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The Question

(Submitted July 09, 1997)

Is it possible that high speed (close to c) particles are flying around a neutron star/black hole? And if so, could this in effect 'focus' the X-rays so they will only be emitted along the plane of the accretion disk?

If so, imagine the body slowly tilting from north to south. We would only see the X-rays when our viewpoint is in the same plane as the accretion disk.

The Answer

That's an interesting question. Matter accreting onto a black hole can reach relativistic speeds. I think the question you are asking is if the energy density in the accretion disk is high enough to cause significant light bending. The answer is no. The gravitational field of the black hole or neutron star dominates.

If we are looking at the disk almost edge-on and the disk is flared (i.e. gets thicker towards its outside edge) it will obscure the central X-ray source. If the disk is warped or is precessing (wobbling) we may see a periodic modulation of the X-ray flux.

Damian Audley
For the Ask an Astrophysicist Team

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