to an actual event associated to the supposed gravitational waves being measured. If you build a cat detector (or a unicorn detector), you gotta first show that it's triggered only by cats (unicorns). You need a cat, or at least the independent signal of a cat, in order to do that. You do not prove both its accuracy and the existence of cats just because it clicks.
this is a very specific signal called a "ringdown."

Yes, this is a key point. But complex system may yield patterns, especially when they are subjected to targeted data filtering. When the existence of a phenomenon depends only on the signal of an apparatus built to verify its existence, I smell bias.
As I wrote, I'd find detection associated with a concurring external event far more convincing. LIGO has already declared its ability to deliver on that: http://m.caltech.edu/news/ligo-sheds-light-cosmic-event-1367 .
I'm looking forward to it.
tttito
5 / 5 (3) Jun 02, 2017
To clarify my last remark. LIGO confidently ruled out that GRB 070201 could have originated in Andromeda from a broad class of events. This means that events of that class originating at a comparable distance would be detected, then and even more so now. If they will detect purported gravitational waves and, say, a concurring gamma ray burst along the lines of GRB 070201, then I'll be convinced. But "Trust our models, trust that the universe we are building to make sense of our signal in the way we want and hope is real!" in my opinion is not something a scientist should swallow without chewing.
Thank you for your attention and for the valuable feedback.
Hat1208
4.3 / 5 (6) Jun 02, 2017
Uhm, "what else could this possibly be?" is hardly a scientific argument. I am looking forward to detection of gravitational waves from an otherwise observable event. LIGO is picking up a signal, but whether it's a gravitational wave or a measurement snafu is not entirely obvious to me. "A posteriori" data fitting works wonders. I'd find detection associated with a gamma-ray burst (à la GRB 070201, which however did not trigger detection) far more convincing.

Talk about building assumptions into your error model.

Protoplasmix
5 / 5 (1) Jun 02, 2017
So by collapsing the first star's size reduces and it's gravitational field forces increases, making it able to capture the light.
The collapse of a star does not increase its (far) gravitational field. Gravity is a function of mass (not density) and that doesn't change.

If you were to replace the sun with a 1-solar-mass black hole we would orbit it just the way we orbit the sun now. No difference whatsoever (OK, it would be a little darker).
True, and true. An interesting aside (re density, or "compact") would be replacing the sun with a spinning neutron star that had surface irregularities and/or starquakes – then GWs would be detected. (Quite dark then too, but we'd be fine utilizing the thorium fuel cycle, e.g., molten salt reactor. Why are we burning fossil fuels at all? The corrupt humans with all the guns and money, that's why).
burky
2 / 5 (4) Jun 02, 2017
All three detected events by LIGO so far seem to either coincide with or be uncomfortably close to lunar events (new, full). For those who argue that moon's pull should be smooth and should not trigger an event, we should be aware that almost no real-world effect is in fact smooth, given that complex interactions abound. Take turbulence, for example. That's especially a concern, given LIGO's extremely sensitive detector. Secondly, LIGO was also built to detect collisions by neutron stars. If LIGO detects any such event, that would have made it easier for the broader astronomy community to help verify an event. Instead, what LIGO now has amounts to a literally black hole data point that lends itself to relatively arbitrary interpretation. True, there's the signature ringdown. But as others have already pointed out, data filtering/fitting works wonders. Yes, yes, we now know black holes jiggle. With more detectors coming online in the future, we can then have a much convincing picture.
tttito
5 / 5 (1) Jun 02, 2017
"four separate sites around the world, nearly simultaneously (speed-of-light delay between the four sites), and nothing like it for a year or so of watching.

Uhm, four is better than two, but here it says: "The detection, announced by researchers on 1 June, was made in January by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Louisiana and Washington state. " and "Some time this summer, LIGO's sister observatory Virgo should come online in Italy, and a fourth interferometer is due to start operations in Japan perhaps as early as next year." https://www.natur...12333208

tttito
5 / 5 (1) Jun 02, 2017
All three detected events by LIGO so far seem to either coincide with or be uncomfortably close to lunar events (new, full)


Wow! Regardless of its scientific merit, this has huge entertainment value!
antialias_physorg
5 / 5 (4) Jun 02, 2017
lunar events (new, full)

Seriously? I mean...seriously? You post *this* on a science website as an argument?
Do you even know what new/full moon is?

I..

This..

