B Gravitational Radiation: Effects on Objects & Black Holes

[wolram]

I am just trying to understand if gravitational radiation does work when passing through an object?
And how much mass or energy typically is lost from the merging of 2 Black Holes?

 

[DaveC426913]

I am just trying to understand if gravitational radiation does work when passing through an object?

Surely it must. It distorts matter.

And how much mass or energy typically is lost from the merging of 2 Black Holes?

The articles say that the equivalent of 3 suns of mass are converted to energy in an instant.

 

[wolram]

Surely it must. It distorts matter.
The articles say that the equivalent of 3 suns of mass are converted to energy in an instant.

Did we pick this up in the electro magnetic spectrum?

 

[Jonathan Scott]

Did we pick this up in the electro magnetic spectrum?

Er, no, because it was gravitational, not electromagnetic.

There's now a Wikipedia article on Gravitational wave observation which mentions that they checked with neutrino observatories but didn't see anything statistically significant and also had a look around with Swift but didn't spot anything new in the gamma, x-ray, ultraviolet or optical spectrum.

 

[DaveC426913]

The total power output in gravitational waves during the brief collision of these black holes was 50 times greater than all of the power put out by all of the stars of the Universe put together. Whoa. Because the collision was so short, the energy released wasn't quite that much, just the equivalent of taking three suns and annihilating them, NBD.

 

[DaveC426913]

Er, no, because it was gravitational, not electromagnetic.

I think the question is: are they referring to only the energy released in the form of the grav waves, and what about the release in EMR?

[ EDIT ] Ah, I see you addressed that.

 

[wolram]

I do not want to be pessimistic or put the mockers on a fantastic discovery, but is there any secondary evidence for this merger?

 

[Jonathan Scott]

I do not want to be pessimistic or put the mockers on a fantastic discovery, but is there any secondary evidence for this merger?

There is no evidence apart from the gravitational wave observation, but if you look at the evidence, it matches the theoretical prediction for inspiral and merging quite beautifully.

I would however like to point out that the use of the term "black hole" in this context is presumably simply because GR says that something that massive but small (as indicated by the high rotation rate achieved just before merging) must be a black hole. The lack of visible electromagnetic emission could be considered minor but positive evidence for this prediction. However, as far as I know, the result does not actually provide sufficient detail of the collision process to confirm this particular aspect of GR's predictions.

 

[DaveC426913]

Read this:
http://www.sciencealert.com/live-update-big-gravitational-wave-announcement-is-happening-right-now

 

[PeterDonis]

I am just trying to understand if gravitational radiation does work when passing through an object?

Yes. MTW has a discussion of this, where they treat a simple scenario of two masses connected by a spring that are set in motion by a passing GW; the process transfers energy to the mass-spring system.

 

[wolram]

Thank you for the replies, answers guys.

 

[Chalnoth]

I am just trying to understand if gravitational radiation does work when passing through an object?

Yes. But very, very little. The LIGO detectors, for instance, have to detect length changes that are of the order of the size of an atomic nucleus across four kilometers. Their noise is actually dominated by the quantum uncertainty in the position of the mirror. They may carry a lot of energy, but matter is almost entirely unaffected.

And how much mass or energy typically is lost from the merging of 2 Black Holes?

I don't know how it scales with mass, but this event involved the merger of black holes of about 35 and 30 solar masses. As mentioned above, about 3 solar masses in energy was emitted in the form of gravitational waves, so about 5% of their total mass energy was emitted in less than a second.

 

[Chalnoth]

I do not want to be pessimistic or put the mockers on a fantastic discovery, but is there any secondary evidence for this merger?

The nice thing about black hole-black hole mergers is that they produce a really distinctive signal, one that depends not only upon the masses of the black holes but also upon their rotation. They were actually able to show that the rotation of the resulting larger black hole was consistent with the spin and orbit of the pre-collision black holes. This event was separately detected in the two LIGO observatories, so we know it's not just some local source that weirdly looked a lot like a far-away BH-BH merger.

My bet is that we'll detect a handful of additional events over the next year or two, but as detector sensitivity increases we'll start seeing dozens and then hundreds of BH-BH mergers in gravity wave detectors. If we're lucky, we might even capture a visible signal from some of them (there might be some visible signal if there is some normal matter in close orbit around the black holes as they are merging).

 

[DaveC426913]

Yes. But very, very little. The LIGO detectors, for instance, have to detect length changes that are of the order of the size of an atomic nucleus across four kilometers.

I thought I'd read that it was 5 orders of magnitude smaller: 1/10,000th the diameter of a proton.

 

[Jonathan Scott]

There is no evidence apart from the gravitational wave observation, but if you look at the evidence, it matches the theoretical prediction for inspiral and merging quite beautifully.

I would however like to point out that the use of the term "black hole" in this context is presumably simply because GR says that something that massive but small (as indicated by the high rotation rate achieved just before merging) must be a black hole. The lack of visible electromagnetic emission could be considered minor but positive evidence for this prediction. However, as far as I know, the result does not actually provide sufficient detail of the collision process to confirm this particular aspect of GR's predictions.

And now a surprise!

The Fermi Gamma-ray space telescope apparently detected a bright gamma burst 0.4 seconds after the LIGO signal which is compatible with the same area of the sky and highly likely to be related. This was not expected from a black hole merger.

I didn't see anything specific about the Fermi observation, but there's a paper http://arxiv.org/abs/1602.04735 which discusses a theory that the gamma ray flash could have been caused by the collision being within a star. Doesn't sound very plausible to me, as I'd have thought that it would have been brighter earlier.

(Personally, I have long been sceptical about the accuracy of GR in extremely strong field situations, and especially about black holes, so for me this is a very interesting development).

 

[rootone]

Black holes merging inside a star?
How is that even possible - wouldn't the star be torn apart and/or consumed by the black holes before they could get inside it?
Colliding of accretion disks prior to (or even subsequent to) the final merger seems more reasonable to me.

 

[Dirk Pons]

Black holes are not supposed to make GRBs, so this is going to be a difficult one to explain. Maybe the two black holes somehow formed inside the star? But then they need to keep themselves apart long enough to eventually inspiral, but somehow also support the star from collapsing until the very end... wow that is a challenge.

 

[DaveC426913]

Maybe the two black holes somehow formed inside the star? But then they need to keep themselves apart long enough to eventually inspiral, but somehow also support the star from collapsing until the very end... wow that is a challenge.

Well, seeing as the BHs themselves are almost 60 solar masses, and any star above 20 will become a BH itself, it's pretty elementary that no star could exist large enough to contain them.

 

[Chalnoth]

Well, seeing as the BHs themselves are almost 60 solar masses, and any star above 20 will become a BH itself, it's pretty elementary that no star could exist large enough to contain them.

Stars can be over two hundred solar masses. They don't have very long lifetimes at those masses, but they do exist.