6 ms·

I'm a grad student with LIGO. Yeah, the rate of intermediate mass black hole mergers was totally unexpected and has caused a bunch of active discussion on form

I'm a grad student with LIGO. Yeah, the rate of intermediate mass black hole mergers was totally unexpected and has caused a bunch of active discussion on formation mechanisms. In short, intermediate mass black holes are too big to be generated from star collapses, which means they (likely) come from smaller BH mergers. But because these things take so long (GWs radiate energy very slowly until the bodies are very close and fast), we didn't previously expect there to be large populations of them. It has been surprising to see that there are enough of them to sustain a pretty decent IMBH merger rate.

nerfhammer 9y ago
Will we ever hear neutron stars colliding with other large masses any time soon?
- stefco_ 9y ago
  LIGO also searches for BH/NS mergers and for NS/NS mergers. None have been announced yet, but they are definitely something we look for. BH/NS and NS/NS mergers are exciting because they involve conventional matter and are likely to give off neutrinos and light as well as GWs. This means that EM followup is more likely to be worthwhile. The smaller mass of neutron stars means they are more common, and the NS event-rate is expected to be much higher than the BH event rate. But BH events are louder due to the extra mass, so we can search in a much much larger volume of space, which so far has been favorable for BBH (binary black hole) merger detections. Another interesting thing about BNS mergers is that, because they get closer/faster before merging, their signal should climb to higher frequencies and spends much, much longer in our sensitive band than BBH mergers (this is also true for lighter BBH mergers vs. heavier ones). This is really cool because it means that BNS mergers can be fit much more tightly to model waveforms, allowing for more precise parameter estimation (among other things) given the same peak signal-to-noise ratio.
  - nerfhammer 9y ago
    NS-NS collision, everything doesn't disappear into an event horizon, wouldn't they deform and maybe some mass gets ejected, so would the impact event sound more complex/irregular? It would be cool if we could hear a NS-NS collision of sufficient masses such that we could hear a BH being born for the first time. Will we reasonably ever hear a supermassive BH collision? I would assume their loudness to rarity ratio is just too low.
    - ssijak 9y ago
      How cool would be to be bale to see a video of that merger? One can only dream..
      - stefco_ 9y ago
        These gorgeous, physically-correct simulations are about as close as you'll get for now: https://www.black-holes.org/explore/movies https://www.black-holes.org/explore/movies
    - stefco_ 9y ago
      One problem is that supermassive BHs merge at very low frequencies; they merge before their orbits get fast. LIGO's sensitivity range is in about the same range of frequencies as the human ear. NSNS mergers reach our sensitivity sweet spot for a few seconds; intermediate mass BHBH mergers get into the low end of our sweet spot. Supermassive black holes merge at very low frequencies outside of our sensitive band. LISA is a planned space-based observatory that would be sensitive in those bands: https://lisa.nasa.gov/ https://lisa.nasa.gov/
    - raattgift 9y ago
      Yes, NNS and BNS collisions are very messy. NNS are also very likely to form a BH. > Will we reasonably ever hear a supermassive BH collision? Hopefully! They'll certianly be looked for. There are some extremely massive SMBHs out there (e.g. Blazar QSO B0218+357), and it's reasonable to think that at least some of them are the result of mergers of SMBHs rather than, say, a rain of smaller BHs (and dust, gas and stars) onto an already big BH (which may also happen). https://www.youtube.com/watch?v=vw2sLcyV7Vc https://www.youtube.com/watch?v=vw2sLcyV7Vc https://www.youtube.com/watch?v=ow9JCXy1QdY https://www.youtube.com/watch?v=ow9JCXy1QdY http://newscenter.lbl.gov/2017/08/02/new-space-simulations-neutron-star-black-hole-mergers/ http://newscenter.lbl.gov/2017/08/02/new-space-simulations-n...
deleted 9y ago
[deleted]
perlgeek 9y ago
How likely is it that there are feeding mechanisms for black holes that make them this large? I guess the main problem is that you'd need friction to slow down matter that's attracted by the black hole, so it doesn't just orbit it...
- stefco_ 9y ago
  I don't keep up with the latest material here, but there is some stuff I've picked up. For one thing, it's probably not ordinary matter falling into the black holes. When ordinary matter falls into a black hole, it usually forms a bright, glowing accretion disk. We would see that with an ordinary telescope, especially given just how much matter would need to be accreted. (We're talking about dozens of suns worth of mass for each of these intermediate mass black holes!) You can also have three-body interactions. A pair of black holes in a circular orbit at a decent distance will merge on a timescale of billions of years. But if a third black hole comes in and disrupts the orbit, it can knock those two black holes closer together, at which point the GW power gets much higher and the merge can finish on a reasonable timescale. For these reasons, some papers I've seen suggest that there might be large collections of black holes that are dense enough for three-body interactions to be relatively common.
jacquesm 9y ago
Could they be reflected waves reaching 'the end of the pond' and coming back and so you see a lot more of them than that there are actual events? (Probably a very silly question)
- vorotato 9y ago
  pray tell what reflects gravity
  - gort 9y ago
    If the universe isn't infinite, isn't the idea that things sort of "wrap around"?
    - 6nf 9y ago
      No the idea is that the universe is expanding. It's not infinite but it's expanding faster than C and therefore it's impossible to reach the edge.
      - stefco_ 9y ago
        Yeah but another idea is that it is isotropic, which is borne out by observation. This leaves a few obvious possiblities: 1. It's infinite and homogeneous 2. It's finite but periodic (like the Earth; go straight long enough and end up where you were) 3. It's slowly varying, so that within our Hubble volume (the volume within the horizon receding from us at the speed of light, beyond which we can't see) everything looks isotropic; in other words, it varies, but slowly So what you're saying is true from our position in space, but it should also (if points 1 and 2 are true) be true everywhere in space, and the question of the large scale structure of the universe remains valid.
plaidfuji 9y ago
Is anyone in the community skeptical of what you're actually observing though? If this rate was so unexpected, isn't there a possibility that what's being observed is not what you think it is?

