The first discovery of a planet outside the solar system was a real scientific achievement. The first discovered exoplanets were discovered using ground-based observatories, so at first their number was small. But with the launch of new, more powerful space telescopes such as Kepler, the number of open worlds began to skyrocket. By February of this year, scientists have confirmed the discovery of 3,728 exoplanets located in 2,794 systems, 622 of which have more than one planet.
More recently, astronomers have reported a new achievement. Astrophysicists from the University of Oklahoma (USA) have, for the first time in history, observed planets located in another galaxy. Using the predictive method described in Einstein's theory of general relativity, the team found evidence of planets in a galaxy about 3.8 billion light-years away.
An article detailing the discovery, titled "Probing Other Galaxies with Quasar Microlensing," was recently published in the Astrophysical Journal Letters. The study was led by PhD Xinyu Dai and Professor Eduardo Gerras from the Department of Physics and Astronomy at the University of Oklahoma.
For their research, astrophysicists used the method of gravitational microlensing, where a massive astronomical object like a star acts as a lens, which, with the help of its gravitational fields, changes the direction and focuses the propagation of electromagnetic radiation, just as an ordinary lens changes the direction of a light beam. Gravitational microlensing is a scaled-down gravitational lensing technique. In the latter, much larger objects, such as galaxies or even clusters of galaxies, act as a lens, which change the direction of the light of the observed object located behind the lens. Both options are used in the transit method for detecting planets. When a planet passes a star relative to the observer (i.e. makes a transit),the star's light changes accordingly, and thus scientists can determine the presence of a planet.
In addition to the microlensing method, which detects the presence of objects located only at really very large distances from us (we are talking about billions of light years), the researchers used data from the space X-ray observatory "Chandra" to study the quasar RX J1131-1231. First of all, scientists were interested in the microlensing properties of a supermassive black hole located next to this quasar.
In addition, the scientists also used the computing power of a supercomputer to calculate the microlensing models that were used. As part of their analysis of the data, the researchers found energy shifts that could be attributed to the presence of approximately 2,000 unrelated planets located between the quasar and Earth, with masses ranging from the mass of the Moon to Jupiter.
Image of the gravitational lens of the galaxy RX J1131-1231 with a lenticular galaxy in the center and four images of the quasar in the background. Researchers suggest that in this image, there are trillions of planets in the center of an elliptical galaxy.
“We are very pleased with this discovery. For the first time, planets have been discovered outside our galaxy. It is the presence of planets that can best explain the signatures that we observed in the study using the microlensing method. Through data modeling and analysis of the high frequencies of these signatures, we tried to find out a lot of their sources,”commented Xinyu Dai in a published press release.
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Scientists have already discovered 53 planets inside the Milky Way using microlensing, but this is the first time that astronomers have been able to detect signs of planets in other galaxies. As in the case of exoplanets outside the solar system, scientists until this moment were not sure that planets could exist in other galaxies. This discovery takes the exploration of space outside the solar system to a truly new level.
Eduardo Gerras notes that the discovery was made possible by significant advances in both modeling techniques and hardware in recent years.
“This is an example of how effective our methods of analyzing extragalactic microlensing data can be. This galaxy is located about 3.8 billion light-years away, and we have no way of directly observing these planets. Even our best telescopes cannot do that. This can only be imagined in science fiction. Nevertheless, we are really able to study them, confirming not only their existence, but even assuming their masses."
In the coming years, several new and most modern observatories should open and operate at once, which will make it possible to make even more amazing discoveries. The James Webb Space Telescope, the European Extremely Large Telescope, and the Colossus Telescope are just a few of the names on the list.
