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2013: Jay Strader research group discovers densest known galaxy

MSU Astronomy & Astrophysics Assistant Professor Jay Strader (pictured at lower right) was the lead author for an Astrophysical Journal Letter (volume 775, letter 6, 20 Sept 2013) describing the characteristics of an ultra-compact galaxy called M60-UCD1, with a density 15,000 times that of the region of the Milky Way near the Sun, making it the densest galaxy currently known. Typical spacing between stars in M60-UCD1 is only 4% that found in our stellar neighborhood.

[photo of Dr. Jay Strader]
Dr. Jay Strader

The research group which wrote the paper used data from NASA's Hubble Space Telescope and Chandra X-ray Observatory along with a number of ground-based optical telescopes. It had members from six other universities and institutions besides MSU's Dr. Strader.

The ultra-compact class of galaxies is a relatively recent addition to the list of known galaxy types, having been discovered within the past dozen or so years. Earlier observations mistook them for unusual single stars, larger galaxies much farther away, or smaller dense clusters much closer to us. Since surveys in 1999 and 2000 demonstrated that the earlier explanations were not correct, a concerted effort has been made to investigate them in greater detail and expand the search for others of this new type.

In the case of the M60-UCD1 galaxy, about half of its mass of approximately 200 million times that of our sun is found within a radius of 24 parsecs (78 light years), with the galaxy as a whole being about 98 parsecs (320 light years) in diameter. There is also evidence of a central supermassive black hole, as can be found in other galaxies such as our Milky Way. It is one of numerous satellite galaxies surrounding the large elliptical galaxy M60 (also known as NGC 4649), one of a large cluster of galaxies in the direction of the constellation Virgo as seen from the Earth. M60 is approximately 54 million light years from Earth.

Dr. Strader's paper describes his group's investigation into the properties of M60-UCD1 as well as discussing possible explanations of how it came to have the characteristics they observed.

For further details, see the following articles.