|
These images, an optical (left) and X-ray (right) are of the galaxy
cluster Virgo. The optical image shows the visible galaxies in the
cluster, while the X-ray image displays the hot gas between the
galaxies.
This ROSAT image (right) of the Virgo cluster of galaxies reveals a hot X-ray
emitting plasma or gas with a temperature of 10-100 million degrees pervading
the cluster. False colors have been used to represent the intensity of X-ray
emission. The large area of X-ray emission, just below and left of
center, is about 1 million light-years across. The giant elliptical
galaxy M87, the biggest member of the cluster, is centered in that area while
other cluster members are scattered around it. By adding up the amount of
X-ray emitting gas astronomers have found that its total mass is up to
5 times the total mass of the cluster galaxies themselves - yet all this
matter still does not produce nearly enough gravity to keep the cluster from
flying apart! Where is the unseen mass? Because galaxy clusters are the
largest structures in the Universe, this mysterious Dark Matter must dominate
the cosmos but its nature is still an open question.
|