A GALAXY BLAZES WITH STAR FORMATION
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,
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.
Credit: NASA and the Hubble
Heritage Team (STScI/AURA)
Acknowledgment: G.R. Meurer and T.M. Heckman (JHU),
C. Leitherer, J. Harris and D. Calzetti (STScI),
and M. Sirianni (JHU)