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This could be a really interesting discovery if it holds up. Astronomers have long known the existence of stellar mass black holes and supermassive black holes
by antognini 9y ago
This could be a really interesting discovery if it holds up. Astronomers have long known the existence of stellar mass black holes and supermassive black holes. But intermediate mass black holes (between, ~10^3 -- 10^5 solar masses) have been much more controversial. Now there are probably a handful of solid detections of IMBHs, but they are all in globular clusters. This is the first IMBH found in the Galaxy itself.
This is important because the formation mechanism of both IMBHs and SMBHs are unknown. There are two main competing models for SMBH formation: direct collapse and accretion. In the case of direct collapse you have a big cloud of gas that just collapses into a SMBH as the galaxy is forming. In the case of accretion, the SMBH starts off as a collection of stellar mass black holes which then merge into an IMBH, which then accretes gas to become a SMBH. A problem for the accretion model has long been the lack of any evidence for IMBHs --- this could change that.
It was also thought that if IMBHs existed anywhere, they would be in globular clusters. There the stellar densities are high enough that you might expect stellar mass black holes to coalesce into an IMBH in a reasonable amount of time (for reference, a globular cluster packs about a million stars in the space between our Sun and the nearest star). The fact that there is an IMBH in the galaxy might mean that it's considerably easier to form IMBHs than previously believed.
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- manyoso 9y agoWhy are those two models competing? Couldn't it be that SMBH are formed via both direct collapse and accretion? Finding evidence for one should not rule out the other I would think.
- antognini 9y agoGenerally in astronomy, physical processes have so many orders of magnitude to work with that if you have several physically possible mechanisms, one will be many orders of magnitude more effective than the others and will completely dominate. It's fairly unusual for there to be some sort of "cosmic coincidence" that leads to two processes having almost exactly the same effectiveness. (Type Ia SN may be an exception to this --- they may be produced roughly equally by accretion from ordinary stars and WD-WD mergers.)
- dwaltrip 9y agoFor the unfamiliar: SN = supernova WD = white-dwarf (a stellar remnant)
- scatters 9y agoIf stellar mass black holes are merging to form IMBHs, wouldn't we expect to detect such collision events frequently? Or have we not yet collected enough gravitational wave data to put bounds on those events?
- antognini 9y agoYes, globular clusters are expected to be prime locations for BH-BH mergers and gravitational wave events. The few GW detections we now have put some bounds on the BH-BH merger rate, but as far as I know, those bounds are consistent with the rates needed for IMBH formation.
- biggc 9y ago> In the case of direct collapse you have a big cloud of gas that just collapses into a SMBH as the galaxy is forming. In the case of accretion, the SMBH starts off as a collection of stellar mass black holes which then merge into an IMBH, which then accretes gas to become a SMBH. Could you clarify if SMBH is shorthand for "Stellar Mass Black Hole" or "SuperMassive Black Hole"?
- antognini 9y agoOh, sorry, that is pretty confusing. SMBH stands for "supermassive black hole." BH on its own usually refers to a stellar mass black hole. (Astronomers have lots of weird conventions.)
- Pxtl 9y agoLike using scientific notation for 1000 and 100,000?
- infogulch 9y agoIn those two cases scientific notation may not be very helpful. But consider that astronomers could very easily be comparing them to many other numbers with a huge range of magnitude, and it makes sense to just use it everywhere. Also scientific notation conveys the real precision where just "1000" could mean "1000 +-1” or "1000 +-1000", which by itself can be even more important than any other reason.
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