Wednesday, February 14, 2018

Across The Universe - Galaxy NGC 474: Shells and Star Streams

Galaxy NGC 474: Shells and Star Streams:

Discover the cosmos!
Each day a different image or photograph of our fascinating universe is
featured, along with a brief explanation written by a professional astronomer.

2018 February 6

See Explanation.  Clicking on the picture will download  the highest resolution version available.
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
to ripple through the galactic giant.

Regardless of the actual cause, the
featured image
dramatically highlights the increasing consensus that at least some elliptical
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
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