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Huh. IIRC, black hole mergers are also a likely source of short gamma ray bursts. So I suspect at 1 AU, one would need a lot of shielding to not get fried by th

by krylon 9y ago

Huh. IIRC, black hole mergers are also a likely source of short gamma ray bursts. So I suspect at 1 AU, one would need a lot of shielding to not get fried by the gamma rays. EDIT: What I meant to say was: It would probably be quite awesome to experience such an event up close, provided it is possible to do so safely. ;-)

dwaltrip 9y ago
I believe that black hole mergers are dark in the entire electromagnetic (EM) spectrum. This is why the recent binary neutron star merger was so groundbreaking -- it emitted both gravitational waves and a broad spectrum of EM waves. Indeed, though, it would be awesome to witness the collision and resulting gwaves personally, if such a thing was possible :)
- krylon 9y ago
  > I believe that black hole mergers are dark in the entire electromagnetic (EM) spectrum. Now that I think about it - yes, of course. It's why they are called _black_ holes. ;-) facepalm
  - vecter 9y ago
    That doesn't follow from the fact that black holes are "black". For example, black holes can emit a ton of radiation from accretion disk as matter accelerates and falls inwards, radiating huge amounts of energy [0]. Two naked black holes merging probably wouldn't emit much (if any) EM radiation, but if they had very active accretion disks, then it's certainly possible there would be a ton of EM activity. [0] https://en.wikipedia.org/wiki/Accretion_disk https://en.wikipedia.org/wiki/Accretion_disk
    - krylon 9y ago
      Yes. I had not thought of that. But if either of the black holes (or both) had an accretion disk at the time of the collision, they would have been "visible" before. I am not sure, though, if regular (stellar-mass) black holes with an accretion disk emit enough EM radiation to be visible at such distances, or if it would become lost among the radiation emitted by the rest of the galaxy. (A merger between two supermassive black holes with active accretion disks must be a spectacular sight even from a safe distance.)
- raverbashing 9y ago
  Nah I think there are some effects in the visible range. You probably have some kind of accretion disk that gets shaken up by the merger, there might also be some effects due to Hawking radiation But they're probably only visible from close range (like the 1AU mentioned above) and are too faint to be seen from 1Bi light years like the event that they captured
- russdill 9y ago
  That's assuming they are "naked" and not surrounded by rotating disks of gas and dust.
  - dwaltrip 9y ago
    AFAIK, only supermassive black holes at the center of galaxies have disks of material that is falling inward (and emitting significant amounts of light in the process). Even then, they only actively feed in that way for a short period of time -- I think something like 10k years. All of the LIGO observations have been of more basic stellar mass black holes merging together.
    - raattgift 9y ago
      > AFAIK, only supermassive black holes at the center of galaxies have disks of material that is falling inward Stellar binaries are extremely common, and there is a reasonably large supply of binarys where one star has become a compact object. Their companion stars often drop lots of matter onto them, resulting in a reasonable supply of black holes. Diskoseismologists and others working on Swift have catalogued hundreds of stellar mass black hole accretion disks. Examples from Swift: http://adsabs.harvard.edu/abs/2013ApJ...769...16R http://adsabs.harvard.edu/abs/2013ApJ...769...16R https://arxiv.org/abs/1112.2249 https://arxiv.org/abs/1112.2249 (preprint version) Swift also spotted ASASSN-14li which was a star being shredded by an SMBH and forming an early accretion structure. The event has been followed up by other observatories (notably Chandra and the European very long baseline interferometry network). ASASSN-14li is an easy google search term (the trick is knowing the term in the first place :-) ), hopefully you will enjoy some of the hits. :-)
      - dwaltrip 9y ago
        Ah, interesting. That makes a lot of sense. Would it be correct to say that if both objects in a binary pair are SMBHs, they would very likely not have an accretion disk, as the companion would be unable to send over any material?
        9y ago
antognini 9y ago
Gamma-ray bursts were believed to be due to mergers of two neutron stars, not black holes. LIGO's observation of a NS-NS merger coincident with a gamma-ray burst has strongly confirmed this picture.
- krylon 9y ago
  I see. In the back of my mind there was still the possibility that it could have been created by two black holes merging or a neutron star falling into a black hole. ... I wonder, if a neutron star and a black hole merge, does the neutron star get shredded early enough to form an accretion disk, or does it just disappear like a marble falling into a hole? For some reason my imagination is quite lively today, these questions just keep popping up in my head like banner ads. ;-)

