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NASA Astronomy Picture of the Day

🌌 NASA Astronomy Picture of the Day

Galaxy Cluster A2199 Credit:

Date: 1997-01-22

Galaxy Cluster A2199
Credit:

View HD Image

Explanation:

It's bigger than a bread box. In fact, it's
much bigger than all bread boxes put together. Abell 2199
is huge. In fact, it is a close, large cluster of galaxies,
containing several thousands of galaxies
centered around a central dominant galaxy. "Close,"
however, is only relative to other clusters of galaxies,
since light takes about 50 million years to reach us from
A2199. All of the fuzzy objects in the above picture are galaxies,
but these galaxies do not contain most of the matter in
the cluster. By studying clusters like A2199, astronomers conclude
that some form of dark matter
dominates the motion of the bright galaxies. What, exactly, this
dark matter
is poses one of the greatest astronomical puzzles of modern times.