Senior Media Relations Representative
CASE, WIYN ASTRONOMERS DISCOVER
NEW GALAXY ORBITING ANDROMEDA
Morrison, Paul Harding and Denise Hurley-Keller of Case’s department of
astronomy and George Jacoby of the WIYN Observatory in
"This is particularly exciting because it allows us to watch the on-going build-up of the nearby Andromeda galaxy from smaller galaxies", says Morrison.
astronomers used Case's Burrell Schmidt telescope and the 3.5m WIYN telescope
to identify the galaxy, which is being torn apart into star streams which trace
its orbit the way a jet’s contrail shows its route. Both telescopes
are located at Kitt Peak National Observatory near
Andromeda (M31) is the nearest large spiral galaxy to our own Milky Way galaxy—a "mere" two million light years away. It is visible with the naked eye in a dark site in the constellation of Andromeda, south of Cassiopeia, and was noted over 1,000 years ago by the Persian astronomer Azophi Al-Sufi. It is a member of the Local Group of approximately 30 galaxies in our celestial "backyard".
In early August, as Morrison finished analyzing the data on these stars, she was amazed to find a new dwarf galaxy orbiting Andromeda. It is a "see-thru" galaxy which was only discovered once the astronomers obtained velocity measurements for some of its stars, said Morrison.
She adds that the reason Andromeda VIII escaped detection was its extremely tenuous nature, plus the fact that it is located in front of the bright regions of Andromeda's disk.
Andromeda VIII's total brightness is comparable to that of M31's well-known companion M32, but it is spread over an area of the sky ten times or more larger than M32. Its elongated shape is caused by M31's gravitational pull, which stretches it out due the stronger gravity on the side nearest Andromeda.
Because of Andromeda's large mass and its gravitational pull on the dwarf galaxy, it is coming apart in a stream of stars as the galaxy orbits Andromeda.
Morrison and her collaborators also suggested that a very faint stream of stars, detected near M31 in 2001 by astronomer R. A. Ibata and colleagues, was pulled off Andromeda VIII in an earlier passage around the parent galaxy. "Future research in this area should provide rich and fruitful results", states Morrison.
Theory has predicted for decades that galaxies are assembled in a "bottom-up" process, forming first as small galaxies that later merge to form large ones.
"Since 1994, when Ibata and colleagues announced the discovery of a new satellite in the process of being swallowed by the Milky Way, we have been able to actually see the process taking part in our own galaxy," states Morrison. "Now we find the same process in our nearest large neighbor."
She adds that now it looks like Andromeda is even more inundated by small galaxies than the Milky Way. Ibata and colleagues have taken deep images of M31 which show a rich collection of star streams wreathed about the galaxy. Morrison and her colleagues have now identified the source of one of these star streams. They plan
future observations to connect the different star streams with their progenitors, and thus learn more about the properties of the companion, the Andromeda galaxy and its elusive dark matter halo.
Morrison's galaxy research was supported by a five-year National Science Foundation Early Career Development Award.
An image of M31 with the position of Andromeda VIII marked is available at http://smaug.cwru.edu/heather/stars.jpg. (Photo credit: Robert Gendler, Nancy Lin.) A movie which shows a large galaxy tearing apart a smaller one in the way that the Andromeda spiral is tearing apart Andromeda VIII is available at http://www.astro.wesleyan.edu/~kvj/mw.html (Movie credit: Kathryn Johnston).
The Burrell Schmidt telescope is part of Case's Warner and Swasey Observatory. The WIYN 3.5-meter telescope is a
partnership of the
Contact: Dr Heather Morrison, CWRU, 216-368 6698, firstname.lastname@example.org
Dr Paul Harding, email@example.com, 216-368 6696