Simulations suggest other phenomenon besides black holes merging could produce gravity waves

May 2, 2016 by Bob Yirka report
Credit: V. Cardoso et al., Phys. Rev. Lett. (2016) , via Physics

(Phys.org)—A team of researchers with the University of Lisbon has created simulations that indicate that the gravitational waves detected by researchers with the LIGO project, and which are believed to have come about due to two black holes colliding, could just have easily come from another object such as a gravaster (objects which are believed to have their insides made of dark energy) or even a wormhole. In their paper published in Physical Review Letters, the team describes the simulations they created, what was seen and what they are hoping to find in the future.

Researchers working on the LIGO project created a lot of excitement earlier this year when they announced that they had made the first ever detection of . Most in the field believe that such waves are, or were, the result of two colliding. But, simulations created in this latest effort suggest that other sources are possible as well.

At issue are ringdowns, which are parts of the gravitational radiation that is emitted when a new but distorted black hole forms and takes shape after two other black holes have collided—as the waves decay a ringdown signal is emitted. But, other events can lead to ringdowns too, the researchers suggest, by so-called black-hole mimics—objects that are extremely compact, but do not have an event horizon—instead, they have light rings. In simulating and then comparing the ringdowns from such objects with those from black holes merging, the team found that under the right set of conditions, the two could be very nearly indistinguishable. But, they also report, as the ringdowns die out, the echoes they create take a long time to die, but as they do, the signal types eventually diverge, offering a means for identifying the original source.

Sadly, data from the LIGO project was not strong enough to show whether the ringdown die out resembled that of the simulated signal from a black hole collision or from some other object. But, going forward, as updates are made to equipment and future signals are detected, it should be possible, the team reports, to spot the differences, if the simulations are correct.

Explore further: LIGO researchers suggest background noise due to gravity waves may be much greater than thought

More information: Vitor Cardoso et al. Is the Gravitational-Wave Ringdown a Probe of the Event Horizon?, Physical Review Letters (2016). DOI: 10.1103/PhysRevLett.116.171101 , On Arxiv: http://arxiv.org/abs/1602.07309

ABSTRACT
It is commonly believed that the ringdown signal from a binary coalescence provides a conclusive proof for the formation of an event horizon after the merger. This expectation is based on the assumption that the ringdown waveform at intermediate times is dominated by the quasinormal modes of the final object. We point out that this assumption should be taken with great care, and that very compact objects with a light ring will display a similar ringdown stage, even when their quasinormal-mode spectrum is completely different from that of a black hole. In other words, universal ringdown waveforms indicate the presence of light rings, rather than of horizons. Only precision observations of the late-time ringdown signal, where the differences in the quasinormal-mode spectrum eventually show up, can be used to rule out exotic alternatives to black holes and to test quantum effects at the horizon scale.

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antialias_physorg
4.6 / 5 (10) May 02, 2016
OK...if I'm reading their paper correct (and I'm not at all sure that I do) they are saying that the ringdown characteristics will be different due to the different extents of gravastars/wormholes as opposed to black holes. So therefore w' / w'' of the quasinormal modes is different.

But shouldn't that difference also show up in the chirp part of the signal (possibly the chirp for 'true' black holes should be shorter than those for other types of super dense objects?). That difference would be a lot easier to discern than the tail end of the ringdown.
axemaster
4.6 / 5 (9) May 02, 2016
Perhaps it's different at the end because when black holes merge, the mass concentrations merge to the very center, while with material objects the matter will stop at a finite radius? So the radiated gravity waves would be different at the end.
antialias_physorg
4.6 / 5 (9) May 02, 2016
Perhaps it's different at the end because when black holes merge, the mass concentrations merge to the very center, while with material objects the matter will stop at a finite radius? So the radiated gravity waves would be different at the end.


Looking at figure 4 of the linked arxiv article it seems that they are taking the opposite case (wormhole) where the merger doesn't happen at the center but the particle passes through...which allows for a ringdown signal that continues on longer than that of a black hole merger (which stops as the singularities - or whatever counts as a center for a BH - merge)

Totally weird. It's vexing that the signal difference only happens at the tail end of the ringdown. Been rerereading the paper, but I'm having a hard time understanding a few parts. Can you slog through it?
compose
May 02, 2016
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antialias_physorg
4.5 / 5 (15) May 02, 2016
The LIGO signal published was carefully selected from many others by its similarity to mainstream model of black holes - so I don't quite understand, how it could serve as an evidence of their violation.


