New class of enormous spiral galaxies discovered
Astronomershave discovered an entirely new breed of super massivegalaxies that had previously been hiding in plain sight among spiral galaxies such as our own Milky Way. The vast galacticstructures rank among the most luminous and largest of any galaxiesdiscovered to date, and are believed to shine up to 14 times brighterthan the Milky Way galaxy.
The discovery was madeby scientists searching through a NASA archive known as the NASA/IPACExtragalactic Database (NED) for evidence of massive galaxies within3.5 billion light-years from Earth. NED contains data on over 100million galaxies, combining a number of disparate databases includingthe catalogues of the Spitzer and WISE missions, and the SloanDigital Sky Survey.
The astronomers hadexpected to find a number of ancient galaxies known as ellipticals,but instead discovered that, out of the 800,000 samplegalaxies included in the study, 53 of the brightest examples were infact spiral-shaped.
Each of the newlydiscovered leviathan galaxies boasts a mass of up to 10 times thatof the Milky Way, while retaining distinctive spiral arms in a frameup to 440,000 light-years across. The vast galaxies had remainedhidden up until now by blending in with their closer, and more commonspiral galaxy cousins.
The existence of theenormous spiral galaxies will require astronomers to develop newtheories allowing for the development of the vast structures, as nosuch provision exists for super spirals in the current galacticevolutionary model.
According to thetheory, the growth of a spiral galaxy would be limited to apredetermined mass at which any further interstellar gas entering agalaxy would be drawn in at such a velocity that it would fail toignite further star birth. This is a phenomena known as "quenching."
However, the teamresponsible for the discovery may have already found an explanationfor the creation of the huge galaxies that would avoid falling foulof the quenching theory – four of the super spirals identified in thestudy appear to contain two galactic nuclei.
The team suggests thata special type of merger in the distant past between two smallerspiral galaxies could avoid smashing together to become a lessdefined elliptical galaxy, and instead merge to form a single vastspiral monster. The four examples of super spirals with two galacticnuclei are therefore galaxies that had not yet completed the mergingprocess.
Potential evidence forsuper spiral creation via merger could be found in the impressiverate of star creation exhibited by the newly discovered galaxies.Ultraviolet and infrared light emissions from the super spiralsindicate that they are producing up to 30 times as many stars as thenumber created in our own Milky Way galaxy.
The dramatic burst ofstar creation could be explained by the infusion of new material froma collision between two galaxies – a process that has been observedin the past, and is expected to take place in our own galaxy when thevast gas cloud is set to rejoin the Milky Way around 30 million yearsfrom now.
A paper on the researchhas been published online in The Astrophysical Journal.