Expert: Jayendra Upadhye - 8/9/2007

Question
When two Neutron stars in orbit eventually combine together into one star (presumably a black hole) where does the energy released from this event come from?  There's are no hydrogen atoms to fuse together nor any other atoms since the two stars are only made of neutrons.


Answer
Hi,
The answer lies in the work energy theorem.
And at the root of it all lie mass and gravitation.
Simply stated..
It states that in conservative "point" fields (such as gravitational field),
1 - a mass converts its kinetic energy into stored potential energy when moving against the field or away from the gravitating body , and
2 - converts potential energy into kinetic enrgy when it moved with the field or towards the gravitating body.

When a block of wood falls to the ground from a hieght, the "plonk" it makes (sound and impact energy) is derived purely from its mass and hieght of drop! (no atomic fusion / fission involved).

Likewise, the two "atomically inert" neutron bodies when they collide and fuse, let off an immense burst of energy which is purely the locked up gravitational potential energy stored in their immense masses and the strong gravitation exerted by each on the other! (Again no fission / fusion involoved).

But pure mechanics aside, I would be foolish to say another source does not exist. I am not a physicist dealing in quarks and other quiant fundamental particles and the strong electromagnetic force and the energy released when it "strikes"! (i know zero about what happens at micro micro quark levels in such situations).

Anyways if a black hole results due to their accumulated mass, why bother? No energy released or stored will ever escape! (except by the negligible hawking toute).

Jayen