|
 |
 advertisement
| |
|
|
|
|
|
Hubble Sees Galactic Evolution in Odd Stellar Collection
By SPACE.com Staff
posted: 02:16 pm ET
07 March 2003
|
EMBARGOED FOR A newly released photograph from the Hubble Space Telescope shows thousands of young and old stars in the central region of a small galaxy called NGC 1705. The galaxy is known as a dwarf irregular because it lacks structure common to larger galaxies. The galaxy is about 17 million light years away and is thought to be very old. Astronomers suspect dwarf galaxies were the first type to form in the universe, so understanding how dwarf irregular galaxies evolve should provide clues about galaxy formation and evolution in general. In particular, NGC 1705 is seen a as a useful laboratory for studying the history of star formation. Young stars, hot and blue in the new image, are concentrated toward the galaxy's center. Older stars, typically cooler and showing up as red, are more spread out through the galaxy. NGC 1705 has been forming new stars throughout its lifetime, astronomers say, but a burst of star-formation activity occurred as recently as 26 to 31 million years ago. This starburst activity generated many of the young stars on the outskirts of this galaxy's core as well as in the cluster around the middle. Galaxies like NGC 1705 are thought to represent the building blocks from which more massive spiral and elliptical galaxies formed, often through mergers. Some small galaxies near our own Milky Way are thought to be leftovers of the galaxy-formation process. The Hubble observations of the stars in NGC 1705 and other similar irregular galaxies near to our own show that these galaxies are several billion years old. NGC 1705 could be as old as 13.5 billion years, which is practically the beginning of the universe, according to a separate recent study. Dwarf irregular galaxies seem to have consumed only a tiny part of their reservoir of gas, the stuff of star formation and galaxy development. Their stars have a much lower fraction of heavy elements than does the Sun. All heavy elements (those heavier than hydrogen, helium and lithium) are created by stars and typically cast into space when stars die. It is in this manner that subsequent generations of stars in a galaxy hold telltale signs of a more diverse range of heavier and heavier elements, commonly referred to by astronomers as metals. Astronomers therefore think that only a few generations of stars have formed in NGC 1705. The image, released today, was taken in separate exposures in March 1999 and November 2000 by an international science team led by Monica Tosi at Italy's National Institute of Astrophysics (INAF) at the Osservatorio Astronomico di Bologna. The Hubble telescope is a cooperative effort between NASA and the European Space Agency.
|
|
|
|
|
