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Spin doctors: Astrophysicists discover when galaxies rotate, size matters

ARC Center for Excellence in Astrophysics in 3 dimensions

Exploring the skies gives clues to how they change over time

The direction the galaxy spins depends on its mass, the researchers found.

A team of astrophysicists analyzed 1418 galaxies and found that small ones are likely to rotate on a different axis to large ones. The rotation was measured relative to the closest "cosmic strand" to any galaxy – the largest structures in the universe.

Filaments are huge formations of filaments that contain huge amounts of matter – including galaxies, gases and, by modeling, dark matter. They can be 500 million light-years long, but only 20 million light-years. At their largest scale, filaments divide the universe into a huge gravitational coupled grid interspersed with huge dark matter voids.

"It's worth noting that the backbone of the cosmic filaments is a fairly large galactic migration pathway, with many galaxies meeting and merging along the way," says lead researcher Charlotte Welker, an astro-3D researcher who works initially at International Center for Research in Radio Astronomy (ICRAR) and now at McMaster University in Canada.

ASTRO 3D is the ARC Center for Excellence in All Australian Astrophysics, based in Australia.

Filaments are why the universe looks a bit like a honeycomb, or a cosmic bottle of chocolate Aero.

Using data gathered from an instrument called the Sydney-AAA Multi-Object-Integrated-Spectrographic Field (SAMI) of the Australian Anglo-Australian Telescope (AAT), Dr. Welker, second author and lead researcher at ASTRO 3D Professor Boss The University of Sydney and colleagues from Australia, the United States, France and Korea studied all of the target galaxies and measured rotation relative to the nearest fiber.

They found that the smaller ones tended to rotate in direct alignment with the threads, while the larger ones rotated at right angles. Alignment shifts from first to second as galaxies, attracted by gravity to the backbone of the array, collide and merge with others, gaining mass.

It's a phenomenon that Dr. Welker has compared to skating in the company of a friend.

"The entrance can be sudden," she says. "Joining another galaxy can be all that is needed.

"Imagine slipping on a friend and attracting you. If you grasp your friend's hand while still moving faster, you will both start rotating on a vertical axis – turning normally on your horizontal path.

"But if a little cat – much lighter matter – runs after your friend and jumps on her, she probably won't start spinning. Takeee needs a lot of cats to jump at once to change her rotation. "

Co-author Scott Kaur of the University of Sydney, also director of the ASTRO 3D, says the result offers insight into the deep structure of the Universe.

"Virtually all galaxies rotate, and this rotation is fundamental to how galaxies are formed," he says.

"For example, most galaxies are in flat rotating disks, like our Milky Way. Our result helps us understand how this galactic rotation evolves through cosmic time. "

He adds that the new instrument, called Hector, set to be installed on the Anglo-Australian telescope next year, will allow for a significant expansion of research in this area.

"Hector will be able to conduct research five times larger than SAMI," he says. "With this we will be able to dig into the details of this turning path to better understand the physics behind it."

The Milky Way, by the way, has a rotation that is well aligned with the nearest cosmic thread, but belongs to the class of medium-sized galaxies that, above all, do not show a clear tendency for parallel or normal rotations.

"We would like to say that there is no choice of tea or coffee in the group of people," says Dr. Welker. "Individuals may still prefer tea or coffee, but overall there is no general tendency toward coffee in the group."

The research is available for early access to the Royal Astronomical Society's Monthly Notices (MRLS) journal and is also available entirely on the arxiv print site.

ASTRO3D is an ARC Center for Excellence in Astrophysics in 3 dimensions.

/ Public announcement.

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