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Extra-galactic planet discovered

A planet formed within another galaxy has been discovered for the first time.

The Jupiter-sized world orbits a star that was drawn into our own galaxy, the Milky Way, six to nine billion years ago.

It inhabits the Helmi stream, a group of stars that originally belonged to a neighbouring dwarf galaxy.

Gravity eventually caused the dwarf to be devoured by the Milky Way in an act of "galactic cannibalism".

Dr Rainer Klement, from the Max Planck Institute for Astronomy in Heidelberg, Germany, said: "This discovery is very exciting. For the first time, astronomers have detected a planetary system in a stellar stream of extra-galactic origin.

"Because of the great distances involved, there are no confirmed detections of planets in other galaxies. But this cosmic merger has brought an extra-galactic planet within our reach."

The parent star, known as HIP 13044, lies around 2,000 light years from Earth in the southern constellation of Fornax, the Furnace. Astronomers found the planet from the way the tug of its gravity caused the star to "wobble".

The planet, HIP 13044 b, is a so-called "hot Jupiter", a giant world whose orbit closely hugs its parent star. It is just 0.055 astronomical units - the distance between the Earth and the Sun - away from HIP 13044.

The planet is one of the few known that have survived the massive "red giant" expansion of an ageing host star.

Lead astronomer Dr Johnny Setiawan, also from the Max Planck Institute for Astronomy, said: "This discovery is particularly intriguing when we consider the distant future of our own planetary system, as the Sun is also expected to become a red giant in about five billion years."

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