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Astronomers spot first possible exoplanet outside our galaxy

The Guardian: Astronomers spot first possible exoplanet outside our galaxy

Saturn-sized planet candidate has been identified in Whirlpool Galaxy 28m light years away

An artist's illustration depicts the X-ray binary and possible planet.
Illustration depicting X-ray binary and possible planet. Material from the companion star (right) is pulled on to black hole, forming a disk around the dense object. Photograph: Chandra X-ray Observatory
Science correspondent

A possible Saturn-sized planet identified in the distant Whirlpool Galaxy could be the first exoplanet to be detected outside the Milky Way.

The exoplanet candidate appears to be orbiting an X-ray binary – made up of a normal star and a collapsed star or black hole – with its distance from this binary roughly equivalent to the distance of Uranus from the sun.

The discovery opens up a new window to search for exoplanets – planets orbiting stars beyond our Sun – at greater distances than ever before. Although nearly 5,000 exoplanets have been detected so far, all of them are in the Milky Way galaxy – with few further than about 3,000 light years from Earth.

An exoplanet in the spiral Messier 51 (M51) galaxy – also called the Whirlpool Galaxy because of its distinctive shape – would be about 28m light years away.

Dr Rosanne Di Stefano of the Center for Astrophysics at Harvard and Smithsonian in Cambridge, US, who led the research, said: “Since the 1750s, it has been conjectured that the dim distant nebulas, now called galaxies, are island universes: large, gravitationally-bound stellar populations similar to our home, the Milky Way. Our discovery of the planet candidate … gives us the first peek into external populations of planetary systems, extending the reach of planet searches to distances roughly 10,000 times more distant.”

A combination image of M51 in X-rays from Chandra (purple and blue) and optical light from NASA’s Hubble Space Telescope (red, green, and blue). A box marks the location of the possible planet candidate, an X-ray binary known as M51-ULS-1. NB Image has been rotated 90 degrees clockwise.
A combination image of M51 in X-rays from Chandra (purple and blue) and optical light from Nasa’s Hubble telescope (red, green, and blue). A box marks the location of the possible planet candidate, an X-ray binary known as M51-ULS-1. Image has been rotated 90 degrees clockwise.Photograph: X-ray: Nasa/CXC/SAO/R. DiStefano, et al.; Optical: Nasa/ESA/STScI/Grendler

 






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