For the first time in nearly a century, astronomers have been able to accurately measure how much effect can a galactic rotation have on its overall shape. It turns out to be massive. Considering the vastness of even a small galaxy, measuring a perfect 3D shape is an extremely complex job. But researchers from the University of Sydney and several other institutions in Australia have found a way to measure it. Their study is now accepted in the Journal Monthly Notices of the Royal Astronomical Society.
‘It is the first time that we have been able to determine how rotational speed of a galaxy can affect its overall shape,’ said Dr. Caroline Foster, the lead author of research paper, who currently is a Fellow at the University of Sydney and contributed to this discovery while researching at the Australian Astronomical Observatory.
They (galaxies) can present itself in a shape of a pancake, a football, a sea hedgehog, or something intermediate. The research founded that galaxies which are spinning faster are flat and smooth unlike their slow revolving relatives. ‘This is also applicable in the case of spiral galaxies, faster spinning spirals are more likely to have smoother circular disks than slower ones,’ explained Prof. Scott M. Croom, a senior member of the research team.
The team investigated a sample of over 840 galaxies (845 to be exact) which is the biggest extragalactic study till date. The large number was crucial for the success of this study, due to the fact that galactic shape is largely influenced by events such as galactic mergers in the past and the presence of other massive objects in a close proximity.
Journal Reference: The intrinsic shape of kinematically selected galaxies
To find accurate results, the team deployed an optimized computer algorithm which will process various shapes of galaxies using an already existing method to reverse kinematic and ellipticitic ill-alignments. The results matched data from previous studies conducted on intrinsic galaxies and the ATLAS 3D data. These results indicate that a large amount of galaxies is oblate axisymmetric.
Galaxies from the SAMI survey, Japan’s Subaru telescope. Courtesy: D. Taranu, (UWA) C. Foster (USYD) and NAOJ
‘We proved that the essential shape of galaxies differs due to their rotational speed which is measured by ‘spin’ parameter proxy λRe. Precisely, galaxies with high spin rate are axisymmetric or simply flattened, while low spin rate systems have a much higher chances of triaxiality,’ said team members.
The initial findings were done with the help of SAMI (Sydney-AAO Multi-object Integral unit) galaxy survey. Researchers derived their results from stellar kinematic maps and imaging data instrument.
SAMI Galaxy Survey
SAMI or Sydney-AAO Multi-object Integral field unit is an advance surveying instrument which is mounted on the Anglo Australian Telescope (AAT), situated at the Siding Spring Observatory, Australia. It was designed to collect information on more than 3500 different galaxies across a very large patch of space. The instrument can investigate as much as 13 galaxies at a time.
With more than a dozen advanced imaging fibre bundles known as hexabundles, it can observe a vast number of galaxies in a small patch of open space. It was developed by a collaboration between the Australian Astronomical Observatory and The University of Sydney with backing from ARC Centre of Excellence for All-sky Astrophysics. The instrument can investigate as much as 13 galaxies at a time.