July 26, 2011
The cosmos is full of spectacular things: ringed planets, exploding suns, rivers of stars across the night.
Galaxy NGC 474: Cosmic Blender
Birthday · July 26, 2011
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APOD published July 26, 2011. Credit: P.-A. Duc (CEA, CFHT), Atlas 3D Collaboration. A publication-date match, not a photo taken on your date. Independent of NASA.
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
Image credit: P.-A. Duc (CEA, CFHT), Atlas 3D Collaboration