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The Question

(Submitted October 23, 1997)

Can you tell me the differences between exoplanets and brown dwarfs please. Also I could not find any book regarding this. Is it because brown dwarfs and exoplanets are new to us?

The Answer

This is somewhat outside our field of expertise (which is X-ray, gamma-ray and cosmic ray astrophysics), but I've managed to find a definition in the 'EXOPLANETS' pages at:

The difference is in how they formed: brown dwarfs formed through the collapse of a molecular cloud, planets formed around a protostar through accretion of planetesimals and gas.

I think the subject of (theoretical studies of, and searches for) brown dwarfs and exoplanets have been with us for a long time. However, until recently, we had had very little data --- it is only within the last few years that many important discoveries have been made. So I think you are basically correct as to why you cannot find books on these subjects.

Best wishes,

Koji Mukai
for Ask an Astrophysicist

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