# What kind of matter are black holes made of?

Imagine a black hole originally formed from, for example, Rubidium atoms. On the other hand, one made from, for example, Helium atoms. Will it be there any difference between the two? Or perhaps once formed it all turns into the same type of matter?

Can the "composition" of the matter-energy in the black hole be inferred somehow?

Could one say that "black hole substance" is a distinct form or state of matter different from other forms or states of matter?

• Neutron stars consist of neutrons (in some way), not of different kinds of elements. – Pieter Apr 23 '18 at 20:28
• See the no-hair theorem. – Ruslan Apr 23 '18 at 20:31
• Related: physics.stackexchange.com/q/18981/2451 and links therein. – Qmechanic Apr 23 '18 at 21:38
• @Pieter Neutron stars are not pure neutronium. See en.wikipedia.org/wiki/Neutron_star#Structure – PM 2Ring Jun 18 '18 at 12:51
• @PM2Ring That is why I had added "in some way". And it is still true that the abundances of nuclei in a neutron star would not depend what elements there were in the parent star. – Pieter Jun 18 '18 at 14:37

• "Assuming they have same the mass, net electric charge, and angular momentum any two black holes will be identical."--Isn't it kind of important to amend this by saying that this is true only when we speak thermodynamically? In reality, of course, two black holes with the same macroscopic description can differ drastically, to wit, the ensemble of the black hole(s) described with a given set of $M, J, Q$ has very high entropy. – Dvij Mankad Apr 16 '19 at 15:05