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M82 in Context
 X-ray of M82
Credit: NASA/CXC/SAO/PSU/CMU
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Starburst Galaxies
A starburst galaxy is a galaxy experiencing a period of intense
star forming activity. Although this activity may last for ten
million years or more, that is like a month in the life of a ten
billion year old galaxy. During a starburst, stars can form at
tens, even hundreds of times greater rates than the star
formation rate in normal galaxies. Many of these newly formed
stars are very massive and very bright, so starburst galaxies
are among the most luminous galaxies.
The burst occurs over a region a few thousand light years in
diameter. The most popular theory for the cause of a starburst
is that it is triggered by a close encounter or collision with
another galaxy. This collision sends shock waves rushing through
the galaxy. These shock waves push on giant clouds of gas and
dust, causing them to collapse and form a few hundred stars. The
massive stars use up their fuel quickly and explode as
supernovas, which produces more shock waves and more star
formation. In this way, a chain reaction of star formation and
supernovas can sweep through the central region of a galaxy,
where most of the gas is located. When most of the gas is used
up or blown away by the explosions, the starburst ends.
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.
 Starburst-driven Galactic Winds
Credit: D.Strickland
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X-ray observations play an important role in understanding
starburst galaxies. The rapid rate of supernovas heats the gas
in the galaxy to millions of degrees. An expanding bubble of hot
gas extends beyond the galaxy in a starburst wind.
X-ray observations provide the best means for studying the
formation and expansion of starburst winds. This information can
be very important for understanding how much gas is blown out of
a galaxy by a starburst wind. Since gas is the source of new
stars, the starburst wind can have an important effect on the
future evolution of the galaxy.
Starburst winds carry with them the carbon, nitrogen, oxygen, iron and other
heavy elements blown out of stars in supernovas. They are probably the main
way in which these elements are spread throughout the universe. With Chandra,
astronomers hope to detect these elements in starburst winds and get a better
idea of what the gas between galaxies is made of and where it came from.
Return to M82 (14 Jan 00)
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