Unfortunately, stars don't have birth certificates. So, astronomers have a tough time figuring out their ages. Knowing a star's age is critical for understanding how our Milky Way galaxy built itself up over billions of years from smaller galaxies.

http://www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html

Gamma-ray beams seen in the Milky Way's central black hole suggest that the galaxy's center was much more active in the past, according to new research.

Visible in the constellation of Andromeda, NGC 891 is located approximately 30 million light-years away from Earth.

Researchers have discovered a dazzling display of billions of new stars in a galaxy-packed filament about 4,500 light years away in the Cygnus-X star-forming region of the Cygnus constellation.