Eight Weird, Spindle-Like Galaxies Discovered by Astronomers

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An elliptical galaxy in prolate rotation. J. Chang, PMO / T. Müller, HdA

Scientists have discovered eight new spindle-like galaxies—huge structures once thought to be extremely rare features of the cosmos.

Traditionally, we think of galaxies as being flat, rotating disks made up of billions of stars, with a black hole at their center. Scientists say another type, known as “prolate rotators,” are cigar-shaped galaxies that rotate along their axes, making them look like spindles. Until now, only a handful of them had ever been observed.

The surprising discovery of the eight prolate rotators, nearly doubling the total known number, to 20 from 12, was accomplished using data from the Calar Alto Legacy Integral Field Area Survey (CALIFA), a systematic mapping of more than 600 galaxies in the local universe. Athanasia Tsatsi of the Max Planck Institute for Astronomy, Germany, and colleagues published their findings in the journal Astronomy & Astrophysics.

“Our findings suggest that prolate rotation in massive 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 researchers said.

The discovery allowed the team to analyze how these galaxies might have formed. Galaxies such as the Milky Way grow when other, smaller galaxies merge with them. But with prolate rotators, two giant disk galaxies collide to create the spindly galaxies observed.

Previously, the relative lack of prolate rotation galaxies meant scientists could not get a clear view of how they could have formed. But with a larger dataset, they were able to run various simulations, providing models on which to base their formation hypothesis.

The key is the presence of gas. If the merging galaxies have plenty of gas, they will remain in the flat disk shape. However, when gas is absent, the stars in the galaxies are not constrained by the motion of the gas.

Models revealed that prolate galaxies emerge when two gasless galaxies are orientated at right angles. One of the galaxies then develops a strong bar shape. As they merge, this shape remains and turns into the spindle galaxy we observe.

The findings also suggest prolate rotators probably formed about 10 billion years ago, very early on in the history of the universe. However, the team says it is now up to observational astronomers to make new predictions about the properties of these galaxies.

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