STELLAR CHEMISTRY

New Discovery Poses Challenge To Galaxy Formation Theories

Bloomington IN (SPX) Apr 17, 2009

A team led by an Indiana University astronomer has found a sample of massive galaxies with properties that suggest they may have formed relatively recently.

This would run counter to the widely-held belief that massive, luminous galaxies (like our own Milky Way Galaxy) began their formation and evolution shortly after the Big Bang, some 13 billion years ago.

Further research into the nature of these objects could open new windows into the study of the origin and early evolution of galaxies.

John Salzer, principal investigator for the study published today in Astrophysical Journal Letters, said that the 15 galaxies in the sample exhibit luminosities (a measure of their total light output) that indicate that they are massive systems like the Milky Way and other so-called "giant" galaxies.

However, these particular galaxies are unusual because they have chemical abundances that suggest very little stellar evolution has taken place within them. Their relatively low abundances of "heavy" elements (elements heavier than helium, called "metals" by astronomers) imply the galaxies are cosmologically young and may have formed recently.

The chemical abundances of the galaxies, combined with some simple assumptions about how stellar evolution and chemical enrichment progress in galaxies in general, suggest that they may only be 3 or 4 billion years old, and therefore formed 9 to 10 billion years after the Big Bang. Most theories of galaxy formation predict that massive, luminous systems like these should have formed much earlier.

If this overall interpretation proves correct, the galaxies may allow astronomers to investigate phases of the galaxy formation and evolution process that have been difficult to study because they normally occur at such early times in the Universe, and therefore at very large distances from us.

"These objects may represent a unique window on the process of galaxy formation, allowing us to study relatively nearby systems that are undergoing a phase in their evolution that is analogous to the types of events that, for most galaxies, typically occurred much earlier in the history of the Universe," Salzer said.

Taken from “Space Daily” (April 17, 2009)