Scientists using NASA’s Hubble Space Telescope are
studying the colors of star clusters to determine the age and
history of starburst galaxies, a technique somewhat similar to
the process of learning the age of a tree by counting its
rings.

This month’s Hubble Heritage image showcases the galaxy
NGC 3310. It is one of several starburst galaxies, which are
hotbeds of star formation, being studied by Dr. Gerhardt
Meurer and a team of scientists at Johns Hopkins University,
Laurel, Md.

The picture, taken by Hubble’s Wide Field and Planetary
Camera 2, is online
at http://heritage.stsci.edu and
http://oposite.stsci.edu/pubinfo/pr/2001/26 and
http://www.jpl.nasa.gov/images/wfpc . The camera was designed
and built by NASA’s Jet Propulsion Laboratory, Pasadena,
Calif.

Most galaxies form new stars at a fairly slow rate, but
starburst galaxies blaze with extremely active star formation.
Measuring the clusters’ colors yields information about
stellar temperatures. Since young stars are blue and older
stars redder, the colors relate to their ages.

NGC 3310 is forming clusters of new stars at a prodigious
rate. The new image shows several hundred star clusters,
visible 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.

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 their ages range between about one million and more than
one hundred million years. This suggests that the starburst
“turned on” more than 100 million years ago. It may have been
triggered when NGC 3310 collided with a companion galaxy.

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, once triggered, the starbursting can continue for a long
time.

Located in the direction of the constellation Ursa Major,
NGC 3310 is about 59 million light years from Earth. The
image is based on observations made by the Wide Field and
Planetary Camera 2 in March 1997 and September 2000. The
Hubble Heritage Team created the color rendition of the
combined images.

The Space Telescope Science Institute is operated by the
Association of Universities for Research in Astronomy, Inc.,
for NASA, under contract with the Goddard Space Flight Center,
Greenbelt, Md. The Hubble Space Telescope is a project of
international cooperation between NASA and the European Space
Agency. JPL is a division of the California Institute of
Technology in Pasadena.

Additional information about the Hubble Space Telescope
is available at http://hubble.stsci.edu. More information
about the Wide Field and Planetary Camera 2 is available at
http://wfpc2.jpl.nasa.gov

Image Credit: NASA and The Hubble Heritage Team (STScI/AURA)
Acknowledgment: G.R. Meurer and T.M. Heckman (JHU), and C.
Leitherer, J. Harris and D. Calzetti (STScI), M. Sirianni
(JHU)