A Close Neighbour

Andromeda, the nearest major galaxy to the Milky Way, is shown here in this wide-field optical image from Kitt Peak.

Located in the constellation of Andromeda (the Princess), the Andromeda Galaxy is a large spiral galaxy over 65,000 light years in diameter and approximately 2.9 million light years from Earth.
(Credit: NOAO/AURA/NSF/T.Rector & B.A.Wolpa)

The central region of Andromeda is shown in a composite image, with X-rays from NASA's Chandra X-ray Observatory (blue) combined with the optical image. Astronomers believe that Andromeda, also known as Andromeda Galaxy (M31), and the Milky Way will merge in a few billion years.

In the composite image (insert), hot, X-ray bright gas is seen to envelop the middle of Andromeda. Point sources are also prominent, which mostly reveal pairs of stars that are interacting with each other. Many of these double stars are thought to include white dwarfs pulling large amounts of material away from a companion star. When the amount of gas being dumped onto the white dwarf gets too high a thermonuclear explosion occurs on the surface of the white dwarf, emitting bright X-rays. (Credit: NASA/CXC/MPE/W.Pietsch et al)

Andromeda Galaxy (M31):
A New Look at a Close Neighbor from Chandra
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Ancient Galaxy collision

Astronomers surveying the Andromeda galaxy have discovered an association of stars in its outskirts, which they believe to be part of a separate galaxy that merged with Andromeda about 700 million years ago.

The findings suggest that Andromeda's outer swathes of stars are from the same parent galaxy, and may help astronomers determine the Andromeda's total mass.

Large galaxies are believed to be built partly by the merging of smaller galaxies, an event that destroys the smaller galaxy.

The strong gravitational forces of a large galaxy can rip apart a small galaxy, producing loose streams of stars that astronomers call tidal debris. Measuring the amount of the tidal debris that exists in present-day galaxies allows astronomers to examine the role mergers play in galaxy formation.

(Image courtesy of University Of Massachusetts Amherst)
Read more Evidence Of Ancient Galactic Collision Found
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