A team of scientists led by Dr. Patrick Ogle from the California Institute of Technology has discovered a new type of galaxy called a super spiral.
Images of super spiral galaxies. Examples with peculiar morphology: (1) multi-arm spiral, (8) asymmetric two-arm spiral, (21) ring galaxy, (23) possible tidal arm, (33) asymmetric disk, (34) possible secondary bulge, (53) partial arms or shells. Image credit: SDSS.
According to the team, super spirals are very luminous — they can shine with anywhere from 8 to 14 times the brightness of our Milky Way Galaxy.
They are also giant and massive, with diameter 186,000-437,000 light-years and stellar mass between 30 and 340 billion solar masses.
These galaxies give off copious UV and mid-IR light, signifying a breakneck pace of churning out new stars. Their star formation rate is as high as 30 times that of our own Galaxy.
Dr. Ogle and co-authors chanced upon super spirals as they searched for extremely luminous, massive galaxies in the NASA/IPAC Extragalactic Database (NED).
“Remarkably, the finding of super spiral galaxies came out of purely analyzing the contents of the NED database, thus reaping the benefits of the careful, systematic merging of data from many sources on the same galaxies,” said team member Dr. George Helou, also from the California Institute of Technology.
The astronomers expected that humongous, mature galaxies called ellipticals would dominate their search within NED for the most luminous galaxies. But a tremendous surprise lay in store for the team.
In a sample of about 800,000 galaxies no more than 3.5 billion light-years from Earth, 53 of the brightest galaxies intriguingly had a spiral, rather than elliptical, shape.
The team double-checked the distances to the spirals and saw that none were nearby – even the closest lay some 1.2 billion light-years away.
This galaxy, named SDSS J094700.08+254045.7, is one of the biggest and brightest super spirals; its starry disk and spiral arms stretch about 320,000 light-years across, or more than three times the breadth of our Milky Way Galaxy. Image credit: SDSS.
A hint about the potential origin of these super spiral galaxies is that 4 out of the 53 seen by the astronomers clearly contain two galactic nuclei, instead of just one as usual.
“Double nuclei are a telltale sign of two galaxies having just merged together. Conventionally, mergers of spiral galaxies are destined to become bloated, elliptical galaxies,” the scientists explained.
Yet they speculate that a special merger involving two, gas-rich spiral galaxies could see their pooled gases settle down into a new, larger stellar disk — a super spiral.
“Super spirals could fundamentally change our understanding of the formation and evolution of the most massive galaxies,” said Dr. Ogle, who is lead author of a paper published in the Astrophysical Journal (arXiv.org preprint).
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Patrick M. Ogle et al. 2016. Superluminous Spiral Galaxies. ApJ 817, 109; doi: 10.3847/0004-637X/817/2/109
