Friday, April 16, 2010

From the X Files: Unknown Object in Nearby Galaxy Sending Mysterious Radio Waves

There is something strange is lurking in the galactic neighborhood. An unknown object in galaxy M82 12 million light-years away has started sending out radio waves, and the emission does not look like anything seen anywhere in the universe before except perhaps by Ford Prefect. M82 is starburst galaxy five times as bright as the Milky Way and one hundred times as bright as our galaxy's center.

"We don't know what it is," says co-discoverer Tom Muxlow of Jodrell Bank Centre for Astrophysics near Macclesfield, UK. But its apparent sideways velocity is four times the speed of light. This "superluminal" motion occurs usually in high-speed jets of material bursting out by black holes.

“The new object, which appeared in May 2009, has left us scratching our heads - we’ve never seen anything quite like this before,” said Dr Muxlow. “The object turned on very rapidly within a few days and shows no sign of decaying in brightness over the first few months of its existence. The new young supernova explosions that we were expecting to see in M82 brighten at radio wavelengths over several weeks and then decay over several months, so that explanation seems unlikely.

The object was discovered while Muxlow and his colleagues were monitoring an unrelated stellar explosion in M82 using the MERLIN network of radio telescopes in the UK. Unlike supernova emissions, which usually get brighter over a few weeks and then fade away over months, the enigmatic source has hardly changed in brightness over the course of a year, and its spectrum is steady.

Yet it does seem to be moving – and fast: its apparent sideways velocity is four times the speed of light. Such apparent "superluminal" motion has been seen before in high-speed jets of material squirted out by some black holes. The stuff in these jets is moving towards us at a slight angle and travelling at a fair fraction of the speed of light, and the effects of relativity produce a kind of optical illusion that makes the motion appear superluminal.

The object is not quite in the middle of M82, where astronomers would expect to find the kind of supermassive central black hole that most other galaxies, including the Milky Way, have. Which leaves the possibility that it could be a smaller-scale "microquasar".

A microquasar is formed after a very massive star explodes, leaving behind a black hole around 10 to 20 times the mass of the sun, which then starts feeding on gas from a surviving companion star. Microquasars do emit radio waves – but none seen in our galaxy is as bright as the new source in M82. Microquasars also produce plenty of X-rays, whereas no X-rays have been seen from the mystery object. "So that's not right either", Muxlow said in an interview with New Scientist. Maybe it's a megamicroquasar?

Muxlow's best guess without having consulted Deep Thought is still that the radio source is some kind of dense object accreting surrounding material, perhaps a large black hole or a black hole in an unusual environment -a phenomena perhaps more common in M82 because it is a "starburst" galaxy – a cosmic cauldron where massive stars are forming and exploding at a much higher rate than in the Milky Way, creating new black holes.

“We have just started processing data from an array of 20 radio telescopes across the Earth were taken for the central nuclear region of M82. These images will allow us to examine the structure of the new radio source in detail. However, processing such huge datasets takes significant amounts of computing effort and painstaking work. Only then will we be able to see if it is some rare form of micro-quasar. Watch this space…!” said Muxlow.


Casey Kazan via Royal Astronomical Society and New Scientist
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