6 ms·

If you turn a detector on - and, as soon as you do that, you detect some event, chances are those events are happening, like, all the freaking time. There's go

If you turn a detector on - and, as soon as you do that, you detect some event, chances are those events are happening, like, all the freaking time. There's got to be some interesting implications here for cosmology.

perlgeek 9y ago
As an armchair scientist, I mostly wonder about mass estimations. If there's a whole class of objects (black holes around 20 to 50 solar masses) that were previously thought to be virtually non-existent, and now turn out to pretty common, does that mean we can explain away at least some of the proposed dark matter? What if we keep finding more non-radiant objects that still (presumably) made of ordinary matter? Can these classes of objects account for the "missing" matter in galaxy rotation curves? Or would their distribution be simply wrong? Exciting times to live in, for sure!
- btouellette 9y ago
  The word you're looking for is MACHO (massive compact halo object) and using microlensing observations you can make all kinds of statistical arguments for how likely objects of different masses are to make up the missing matter to match galaxy rotation curves to observations. Basically it doesn't seem likely that there are nearly enough intermediate mass black holes to explain dark matter. Because microlensing is gravitational it doesn't matter what kind of object the MACHO is. https://en.wikipedia.org/wiki/Massive_compact_halo_object https://en.wikipedia.org/wiki/Massive_compact_halo_object http://iopscience.iop.org/article/10.1086/319636 http://iopscience.iop.org/article/10.1086/319636
  - spchampion2 9y ago
    It would be interesting to take the modeled number of MACHO black holes based on lensing studies and compare it to the modeled numbers of intermediate black holes based on LIGO data. I'd love to know if those two numbers substantially differ.
    - raattgift 9y ago
      For several reasons it's more likely that the IMBHs are in clusters like the large Magellanic cloud (LMC) and in some galactic centres rather than far from the centres of galaxies. You can in principle have huge numbers of IMBHs without any of them being MACHOs, HO for halo objects. They can form by having lots of first generation stars collapsing into BHs in open clusters, with resulting many-body interactions knocking BHs into one another (a BBH merger that gives a big linear kick to the resulting BH during balding, for example). We've looked for signs of black holes in our galaxy's halo (they would gravitationally lense nearby background objects like the LMC and M31 such that we could already pick out the distortions. Our galaxy may be unusual (Sag A* is fairly low-mass, for instance) but the density requirement for MACHO to be a large component of the flat rotation curve of most galaxies (ours being special) would seriously violate the Copernican principle. Moreover, it's really really hard to get a stable galactic evolution when you make MACHOs the sole invisible contributor to rotation curves. Worst of all, baryon acoustic oscillations appear in the cosmic microwave background more and more clearly as we study it more closely, which effectively rules out large Jupiters/brown dwarfs/neutron stars, and nobody knows how to get enough black holes that survive billions of years when you have to have them already exist between reionization and recombination. But who knows, maybe we'll see a lot of signs of primordial BHs evaporating in halos by (big) surprise.
stefco_ 9y ago
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.

perlgeek 9y ago

As an armchair scientist, I mostly wonder about mass estimations. If there's a whole class of objects (black holes around 20 to 50 solar masses) that were previously thought to be virtually non-existent, and now turn out to pretty common, does that mean we can explain away at least some of the proposed dark matter? What if we keep finding more non-radiant objects that still (presumably) made of ordinary matter? Can these classes of objects account for the "missing" matter in galaxy rotation curves? Or would their distribution be simply wrong? Exciting times to live in, for sure!

btouellette 9y ago
The word you're looking for is MACHO (massive compact halo object) and using microlensing observations you can make all kinds of statistical arguments for how likely objects of different masses are to make up the missing matter to match galaxy rotation curves to observations. Basically it doesn't seem likely that there are nearly enough intermediate mass black holes to explain dark matter. Because microlensing is gravitational it doesn't matter what kind of object the MACHO is. https://en.wikipedia.org/wiki/Massive_compact_halo_object https://en.wikipedia.org/wiki/Massive_compact_halo_object http://iopscience.iop.org/article/10.1086/319636 http://iopscience.iop.org/article/10.1086/319636
- spchampion2 9y ago
  It would be interesting to take the modeled number of MACHO black holes based on lensing studies and compare it to the modeled numbers of intermediate black holes based on LIGO data. I'd love to know if those two numbers substantially differ.
  - raattgift 9y ago
    For several reasons it's more likely that the IMBHs are in clusters like the large Magellanic cloud (LMC) and in some galactic centres rather than far from the centres of galaxies. You can in principle have huge numbers of IMBHs without any of them being MACHOs, HO for halo objects. They can form by having lots of first generation stars collapsing into BHs in open clusters, with resulting many-body interactions knocking BHs into one another (a BBH merger that gives a big linear kick to the resulting BH during balding, for example). We've looked for signs of black holes in our galaxy's halo (they would gravitationally lense nearby background objects like the LMC and M31 such that we could already pick out the distortions. Our galaxy may be unusual (Sag A* is fairly low-mass, for instance) but the density requirement for MACHO to be a large component of the flat rotation curve of most galaxies (ours being special) would seriously violate the Copernican principle. Moreover, it's really really hard to get a stable galactic evolution when you make MACHOs the sole invisible contributor to rotation curves. Worst of all, baryon acoustic oscillations appear in the cosmic microwave background more and more clearly as we study it more closely, which effectively rules out large Jupiters/brown dwarfs/neutron stars, and nobody knows how to get enough black holes that survive billions of years when you have to have them already exist between reionization and recombination. But who knows, maybe we'll see a lot of signs of primordial BHs evaporating in halos by (big) surprise.

stefco_ 9y ago

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.