by krylon 9y ago

dwaltrip 9y ago

I believe that black hole mergers are dark in the entire electromagnetic (EM) spectrum. This is why the recent binary neutron star merger was so groundbreaking -- it emitted both gravitational waves and a broad spectrum of EM waves. Indeed, though, it would be awesome to witness the collision and resulting gwaves personally, if such a thing was possible :)

krylon 9y ago
> I believe that black hole mergers are dark in the entire electromagnetic (EM) spectrum. Now that I think about it - yes, of course. It's why they are called _black_ holes. ;-) facepalm
- vecter 9y ago
  That doesn't follow from the fact that black holes are "black". For example, black holes can emit a ton of radiation from accretion disk as matter accelerates and falls inwards, radiating huge amounts of energy [0]. Two naked black holes merging probably wouldn't emit much (if any) EM radiation, but if they had very active accretion disks, then it's certainly possible there would be a ton of EM activity. [0] https://en.wikipedia.org/wiki/Accretion_disk https://en.wikipedia.org/wiki/Accretion_disk
  - krylon 9y ago
    Yes. I had not thought of that. But if either of the black holes (or both) had an accretion disk at the time of the collision, they would have been "visible" before. I am not sure, though, if regular (stellar-mass) black holes with an accretion disk emit enough EM radiation to be visible at such distances, or if it would become lost among the radiation emitted by the rest of the galaxy. (A merger between two supermassive black holes with active accretion disks must be a spectacular sight even from a safe distance.)
raverbashing 9y ago
Nah I think there are some effects in the visible range. You probably have some kind of accretion disk that gets shaken up by the merger, there might also be some effects due to Hawking radiation But they're probably only visible from close range (like the 1AU mentioned above) and are too faint to be seen from 1Bi light years like the event that they captured
russdill 9y ago
That's assuming they are "naked" and not surrounded by rotating disks of gas and dust.
- dwaltrip 9y ago
  AFAIK, only supermassive black holes at the center of galaxies have disks of material that is falling inward (and emitting significant amounts of light in the process). Even then, they only actively feed in that way for a short period of time -- I think something like 10k years. All of the LIGO observations have been of more basic stellar mass black holes merging together.
  - raattgift 9y ago
    > AFAIK, only supermassive black holes at the center of galaxies have disks of material that is falling inward Stellar binaries are extremely common, and there is a reasonably large supply of binarys where one star has become a compact object. Their companion stars often drop lots of matter onto them, resulting in a reasonable supply of black holes. Diskoseismologists and others working on Swift have catalogued hundreds of stellar mass black hole accretion disks. Examples from Swift: http://adsabs.harvard.edu/abs/2013ApJ...769...16R http://adsabs.harvard.edu/abs/2013ApJ...769...16R https://arxiv.org/abs/1112.2249 https://arxiv.org/abs/1112.2249 (preprint version) Swift also spotted ASASSN-14li which was a star being shredded by an SMBH and forming an early accretion structure. The event has been followed up by other observatories (notably Chandra and the European very long baseline interferometry network). ASASSN-14li is an easy google search term (the trick is knowing the term in the first place :-) ), hopefully you will enjoy some of the hits. :-)
    - dwaltrip 9y ago
      Ah, interesting. That makes a lot of sense. Would it be correct to say that if both objects in a binary pair are SMBHs, they would very likely not have an accretion disk, as the companion would be unable to send over any material?
      - 9y ago

antognini 9y ago

Gamma-ray bursts were believed to be due to mergers of two neutron stars, not black holes. LIGO's observation of a NS-NS merger coincident with a gamma-ray burst has strongly confirmed this picture.

krylon 9y ago
I see. In the back of my mind there was still the possibility that it could have been created by two black holes merging or a neutron star falling into a black hole. ... I wonder, if a neutron star and a black hole merge, does the neutron star get shredded early enough to form an accretion disk, or does it just disappear like a marble falling into a hole? For some reason my imagination is quite lively today, these questions just keep popping up in my head like banner ads. ;-)