spaceSpace and PhysicsspaceAstronomy

There's Another Galaxy Orbiting Our Own, And It's Being Ripped Apart


Jonathan O'Callaghan

Senior Staff Writer

The SMC, as seen by the Herschel Space Observatory. ESA/NASA/JPL-Caltech/STScI

Scientists have discovered that one of our neighboring galaxies, the Small Magellanic Cloud (SMC), is slowly being torn apart by its companion galaxy.

The study, led by Paul Zivick from the University of Virginia, is available on arXiv and has been submitted to the Astrophysical Journal for publication.


Using the Hubble telescope, the team monitored the movement of stars in the SMC, which orbits our Milky Way at a distance of about 200,000 light-years. And they found that the galaxy didn’t seem to be rotating, but instead parts of it were being pulled by its companion – the Large Magellanic Cloud (LMC).

From this, they were able to make the surprising discovery that the two galaxies collided about 150 million years ago. It’s unlikely they collided head-on (a “bulls-eye" hit), but it does look like they at least glanced each other. It’s thought their centers passed each other at a distance of about 25,000 light-years.

“It seems extremely likely that the Clouds have hit each other,” the team wrote in their paper. “The fact that the SMC is in reality an extended body… strengthens this argument further.”

But looking to the future, the SMC is set for some rather turbulent times. Gurtina Besla from the University of Arizona in Tucson, one of the study’s co-authors, told New Scientist that the galaxy would completely change its type as it is losing both stars and gas.


“Right now it’s an irregular galaxy, full of gas that’s spawning the bright new stars that set it aglow,” New Scientist noted. “But [Besla] says the galaxy will lose its gas and eventually become a dwarf elliptical galaxy, a duller type that gives birth to no stars at all.”

The SMC is expected to survive, thanks to dark matter holding it together. Future data, from ESA’s Gaia spacecraft for example, could also tell us more about the center of the SMC itself; we’re still not exactly sure where it is.

And the team hope their research can tell us a bit more about how star formation is occurring in the two Clouds, as well as telling us if they’ve orbited our own Milky Way once or twice. It gives us a neat look, too, at the effects one galaxy can have on another, even quite a while after a collision.

[H/T: New Scientist]


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