Words fail me.
burky
not rated yet Jun 02, 2017
lunar events (new, full)

Seriously? I mean...seriously? You post *this* on a science website as an argument?
Do you even know what new/full moon is?

I..

This..

Words fail me.

I was not talking about GW there regarding the pull from the moon. I was talking about plain old gravity pull on the massive suspended LIGO mirrors. But what have you detected in my previous comment that had you almost pass out? It appears that you are more sensitive than LIGO and more entitled to expressing your own scientific opinions on a public website than LIGO was entitled to the billion in public funding. Well, then, educate me about what new/full moon is, Professor Antialias.
antialias_physorg
5 / 5 (3) Jun 02, 2017
I was talking about plain old gravity pull on the massive suspended LIGO mirrors.

Look at the signal. Read the articles published on it. Linking this to the moon is beyond idiotic. You make the EU crowd seem sane by comparison. The moon doesn't just change its pull to create a chirp and ringdown signal because it's full or new or half or whatnot.

(By the time delay of the signal between the detectors we can get a rough direction of where the signal came from. Hint. Not the moon.)

Da Schneib
5 / 5 (1) Jun 02, 2017
@tttito (and apologies for misspelling it earlier):
My point is that you have to show first that the signal corresponds to an actual event associated to the supposed gravitational waves being measured.
OK. So first, I did point out that the exact signature is predicted, and has been for decades. Second, this is not a random fluctuation; such a fluctuation could not happen (nearly) simultaneously at four widely geographically separated sites. Four of them, in fact, two of which use equipment of significantly different design with different software and different algorithms. They all saw it.

So we know for sure an event occurred, and we know for sure its signature matches the prediction of theory, a theory which has already been widely confirmed by experiments that involve phenomena not associated with gravity waves. Bear in mind as well that the characteristics are sufficient not merely to say, Gee, we saw a gravity wave,
[contd]
Da Schneib
5 / 5 (1) Jun 02, 2017
[contd]
but rather, Gee, we saw a gravity wave, and its characteristics indicate two black holes of masses X and Y at this distance. I haven't checked the findings yet so I'll make no statements about direction, but with four data swathes I'll be surprised if they can't get that too. Certainly by the time the Japanese detector undergoing final test and tuning comes on line, we'll have the best shot we're going to get with detectors in Europe, the US, and Asia.

The signs of having done all their homework and eliminated every little thing to make as sure as it's possible to be with state-of-the-art hardware and processing are all there. I think you're mischaracterizing this, particularly when you ignore the fact that these are four completely geographically separate systems two of which use different technology, and they all got the same result at the same time. Each detector is capable of establishing by itself that it has seen a gravity wave; and all four of them did.
[contd]
burky
5 / 5 (1) Jun 02, 2017
I was talking about plain old gravity pull on the massive suspended LIGO mirrors.

Look at the signal. Read the articles published on it. Linking this to the moon is beyond idiotic. You make the EU crowd seem sane by comparison. The moon doesn't just change its pull to create a chirp and ringdown signal because it's full or new or half or whatnot.

(By the time delay of the signal between the detectors we can get a rough direction of where the signal came from. Hint. Not the moon.)



I assume that, in making inference about where the signal came from by the time delay of the signal between the detectors, you are again relying on your model. Have you ruled out all other possibilities (beyond your model)? I was offering an example of other possibilities that you are welcome to refute. But please refrain from making personal attacks - you don't even know whom I am or my background. Please.
tttito
5 / 5 (1) Jun 02, 2017
It is a fact that LIGO takes into account the Moon's gravity ([1]).
It is also known that full and new moons correspond to increased earthquake magnitude ([2]), via tidal stresses, which may well affect the LIGO mirrors.
I doubt that's related to the signal, but I don't see why anyone should be insulted for bringing it up.
[1] http://www.ast.ca...ask/2519
[2] https://www.scien...hquakes/
Da Schneib
3 / 5 (2) Jun 02, 2017
[contd]
If you build a cat detector (or a unicorn detector), you gotta first show that it's triggered only by cats (unicorns). You need a cat, or at least the independent signal of a cat, in order to do that. You do not prove both its accuracy and the existence of cats just because it clicks.
I'd say we made a detailed description of a unicorn, not just "looks like a horse and has a horn" but like, possible hair colors, structure of the cannon bones, DNA, what it eats and what it excretes, how fast it can run, etc., etc., etc., and then we made our unicorn detector. And we found a unicorn. Nobody's ever seen one before, so how else can you test it? Once you've detected one, *now* you have a unicorn. Examination of the process of specification is what shows the rigor in the design of the detector; if the specification is sufficiently rigorous, then you don't absolutely have to have a unicorn to declare your detector saw one. And this is inherent;
[contd]
Da Schneib
3 / 5 (2) Jun 02, 2017
[contd]
the entire purpose of science is to find things that have never been found before, to make predictions and validate them by looking for data that confirms-- and, importantly, denies-- them, and to, in terms of your thought experiment, find unicorns. When no one has ever seen a unicorn before.

