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Click to see selection as Astronomy Picture of the Day (APOD) - September 11, 2001
Most galaxies form new stars at a fairly slow rate, but
members of a rare class known as "starburst" galaxies
blaze with extremely active star formation. Scientists
using NASA's Hubble Space Telescope are perfecting a
technique to determine the history of starburst activity
in galaxies by using the colors of star clusters. Measuring
the clusters' colors yields information about stellar
temperatures. Since young stars are blue, and older stars
redder, the colors can be related to the ages, somewhat
similar to counting the rings in a fallen tree trunk in
order to determine the tree's age.
The galaxy NGC 3310 is forming clusters of new stars at
a prodigious rate. Astronomer Gerhardt Meurer of The Johns
Hopkins University leads a team of collaborators who are
studying several starburst galaxies, including NGC 3310,
which is showcased in this month's Hubble Heritage image.
There are several hundred star clusters in NGC 3310,
visible in the Heritage image as the bright blue diffuse
objects that trace the galaxy's spiral arms. Each of
these star clusters represents the formation of up to
about a million stars, a process that takes less than
100,000 years. In addition, hundreds of individual young,
luminous stars can be seen throughout the galaxy.
Once formed, the star clusters become redder with age
as the most massive and bluest stars exhaust their fuel
and burn out. Measurements in this image of the wide
range of cluster colors show that they have ages ranging
from about one million up to more than one hundred million
years. This suggests that the starburst "turned on" over
100 million years ago. It may have been triggered when
a companion galaxy collided with NGC 3310.
These observations may change astronomers' view of
starbursts. Starbursts were once thought to be brief
episodes, resulting from catastrophic events like a
galactic collision. However, the wide range of cluster
ages in NGC 3310 suggests that the starbursting can
continue for an extended interval, once triggered.
Located in the direction of the constellation Ursa Major,
NGC 3310 has a distance of about 59 million light-years.
Hubble's Wide Field Planetary Camera 2 was used to make
observations of NGC 3310 in March 1997 and again in
September 2000. The color rendition of the combined
images was created by the Hubble Heritage Team.
September 6, 2001
Image Credit: NASA and the Hubble Heritage Team (STScI/AURA)