Astronomers discover unusual spindle-like galaxies

October 12, 2017
An elliptical galaxy in prolate rotation. The galaxy resembles the shape of a cigar, with its stars rotating around the galaxy's long axis, similar to a spindle. the background image is a snapshot of a simulation by A. Tsatsi and colleagues. Credit: J. Chang, PMO / T. Müller, HdA

Galaxies are majestic, rotating wheels of stars? Not in the case of the spindle-like galaxies studied by Athanasia Tsatsi (Max Planck Institute for Astronomy) and her colleagues. Using the CALIFA survey, the astronomers found that these slender galaxies, which rotate along their longest axis, are much more common than previously thought. The new data allowed the astronomers to create a model for how these unusual galaxies probably formed, namely out of a special kind of merger of two spiral galaxies. The results have been published in the journal Astronomy & Astrophysics.

When most people think of , they think of majestic spiral galaxies like that of our home galaxy, the Milky Way: billions of stars, rotating in a flat disk similar to the way that a wheel rotates around its central axis. But there is another kind of galaxy, which used to be thought very rare: so-called prolate rotators, each shaped like a cigar, which rotates along its long axis, like a spindle.

Now, a group of astronomers led by Athanasia Tsatsi of the Max Planck Institute for Astronomy has completed a thorough study of these cosmic spindles. Using data from the CALIFA survey, a systematic study that examined the velocity structure of more than 600 galaxies, the astronomers discovered eight new prolate rotating galaxies, almost doubling the total known number of such galaxies (from 12 to 20). Cosmic spindles are considerably less rare than astronomers had thought!

Given the high quality of their data, the astronomers were able to propose a plausible explanation for how these cosmic spindles come into existence. In general, galaxies grow when they merge with other galaxies. Several mergers with smaller galaxies have made our own Milky Way the stately disk it is today. To make a cosmic , two large disk galaxies need to collide at right angles, as shown in this animation:

The formation of an elliptical galaxy in prolate rotation. The mechanism shown here was proposed by Athanasia Tsatsi and her colleagues in order to explain the recent discoveries of galaxies of this kind with the CALIFA survey. The formation involves a polar merger of two spiral galaxies. One of the spiral galaxies develops a marked elongated structure (a "bar," to use the technical term) before the merger, which gives the resulting elliptical galaxy its cigar-like (prolate) shape. The stars of the second spiral galaxy end up orbiting around the bar of the first companion. Together they form a cigar-shaped elliptical galaxy that rotates like a spindle around its long axis. Movie: J. Chang, PMO / T. Müller, HdA

As the galaxies begin to interact via gravitational attraction, one of them forms a bar: an elongated structure near the center. That bar becomes the cigar-like shape of the merged galaxy, while the orbiting stars of the other galaxy imbue the merged galaxy with its overall sense of rotation.

The results are an interesting piece of the puzzle, explaining a likely formation scenario for an unusual, but not all that uncommon type of galaxy. Tsatsi's team of researchers having put to good use all the information contained in the CALIFA data, the ball is now in the court of the observing astronomers again: the merger simulations make some additional predictions for the detailed properties of prolate rotators. These cannot be distinguished with the current observations, but could be tested with instruments like MUSE, the Multi Unit Spectral Explorer at ESO's Very Large Telescope, an 8-meter-telescope at Paranal Observatory in Chile.

The results here will be published in the journal Astronomy & Astrophysics as Tsatsi et al., "CALIFA reveals prolate rotation in massive early-type galaxies: A polar galaxy merger origin?"

Explore further: Astronomers spun up by galaxy-shape finding

More information: A. Tsatsi et al. CALIFA reveals prolate rotation in massive early-type galaxies: A polar galaxy merger origin?, Astronomy & Astrophysics (2017). DOI: 10.1051/0004-6361/201630218 ,

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5 / 5 (3) Oct 12, 2017
Ok, but what are all the stars past the ends of the major gravitational source of starts rotating around? Shouldn't it start to pull in a get pancaked shape after a while?
1.4 / 5 (10) Oct 13, 2017
Clearly this is not a gravitational system, however a rotating Birkeland current would be a simple explanation.
1 / 5 (1) Oct 13, 2017
It will be found that these are like bar magnets and are merely the core of a larger galaxy where the outer shells are merely harder to detect but look the same as toroidal magnetic shells anywhere.
4 / 5 (4) Oct 13, 2017
Shouldn't it start to pull in a get pancaked shape after a while?

'A while' can be a pretty long time. Consider that the universe is 13 bn years old or thereabouts. Galaxies a bit younger than that. And that the time for stars to revolve around the Milky Way is on teh order of 200mn years.

Eventually the shape will change...however 'eventually' can be long after the last stars burn out or the galaxy runs into another and the shape changes to something completely different.
1 / 5 (4) Oct 13, 2017
"Clearly this is not a gravitational system, however a rotating Birkeland current would be a simple explanation."

I am an enthusiast of plasma cos. and even I find this statement outlandish and desperate... we live in a world where nearly all cosmic motions are assumed to be gravitationally driven, so "clearly" nobody is going to agree with you. There's nothing simple about altering paradigms or it would have been done already.

On the other hand... it seems you can mash two or three galaxies together to form whatever shape we observe... how convenient. Ahhh computer simulations... we "learn" so much from them in this field.

I can see it now..

A cosmic spindle found with too high of a red-shift, which the mainstream interprets as the system being far too old to have been formed by this merger of galaxies. However, nothing will actually change in the current dogma in light of this refuting evidence and we'll keep chugging along like nothing ever happened. :)
5 / 5 (2) Oct 14, 2017
Does this imply that 'barred spirals' have snacked on a smaller neighbour that was yet big enough to distort them ??
3 / 5 (2) Oct 14, 2017
Does this imply that 'barred spirals' have snacked on a smaller neighbour that was yet big enough to distort them ??

Or perhaps in the midst of an ongoing process? The timeline squeezed into the minute and a half video is how many millions of years?
not rated yet Oct 14, 2017
One thing that is not shown or discussed is where the black holes are (assuming all galaxies must have something very heavy acting as the overall center of mass). Wondering if these galaxies are remnants with no supermassive black holes and thats why they can stretch out as they merge.
not rated yet Oct 15, 2017
One thing that is not shown or discussed is where the black holes are

Really depends on how off-kilter the galaxies merged. The black holes - at such a short time after the merger - could be basically anywhere (or even be expelled from the entire galaxy altogether if the centers passed each other by closely)
1 / 5 (3) Oct 16, 2017
One thing that is not shown or discussed is where the black holes are

Right alongside the leprechauns and unicorns in Neverneverland...

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