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Two galaxies make strange traveling pair, but do they interact?

September 06, 2012|By Thomas H. Maugh II
  • The elliptical galaxy M60, center, and the spiral galaxy NGC 4647, upper right, lie only 9 million light-years apart.
The elliptical galaxy M60, center, and the spiral galaxy NGC 4647, upper… (NASA / ESO )

An unusual pair of galaxies travel through the interstellar cosmos in this striking image obtained by NASA's Hubble Space Telescope. The unusual pair are jointly called Arp 116, but are composed of a large elliptical galaxy known as M60 and a smaller spiral galaxy called NGC 4647.

The pair lies in the Virgo cluster of galaxies, where M60 is the third brightest object. It has a diameter of 120,000 light-years and a mass about 1 trillion times that of the sun. A massive black hole with a mass of about 4.5 billion times that of the sun lies at its center. NGC 4647 is about two-thirds the size of M60 and has a mass about the same as our own Milky Way galaxy. The two galaxies lie about 54 million and 63 million light-years away from Earth, respectively, so their apparent size difference in the image is very close to the actual difference.

M60 has a golden color because of the many old, cool and red stars in it. NCG 4647, however, has many young and hot stars that give it a blue tinge.

Although the two galaxies appear to overlap in the image, they do not. But because of their proximity, researchers have been attempting to determine whether they are interacting. There is no evidence of new star formation between them, which would be the case if their mutual gravitational pull were disrupting gas clouds, causing them to collapse into new stars. But detailed images of the pair do suggest there is some form of tidal interaction beginning between them.

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