On January 9 1992, two planets orbiting the pulsar PSR 1257+12 had been confirmed. This is generally considered to be the first definitive detection of planets beyond our own solar system. And now, as of February 1 2018, planets beyond our own galaxy have been confirmed.
In an incredible discovery, astrophysicists have detected multiple planets in another galaxy some 3.8 billion light-years away. These planets range in mass from the size of our moon to as large as Jupiter and were detected by using a technique called gravitational microlensing.
This very technique has been used to find 53 exoplanets in our own Milky Way and is the only known way of finding the smallest and most distant worlds, thousands of light-years away. But, of course, it’s not the only way to find exoplanets. As of this month, 3,728 planets have been confirmed in 2,794 systems, with 622 systems having more than one planet.
So how does it work?
As a planet orbits a star, the gravitational field of the system can bend the light of a distant star behind it.
We know what this looks like when it’s just two stars, so when a planet enters the area it creates a further disturbance in the light that reaches us. This result is a recognisable signature for the planet. Gravitational Microlensing is a scaled-down version of Gravitational Lensing, where an intervening object (such as a galaxy cluster) is used to focus light from a galaxy or other large object located behind it. It also incorporates a key element of the highly-effective Transit Method, where stars are monitored for dips in brightness to indicate the presence of an exoplanet.
Oklahoma University astronomers Xinyu Dai and Eduardo Guerras studied a quasar 6 billion light-years away called RX J1131-1231, one of the best gravitationally lensed quasars in the sky.
The gravitational field of a galaxy 3.8 billion light-years away between us and the quasar bends light in such a way that it creates four images of the quasar, which is an active supermassive black hole that’s extremely bright in X-ray, thanks to the intense heat of its accretion disc.
Using data from NASA’s Chandra X-ray observatory, the researchers found that there were peculiar line energy shifts in the quasar’s light that could only be explained by planets in the galaxy lensing the quasar.
It turned out to be around 2,000 unbound planets with masses ranging between the Moon and Jupiter, between the galaxy’s stars.
It should be noted that this is the first confirmed news of extragalactic planets. There have been other candidates for extragalactic planets.
Back in 1996, R.E. Schild predicted a 3-Earth-mass planet in the lensing galaxy, YGKOW G1. This microlensing event, however, was not able to be repeated as it was a one-time chance alignment. The predicted planet would lie 4 billion light years away.
Our closest galactic neighbor, the Andromeda galaxy, has a tentative detection of an exogalactic planet as well. A team of scientists also used gravitational lensing to view a star with a smaller companion, weighing just around 6.34 times the mass of Jupiter. This suspected planet would be the first observed in the Andromeda Galaxy.
In the coming years, more sophisticated observatories will be available which will allow for even more possibilities for discoveries. These include space-based instruments like the James Webb Space Telescope (scheduled to launch in Spring of 2019) and ground-based observatories like the ESO’s OverWhelmingly Large (OWL) Telescope, the Very Large Telescope (VLT), the Extremely Large Telescope (ELT), and the Colossus Telescope.
Right now, the odds are good that some of these discoveries will be in neighboring galaxies. One day we can begin to determine just how common planets are in our Universe. Keep in mind that it is estimated that there could be as many as 100 billion planets in the Milky Way Galaxy alone. Couple that with an estimated 1 to 2 trillion galaxies in the Universe.