this is a very specific signal called a "ringdown."

Yes, this is a key point. But complex system may yield patterns, especially when they are subjected to targeted data filtering. When the existence of a phenomenon depends only on the signal of an apparatus built to verify its existence, I smell bias.
I don't. Not at four separate sites, two of which use distinct hardware and different software and different algorithms. Where's the bias going to come from? How do you get the exact same glitch pattern from different hardware if there's not really a glitch? Never mind different filters, different software, different algorithms, etc. I think you're quibbling.
[contd]
Dingbone
Jun 02, 2017
This comment has been removed by a moderator.
tttito
5 / 5 (1) Jun 02, 2017
@Da Schneib Read my comment above. Please provide a reference, possibly more reliable than the linked Nature article therein, for your claim that it's four detectors and not two. As for your arguments, I think I have already addressed them. My point is, again, as far as I am concerned, the signal must correspond to an independently detectable event, Constructing an otherwise undetectable event to fit the measurements through data filtering and parameter/model adjusting will not convince me fully. Fitting a model to in-sample data is just not the same as predicting out-of-sample events, which is the way scientific hypotheses must be tested.
Da Schneib
5 / 5 (1) Jun 02, 2017
[contd]
As I wrote, I'd find detection associated with a concurring external event far more convincing.
I'm going with four concurring events, each separate, each distinct, and each identical despite different hardware, software, and algorithms used for two of them. Remember, each of these is a complete standalone gravitational wave observatory. This is like requiring an "external event" to validate that two telescopes, one in Australia and one in South America, saw the same occultation of Io in its orbit around Jupiter. Like I said, quibbling.

LIGO has already declared its ability to deliver on that: http://m.caltech.edu/news/ligo-sheds-light-cosmic-event-1367 .
I'm looking forward to it.
Meh, the GRB was from 2007. That's original LIGO, and Advanced LIGO wasn't online then.
Da Schneib
5 / 5 (1) Jun 02, 2017
@tttito, for the moment, I'll note that your CalTech reference is for 2007, and that the current status pages for LIGO and VIRGO indicate they are collaborating, and your own reference includes GEO600 and says it's part of the data gathering equipment- and that's in Germany.

I'll have to check the exact dates, but unless I'm mistaken I've got four.

I have to get back to work, so don't expect anything until tonight.
tttito
5 / 5 (1) Jun 02, 2017
Meh, the GRB was from 2007. That's original LIGO, and Advanced LIGO wasn't online then.

That's irrelevant. They stated: "The burst had occurred along a line of sight that was consistent with it originating from one of Andromeda's spiral arms, and a binary coalescence event--the merger of two neutron stars or black holes, for example--was considered among the most likely explanations. Such a monumental cosmic event occurring in a nearby galaxy should have generated gravitational waves that would be easily measured by the ultrasensitive LIGO detectors. The absence of a gravitational-wave signal meant GRB070201 could not have originated in this way in Andromeda. " [1] Did they change their mind? Were they clowns in 2007?
As I wrote "This means that events of that class originating at a comparable distance would be detected, then and even more so now." Even more so now with Advanced LIGO.
[1] http://m.caltech.edu/news/ligo-sheds-light-cosmic-event-1367
Da Schneib
5 / 5 (1) Jun 02, 2017
No, it's not irrelevant; your own source says GEO600 was collaborating with LIGO at the time of that GRB.

You're still quibbling.
Da Schneib
not rated yet Jun 02, 2017
OK, did a little research in a few off moments, apparently VIRGO was taking data previously with LIGO and will be again this summer, but was not taking data when GW170104 was detected. However, they did some data analysis on the LIGO take, and the announcements were by the entire combined LIGO-VIRGO team.

