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The Question

(Submitted October 15, 1998)

How do you know the approximate weight of a neutron star?

The Answer

Using physics, we can calculate how large a star's iron core can be before it collapses to a neutron star, and how large a neutron star can be before it collapses to a black hole. We expect the masses of neutron stars to be within that range.

To find the weight of a specific neutron star, and see whether we got the physics right, we look at neutron stars in orbit around other stars and see how fast they move and in how large an orbit. Using that information and the laws of gravitation we can calculate the neutron star's mass.

David M. Palmer
for Ask an Astrophysicist

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