Science

Exoplanets from another galaxy spotted – take that, Kepler fatigue!

Gravitational microlensing helps astroboffins spot planets 3.8 BEELLION light-years away

By Richard Chirgwin

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The Kepler Space Telescope has found oodles of exoplants, but now astroboffins have spotted the first exoplanets outside our galaxy.

A group of astroboffins from the University of Oklahoma has become the first to demonstrate exoplanet observations in another galaxy – one that's 3.8 billion light years away, or one-third of the distance across the observable universe.

The discovery by a team led by professor Xinyu Dai and postdoc Eduardo Guerras, found the planets' signatures in the spectrum of a gravitationally-microlensed galaxy behind the black hole quasar RXJ 1131−1231.

Gravitational microlensing refers to the phenomenon, predicted by Einstein, that gravity can bend light, resulting in an apparent magnification if the bodies are aligned the right way (from the point of view of the observer).

As the university explains, they believe the planets range in estimated mass from about the size of the moon, through to Jupiter-sized.

Their paper, published in Astrophysical Journal Letters and available here at the arXiv pre-print service, explains that the unbound planets they saw caused “Fe Kα line energy shifts” in the spectrum of RXJ 1131−1231.

They found the line shifts in Chandra X-ray Observatory images of the quasar, and in the paper said what they observed “has never been observed in a non-lensed AGN” [active galactic nucleus – El Reg].

The paper also explains that the researchers focussed on unbounded planets – that is, planets wandering around their galaxies rather than being part of a solar system – because planets orbiting stars don't show up separately from their hosts.

There are around 2,000 moon-to-Jupiter sized planets for each main sequence star in their observations, the researchers wrote, which equates to trillions of stars per galaxy.

In the university's announcement, Guerras said “there is not the slightest chance of observing these planets directly” because of the distances involved. “However, we are able to study them, unveil their presence and even have an idea of their masses. This is very cool science.” ®

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