I'll also point out that we are still talking about two widely separated sites at minimum; this is part of LIGO's error checking.

I am still researching on GEO600.
burky
not rated yet Jun 02, 2017
The moon doesn't just change its pull to create a chirp and ringdown signal because it's full or new or half or whatnot.


Actually, how do we know the moon doesn't just change its gravitational pull at any moment? I doubt the gravitational pull from the moon is perfectly consistent. Is there no (internal) geological activities on the moon that might affect its pull on earthly objects at any moment, especially during new/full moon events when the sun the earth and the moon is aligned? After all, we are looking at an extremely sensitive detector here on earth (thank you!!!). If we were not armed with General Relativity, how would you interpret your data gathered from exactly the same instrument? Would you be telling us an entirely different story? How are we supposed to verify that story other than trusting the rigor of your process?
tttito
not rated yet Jun 02, 2017
We are discussing two separate issues. The first is the number of detectors involved in the 2017 experiment. The relevant source, a Nature article, which I mentioned above, is this one: https://www.natur...12333208 .
Then there is the LIGO 2007 claim about GRB070201, which for some reason you don't like: http://m.caltech.edu/news/ligo-sheds-light-cosmic-event-1367
The first issue is not so complex. Nature states that it is two detectors, you say it is four. Is Nature wrong?
"The detection, announced by researchers on 1 June, was made in January by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Louisiana and Washington state. "
As for the second issue, I don't see your point.
Da Schneib
not rated yet Jun 02, 2017
I'm fine with the CalTech article, they checked a 2007 GRB070201 to see if they found a glitch at LIGO, they saw nothing. That places it outside LIGO (of that time) detection limits. That means it's not a big gravity event, not close, or both. All that shows is GRBs aren't nearby black hole mergers.

First issue is sloppy science reporting on GW170104 unless GEO600 wasn't collecting data then, which I'm trying to establish. Pretty sure it was, they just didn't mention it, unless they are upgrading/testing.

Second issue point is, GEO600 has been part of LSC since at latest 2007 according to your own source. Did you miss that in the CalTech link you posted?

Side note: Can we refer to these events by their designations please?
Da Schneib
not rated yet Jun 02, 2017
Oh, and one more thing: note that unless it's been taken offline, there are actually two observatories at the Hanford site, and the Hanford and Livingston sites are ca. 3000 km apart. You have not yet addressed the second point, which is that two completely separate installations, each a fully functional GWO capable of detecting the "chirp" signal separately without reference to data from the other site, saw the same thing at essentially the same time and nothing remotely like it for many observing months and over a calendar year before that.

I still want to know what you propose made that "chirp" at two widely separated sites' completely separate data at the same time (again, within speed-of-light delay time). I've got something that makes exactly that "chirp," and it's called the Theory of General Relativity. And it wasn't the freakin' Moon, sorry that's a non-starter. Nor was it an earthquake, they monitor for those you know.
Da Schneib
not rated yet Jun 02, 2017
I'm looking for how you get the same signal, quite a unique one, at two completely separate pieces of hardware at geographically separate sites 3000 km apart at the same time (allowing for speed of light delay). That's the part that makes most of this silly. Data processing and claims about filtering are handwaving; separate data with the same datum from 3000 km apart is a cold hard brute fact.

We can quibble about 2, 3, 4, or 5 observatories, and different hardware, and so forth until the cows come home and it's only going to add a little bit of reliability; two observatories pushes it from 1 in a thousand to one in a million, and that's the big jump.
Da Schneib
not rated yet Jun 02, 2017
GEO600 science data collection runs with aLIGO are a bit fuzzy; they took data with aLIGO on the first run, where the first two GWs were detected. I don't know what their current status is and I'm tired of looking when we've got high sigma with two separate observatories and the only objection you can come up with is handwaving about "filtering."

If someone tells me two observatories at opposite ends of a continent see the same thing at the same time, I'm gonna give a great deal of credence to the idea that something really happened. If someone has a theory that predicted it, I'm gonna give even more.

Get something a little more concrete and get back to me.

If you seriously believe we won't see things with another GWO added when VIRGO comes online in the summer, I will wait for the results-- and I will expect you to capitulate and admit it when they come in.
burky
not rated yet Jun 02, 2017
We can quibble about 2, 3, 4, or 5 observatories, and different hardware, and so forth until the cows come home and it's only going to add a little bit of reliability; two observatories pushes it from 1 in a thousand to one in a million, and that's the big jump.


