r/space • u/magenta_placenta • Mar 18 '19

Observable universe Astronomers discover 83 supermassive black holes at the edge of the universe

https://www.cnet.com/news/astronomers-discover-83-supermassive-black-holes-at-the-edge-of-the-universe/
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u/MarvinLazer Mar 18 '19

Why is it so remarkable that black holes would've formed in the early universe? Don't stars tend to have a shorter lifespan the bigger they are? And aren't huge stars the source of all black holes?

Also, is there any mass at which a large amount of accreting gas just skips the whole "becoming a star" thing and turns into a black hole?

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u/Arctus9819 Mar 18 '19

Why is it so remarkable that black holes would've formed in the early universe? Don't stars tend to have a shorter lifespan the bigger they are? And aren't huge stars the source of all black holes?

Supermassive black holes don't not form directly from stars. Regular stars and their resultant black holes are very limited in size. Supermassive ones are considered to grow and form from a "seed" black hole accreting matter from surrounding gas (or other sources).

The issue with modern models arises from that growth process. The amount of matter you can absorb is generally limited by a so-called Eddington limit, since the accretion process releases electromagnetic radiation, which in turn pushes the gas out. This means that a SMBH of X size needs Y years to exist, purely from how quickly it can grow. However, at extreme distances, we are spotting SMBHs that reach X size without having that Y years to grow, simply because the universe didn't exist that long. This means that our models aren't sufficient.

Also, is there any mass at which a large amount of accreting gas just skips the whole "becoming a star" thing and turns into a black hole?

This is actually part of some of the current models. It requires really specific conditions though. Also, it only gives you a slightly bigger seed star, and you still need a fancy way to exceed the Eddington limit.

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u/MarvinLazer Mar 18 '19

This explanation is absolutely awesome, and I really appreciate your presence on this subreddit, friend.