A Famous Black Hole Gets an Update

https://www.nytimes.com/2021/02/18/science/cygnus-black-hole-astronomy.html

by furcyd • 5 years ago

33 10 5 years ago

This is undoubtedly a stupid question but I didn't see it covered by the article - this thing has been feeding on its neighbour for some time, is it inconceivable that it's now one or two solar masses larger than it was when it formed? Then it would have formed within the expected limit for new black holes (which I think is what they mean by the ~20Msol limit), but still be bigger today. What am I missing?

omrjml2• 5 years ago

Yes, they would gain mass from feeding but not get 40% bigger while still in that binary configuration. So it seems these BHs start out bigger than previously assumed.

danparsonson5• 5 years ago

Yes, they would gain mass from feeding but not get 40% bigger while still in that binary configuration

Why not? (also, one solar mass increase over twenty would be 5% larger wouldn't it?)

sandworm1012• 5 years ago

There are upper and lower limits for "stellar" black holes, the ones formed from stars. When some big stars die they form black holes, but the size of those resulting holes doesn't scale exactly with the size of the star. The really big stars will form a BH but will also eject most of their mass outwards. So there is an upper limit to the size of a BH formed from a star. This thing is bigger than that limit. It can grow by feeding off its binary but that doesn't account for all of its extra size. It could have merged with another BH, but its hard to see how that would have happened without destroying/ejecting the close binary star we still see today. Either something very very strange happened in the life of this BH (possible) or our models need to be refined (likely).

https://en.wikipedia.org/wiki/Stellar_black_hole

danparsonson5• 5 years ago

So do I take it that the twenty solar mass figure they were talking about in the article is not the (currently understood) upper limit to stellar black hole mass, but refers to something else?

The line I'm referring to is "...Astronomers know of a few dozen black hole X-ray binary systems in the Milky Way and nearby, all of which have imputed masses of less than 20 times that of the sun. That apparent limit suggested that it was hard for black holes to grow more massive..."

A Famous Black Hole Gets an Update

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