Black hole’s twin jets shine bright

galaxy Pictor AImage copyright

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The jets shine in X-ray wavelengths (shown in blue) while radio waves (red) reveal twin “lobes”

Astronomers have published new images of a bright jet of material, long enough to cross the Milky Way three times, fired into space by the black hole at the heart of a distant galaxy.

The observations confirm the existence of a second jet, blasting in the opposite direction.

The study uses this galaxy, Pictor A, to test ideas about what makes jets like these emit very bright X-rays.

It appears in the Monthly Notices of the Royal Astronomical Society.

To make their observations, the team combined 15 years of X-ray data, from Nasa’s Chandra space telescope, with images taken in radio wavelengths by the Australia Telescope Compact Array.

Chandra has been in orbit since 1999 – and interest in Pictor A was sparked right back at the beginning of its mission, according to Martin Hardcastle from the University of Hertfordshire, UK.

“The early images from Chandra showed there was this very bright jet,” Prof Hardcastle, the study’s lead author, told the BBC.

“At that stage we didn’t really understand it, because the data were good enough to make an image of the jet, but not to do this kind of detailed analysis.”

The new images have five or six times the resolution of our previous best views of Pictor A, he added, meaning that new features can be detected and the physics of the jet probed in detail.

Blowing up balloons

Most big galaxies have a supermassive black hole at their centre, and Pictor A – five million light-years from Earth – is no exception.

In its case, the immense quantities of stuff swirling towards the black hole release so much energy that a beam of high-energy particles is spat across space, at very nearly light speed.

A second jet, fired in the opposite direction, was only an indistinct shadow in previous images, Prof Hardcastle said.

“In some work we did on an interim version of this data set, we thought we could see it. But now it’s definitely there.”

Image copyright
NASA/CXC/U Hertfordshire

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X-ray image: The jet on the left is moving away from us, so appears fainter

Image copyright

Image caption

“Twin bubbles”: Clouds of hot material emit radio waves

This “counterjet” – to the left in the blue X-ray image – appears much fainter than its twin and the team believes this is because it is moving away from us, at the same breakneck speed. According to the principles of relativity, this makes it look dimmer.

“It’s like the Doppler effect only more so,” said Prof Hardcastle. “In special relativity it actually effects the amplitude as well as the frequency of the emission.”

Blooming outwards from the twin beams are two clouds of hot material, clearly visible in the radio wave images (displayed in red in these images).

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