"The black holes collide in complete darkness. None of the energy exploding from the collision comes out as light. No telescope will ever see the event." -Janna Levin
Whenever there’s a catastrophic, cataclysmic event in space, there’s almost always a tremendous release of energy that accompanies it. A supernova emits light; a neutron star merger emits gamma rays; a quasar emits radio waves; merging black holes emit gravitational waves. But if there’s any sort of matter present outside the event horizons of these black holes, they have the potential to emit electromagnetic radiation, or light signals, too.
Our best models and simulations don’t predict much, but sometimes the Universe surprises us! With the third LIGO merger, there were two independent teams that claimed an electromagnetic counterpart within 24 hours of the gravitational wave signal. One was an afterglow in gamma rays and the optical, occurring about 19 hours after-the-fact, while the other was an X-ray burst occurring just half a second before the merger.
"... an afterglow in gamma rays and the optical, occurring about 19 hours after-the-fact"
I know that 19 hours is like a blink in cosmic terms, but just wondering... if both EM waves and grav. waves propagate at the same speed, why a delay of 19 hours? Given the violent nature of the event.. one would guess that gamma rays where being produced during the merger, at the exact moment of it... but 19 hours after it... maybe not from the event as such but from BH feeding on the material that is nearby?
What would it look like to the instruments if a black hole jet was pointed at us for a fraction of a second? The way I understand black hole mergers, the two merging partners do not have coplanar axis of spins, The resolving into a unified axis for the product black hole is accomplished during the ringdown phase. If in that realignment process the jets from one or the other of the merging black holes swept across the patch of sky where we are located, would that be consistent with what was seen in either the instantaneous or delayed readings?
@1: Just blue skying (or maybe black skying, heh), I'd say space is not a perfect vacuum. Light is technically traveling through a medium,albeit a very disperse one. So maybe that justifies thinking it might come after the gravitational signal? IIRC neutrinos are expected to arrive first after a supernova, for basically the same reason.
Just eyeballing it, that data looks pretty weak to me. Not only are the signals not a whole lot stronger than the noise , but the fact that they're looking for peaks both before and after the gravitational signal with no real time constraints seems to me a lot like data mining. If you look at enough data, the LIGO results will eventually be found to correlate with something. That doesn't mean much Without a mechanistic hypothesis that makes a prediction about the timing and type of signal, and/or a reproduced observation, I'd say there's no particular reason to believe this...yet. But by all means, let's take more observations and see if one of these types of signals is consistently reproduced. :)
Obviously it would depend on the density of matter near the BHs. One case would be one or both BHs have accretion disks, and the inner portions, within a few Schwarzchild radii are going to go through some interesting dynamics. I can also imagine a farther field case, where an accretion disk is around the pair.
Again, this disk is going to be subject to a wild ride. Could that frictionally heat portions of the disk, or cause portions to get closer to the BHs? Could it generate extreme mag fields that produce some sort of flares off the disk?
Now if the gravitational radiation from the merger is unsymmetric, will the combined BH receive enough of a kick to give it high velocity? What effect would that have on any accretion disk(s)? Could it plow into nearby gas clouds?
Light is technically traveling through a medium,albeit a very disperse one. So maybe that justifies thinking it might come after the gravitational signal?
That is a really great question. Does gravity travel through a medium faster than does light? If the force is mediated via Gravaton, you'd think it would travel at the same speed as light, that is to say 'slower through a medium' as both Gravatons and Photons are massless particles. However if gravitational waves are a ripple in space-time itself rather than a Graviton-facilitated phenomena then intervening medium wouldn't matter. I would be very interested to see what Ethan has to say on that.
".. So maybe that justifies thinking it might come after the gravitational signal? IIRC neutrinos are expected to arrive first after a supernova, for basically the same reason."
hmm.. interesting observation. Neutrinos have mass however, and their speed while very close to "c", would still be slightly less then c... given vast distances... it would be normal for them to trail behind.
My gut feeling (not science) tells me that interstellar space is "vacuum enough" .. that light doesn't get that much impedence. Because if that was the case.. then most of our distance/time measurements in cosmology would be way off (since we take the speed of light in space to be the speed of light in "perfect" vacuum). But like Denier wrote... am looking forward to Ethan perhaps addressing this in Questions of the Week.
@Sinisa Lazarek #6,
"My gut feeling (not science) tells me that interstellar space is “vacuum enough”"
Gut-wise, if 'interstellar space' is 'vacuum enough' than gravity waves wouldn't be able to travel.
We can't combine QM with GR because QM hasn't got a medium, albeit the Higgs Field.
gravity waves propagate through space-time itself. They don't require any medium. Just like light doesn't require any ether in order to propagate.
Your second sentence I just don't understand. You think GR needs some medium?? It doesn't, nor does it deal with any.
p.s. there is nothing special about Higgs field in comparison to others... all fields are same, that's why they are called "fields".
@Sinisa Lazarek #8,
Maxwell's Fields theory is based on a mechanical model, so of course in theory there is no longer a medium once you have figured out the math … just like 1+1=2 are abstract numbers.
The same goes for the Higgs Field if you read what Englert has to say about the origin of the idea and his view of a medium rather than the analogy of the popular crowd.
"... in theory there is no longer a medium..."
no, not in theory... in reality. And there never way one. Michelson-Morley experiment... and others after it, proved that conclusively. You can try and hide your errs in words, but that won't change reality. Until such time as you can show experimental evidence of a medium, you are wrong as wrong can be.
@Sinisa Lazarek #11,
"If aether exists, the Earth moving through it would cause a "wind" in the same way that there seems to be a wind outside a moving car. To a person in the car, the air outside the car would seem like a moving substance. In the same way, aether should seem like a moving substance to things on Earth."
A medium made out of a foam can fix this as it is able to be solid and liquid.
"..foam can fix this as it is able to be solid and liquid."
ROFL ... it doesn't fix anything, nor does the phase of it change anything. You don't seem to understand the underlying physics of it. More troubling is that you don't seem to care. There are plenty of unknowns out there to explore and discover.... yet you seem to fixate on what you see as "problems", but which have been "solved" decades if not centuries ago. Reconsider who needs to grow up.
@Sinisa Lazarek. #13,
The MM-experiment was to proof the concer of an Ether-wind, nothing more nothing less. Not finding an Ether-wind doesn't exclude that there is a medium, one that doesn't generate 'wind' thus we can look at other compositions - foam - …
"… you seem to fixate on what you see as “problems”, but which have been “solved” decades if not centuries ago."
I have no problem with GR for instance, a perfectly good theory, which doesn't exclude that we can still look deeper at what SpaceTime is made of. It seems that you have stopped looking, being happy with GR as it is, fine for you, but not everyone is obliged to do so.
Autocorrect error: concer - concept
"I have no problem with GR for instance"
yet you obviously don't understand it.. hence your "if ‘interstellar space’ is ‘vacuum enough’ than gravity waves wouldn’t be able to travel." How do you hope to look deeper if you can't even look and understand the surface?
"It seems that you have stopped looking, being happy with GR as it is"
nice try... look deeper.
@Sinisa Lazarek #16,
Sure, on paper and calculation-wise Gravity waves can travel, without a medium, I have no problem with that.