You know our speed

Some Australian astronomers are going to publish in the journal The Astrophysical Journal, the more detailed study of the relationship between the speed of rotation of spiral galaxies and their shape, which varies from nearly flat discs to real balls.


M81, an example of the galaxy rather “fat”.

Credit: NASA / ESA / Hubble Heritage Team (STScI / AURA)

Some of the disks of spiral galaxies are almost flat. Others are thicker, with the bulb protruding and visible in the center. It’s a question kinematics: the stars of the galaxies rotate faster than thinner around the center of the galaxy than is the star of spheroidal galaxies (imagine pizza that is rotated in the air by a skilled pizza maker and it will all be a bit lighter).

Now a new research, led by the International Centre for Radio Astronomy Research (ICRAR) of Perth, has been able to measure the effects of the rotations of galaxies with a precision ten times greater than in recent studies, thus leading to a better understanding of relationship between their shape, their speed of rotation and their mass. The study is being published in the Astrophysical Journal.

Of the irregular shape of the galaxies we realize just looking  up at the sky at night : “The white band of the Milky Way is a relatively thin band of constant thickness,” says Danail Obreschkow, associate professor at the University of Western Australia and who coordinated the study. “However, when you look at the exact center near the constellation Sagittarius you can actually see a thickening of the Milky Way , which is the bulb. Some galaxies are very flat disk of stars and others are thicker or even spherical.”

” Much of the research of the last century have been devoted to understanding this great diversity of galaxies in the Universe ,” says Obreschkow . But these studies were based mainly on observations of optical images. It was therefore difficult to distinguish incontrovertibly the various curves of galaxies, as well as understand exactly how they do their speed modeled shapes. “With this research we have taken a step forward towards the understanding of how this happened , proving that the rotation of spiral galaxies is a key factor in their form .”

The study examined 16 galaxies located between 10 million and 50 million light years from Earth using data from a survey called THINGS, using data collected by the Very Large Array ( VLA) in New Mexico , one of the largest radio telescopes in the world

“This survey shows THINGS cold gas in galaxies, where it is and how it moves,” says Obreschkow . “This is a key point. If you want to measure the rotation, you cannot just take a photograph: we must take a special kind of photo that shows the movement. “

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