Astronomers have detected an extremely rare laser emission from the "spectacular" Ant Nebula which suggests a double star system is hidden at its core.

The rare laser blast is connected to the death of a star and was detected by the European Space Agency's Herschel space observatory.

When stars the middleweight size of our sun get to the end of their lives they shrink into dense white dwarfs, ejecting off their outer layers of gas and dust and creating a nebula.

Last week, research revealed that our sun would create a planetary nebula when it dies in 10 billion years, leaving behind a ghostly ring like that of Abell 39.

The Ant Nebula is one such cloud made of dust, hydrogen, helium and other ionised gases and the laser emission suggests that its striking appearance - which has earned it its name - is hiding an even more dramatic demise for its original star.


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Image: A picture of a planetary nebula taken in 1997. Pic: TA Rector and BA Wolpa

In space, lasers are quite different from how they appear on Earth, although they remain focused beams of light occurring at very different wavelengths and under rare conditions.

By coincidence, astronomer Donald Menzel who first observed and classified the Ant Nebula in the 1920s (it is officially known as Menzel 3 after him) was the first person to suggest that lasers could occur naturally.

The term laser originated as an acronym of "light amplification by stimulated emission of radiation", and Menzel was the first to suggest that it could occur in nebulae in space - before they had even been invented in laboratories.

Dr Isabel Aleman, lead author of a paper describing the new results, said: "We detected a very rare type of emission called hydrogen recombination laser emission, which is only produced in a narrow range of physical conditions.

"Such emission has only been identified in a handful of objects before and it is a happy coincidence that we detected the kind of emission that Menzel suggested, in one of the planetary nebulae that he discovered."

Hydrogen recombination laser emissions need a very dense gas - ten thousand times more dense than the gas in typical nebulae - close to the star.

Normally, the region of space close to the dead star is quite empty because its material has been ejected outwards, with any lingering gas falling back into the star.

But this is not the case for the gas at the core of the Ant Nebula.

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Image: The Orion Nebula and its associated cluster of young stars. Pic: ESO/G. Beccari

Co-author Professor Albert Zijlstra, from the Jodrell Bank Centre for Astrophysics at University of Manchester, sad: "The only way to keep such dense gas close to the star is if it is orbiting around it in a disc.

"In this nebula, we have actually observed a dense disc in the very centre that is seen approximately edge-on. This orientation helps to amplify the laser signal.

"The disc suggests there is a binary companion, because it is hard to get the ejected gas to go into orbit unless a companion star deflects it in the right direction. The laser gives us a unique way to probe the disc around the dying star, deep inside the planetary nebula."

Astronomers have not yet seen the expected second star, hidden in the heart of the Ant Nebula.