Spacetime ripples from dying black holes could help reveal how they formed

Sep 17, 2012
This artist's concept shows a galaxy with a supermassive black hole at its core. The black hole is shooting out jets of radio waves. Image credit: NASA/JPL-Caltech

(Phys.org)—Researchers from Cardiff University have discovered a new property of black holes: their dying tones could reveal the cosmic crash that produced them.

Black holes are regions of space where is so strong that not even light can escape and so isolated black holes are truly dark objects and don't emit any form of radiation.

However, black holes that get deformed, because of other black holes or stars crashing into them, are known to emit a new sort of , called gravitational waves, which predicted nearly a hundred years ago.

Gravitational waves are ripples in the fabric of spacetime that travel at the but they are extremely difficult to detect.

Kilometer-sized laser interferometers are being built in the US, Europe, Japan and India, to detect these waves from colliding black holes and other . They are sensitive to gravitational waves in roughly the same as audible , and can be thought of as a microphone to gravitational waves.

Two black holes orbiting around each other emit gravitational waves and lose energy; eventually they come together and collide to produce a black hole that is initially highly deformed. Gravitational waves from a deformed black hole come out not in one tone but in a mixture of a number of different tones, very much like the dying tones of a ringing bell.

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In the case of black holes, the frequency of each tone and rate at which the tones decay depend only on the two parameters that characterize a black hole: its mass and how rapidly it spins.

Therefore scientists have long believed that by detecting the of a black hole and measuring their frequencies one can measure the mass and spin of a black hole without going anywhere near it.

Ioannis Kamaretsos, Mark Hannam and B. Sathyaprakash of Cardiff University used Cardiff's powerful ARCCA cluster to perform a large number of of a pair of black holes crashing against each other, and found that the different tones of a ringing black hole can actually tell us much more.

The team's findings will appear in the Physical Review Letters.

"By comparing the strengths of the different tones, it is possible not only to learn about the final black hole, but also the properties of the original two black holes that took part in the collision," explained Ioannis Kamaretsos, who performed the simulations as part of his PhD research.

He added, "It is exciting that the details of the late inspiral and merger are imprinted on the waves from the deformed final black hole. If General Relativity is correct, we may be able to make clear how very massive black holes in the centres of galaxies have shaped galactic evolution.

We never guessed it would be possible to weigh two black holes after they've collided and merged," said Dr Mark Hannam.

"We might even be able to use these results to test Einstein's general theory of relativity. We can compare the waves we observe from the orbiting black holes with the waves from the merged black hole, and check whether they are consistent," he added.

Professor B Sathyaprakash, who has spent his whole career studying commented: "It is quite remarkable. As in any new research, our finding opens up new questions: how accurately can we measure the parameters of the progenitor binary, whether our results hold good for more generic systems where initial black hole spins are arbitrarily oriented, etc. We will be addressing these questions in the coming years.

"Advanced gravitational wave detectors that are currently being built will provide us an opportunity to test our predictions in the coming decade."

Their research opens up a new avenue for studying the properties of the binary that produced the final black hole even when the binary itself is not visible to a gravitational wave detector. Future gravitational wave detectors should be able to study far heavier than what was thought possible before and hence enhance their science reach.

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User comments : 17

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El_Nose
3.2 / 5 (5) Sep 17, 2012
I am sorry I do not know ... but what are the dying tones of a ringing bell... and what do they sound like??
indio007
1.8 / 5 (5) Sep 17, 2012
I am sorry I do not know ... but what are the dying tones of a ringing bell... and what do they sound like??


They sound like bovine flatulence.
Parsec
5 / 5 (8) Sep 17, 2012
I am sorry I do not know ... but what are the dying tones of a ringing bell... and what do they sound like??

Only a phys org article would expect its readers to have seen the decaying tones of a bell or gong on an o-scope. If you haven't, the reference adds nothing to the article, because what you hear is a decaying main tone with all of its harmonics also decaying.

This article is also annoying because to my knowledge a gravity wave has never actually been detected by anything, from anything. And this wasn't mentioned.
PaxAeterna
4.5 / 5 (4) Sep 17, 2012
To expand a little on what Parsec said. Dying means decaying. The moment you stike the bell its sound starts to "die" or decay. A bell has a lot of harmonics, which gives it its clangy sound compared to other instruments.

They are simply comparing the simple harmonics of the wave of a black hole and the more complex, more harmonic containing wave of a newly merged black hole to the simple wave of a stringed instrument for example and the much more complex tones of a bell.

A bell also loses harmonics as it decays as does the merging blackholes.
Lurker2358
1 / 5 (4) Sep 17, 2012
Only a phys org article would expect its readers to have seen the decaying tones of a bell or gong on an o-scope. If you haven't, the reference adds nothing to the article, because what you hear is a decaying main tone with all of its harmonics also decaying.

This article is also annoying because to my knowledge a gravity wave has never actually been detected by anything, from anything. And this wasn't mentioned.


Based on works by Hawking and a few others on black holes, absolutely no "information" is supposed to escape a black hole, by any means, except possibly through "Hawking radiation".

Even if a gravity wave could escape, it would only carry away a portion of the black hole's angular momentum from it's rotation, which would effect it's overall mass by a relatively insignificant amount, and certainly wouldn't "kill" or "destroy" a black hole.

