Here's what 'greedy' galaxy likes to snack on

A new research has revealed the snacking habits of a "greedy" galaxy after it was caught gobbling on its neighbours and leaving crumbs of evidence about its dietary past.

Galaxies grow by churning loose gas from their surroundings into new stars, or by swallowing neighbouring galaxies whole. However, they normally leave very few traces of their cannibalistic habits.

The study by a team of Australian and Spanish astronomers not only reveals a spiral galaxy devouring a nearby compact dwarf galaxy, but shows evidence of its past galactic snacks in unprecedented detail.

The team used the unique capabilities of the 3.9-metre Anglo-Australian Telescope (AAT), near Coonabarabran, New South Wales, to measure the level of chemical enrichment in the gas across the entire face of galaxy NGC 1512.

Chemical enrichment occurs when stars churn the hydrogen and helium from the Big Bang into heavier elements through nuclear reactions at their cores. These new elements are released back into space when the stars die, enriching the surrounding gas with chemicals like oxygen, which the team measured.

Researcher Angel R. Lopez-Sanchez said that they 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.

Lopez-Sanchez added that 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 unique combination of these data provides a very powerful tool to disentangle the nature and evolution of galaxies, noted Lopez-Sanchez, adding that they will observe several more galaxies using the same proven techniques to improve the understanding of the past behaviour of galaxies in local Universe.

The study appears in Monthly Notices of the Royal Astronomical Society (MNRAS).