Supermassive Black Hole
Belinda Smith posted..
There's a limit to how big a supermassive black hole can become before it
stunts it own growth, calculations suggest. Kohei Inayoshi and Zoltan Haiman
from Columbia University in New York, US, modelled the evolution of a
supermassive black hole over the lifetime of the universe – 13.8 billion years
– and found once they get to around 10 billion times the mass of the sun,
they top out. At this point, the majority of the gas flowing to and feeding
a supermassive black hole instead gets caught in the surrounding disc,
triggering star formation light-years away and more than far enough to remain
safe from the black hole. Starved of fuel, the black hole slows growth. The
work, published in The Astrophysical Journal, explains why we don't detect
supermassive black holes more than ten billion solar masses today.
Most large galaxies, it's thought, harbour a supermassive black hole in their
centre. We have one in the centre of our galaxy, the Milky Way – it's thought
to be around 4.5 million times more massive than the sun. But it's tiny to some
of the monsters we've detected. Some are in the tens of billions of solar masses.
But that's as massive as they seem to get. Why is this? Inayoshi and Haiman
thought the process of rapid black hole growth could eventually be the very thing
that slows them. They decided to model it and see what happened. For a super-massive
black hole to grow larger than the largest we've seen, it would need to guzzle
around 1,000 solar masses each year. That fuel has to come from somewhere and as
time wears on, they must use gas from further afield. But once the gas is pulled
from the outer reaches of the galaxy, it gets stuck tens of hundreds of light-years
from the black hole. Food slows to a trickle. This, in turn, changes the physics
of the black hole's disc. The inner portion of the disc puffs up and blasts strong
jets, further suppressing feeding and thus, growth. The pair's upper limit size
calculations support another study published in the Monthly Notices of the Royal
Astronomical Society by the UK's University of Leicester's Andrew King in December
last year, which attributed slowed growth to fragmentation of the disc.
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https://cosmosmagazine.com/space/how-ma ... k-hole-get