The universe’s ‘evil eye’: Bizarre shape is spotted as two galaxies crash together at 225,000mph.
Astronomers from Ohio State University used the Atacama Large Millimeter/submillimeter Array (ALMA) to discover the tsunami of stars and gas that is crashing midway through the disk of a spiral galaxy known as IC 2163.
‘Although galaxy collisions of this type are not uncommon, only a few galaxies with eye-like, or ocular, structures are known to exist,’ said Dr Michele Kaufman, lead author on a paper published today in the Astrophysical Journal.
Dr Kaufman and her colleagues said finding similar eye-shaped galaxies is rare because of their short lifetimes.
‘Galactic eyelids last only a few tens of millions of years, which is incredibly brief in the lifespan of a galaxy.
‘Finding one in such a newly formed state gives us an exceptional opportunity to study what happens when one galaxy grazes another,’ said Dr Kaufman.
The interacting pair of galaxies sit in a battleground approximately 114 million light-years from Earth.
The galaxies have brushed past each other, with the edges of their outer spiral arms scraping together.
This encounter is likely to be the first step in an eventual merger of the two galaxies.
The astronomers made the most detailed measurements yet of the motion of carbon monoxide gas, a tracer of the fuel for star formation, in the galaxy’s narrow eyelids.
The gas in the outer portion of IC 2163’s eyelids is racing inward at speeds in excess of 62 miles (100 km) a second.
But as it moves inwards the gas quickly decelerates and starts to move in a chaotic way, eventually changing direction to align itself with the rotation of the galaxy.
‘What we observe in this galaxy is very much like a massive ocean wave barreling toward shore until it interacts with the shallows, causing it to lose momentum and dump all of its water and sand on the beach,’ said Dr Bruce Elmegreen, co-author and scientist at IBM’s T.J. Watson Research Center in Yorktown Heights, New York.
‘Not only do we find a rapid deceleration of the gas as it moves from the outer to the inner edge of the eyelids, but we also measure that the more rapidly it decelerates, the denser the molecular gas becomes,’ said Dr Kaufman.
‘This direct measurement of compression shows how the encounter between the two galaxies drives gas to pile up, spawn new star clusters and form these dazzling eyelid features.’
Computer models predict eyelid-like features could evolve if galaxies interacted in a very specific manner.
‘This evidence for a strong shock in the eyelids is terrific. It’s all very well to have a theory and simulations suggesting it should be true, but real observational evidence is great,’ said Curtis Struck, a professor of astrophysics at Iowa State University.
‘ALMA showed us that the velocities of the molecular gas in the eyelids are on the right track with the predictions we get from computer models,’ said Dr Kaufman.
‘This critical test of encounter simulations was not possible before.’
These kind of collisions between galaxies are thought to have been common in the early universe, when galaxies were closer together.
At that time, however, galactic disks tended to be clumpy and irregular in their structure, so it is likely other processes prevented the formation of similar eyelid features.
The authors will continue to study this unusual galaxy pair and currently are comparing the locations, ages, and masses of the star clusters seen with Nasa’s Hubble Space Telescope with the properties of the molecular clouds observed with ALMA.
Images of the galaxies released in December 2014 showed the large number of super-bright sources of X-rays that may indicate a new type of black hole.