New class of enormous spiral galaxies discovered
Astronomers have discovered an entirely new breed of super massive galaxies that had previously been hiding in plain sight among spiral galaxies such as our own Milky Way. The vast galactic structures rank among the most luminous and largest of any galaxies discovered to date, and are believed to shine up to 14 times brighter than the Milky Way galaxy.
The discovery was made by scientists searching through a NASA archive known as the NASA/IPAC Extragalactic Database (NED) for evidence of massive galaxies within 3.5 billion light-years from Earth. NED contains data on over 100 million galaxies, combining a number of disparate databases including the catalogues of the Spitzer and WISE missions, and the Sloan Digital Sky Survey.
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The astronomers had expected to find a number of ancient galaxies known as ellipticals, but instead discovered that, out of the 800,000 sample galaxies included in the study, 53 of the brightest examples were in fact spiral-shaped.
Each of the newly discovered leviathan galaxies boasts a mass of up to 10 times that of the Milky Way, while retaining distinctive spiral arms in a frame up to 440,000 light-years across. The vast galaxies had remained hidden up until now by blending in with their closer, and more common spiral galaxy cousins.
The existence of the enormous spiral galaxies will require astronomers to develop new theories allowing for the development of the vast structures, as no such provision exists for super spirals in the current galactic evolutionary model.
According to the theory, the growth of a spiral galaxy would be limited to a predetermined mass at which any further interstellar gas entering a galaxy would be drawn in at such a velocity that it would fail to ignite further star birth. This is a phenomena known as "quenching."
However, the team responsible for the discovery may have already found an explanation for the creation of the huge galaxies that would avoid falling foul of the quenching theory – four of the super spirals identified in the study appear to contain two galactic nuclei.
The team suggests that a special type of merger in the distant past between two smaller spiral galaxies could avoid smashing together to become a less defined elliptical galaxy, and instead merge to form a single vast spiral monster. The four examples of super spirals with two galactic nuclei are therefore galaxies that had not yet completed the merging process.
Potential evidence for super spiral creation via merger could be found in the impressive rate of star creation exhibited by the newly discovered galaxies. Ultraviolet and infrared light emissions from the super spirals indicate that they are producing up to 30 times as many stars as the number created in our own Milky Way galaxy.
The dramatic burst of star creation could be explained by the infusion of new material from a collision between two galaxies – a process that has been observed in the past, and is expected to take place in our own galaxy when the vast gas cloud is set to rejoin the Milky Way around 30 million years from now.
A paper on the research has been published online in The Astrophysical Journal.