# Initial EH in Collapsing Star

Staff Emeritus
I was reading Stephen Hawking offers new resolution of black hole paradox. Most is over my head but when he mentions particles falling in through the EH, it raises a question.

When a BH is created in a collapsing star, does the EH first appear at zero radius and grow outward, or does the EH first appear with non-zero radius? In the latter case, there would be some stellar mass captured inside that never did fall in through the EH.

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## Answers and Replies

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does the EH first appear at zero radius and grow outward, or does the EH first appear with non-zero radius?
The latter.

mathman
The event horizon is defined by the mass of the star. Once the collapsing star radius is smaller than the event horizon radius, it is a black hole.

The event horizon is defined by the mass of the star. Once the collapsing star radius is smaller than the event horizon radius, it is a black hole.
It is not that easy (even without rotation) because the event horizon appears inside the collapsing star.

stevebd1
Gold Member
When a BH is created in a collapsing star, does the EH first appear at zero radius and grow outward, or does the EH first appear with non-zero radius? In the latter case, there would be some stellar mass captured inside that never did fall in through the EH.
You might find this link useful- http://www.astro.ucla.edu/~wright/bh-st.html

Staff Emeritus
Thanks for the replies. But now I don't understand how Hawking can say that a hologram at the event horizon resolves the information paradox.

The Information Paradox for Black Holes
S. W. Hawking
http://arxiv.org/abs/1509.01147

Hawking's reasoning seems to apply only to particles that fell in through the EH. It would not address the information of mass trapped inside during stellar collapse which never did cross the EH.

Chronos