20 Oct 2016

Milky Way: Secrets of galaxy revealed in most detailed hydrogen map yet

A team of scientists from Australia and Germany have created the most detailed hydrogen map ever produced of the Milky Way.

The map was pieced together using data collected over the past 10 years by two radio telescopes.

Perth-based astronomer Professor Lister Staveley-Smith, from the International Centre for Radio Astronomy Research (ICRAR), said other studies had mapped smaller areas of the galaxy in greater detail, but this map was the first of its quality covering the whole sky.

"We've kind of just put the data together from both hemispheres, a bit like putting maps of our own world together from the Northern Hemisphere and the Southern Hemisphere and picturing the globe for the first time," Professor Staveley-Smith told the ABC.

Astronomers used the two telescopes — in Parkes, New South Wales and Effelsberg, Germany — to study neutral hydrogen, the most abundant element in the universe.

"What it gives us is a map of the sky in hydrogen that normal telescopes, normal optical telescopes, can't see," Professor Staveley-Smith said.

The map, produced by a survey named the HI4PI, shows the Milky Way's finer details, including the boundaries of super shells created by giant explosions.
"We're seeing gas, we're seeing the interstellar medium, we're seeing the stuff which stars will later form from," he said.

"It's very important to understand the structure of gas in our own galaxy and the amount of gas in our own galaxy, its dynamics, in order that we can study the past evolution of the Milky Way and its likely future evolution."

An animation of the data shows two revolving spheres, similar to the globe of the Earth, with the sky plotted on each.

"Instead of viewing that sphere from the inside, which is what we do when we look at the sky, we can sort of paint that picture on the outside of a globe and sort of take ourselves outside and look at the sky the other way around," Professor Staveley-Smith said.

The map's sensitivity means scientists can see the two nearest galaxies to Earth — the Magellanic Clouds — and the stream of gas flowing from them across the Milky Way.

"I think this map, for the first time, will allow us to piece together the exact continuity of that stream across the two hemispheres," he said.

"That's what I'm most excited about."

Professor Staveley-Smith, who is based at the University of Western Australia, said only the Square Kilometre Array (SKA) telescope would produce maps of higher resolution.

The SKA, which will be the world's largest radio telescope, is being built in WA and South Africa.

Scientists from the HI4PI project have published their findings in the journal Astronomy and Astrophysics.

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