X-Ray Stars in M15
Side by side, two
x-ray stars greeted astronomers in
this false-color Chandra Observatory
x-ray image of a
region near the core of globular star
cluster M15.
The greeting was a pleasant surprise, as all previous x-ray
images of the cluster showed only one such source where
Chandra's
sharper x-ray vision now reveals two.
These x-ray sources are modeled as
neutron star
binary systems.
Each is a city-sized neutron star in close orbit with
a normal stellar companion.
X-rays are generated
as matter from the normal star
falls onto
the compact neutron star.
This break through explains
why observations of the
previously recognized lone neutron star binary system in M15
were difficult to reconcile with any single model.
It also suggests that other globular star clusters which
roam the halo
of our Milky Way galaxy and
seem to contain
only one such neutron star x-ray source may in fact
contain more.
An optical Hubble Space Telescope image of the dense
M15 cluster is inset at the upper right.