24 July 2019
Nick Carne
Nick Carne is the editor of Cosmos Online and editorial manager for The Royal Institution of Australia.
Astronomers say the discovery of vast amounts of hydrogen gas in a galaxy 60 million light-years from Earth resolves a long-standing mystery related to the formation and evolution of galaxies.
The work by an international team is based on observations made last year with the South African Radio Astronomy Observatory’s new MeerKAT telescope in the Northern Cape.
NGC 1316 is the brightest galaxy at visible wavelengths in a nearby cluster of galaxies located in the direction of the Fornax constellation. It is also known as the radio galaxy “Fornax A” and is the fourth brightest source of astronomical radio waves in the entire sky.
It is clear from its irregular shape in visible light images, the researchers say, that this peculiar galaxy formed through a collision and merger of two major galaxies a few billion years ago, followed by subsequent merging with smaller satellite galaxies.
What has long been a mystery, however, is why NGC 1316 seems to have so little hydrogen gas – the raw fuel that is present in many galaxies alongside heavier dust grains and ultimately makes up stars throughout the universe.
“In this article we show new radio images obtained with MeerKAT which reveal where all that hydrogen was hiding,” says lead author Paolo Serra of the Italian National Institute for Astrophysics Observatory of Cagliari.
“It’s distributed in two long, faint, gaseous tails, stretching to a large distance from the galaxy.”
The radio tails were found at the same location as tails made up of stars discernible in sensitive visible light images, and were generated by tidal forces in action during the merger, Serra says.
“The amount of gas found is consistent with that expected based on merger theory, and on the fact that the smallest progenitor galaxy was like the Milky Way,” he says.
“Thus, thanks to these observations all pieces of the puzzle are now in place, and we finally have a more precise and coherent understanding of the formation of this famous galaxy.”
The findings will be published in the journal Astronomy & Astrophysics. The paper currently available on the pre-print server arXiv.