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Starburst Galaxies
Chandra image of
Arp 220
(NASA/SAO/CXC/J.McDowell)
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The infrared satellite
IRAS discovered thousands of starburst galaxies. Many of the new stars remain
surrounded by dust and gas for a million years. Their light is absorbed by the
dust, which radiates away the heat as infrared radiation. The "heat radiation"
produced by hot sidewalks on a summer day is infrared radiation. Starburst
galaxies are rare among nearby galaxies, but they were common many billions of
years ago. The universe is expanding, so galaxies were much closer together in
the past and collisions or close encounters were more frequent, causing more
starbursts.
Chandra observations are playing an important role in understanding starburst
galaxies. The rapid rate of supernova explosions in these galaxies produces
expanding bubbles of multimillion degree gas. Several striking examples of these
superbubbles can be seen in the Chandra image of two colliding galaxies known as
the Antennae.
 Starburst-driven galactic winds
(D.Strickland)
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When the starburst is sufficiently intense, it can create a superbubble so hot
and energetic that it expands out of the galaxy in what is called a superwind.
Dramatic examples of superwinds can be seen in Chandra's images of M82, Arp 220
and NGC 253.
Superwinds are thought to contain the carbon, nitrogen, oxygen, iron and other
heavy elements dispersed by supernovas and spread these elements throughout the
space between galaxies. With Chandra, astronomers hope to measure the amounts of
these elements in the superwinds.
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