spaceSpace and Physics

Cigar Galaxies Are Way More Common Than We Thought


Jonathan O'Callaghan

Senior Staff Writer

Artist's impression of a cigar galaxy. J. Chang, PMO / T. Müller, HdA

The universe is a weird place. We’ve got planets that rain diamonds, stars that rotate super-rapidly, and bizarre flashes of radio waves that we can’t explain.

For me, though, there’s a peculiar type of galaxy that really piques my interest. It’s known as a “cigar galaxy”, although its technical name is a prolate rotator. Like a spindle, these galaxies are shaped like a cigar and rotate along their longest axis. Yeah, they’re awesome.


Thing is, we thought they were super rare. Like, we had only found 12 of them in the universe. But a new study, looking at just 600 galaxies, has found eight more. This suggests they might not be that rare after all – and we’ve also got a handle on how they might form. Let’s dive in!

A study describing these findings was published in the journal Astronomy and Astrophysics and led by the Max Planck Institute for Astronomy in Germany.

“Until now astronomers thought that this type of galaxy is extremely rare,” Athanasia Tsatsi, the study's lead author, told IFLScience. “It was really surprising to see so many galaxies with such a feature, practically ten times more than expected!”

The researchers used data from the Calar Alto Legacy Integral Field Area (CALIFA) survey to reach their findings. This is a project to study the light from 600 galaxies with the Calar Alto Observatory in Spain. Care was taken to make sure these galaxies were picked at random so that they were representative of the universe as a whole.


The coolest thing about this study, though, is that the researchers think they’ve worked out how cigar galaxies form. It would go something like this: First, two spiral galaxies would collide with each other. One would then form a “bar”, eventually creating an elliptical galaxy with a cigar shape. The stars of the other galaxy, meanwhile, orbit the bar of this galaxy. Thus, we get this neat spindle shape.

It’s likely that this process is fairly unusual, but not that uncommon. There might be many more cigar galaxies out there waiting for us to discover, and that’s fine by me.

“Our findings suggest that prolate rotation in massive ETGs [early-type galaxies] might be more common than previously expected, and can help toward a better understanding of their dynamical structure and formation origin,” the team noted in their paper.

“This work, combined with future, higher quality observations of the sample of galaxies presented and orbit-based dynamical modeling, will give better insights into the dynamical nature of this special type of rotators.”

M82, a previously known cigar galaxy, seen by Hubble. NASA/ESA/The Hubble Heritage Team (STScI / AURA)


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