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The Question
(Submitted September 27, 1998)
I read in a German news magazine (Der Spiegel) that there appear to be a
number of stars located outside of galaxies. How is this possible if stars
are only born in galaxies or globular clusters?
The Answer
One often observes galaxies which are interacting with each other
via tidal forces. This happens when two galaxies pass near to each other,
or undergo a glancing collision. The effect of such interactions is to
draw out long streamers of stars and gas from the main body of the galaxy.
This process casts the material off into intergalactic space at high enough
speeds so that it never returns to the parent galaxy.
Thus, one would expect galaxy-galaxy interactions to supply the
intergalactic medium with stars and gas. Therefore it is not surprising
to find stars in intergalactic space, where they do not appear to have
an association with any nearby galaxy.
John Cannizzo
C. Allie Hajian
for "Ask a High-Energy Astronomer"
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