Explanation:
What's happening to galaxy NGC 474?
The multiple layers of emission appear strangely complex and unexpected given the relatively featureless appearance of the
elliptical galaxy in less deep images.
The cause of the shells is currently unknown, but possibly
tidal tails related to debris left over from absorbing numerous small galaxies in the past billion years.
Alternatively the shells may be like ripples in a pond, where the ongoing collision with the spiral galaxy just above
NGC 474
is causing density
waves to ripple though the galactic giant.
Regardless of the actual cause, the
above image
dramatically highlights the increasing consensus that at least some elliptical
galaxies
have formed in the recent past, and that the outer halos of most
large galaxies are not really smooth
but have complexities induced by frequent interactions with --
and accretions of --
smaller nearby galaxies.
The halo of our own
Milky Way Galaxy
is one example of such
unexpected complexity.
NGC 474 spans about 250,000
light years and lies about 100 million light years distant toward the constellation of the Fish
(Pisces).
APOD Lecture and Star Party:
This Friday night at Ft. Wilkins, Michigan
