Galactic 'Eyelids' Show Space Gas 'Tsunami' (Photo)

Eyelid galaxy whirls
The eyelid-like whirls of gas and bright stars in galaxy IC 2163 were caused by a collision with the galaxy NGC 2207. The galaxy's carbon monoxide gas (orange) was detected by the Atacama Large Millimeter/submillimeter Array in Chile. Here, it's overlaid on a Hubble image of the galaxy (blue). An arm of NGC 2207 can be seen at the far right.
(Image: © M. Kaufman; B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble Space Telescope)

Look out! A "tsunami" of gas is crashing through a spiral galaxy, creating an image that bears a striking resemblance to a pair of eyelids.

The turbulent zone formed when a galaxy called IC 2163 brushed by another one, named NGC 2207. The spectacular feature is expected to last a few tens of millions of years, researchers said in a statement. The collision zone, located some 114 million light-years from Earth, was inspected for a new study with the Atacama Large Millimeter/submillimeter Array (ALMA), a large radio observatory in Chile.

"Although galaxy collisions of this type are not uncommon, only a few galaxies with eye-like, or ocular, structures are known to exist," Michele Kaufman, lead author of the new work and an astronomer who was formerly with The Ohio State University, said in a statement that billed the formation as a sort of cosmic "tsunami." [Amazing Star Birth Photos from the ALMA Telescope]

The galaxies IC 2163, at left, and NGC 2207 brushed against each other, producing these swirls of stars and gas. (Orange is carbon dioxide gas, imaged by ALMA, and blue is a Hubble view of the duo.)
(Image: © M. Kaufman; B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble Space Telescope)

The collision zone, some 114 million years away from Earth, was observed with the Atacama Large Millimeter/submillimeter Array (ALMA). The galaxies first rubbed against each other with their outer spiral arms, but they are expected to merge eventually.

Astronomers used ALMA's fine resolution to peer at carbon monoxide gas — a common fuel for star formation — in the galaxy. They saw gas in the outer zone of IC 2163 moving inward from the "eyelid" at more than 60 miles per second (100 kilometers per second).

But it doesn't keep up that pace. According to the observations, the gas decelerates as it moves to the inside, and then changes direction to move with the galaxy's rotation instead of heading straight for the center. The gas also becomes denser as it decelerates, gathering together in the "eyelid" zone to provide a potential star formation hotspot, the researchers said.

An annotated image of the galaxy IC 2163 incorporating carbon monoxide (orange) and stars (blue).
(Image: © M. Kaufman; B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble Space Telescope)

"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," Bruce Elmegreen, co-author of the paper and a scientist with IBM's Thomas J. Watson Research Center in Yorktown Heights, New York, said in the statement.

A The paper based on the research was published in The Astrophysical Journal, according to the statement; you can read a recent draft on the archival website arXiv.

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