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.
There's got to be some interesting implications here for cosmology.
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.
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.
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.
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/
> 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=ow9JCXy1QdY
http://newscenter.lbl.gov/2017/08/02/new-space-simulations-n...
It's just like how we have optical telescopes for visible light and radio telescopes for light at different frequencies. Different interferometer designs will pick up different phenomena based on what their sensitive band is.
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...
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.
(Probably a very silly question)
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.
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!
https://en.wikipedia.org/wiki/Massive_compact_halo_object http://iopscience.iop.org/article/10.1086/319636
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.