No, with just 2 observatories, you are actually having a hard time locating the source of the event in the sky. With 3 observatories, you can then pinpoint the source. With 4, you might, but hopefully not, identify a contradiction in terms of trying to pinpoint the source. Ultimately, I am looking forward to independent verification. And that might be possible when you are finally able to pinpoint the source.
Da Schneib
3 / 5 (2) Jun 02, 2017
@burky, doesn't matter if we can locate it in the sky. We know it happened, we know how far away it was, we know what the masses involved were.

With two sites we have independent verification; the rest is enhanced resolution, which is exactly what you should expect given how VLBI works with radio waves. The principles are nearly identical.

Are you arguing that "we haven't detected gravity waves?" Because if you are, this is a bankrupt argument; that's why there are two LIGO sites 3000 km apart. If you're arguing "we can't find the direction yet," I have no disagreement with that. Be specific please.
Da Schneib
3 / 5 (2) Jun 02, 2017
Just a little view in for lurkers: The parameters of the "chirp," that is, how many cycles, how their frequency varies over the ringdown, how big the final burst is, how far it is from the ringdown, and other parameters of it give us the distance and the masses. The timing difference between the sites gives us more information, and localizes it, but not to a spot, only a region. The more detectors, the smaller that region gets. As with radio direction finders, two sites gives you a region; but different from radio, with gravity three sites gives you a smaller region, not a spot. This is because of the different mathematical forms of gravity waves and radio waves.

I won't give more because it gets very complicated very fast and I'm just too damn lazy to do the math. We got astrophysicists here, but I'm not sure if we got relativists. If one shows up and can pop some math, more power to ya. I do computers, not physics.
Da Schneib
3 / 5 (2) Jun 02, 2017
Lemme put it this way: I don't insist on every fly around the unicorn's ass be in exactly the same position in order to call it a unicorn.
Protoplasmix
5 / 5 (1) Jun 03, 2017
I won't give more because it gets very complicated very fast and I'm just too damn lazy to do the math.
Lucky for us others have done it and it's not too hard to check:
Analysis of the Frequency Dependence of LIGO Directional Sensitivity (Antenna Pattern) and Implications for Detector Calibration.
See page 4 here for directional sensitivity vs. polarization.
Prospects for early localization of gravitational-wave signals
from compact binary coalescences with advanced detectors
(see Fig. 2 for a three-detector network antenna power pattern, and Fig. 3 for a four-detector network)
Da Schneib
not rated yet Jun 03, 2017
...which is why I didn't do it. For RDFs you don't need to use polarization, much less spherical harmonics. It's much more intuitive.

Ummm thanks.
antialias_physorg
5 / 5 (4) Jun 03, 2017
No, with just 2 observatories, you are actually having a hard time locating the source of the event in the sky.

This paper looks at how the source can be localized (using 2 or more detectors. The 2-detector case constraining the source to a plane)
https://arxiv.org...2264.pdf
With the 3 detector configurations resolution is lowest in plane with the detectors
(With 4 or more that no longer matters unless they are all co-planar)

...and, of course, resolution is always constrained by noise.
Reg Mundy
1 / 5 (1) Jun 03, 2017
They are not gravity waves, they are time distortions. Gravity does not exist, it is just a mathematical concept to model actuality, not reality itself.
Da Schneib
5 / 5 (6) Jun 04, 2017
A gravity physics thread on physorg wouldn't be complete without at least one nutjob claiming there's no gravity.

When you drop something and it doesn't fall, let us know, @Reg.
nikola_milovic_378
Jun 04, 2017
This comment has been removed by a moderator.
Reg Mundy
1 / 5 (1) Jun 04, 2017
@DS
A gravity physics thread on physorg wouldn't be complete without at least one nutjob claiming there's no gravity.

When you drop something and it doesn't fall, let us know, @Reg.

Ask an astronaut on the ISS the same question......
If you were inside a box with no way of communicating with the outside, how could you tell whether you were sitting on the surface of the Earth or onboard a spaceship accelerating at 10metres per second per second? Surely even you can appreciate that there is absolutely NO DIFFERENCE between gravity and acceleration? So, what is "gravity", apart from a totally unnecessary invention? Why don't you try THINKING instead of blurting your dogma on this site?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.