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Unit 7: Astrophysics Page 29
Galaxies several different types of active
galaxies, including radio galaxies
Stars like to live together in (edge-on view of galaxies emitting
families. Galaxies are stars that are jets), quasars (3/4 view of the
pulled and held together by galaxy emitting jets), blazars
gravity. Some galaxies are sparse (aligned so we’re looking straight
while others are packed so dense down into the black hole jet), and
you can’t see through them. others. Our own galaxy, the Milky
Galaxies also like to hang out with Way, has a super-massive black
other galaxies (called galaxy hole at its center, which is
clusters), but not all galaxies currently quiet and dormant.
belong to clusters, and not all stars
belong to a galaxy. Globular and Open Clusters
Active galaxies have very unusual
behavior. Most galaxies have When you look up at the night sky,
super-massive black holes in the it seems like the pinpoints of light
are each isolated from each other.
center, many of which lie dormant.
When viewed through a telescope,
Scientists think active galaxies are
however, single stars can actually
the ones where the black hole is
actively feeding on in-falling transform into tens of millions of
stars. Globular clusters are
material. What scientists can
massive groups of stars held
detect are huge bursts of energy in
together by gravity, using housing
the form of x-ray and gamma rays
spewing up and out of the plane of between tens of thousands to
millions of stars (think New York
the galaxy - a sure sign of a
City). Open clusters are made up
voracious black hole. There are
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