Gobbling galaxy's snacking habits revealed

A team of Australian and Spanish astronomers have caught a greedy galaxy gobbling on its neighbours and leaving crumbs of evidence about its dietary past.

They not only found a spiral galaxy called NGC 1512 devouring a nearby compact dwarf galaxy but got evidence of its past galactic snacks in unprecedented detail.

Galaxies grow by churning loose gas from their surroundings into new stars, or by swallowing neighbouring galaxies.

However, they normally leave very few traces of their cannibalistic habits.

"We were expecting to find fresh gas or gas enriched at the same level as that of the galaxy being consumed, but were surprised to find the gases were actually the remnants of galaxies swallowed earlier," explained Angel R. Lopez-Sanchez, astrophysicist at the Australian Astronomical Observatory (AAO) and Macquarie University.

The diffuse gas in the outer regions of NGC 1512 is not the pristine gas created in the Big Bang but is gas that has already been processed by previous generations of stars.

The dense pockets of hydrogen gas in the outer disk of NGC 1512 accurately pin-point regions of active star formation.

"While galaxy cannibalism has been known for many years this is the first time that it has been observed in such fine detail," added Tobias Westmeier from the International Centre for Radio Astronomy Research in Perth.

By using observations from both ground and space-based telescopes, the team was able to piece together a detailed history for this galaxy.

The team's successful and novel approach to investigating how galaxies grow is being used in a new programme to further refine the best models of galaxy evolution.

The study was published in the journal Monthly Notices of the Royal Astronomical Society (MNRAS).