1) No one is talking violation
2) The difference would show up in a part of the signal that is too weak to detect, yet (so it, naturally, wasn't part of the detection/selection criteria)
compose
May 02, 2016
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ogg_ogg
2.1 / 5 (11) May 02, 2016
So, where's the second paper reporting the 2nd, 3rd, 4th and 5th gravitational wave events? I'm waiting.........
(I chose 4 simply because √4 =2, a significant increase in the confidence we can place in the information.) (It's both a bit greedy, and a bit optimistic)
katesisco
1.4 / 5 (11) May 02, 2016
Before the claim was mediaized, and the sun was long delayed in its magnetic reversal, I suggest there was a detectable 'wave', a magntic soliton perhaps, that swept the Earth and was felt by many other than myself.
Obviously not a gravity wave.
compose
May 02, 2016
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Da Schneib
4.6 / 5 (9) May 02, 2016
Worth pointing out that they still would be gravity waves, and also that either a wormhole or a gravastar would be equal evidence in favor of GRT-- both are out of the mainstream, but neither violates GRT.
compose
May 02, 2016
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compose
May 02, 2016
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compose
May 02, 2016
This comment has been removed by a moderator.
obama_socks
1.7 / 5 (12) May 03, 2016
So, what is going on? Did the chirp actually COME FROM a gravitational wave...or not? Was the signal from the GW or from the GRB that quickly followed? And was all the celebratory hoopla a bit premature like I thought? And where are the rest of the waves? Anything?
What happened to the original EH? Did it disappear after the collision and merging of the 2 BH, or did it renew and reform itself after the formation of one BH from the two.
From two, one...almost like coitus, then a baby BH. Am I making myself clear or not?
And how the hell does a "wormhole" get created from that collision and merger?
Mimath224
4.5 / 5 (8) May 03, 2016
@antialias_physorg, Da Schneib, Hi, sorry I have this 'thing' about simulations...particularly concerning topics of which we know little. How can a simulation include an object such as a 'gravaster (objects which are believed to have their insides made of dark energy)' and that's the first time I've heard that one. I've heard of the Dark-Energy Star and Gravastar but DES is a different hypothetical object to that of Gravastar. How do they put into the simulation, properties of DE when we don't even know what it is? Perhaps you could enlighten this confused layman. Thanks
shavera
4.6 / 5 (11) May 03, 2016
Did the chirp actually COME FROM a gravitational wave...or not?

1) the signal matched the prediction from merging black holes.
2) Scientists, despite the persistent claims of trolls on this site, do actually perform due diligence studies looking to disprove their initial hypothesis.
3) Some scientists have found that there are other types of very hypothetical things that could produce similar kinds of signals.
4) For yet *other* physical reasons, those things aren't particularly likely to exist anyway.
5) Following the principle of invoking the fewest unjustified assumptions, we have good reason to think black holes exist, and that they may orbit, and that their orbits may decay.
6) Science, as a way of describing reality, has generally tended to say that the simplest (point 5) model is the 'scientific answer' to some question. Whether this is the capital-T Truth is not really the point, and may never be known
therefore, for now, merging black holes is the 'answer.'.
shavera
4.7 / 5 (12) May 03, 2016
I think that nearly everything misunderstood about science is point 6. There's a mistaken belief that when science says something happens that it is the absolute true description of reality. This is an exaggeration of the capacity of science. What science can do is predict the outcomes of experiments.

Science, the theory of GR, predicted that black holes exist, orbit, and merge. When such a process occurs, an experiment constructed in a certain way would have a certain kind of signal. Such a signal was found, supporting the initial hypothesis.

It very well could be that some magician in a distant galaxy did some magic to make gravitational waves happen. That might be the "Truth." But it's not a scientific answer to a question Unless we could find evidence of this wizard, proof that they can cause g. waves, proof that they caused the event observed on Earth, and so on.

Ie, a scientific answer is whatever it is, until it isn't because something else tells us otherwise..
antialias_physorg
4.6 / 5 (11) May 03, 2016
How can a simulation include an object such as a 'gravaster

Gravastar are one of these kinds of objects that aren't really forbidden to exist by current theory. That doesn't mean they exist. They're on the 'highly contentious' side of the spectrum.


Ie, a scientific answer is whatever it is, until it isn't because something else tells us otherwise..

Or simply: Science is that which works best. It doesn't concern itself with abstracts like 'truth'.

One can even make a philosophical argument that a scienctific theory either cannot be 100% capital-T truth or that if is then we cannot know that it is.
It's a bit like 'perfection'. Can something be perfect? Maybe. Can you know if it is perfect? No, because you have nothing to measure it by. You could only measure a prefect thing by itself (because anything else would be less perfect by definition)
Da Schneib
4.6 / 5 (9) May 03, 2016
@Da Schneib, Hi, sorry I have this 'thing' about simulations...particularly concerning topics of which we know little. How can a simulation include an object such as a 'gravaster (objects which are believed to have their insides made of dark energy)' and that's the first time I've heard that one. I've heard of the Dark-Energy Star and Gravastar but DES is a different hypothetical object to that of Gravastar. How do they put into the simulation, properties of DE when we don't even know what it is? Perhaps you could enlighten this confused layman. Thanks
Sure. These objects have been hypothesized and by that I mean derived as possible solutions to the Einstein Field Equations of GRT. This makes them mathematically tractable to simulation. The authors of the paper are quibbling, which is something that happens all the time. Their quibbles cannot be immediately dismissed but the path to doing so is clear since there are signature differences we just can't detect yet.
cantdrive85
1.3 / 5 (13) May 03, 2016
I hear unicorn farts are the real cause of GW's.
obama_socks
1.7 / 5 (11) May 05, 2016
They are all the rage in Scienceville.
Benni
1.7 / 5 (11) May 05, 2016
Science, the theory of GR, predicted that black holes exist, orbit, and merge


That General Relativity "predicted that black holes exist......" is pure unadulterated malarky totally made up inside your infertile brain.

You have been on this site making all manner of unfounded statements about many things contradicting Einstein's & SR & GR. You have made statements that MASS & ENERGY are not EQUIVALENT, proving you do not have the slightest comprehension of Special Relativity or that you even knew such a thesis even existed.

Now you claim GR predicts the existence of Black Holes in spite of Einstein's clear denials that his Field Equations could never be used to deflect photons in a manner that BHs could be created.

Okay, then tell us where to locate your claim in GR of BHs. You must have hard numbers Einstein was just to inept to come up with....but you're smarter than Einstein & discovered within his Field Equations what he couldn't.
Mimath224
4.6 / 5 (11) May 05, 2016
antialias_physorg & Da Schneib Thanks for your comments. Much appreciated. Have a nice w/e

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