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Motion of stars holds clue of dark matter shape in barred galaxies

Source: Pixabay

Scientists looking into how the shape of the dark matter halo affects the motion of stars in stellar bars (found at the centre of some galaxies) discovered that out-of-plane bending events of the bar explain the shape.

The skeleton on which galaxies form, evolve, and merge is formed by dark matter. Buckling is a rare violent bar thickening mechanism that occurs in ‘barred galaxies’ or central bar-shaped structures composed of stars.

The motion of their stars determines the shapes and sizes of the trillions of galaxies in the Universe. The Milky Way is a disc galaxy composed of stars moving in circular orbits around the centre in a flattened disc, with a dense collection of stars at the centre known as the bulge.

The shapes of these bulges can range from nearly spherical to as flat as the galaxy disc. In the centre of the Milky Way is a flat boxy or peanut-shaped bulge. The formation of such bulges is caused by the thickening of stellar bars in galaxies. Buckling is an interesting and violent thickening mechanism in which the bar bends out of the plane of the galaxy disc.

“Many recent numerical and observational studies suggest that dark matter halos are spherical, prolate (a sphere squashed from the sides), or oblate (a sphere squashed from the top and bottom) in shape. However, its effect on stellar kinematics in the bulges and bars of galaxies is not well understood,” a Science and Technology Ministry release said.

Ankit Kumar, a PhD student at the Indian Institute of Astrophysics (IIA), an autonomous institute of the Department of Science and Technology, led the current study, which was co-authored by Prof Mousumi Das of the IIA and Dr Sandeep Kumar Kataria of Shanghai’s Jiao Tong University.

At the IIA, the team investigated the dynamical evolution of galaxies using cutting-edge numerical simulations. Their simulations show that bars in prolate dark matter halos undergo three prominent bar buckling (out of plane bending) events in eight billion years, allowing them to be detected for a longer period of time. This is the first time three-bar buckling events have been documented in a study.

Monthly Notices of the Royal Astronomical Society, a peer-reviewed journal, published this work.

“We have studied the effect of non-spherical dark matter halos on the shape of the disk galaxies by generating realistic mock galaxies and evolving them in time using the supercomputing facility available at IIA, Bengaluru,” said Ankit Kumar.

“In our Universe, detection of the ongoing buckling events is very rare. To our knowledge, there are only eight galaxies in the observations which are currently going through buckling. Our study suggests that most barred galaxies may have more oblate or spherical halos rather than prolate halos,” the authors added.

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Brendan Taylor

Brendan Taylor was a TV news producer for 5 and a half years. He is an experienced writer. Brendan covers Breaking News at Insider Paper.

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