Explanation:
Nearly 50 million light-years away in the constellation Ursa Major,
NGC 4013 was long considered an isolated island
universe.
Seen edge-on, the gorgeous spiral
galaxy was
known for its
flattened disk and central bulge of stars, cut by silhouetted dust
lanes.
But this
deep
color image of the region reveals a previously unknown feature
associated with NGC 4013, an enormous, faint looping structure extending
(above
and toward the left) over 80 thousand light-years from the galaxy's
center.
A detailed exploration of
the remarkable
structure reveals it to be a
stream of stars originally belonging to another galaxy, likely a smaller
galaxy
torn
apart by gravitational
tides as it merged with the larger spiral.
Astronomers argue that the newly discovered tidal stream also explains a
warped
distribution of neutral hydrogen gas seen in
radio
images of
NGC 4013 and offers
parallels to the
formation of
our own Milky Way galaxy.
digg_url = 'http://apod.nasa.gov/apod/ap080207.html'; digg_skin =
'compact';
