Shock wave blasts through galaxy

BY DR EMILY BALDWIN

ASTRONOMY NOW

Posted: 23 April, 2009

X-ray emission produced by high energy particles accelerated at the shock front are shown in red and mark the point at which the expanding radio lobe collides with the surrounding galaxy. Image: Chandra.

The Chandra X-ray Observatory has revealed a stunning new image documenting the effects of a shock wave blasting through a galaxy, powered by jets of plasma unleashed by the galaxy's central black hole.

Chandra's deeply penetrating X-ray vision was used to scrutinize the jets of Centaurus A and analysed by team leaders Dr Judith Croston of the University of Hertfordshire and Dr Ralph Kraft of the Harvard-Smithsonian Center for Astrophysics.

"Although we expect that galaxies with these shock waves are common in the Universe, Centaurus A is the only one close enough to study in such detail," says Croston. "By understanding the impact that the jet has on the galaxy, its gas and stars, we can hope to understand how important the shock waves are for the life cycles of other, more distant galaxies."

The observations show that the jets inflate large bubbles filled with energetic particles, driving a shock wave through the stars and gas of the surrounding galaxy at supersonic speeds. As the bubbles expand, particles at the shock front, or bubble edges, are accelerated to extremely high energies, producing intense X-ray and gamma-ray radiation, the first time such observations have been made.

These powerful jets are only found in a small fraction of the largest galaxies which host the biggest black holes. They are likely produced near to a central supermassive black hole, and are propelled close to the speed of light for distances of up to hundreds of thousands of light years.

The bubbles that are carved out are often referred to as radio lobes, and may play an integral role in the life cycle of the Universe's largest galaxies. Centaurus A is also thought to produce many of the high energy cosmic rays that strike the Earth. Croston and Kraft think that their new results will also provide insight into how such high energy particles are produced in galaxies.

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