A Famous Black Hole Gets an Update

Re:A Famous Black Hole Gets an Update by sandworm101 on Friday February 26, 2021 @08:43AM (#26274654)

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

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Re:A Famous Black Hole Gets an Update by danparsonson on Friday February 26, 2021 @09:10AM (#26274882)

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..."

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Re:A Famous Black Hole Gets an Update by sandworm101 on Friday February 26, 2021 @09:26AM (#26275065)

There is a theoretical mass gap based on mathematical models of how stars work. Then there is a mass gap based on observations of real BHs. These gaps don't line up perfectly. Either our observations are imperfect or our math is wrong.

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Re:A Famous Black Hole Gets an Update by danparsonson on Friday February 26, 2021 @10:07AM (#26275458)

Thanks for your answers so far, I'm sorry I'm still being dim - the 'mass gaps' per the Wikipedia article you linked are thought to be in the region of "2 to 5 and 50 to 150 solar masses", and therefore stellar black holes are expected to be around 5-50 solar masses. The NYT article puts Cygnus X1 at 21 solar masses and therefore safely in the realm of possibility, but apparently now big enough to cause a problem, being bigger than 20 solar masses which was some other previous limit (the limit for a binary system?). I don't understand why it couldn't have been <= 20Msol at formation, and then acquired the rest parasitically from it's companion.

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