Explanation:
How old is this galaxy?
The nearby
Local Group
galaxy dubbed the
Sagittarius Dwarf Irregular Galaxy (SagDIG)
is not only very small but also has relatively few elements more massive than
helium.
Now the lack of heavy elements might mean that
SagDIG is very young, so that component stars
had little time to create and disperse massive elements.
Conversely,
SagDIG's diminutive size could indicate that it formed in the early universe, being a surviving
building block of modern
large galaxies.
The above detailed image from the
Hubble Space Telescope
has now resolved enough stars to
solve this mystery: SagDIG is ancient.
Although SagDIG does have some groups of young stars, many stars are very old,
and the galaxy as a whole helps astronomers to understand how the
universe evolved, and show that at least one
metal-poor galaxy is almost as
old as the universe.
Pictured above,
SagDIG spans about 1,500 light years and lies about 3.5 million light years away toward the
constellation of Sagittarius.
