Scientists have new method to determine galaxies' shapes

A new way is developed.
By Laurel Kornfeld | Sep 12, 2017
A new study links the spin rates of galaxies with their shapes, giving scientists the first reliable method of determining those shapes in nearly a century.

Studied by astronomers for over 90 years, galaxies come in a multitude of shapes, including spiral, helical, spherical, football, or even diffuse.

But because scientists observing from Earth cannot see entire galaxies, just their alignments in space and axial spins, they are unable to determine their three-dimensional shapes.

Galaxies are in constant motion, rotating around their axes and moving away from one another due to expansion of the universe.

Researchers at the University of Sydney used the Sidney-AAO Multi-object Integral field unit or SAMI, a multi-object integral field spectrograph, to study the movements of individual stars within 845 galaxies.

Capable of observing 13 galaxies at a time and returning large amounts of data, SAMI made it possible for the scientists to study three times the number of galaxies observed in previous studies.

By knowing a galaxy's shape, scientists are able to piece together its history, such as whether it is the product of past mergers between two or more galaxies.

The faster a galaxy spins, the flatter its shape is. Rapidly spinning spiral galaxies have circular-shaped disks of stars, noted research team member Scott Croom of the University of Sydney.

"This is the first time we've been able to reliably measure how a galaxy's shape depends on any of its other properties--in this case, its rotation speed," said Caroline Foster of the University of Sydney, who led the research team.

Until the invention of SAMI, there was no way for scientists to track the motions of stars within galaxies.

Tracking the directions in which stars move within galaxies enables scientists to find patterns of movement and isolate individual stars' positions.

As a galaxy spins, one side of it moves toward observers and the other away from them.

Through studying the motions of many stars in an individual galaxy, scientists can eventually determine the direction in which that galaxy is rotating.

Some galaxies, especially those with unusual shapes, rotate either very slowly or not at all.

The study's findings have been published in the journal Monthly Notices of the Royal Astronomical Society.

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