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Friday, 29 September, 2000, 06:17 GMT 07:17 UK
On-off flashes excite astronomers
Jet Dr R C Walker
A jet of energetic gas emerges from the galaxy's core
By BBC News Online science editor Dr David Whitehouse

Astronomers have obtained one of the most detailed views ever seen of the central regions of a so-called active galaxy that is ejecting energetic jets of material into space.

The galaxy, catalogued as 3C120, has a supermassive black hole at its core that squirts gas jets in opposite directions. One jet is almost pointed head-on towards the Earth.

Coming towards us boosts its brightness and, by a curious effect of relativity, the jet appears to be leaving 3C120 at faster-than-light speeds. This is an optical illusion, say astronomers.

Observations of the inner parts of this jet show clouds of gas moving outward that brighten and fade as they cross regions of strong magnetic fields wrapped around the galaxy.

On and off

Using co-ordinated, simultaneous observations from many radio telescopes scattered around the globe, astronomers from the Instituto de Astrofisica de Andalucia in Granada, Spain, and St Petersburg State University, Russia, have synthesised the view of the galaxy they would get if they had a radio telescope the size of the Earth.

The research team, led by Dr J Gomez, has captured a 16-month series of radio images showing a series of flashes from one of the jets.

Astronomers say this data could help scientists better understand the formation of such jets and the structure of active galaxies which radiate tremendous amounts of energy.

It is believed that a supermassive black hole at the centre of 3C120 is responsible for driving the jets which are streamers of gas moving at high speeds. In the observations, gas clouds of different sizes and shapes appear to flash on and off.

Astronomers speculate that these features are created by the rotation of the galaxy's magnetic field, and that the apparent off and on flashing of these features happens as the jets interact with a nearby cloud of gas.

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