A team of astrophysicists has announced the detection of several hundred planets in another galaxy, out of the Milky Way. Some would be as small as the Moon and others as large as Jupiter.
The discovery of the first planet outside our system was already exceptional. But since then, planetary astrophysics has come a long way. As of February 1, 2018, 3,728 planets were confirmed in 2,794 systems, including 622 systems with more than one planet. Today, a new step has been taken: a team of astrophysicists from the University of Oklahoma has announced the discovery of the first planets beyond our Galaxy.
For the purposes of their study, the researchers relied on the gravitational microlens technique, which relies on the gravitational force of distant objects to focus light from a star. When a planet passes the star in relation to the observer, the light falls in a measurable way, which can then allow astronomers to determine the presence of a planet. In this respect, the method is a reduced version of the gravitational lens, where an intervening object – such as a cluster of galaxies – is used to focus light from a galaxy or other large object in the background.
So far, 53 exoplanets in the Milky Way have been detected using this method. To find planets beyond our galaxy, however, something a little more powerful than a star was needed. The astronomers studied a quasar 6 billion light-years away from Earth called RX J1131-1231. Specifically, the team relied on the microlens properties of the supermassive black hole located in the center of RX J1131-1231.
Using data from NASA’s Chandra X-ray observatory, the researchers detected oscillations in the light of the quasar that could only be explained by the presence of planets in this galaxy. Astronomers say they have detected the presence of 2000 unrelated planets, some of the same size as the Moon and others as massive as Jupiter. These do not seem to orbit around a star in a conventional solar system, but rather seem to roam freely in the distant galaxy.
“We are very excited about this discovery. This is the first time anyone has discovered planets outside our galaxy,” enthuses astronomer Xinyu Dai, lead author of this study. “These small planets are the best candidates for signatures observed using the microlens technique. We analyzed the high frequency of these signatures by modeling the data to then determine the mass of these planets.”
Of course, the astronomers have not seen these planets directly, and perhaps, they will never be able to do it. But being able to detect them reflects the incredible power of the microlens, not to mention the evidence – even if we knew it – that there are indeed planets in other galaxies. This discovery will undoubtedly bring the study of planets beyond our solar system to a whole new level.