The Umbrella Galaxy is a family of stars in the process of tearing apart another such group.
Also known as NGC 4651, this cosmic cannibal is a near twin of our own Milky Way Galaxy. The name derives from a parasol-like structure near the star formation. This is the remains of the galaxy being consumed by the larger collection of stars.
The distance to the Umbrella Galaxy is uncertain. Measurements place it around 62 million light years from Earth, although there is some disagreement on that figure. It is a member of the Virgo Cluster of galaxies. This group contains up to 2,000 islands of stars, and is a member of the much-larger Virgo Supercluster. Our own Local Group of galaxies is also part of that vast collection.
The "umbrella" of NGC 4651 was discovered in the 1950's. At that time, astronomers believed the faint structure was a dwarf galaxy, orbiting its more-massive companion. Now, researchers believe the feature is the leftover remains of a stellar meal.
Our own Milky Way is also a galactic cannibal, in the process of absorbing the Sagittarius dwarf galaxy. That grouping was discovered just two decades ago. Our family of stars has grown over billions of years by engulfing smaller stellar groups.
David Martínez-Delgado of the University of Heidelberg led research in 2010 studying eight spiral galaxies, including NGC 4651. Three-quarters of these, including the Umbrella Galaxy, exhibited evidence of such intergalactic feasting. Arcs of debris, shells and clouds of stars, each of which could be indicative of mergers, were recorded.
Caroline Foster of the Australian Astronomical Observatory (AAO) led researchers in a follow-up examination of the distinctive galaxy. The team studied the galaxy using the Keck and Subaru telescopes, located in Hawaii.
They looked at movements of small groupings of stars called globular clusters, as well as nebulae and hydrogen gas to determine how the structure was evolving. They found the arc seen as the top of the umbrella is composed of material from a single encounter, rather than a series of mergers. This section of the feature is located roughly 100,000 light years beyond the bright disk of the main galaxy.
"Through new techniques we have been able to measure the movements of the stars in the very distant, very faint, stellar stream in the Umbrella. This allows us to reconstruct the history of the system, which we couldn't before," Foster said.
Study of the Umbrella Galaxy and galactic cannibalism was detailed in the Monthly Notices of the Royal Astronomical Society.
