Not really current news, but based on recent papers, about something I find very interesting.

In the 50s, J A Wheeler proposed that Black Holes could be formed by a suitably large concentration of EM radiation, and he introduced the term Geons, for such concentrations.
Recent ( within the last couple of years ) papers make these processes extremely unlikely ( by 50 orders of magnitude ), due to pair creation effects of QED, and the ability to carry energy/momentum out of the system.

As always, this guy does an excellent job of explaining the whys and hows of this process ...

And I'm getting tired of all the non-science discussion.
( it's in the forum name people ! )

Edited 21 hours ago21 hr by MigL

In the case of a sufficiently large black hole, the energy density is low enough for pair production to be insignificant. Whereas for an ordinary object, mass increases with R³, for a black hole, mass increases with R. Thus, very large black holes have low density and one could construct such a black hole with bricks if one had a sufficient number of them. This kills any "immovable object meets irresistible force" type arguments with regards to black holes.

5 hours ago, KJW said:

This kills any "immovable object meets irresistible force" type arguments with regards to black holes.

I guess you haven't watched the video.

QED keeps the concentration of EM radiation from ever reaching an energy density allowing creation of a BH, due to the Schwinger Effect ( pair creation in a vacuum with sufficiently strong EM field ).
It has nothing to do with conditions after BH creation.

Edited 14 hours ago14 hr by MigL

8 hours ago, MigL said:

  13 hours ago, KJW said:

This kills any "immovable object meets irresistible force" type arguments with regards to black holes.

I guess you haven't watched the video.

QED keeps the concentration of EM radiation from ever reaching an energy density allowing creation of a BH, due to the Schwinger Effect ( pair creation in a vacuum with sufficiently strong EM field ).
It has nothing to do with conditions after BH creation.

I did watch the video. It focused on small black holes for which the energy density is so high that the Schwinger Effect would prevent their formation. But to form a very large black hole, the energy density would be low enough for the Schwinger Effect to be negligible. The point I made about constructing a black hole from bricks is that one doesn't need matter-crushing forces to produce a black hole if the total mass is large enough. I will admit that I am somewhat of a black hole skeptic. Nevertheless, I recognise that simply accumulating sufficient mass into its Schwarzschild radius will create a black hole without the need of any forces that could possibly be thwarted. The invokation of the Schwinger Effect seemed to me to be not entirely unlike the "immovable object meets irresistible force" type argument that one might use against the formation of a black hole.

However, I should remark that I fairly recently derived a result that contradicted a belief I had about black hole formation. I had believed that during the gravitational collapse of matter, the event horizon doesn't form from the centre and expand outwards, but rather forms at the surface of the matter at the instant the entire matter is inside the Schwarzschild radius. My error was due to a misapplication of Birkhoff's theorem and a failure to fully appreciate that the event horizon is due to the gravitational potential. The result I derived is that the event horizon starts to form at the centre of the matter before the surface of the matter is inside the Schwarzschild radius, and expands as the matter shrinks until it reaches the surface when the entire matter is inside the Schwarzschild radius.

Edited 5 hours ago5 hr by KJW