Milky Way's turbulent gas

10 October 2011

A pit of writhing snakes, is how the first picture of turbulent gas in our Milky Way has been described by renowned astronomer, Professor Bryan Gaensler, based in the University of Sydney's School of Physics.

Using a CSIRO radio telescope in eastern Australia, Professor Gaensler and his team were able to make the ground-breaking image that was recently published in Nature.

Turbulent Gas swirling and churning in the Milky Way
Turbulent Gas swirling and churning in the Milky Way

The image shows that the space between the stars in our Galaxy is not empty but is filled with thin gas that continually swirls and churns.

"This is the first time anyone has been able to make a picture of this interstellar turbulence," said Professor Gaensler. "People have been trying to do this for 30 years."

Turbulence makes the Universe magnetic, helps stars form, and spreads the heat from supernova explosions through the Galaxy.

"We now plan to study turbulence throughout the Milky Way. Ultimately this will help us understand why some parts of the Galaxy are hotter than others, and why stars form at particular times in particular places," Professor Gaensler explained.

Led by Professor Gaensler, the team studied a region of our Galaxy about 10,000 light-years away in the constellation Norma by using CSIRO's Australia Telescope Compact Array.

"It is one of the world's best telescopes for this kind of work," said Dr Robert Braun, Chief Scientist at CSIRO Astronomy and Space Science.

The radio telescope was tuned to receive radio waves that come from the Milky Way. As these waves travel through the swirling interstellar gas, one of their properties, polarisation - the direction in which waves vibrate, is very slightly altered, and the radio telescope can detect this.

The researchers measured the polarisation changes over an area of sky and used them to make a spectacular image of overlapping entangled tendrils, resembling writhing snakes. The 'snakes' are regions of gas where the density and magnetic field are changing rapidly as a result of turbulence.

The 'snakes' also show how fast the gas is churning, an important number for describing the turbulence. Team member, Blakesley Burkhart, a PhD student from the University of Wisconsin, made several computer simulations of turbulent gas moving at different speeds. These simulations resembled the 'snakes' picture, with some matching the real picture better than others. By picking the best match, the team concluded that the speed of the swirling in the turbulent interstellar gas is around 70,000 kph, relatively slow by cosmic standards.

Publication: B. M. Gaensler et al. [9 co-authors] "Low Mach number turbulence in interstellar gas revealed by radio polarization gradients." Nature, DOI 10.1038/nature10446.

Contact: Professor Bryan Gaensler

Phone: 02 9351 6053

Email: 0611490c365f17260b1406002b3d2e340b0d0d21327e27091a761217