Extreme galaxy

A Macalester physics and astronomy professor made national science waves last spring when he co-published a report of the discovery of a very extreme galaxy: one where gas is distributed over an area much larger than researchers had expected to find.

Professor John Cannon explains that, compared to other systems investigated to date, this “giant disk” dwarf galaxy has the largest size difference between stars and gas of any known galaxy. This result is important for furthering our understanding of how galaxies form and how they remain stable over time.

Cannon and his collaborators made the discovery during recent astronomy research at Macalester, using data from the Very Large Array (VLA) telescope in New Mexico and the Kitt Peak National Observatory (KPNO) in Arizona.

The KPNO data show the stars in the galaxy; this is how the object would appear to our eyes. Looking at this data, the galaxy has a very small and compact stellar component. The VLA data, on the other hand, show the gaseous component of the galaxy—the material from which those stars form.

“Because the stars are so compact, we expected to see a system that has a similarly compact gaseous disk,” says Cannon. “To our surprise, the gaseous disk is enormous— some 44 times larger than the size of the galaxy as seen in stars. This is certainly a little galaxy doing big things.”

This galaxy, named ADBS 1138, is considered an extreme galaxy because instead of having stars distributed throughout it, all its stars congregate in a very dense center. This suggests that most of the gas—the raw material for star formation—has not been used; no stars are seen in the outer regions of the gaseous disk.

This discovery raises important questions about disk stability and the nature of the mysterious “dark matter” seen in most galaxies.

Cannon’s research about this curious galaxy was published in the May 10, 2009, edition of The Astrophysical Journal.