nerfhammer 9y ago

Will we ever hear neutron stars colliding with other large masses any time soon?

stefco_ 9y ago
LIGO also searches for BH/NS mergers and for NS/NS mergers. None have been announced yet, but they are definitely something we look for. BH/NS and NS/NS mergers are exciting because they involve conventional matter and are likely to give off neutrinos and light as well as GWs. This means that EM followup is more likely to be worthwhile. The smaller mass of neutron stars means they are more common, and the NS event-rate is expected to be much higher than the BH event rate. But BH events are louder due to the extra mass, so we can search in a much much larger volume of space, which so far has been favorable for BBH (binary black hole) merger detections. Another interesting thing about BNS mergers is that, because they get closer/faster before merging, their signal should climb to higher frequencies and spends much, much longer in our sensitive band than BBH mergers (this is also true for lighter BBH mergers vs. heavier ones). This is really cool because it means that BNS mergers can be fit much more tightly to model waveforms, allowing for more precise parameter estimation (among other things) given the same peak signal-to-noise ratio.
- nerfhammer 9y ago
  NS-NS collision, everything doesn't disappear into an event horizon, wouldn't they deform and maybe some mass gets ejected, so would the impact event sound more complex/irregular? It would be cool if we could hear a NS-NS collision of sufficient masses such that we could hear a BH being born for the first time. Will we reasonably ever hear a supermassive BH collision? I would assume their loudness to rarity ratio is just too low.
  - ssijak 9y ago
    How cool would be to be bale to see a video of that merger? One can only dream..
    - stefco_ 9y ago
      These gorgeous, physically-correct simulations are about as close as you'll get for now: https://www.black-holes.org/explore/movies https://www.black-holes.org/explore/movies
  - stefco_ 9y ago
    One problem is that supermassive BHs merge at very low frequencies; they merge before their orbits get fast. LIGO's sensitivity range is in about the same range of frequencies as the human ear. NSNS mergers reach our sensitivity sweet spot for a few seconds; intermediate mass BHBH mergers get into the low end of our sweet spot. Supermassive black holes merge at very low frequencies outside of our sensitive band. LISA is a planned space-based observatory that would be sensitive in those bands: https://lisa.nasa.gov/ https://lisa.nasa.gov/
  - raattgift 9y ago
    Yes, NNS and BNS collisions are very messy. NNS are also very likely to form a BH. > Will we reasonably ever hear a supermassive BH collision? Hopefully! They'll certianly be looked for. There are some extremely massive SMBHs out there (e.g. Blazar QSO B0218+357), and it's reasonable to think that at least some of them are the result of mergers of SMBHs rather than, say, a rain of smaller BHs (and dust, gas and stars) onto an already big BH (which may also happen). https://www.youtube.com/watch?v=vw2sLcyV7Vc https://www.youtube.com/watch?v=vw2sLcyV7Vc https://www.youtube.com/watch?v=ow9JCXy1QdY https://www.youtube.com/watch?v=ow9JCXy1QdY http://newscenter.lbl.gov/2017/08/02/new-space-simulations-neutron-star-black-hole-mergers/ http://newscenter.lbl.gov/2017/08/02/new-space-simulations-n...

deleted 9y ago

[deleted]

perlgeek 9y ago

How likely is it that there are feeding mechanisms for black holes that make them this large? I guess the main problem is that you'd need friction to slow down matter that's attracted by the black hole, so it doesn't just orbit it...

stefco_ 9y ago
I don't keep up with the latest material here, but there is some stuff I've picked up. For one thing, it's probably not ordinary matter falling into the black holes. When ordinary matter falls into a black hole, it usually forms a bright, glowing accretion disk. We would see that with an ordinary telescope, especially given just how much matter would need to be accreted. (We're talking about dozens of suns worth of mass for each of these intermediate mass black holes!) You can also have three-body interactions. A pair of black holes in a circular orbit at a decent distance will merge on a timescale of billions of years. But if a third black hole comes in and disrupts the orbit, it can knock those two black holes closer together, at which point the GW power gets much higher and the merge can finish on a reasonable timescale. For these reasons, some papers I've seen suggest that there might be large collections of black holes that are dense enough for three-body interactions to be relatively common.

jacquesm 9y ago

Could they be reflected waves reaching 'the end of the pond' and coming back and so you see a lot more of them than that there are actual events? (Probably a very silly question)

vorotato 9y ago
pray tell what reflects gravity
- gort 9y ago
  If the universe isn't infinite, isn't the idea that things sort of "wrap around"?
  - 6nf 9y ago
    No the idea is that the universe is expanding. It's not infinite but it's expanding faster than C and therefore it's impossible to reach the edge.
    - stefco_ 9y ago
      Yeah but another idea is that it is isotropic, which is borne out by observation. This leaves a few obvious possiblities: 1. It's infinite and homogeneous 2. It's finite but periodic (like the Earth; go straight long enough and end up where you were) 3. It's slowly varying, so that within our Hubble volume (the volume within the horizon receding from us at the speed of light, beyond which we can't see) everything looks isotropic; in other words, it varies, but slowly So what you're saying is true from our position in space, but it should also (if points 1 and 2 are true) be true everywhere in space, and the question of the large scale structure of the universe remains valid.

plaidfuji 9y ago

Is anyone in the community skeptical of what you're actually observing though? If this rate was so unexpected, isn't there a possibility that what's being observed is not what you think it is?