Over 500 exoplanets have been found within our own galaxy, but no confirmed extragalactic planets have been identified. Until now. Johny Setiawan and his colleagues from the Max Planck Institut have discovered a planet orbiting a star of extragalactic origin.
The star in question, HIP 13044, is currently in our galaxy, having been swallowed by the Milky Way about six to nine billion years ago. At the time of its formation however, it was part of a nearby dwarf galaxy. That means that both it and its planet (HIP 13044 b) which was detected by observing the gravitational wobble of the star, are of extragalactic origin.To make HIP 13044 b even more interesting, it apparently survived its star’s red giant phase. This is a late stage of stellar evolution in which stars about the size of our sun, having depleted their hydrogen reserves, go through an enormous expansion (the sun will expand to encompass the entire orbit of the Earth) and then contract again. Perhaps due to this expansion event, HIP 13044 b is currently extremely close to its star.
This artist's impression shows HIP 13044 b, an exoplanet orbiting a star that entered our galaxy, the Milky Way, from another galaxy. This planet of extragalactic origin was detected by a European team of astronomers using the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in ChileCredit: ESO/L. Calçada