6 ms·

An intermediate-mass black hole candidate in the Milky Way

103 points by Jerry2 9y ago

saagarjha 9y ago
> intermediate-mass black holes (IMBHs), which are formed by the runaway coalescence of stars in young compact star clusters How exactly would this work to produce something with a mass of 10^5 solar masses? Isn't that a bit large for the combination of a couple stars?
- manyoso 9y ago
  You obviously need 10^5 solar masses to make something that large. Whether they come via a number of IMBH's collapsing into one SMBH or otherwise, I don't understand your question.
  - saagarjha 9y ago
    I was wondering where the 10^5 solar masses were coming from–certainly it's not just a couple of stars merging and creating a black hole.
- Florin_Andrei 9y ago
  Well, if you get the process started in a star cluster, you might end up with a pretty hefty BH. Star clusters do lose energy, just very slowly. On a cosmic time scale, it's conceivable that this would lead in some cases to collapse and the formation of large BHs.
- antognini 9y ago
  In globular clusters, dynamical interactions are fairly frequent. A consequence of this is that you end up with a phenomenon called "mass segregation" --- heavy stars sink to the center of the cluster, and lighter ones float to the top. As a consequence, if you get a bunch of stellar mass black holes form (and they remain bound to the globular cluster --- not necessarily guaranteed), they will sink to its center, where they will begin to interact with each other. Over time, they will kick out all lighter stars, removing energy, and shrinking their obrits, until gravitational radiation takes over and causes them to coalesce and all merge together into a single intermediate mass black hole. In the Galaxy, a similar process could take place in a dense open cluster, but the stellar densities are so much lower that it's a lot harder to get the same dynamics. The presence of gas in an open cluster could contribute to the dynamical friction that leads to BH-BH mergers.
  - saagarjha 9y ago
    Ahh, I get it. Thanks for the detailed response!
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.
- deleted 9y ago
  [deleted]
- manyoso 9y ago
  Why 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 ago
    Generally 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.)
hrgeek 9y ago
It's referring to the velocity dispersion of the cloud. If you imagine the cloud is rotating about a central axis, the parts of the cloud spinning toward us will have a higher relative velocity than those spinning away. The spread of these velocities is the velocity dispersion. A broad velocity width then indicates that parts of the cloud are moving rapidly compared to others, as one might observe if the cloud was being accreted by a black hole - the material closest the black hole would be travelling much faster than that at the edge of the cloud.
carapace 9y ago
I thought black holes don't actually exist. https://www.quora.com/In-a-paper-written-in-1939-Albert-Einstein-rejected-the-notion-of-Black-Holes-Schwarzschild%E2%80%99s-singularities-Why https://www.quora.com/In-a-paper-written-in-1939-Albert-Eins... and http://www.nature.com/news/stephen-hawking-there-are-no-black-holes-1.14583 http://www.nature.com/news/stephen-hawking-there-are-no-blac... Can anyone shed some light?
- goodcanadian 9y ago
  In a nutshell, from the first link, Einstein was wrong about the particular issue he wrote about. From the second, well, that was sort of a click-baity title (that Hawking himself used). He is not arguing against black holes, but rather is stating that the event horizon described by general relativity is inconsistent with quantum mechanics. Instead, there is an "apparent horizon." You might say that quantum mechanics makes the event horizon "fuzzy." Regardless, there are most definitely black holes.
  - carapace 9y ago
    Thank you!

103 points by Jerry2 9y ago

> intermediate-mass black holes (IMBHs), which are formed by the runaway coalescence of stars in young compact star clusters How exactly would this work to produce something with a mass of 10^5 solar masses? Isn't that a bit large for the combination of a couple stars?

manyoso 9y ago
You obviously need 10^5 solar masses to make something that large. Whether they come via a number of IMBH's collapsing into one SMBH or otherwise, I don't understand your question.
- saagarjha 9y ago
  I was wondering where the 10^5 solar masses were coming from–certainly it's not just a couple of stars merging and creating a black hole.
Florin_Andrei 9y ago
Well, if you get the process started in a star cluster, you might end up with a pretty hefty BH. Star clusters do lose energy, just very slowly. On a cosmic time scale, it's conceivable that this would lead in some cases to collapse and the formation of large BHs.
antognini 9y ago
In globular clusters, dynamical interactions are fairly frequent. A consequence of this is that you end up with a phenomenon called "mass segregation" --- heavy stars sink to the center of the cluster, and lighter ones float to the top. As a consequence, if you get a bunch of stellar mass black holes form (and they remain bound to the globular cluster --- not necessarily guaranteed), they will sink to its center, where they will begin to interact with each other. Over time, they will kick out all lighter stars, removing energy, and shrinking their obrits, until gravitational radiation takes over and causes them to coalesce and all merge together into a single intermediate mass black hole. In the Galaxy, a similar process could take place in a dense open cluster, but the stellar densities are so much lower that it's a lot harder to get the same dynamics. The presence of gas in an open cluster could contribute to the dynamical friction that leads to BH-BH mergers.
- saagarjha 9y ago
  Ahh, I get it. Thanks for the detailed response!

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.

deleted 9y ago
[deleted]
manyoso 9y ago
Why 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 ago
  Generally 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.)

hrgeek 9y ago

It's referring to the velocity dispersion of the cloud. If you imagine the cloud is rotating about a central axis, the parts of the cloud spinning toward us will have a higher relative velocity than those spinning away. The spread of these velocities is the velocity dispersion. A broad velocity width then indicates that parts of the cloud are moving rapidly compared to others, as one might observe if the cloud was being accreted by a black hole - the material closest the black hole would be travelling much faster than that at the edge of the cloud.

carapace 9y ago

I thought black holes don't actually exist. https://www.quora.com/In-a-paper-written-in-1939-Albert-Einstein-rejected-the-notion-of-Black-Holes-Schwarzschild%E2%80%99s-singularities-Why https://www.quora.com/In-a-paper-written-in-1939-Albert-Eins... and http://www.nature.com/news/stephen-hawking-there-are-no-black-holes-1.14583 http://www.nature.com/news/stephen-hawking-there-are-no-blac... Can anyone shed some light?

goodcanadian 9y ago
In a nutshell, from the first link, Einstein was wrong about the particular issue he wrote about. From the second, well, that was sort of a click-baity title (that Hawking himself used). He is not arguing against black holes, but rather is stating that the event horizon described by general relativity is inconsistent with quantum mechanics. Instead, there is an "apparent horizon." You might say that quantum mechanics makes the event horizon "fuzzy." Regardless, there are most definitely black holes.
- carapace 9y ago
  Thank you!