Is Planet Nine a grapefruit-sized black hole in our Solar System? Search is on.

[gary]

Full press release here :-
https://www.cfa.harvard.edu/news/2020-13

[glend]

I always believed you needed a certain mass to develop a black hole. A grapefruit sized black hole? Sounds impossible.

[Atmos]

There is a theory that there are primordial black holes scattered throughout the cosmos. Usually these micro black holes are typically expected to be much much much smaller and have been used as a way of defining dark matter; although not a widely accepted hypothesis.

Planetary mass black holes could theoretically have been “normal” garden variety ones back 13 billion years ago and reduced in size due to Hawking radiation over the eons.

[Zuts]

The Swarzchild radius is dependent on radius and mass not amount of mass. Any amount of mass if compressed into a small enough sphere will form a black hole.

I think :)

[gary]

Hi Glen,

Hypothesised primordial black holes are remnant bits of matter that
collapsed back in on themselves shortly after the Big Bang.

See
https://en.wikipedia.org/wiki/Primordial_black_hole#:~:text=Primo rdial%20black%20holes%20are%20a,gra vitational%20collapse%2C%20forming% 20black%20holes.

They had at one point been a Dark Matter candidate but a Japanese
research group claimed last year they had proven they can't :-
https://www.universetoday.com/141923/now-we-know-that-dark-matter-isnt-primordial-black-holes/