[ExI] The largest and the smallest Black Holes

[John Clark]

In the last month astronomers have broken records, they have found both the
largest and the smallest Black Holes in the universe, at least so far. The
largest Black Hole is 40 billion solar masses plus or minus 800 million.

A 40-BILLION SOLAR MASS BLACK HOLE IN THE CENTRAL GALAXY OF ABELL 85
<https://arxiv.org/pdf/1907.10608.pdf>

Even more interesting is the discovery of the smallest Black Hole, it's
probably 3.3 solar masses although it could be as large as 6.1 or as small
as 2.6.

A low-mass black hole–giant star binary system
<https://www.sciencemagazinedigital.org/sciencemagazine/01_november_2019/MobilePagedArticle.action?articleId=1534474#articleId1534474>

There are theoretical reasons to think a non-rotating Neutron Star can't
get any more massive than 2.16 solar masses before it collapses into a Black
Hole (unless Quark Stars made of Strange Matter exist), although they might
be as massive as 2.7 solar masses if they're spinning close to the speed of
light. But If a Neutron Star were spinning that fast it would have a huge
magnetic field which would slow it down so it couldn't keep that rate of
spin for long, astronomically speaking.  Magnetars might be Neutron Stars
of that sort, and short lifetime might be why they're so rare, only 23 have
ever been discovered. The most massive Neutron Star ever observed is 2.14
solar masses, very close to the theoretical limit.

John K Clark
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