The only known way that a stellar black hole may die is through hawking radiation in absurd time scales of trillions of years.
Lurker2358
1 / 5 (2) Sep 17, 2012
I said "trillions" above, but I think the real calculation is a lot bigger than that, but I can't remember it. It's probably several orders of magnitude longer, because black holes should still be around even after all (existing) elementary particles decay.

Sonhouse
5 / 5 (2) Sep 17, 2012
Now all we need is a gravity wave detector that actually detects gravity waves....
lengould100
1 / 5 (1) Sep 17, 2012
Assuming gravity waves do exist, and that we can at some point detect them, and that gravity waves generated within the event horizon can escape the event horizon, THEN this should become a useful method to resolve some questions about the form ofa black hole inside the event horizon. Is the entire mass contained in a single dimensionless point? Or is the mass inside distributed in some way through a measurable volume to which known laws of physics might apply?

The key will be to predict the final outcome of the merger of two black holes, at which point the "ringing" gravity waves, generated by two extremely heavy masses rotating about each other, should stop because the two masses become one and the generation of waves should stop. Predict the "final frequency" of the waves, which would depend on a) the size of the orbit of each massive object about the centre of mass b) the velocity of each object orbiting.
lengould100
1 / 5 (1) Sep 17, 2012
[contd] Basically "How small can the orbits get before the two masses merge into a single uniform entity which no longer emits gravity waves?". If the central mass of a black hole is a singularity, then the frequency should get much higher than if the two masses at the time of merger have any significant dimensions.

Critically, of course, assuming the entity can still emit gravity waves once the two massive objects are within their combined event horizon??
Torbjorn_Larsson_OM
3 / 5 (2) Sep 17, 2012
To preserve probabilities of quantum mechanics, black holes do transmit their information before they evaporate. (But it is crunched together to mass, spin and charge.) It is believed that the relativistic Unruh effect does that close to high energy density spacetime, which could in a membrane approximation be described as Hawking radiation. [ http://en.wikiped...h_effect ]

Black holes are relativistic artifacts (well, duh) and emit gravitational waves as other masses. (Say, if non-spherical and spinning fast.)

The time scale for supermassive black holes is ~ 10^80 - 10^100 years, or ~ trillion^8 years. ~ 10^100 years is the time for universe heat death, so it is easy to remember that SMBHs are gone about then.
Sonhouse
5 / 5 (1) Sep 17, 2012
[contd] Basically "How small can the orbits get before the two masses merge into a single uniform entity which no longer emits gravity waves?". If the central mass of a black hole is a singularity, then the frequency should get much higher than if the two masses at the time of merger have any significant dimensions.

Critically, of course, assuming the entity can still emit gravity waves once the two massive objects are within their combined event horizon??

The problem with that, if true, is the present generation of detectors have upper limits of frequency response and would not be able to make that judgment unless you could extrapolate the results of a limited frequency bandwidth.
lengould100
1 / 5 (1) Sep 18, 2012
Perhaps one could build a detector which could do two jobs. 1) establish a baseline "rate of orbital decay" while the frequency was still low enough to be counted. 2) detect the precise time when the gravity waves were no longer emitted, without being sensitive enough to detect the actual final frequency.

With those two items of data, one should be able to answer the question.
Torbjorn_Larsson_OM
3.4 / 5 (7) Sep 18, 2012
@ natello:

"In particle model of Universe the space-time can be understood as a density gradient, similar to water surface."

No. Classical particles exist within spacetime, so you can't make spacetime out of them.

The comments are both fractal failures, I just mention that one example on how it is wrong from first sentence to last.

Please consider that this is a science blog, and that people who is not familiar with science can read it and become confused. So try not to make such comments here. Do them on the crackpot sites they belong on.
vacuum-mechanics
1 / 5 (3) Sep 18, 2012
Spacetime ripples from dying black holes could help reveal how they formed.
Gravitational waves are ripples in the fabric of spacetime that travel at the speed of light but they are extremely difficult to detect…

Yes, but the problem is that conventional space-time is just a void, not a physical medium; how could it vibrates and creating waves which travelling with speed of light. May be this physical view could help to visualize how it works!
http://www.vacuum...=7〈=en
AmritSorli
1.2 / 5 (5) Sep 19, 2012
space-time is only a math model not physical reality
we can only talk about ripples of quantum vacuum
there is no gravity waves
gravity originates from the diminished energy density of quantum vacuum
in binary black holes or neutron stars mass is transforming back into energy of quantum vacuum and it is possible that black holes increase density of quantum vacuum.
in this view ripples of quantum vacuum we can understand as a increased wave of density of quantum vacuum.
Anda
1 / 5 (2) Sep 19, 2012
@ natello:

"In particle model of Universe the space-time can be understood as a density gradient, similar to water surface."

No. Classical particles exist within spacetime, so you can't make spacetime out of them.

The comments are both fractal failures, I just mention that one example on how it is wrong from first sentence to last.

Please consider that this is a science blog, and that people who is not familiar with science can read it and become confused. So try not to make such comments here. Do them on the crackpot sites they belong on.


@torbjon. I think this is our friend "water ripples" and to avoid identification he speaks of "particle model" instead of... Aether
Graeme
not rated yet Sep 23, 2012
lengould100 and Sonhouse:

Once the holes are merged there is no gravitational radiation from the singularities. Because the waves cannot escape the event horizon. What is detected is an out of shape event horizon wobbling and transforming into the expected shape. The frequency does not rise to infinity because anything from close into the event horizon is redshifted severely.