Astroboffins map 845 galaxies in glorious 3D, maybe dark matter too

It's all gone potato-shaped for some galaxies already

A team led by Sydney University's Dr Caroline Foster has created three-dimensional images of 845 galaxies, claiming it is the biggest collection of of 3D galactic representations ever gathered.

Created since 2013, when the Sydney Australian Astronomical Observatory Multi-object Integral Field Spectrograph (SAMI) saw first light, the survey may also help us to figure out where all the dark matter is hiding.

Dr Forster, a research fellow at the Australian Astronomical Observatory (AAO) at the start of the project, told the Australian Broadcasting Corporation's The World Today program "There's a lot of literature, mostly on the theoretical side, that discusses how the true shape, the 3D shape of galaxies changes as a function of what happened to them over the course of their life."

“These [theoretical papers] typically include dark matter in them. Dark matter is one of the mysteries of modern astronomy … if we could pinpoint the true three-dimensional shape of the dark matter behind those galaxies, that would give us a clue about what dark matter might be.”

In the meantime, the SAMI results help confirm what we know about the universe, such as the association between rotation and shape. Faster-spinning galaxies tend towards flatter shapes than those rotating more slowly. Speedily-spinning spiral galaxies have more circular disks.

When two galaxies combine, the result is generally more spherical, as Dr Foster writes at The Conversation here; on the other hand, infalling gas makes a galaxy flatter (by making it spin faster).

Such ideas have been put forward over the 90 years since astroboffins first began studying galaxies – but the SAMI survey has let the group measure the relationship between shape and rotation.

And there have been surprises, such as galaxies that aren't symmetrical on two axes, instead being shaped more like potatoes.

As the AAO explains here, the SAMI instrument studies 13 galaxies at a time through a bundle of optical fibres (one bundle per galaxy, 61 fibres per bundle).

In Dr Foster's survey, SAMI gathered detailed information about the movement both of gas and stars inside its target galaxies.

The study has been published in the Monthly Notices of the Royal Astronomical Society, and Sydney University's media announcement is here. ®

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