Astronomers have found evidence of what may be the first planet to be discovered outside our galaxy.
So far, about 5.
have been identified. “exoplanets” that are outside our Solar System, in orbit of other stars but they have all been located within our galaxy, the Milky Way.
The possible planet is the size of Saturn and was discovered by the Chandra X-ray telescope from NASA, the American space agency. It lies in the Messier galaxy 20, about 20 million light years from the Milky Way.
This discovery is based on so-called transits, in which the passage of a planet in front of a star blocks some of the star’s light and produces a characteristic drop in brightness that can be detected by telescopes.
This general technique has been used to find thousands of exoplanets.
Astrophysicist Rosanne Di Stefano and her colleagues searched for dips in the brightness of X-rays received from a type of object known as bright X-ray binary.
These objects often contain a neutron star or a black hole that extracts gas from a companion star that orbits close. The matter next to a neutron star or black hole overheats and glows at X-ray wavelengths.
Since the region that produces bright X-rays is small, a planet passing in front of it can block most or all of the rays, making transit easier to detect.
Team members used this technique to detect the exoplanet candidate in a binary system called M51-ULS-1.
“The method we have developed and employ is the only method currently implementable for discovering planetary systems in other galaxies,” says BBC News Di Stefano, part of the Center of Harvard-Smithsonian Astrophysics at Harvard University, USA.
” is a unique method, especially suitable for finding planets around X-ray binaries at any distance from which we can measure a curve of light.”
Future of planet hunting
This binary contains a black hole or neutron star orbiting a companion star m a mass about 000 times that of the Sun. A neutron star is the collapsed nucleus of what was once a massive star.
Transit it lasted about three hours, during which the X-ray emission dropped to zero. Based on this and information, astronomers estimate that the planet candidate would be approximately the size of Saturn and would orbit the neutron star or black hole at about twice the distance Saturn is from the Sun.
Di Stefano claims that techniques that have been so successful for finding exoplanets in the Milky Way do not work when looking at other galaxies.
In part, this is because the large distances involved reduce the amount of light reaching to the telescope and also mean that many objects are crammed into a small space (as seen from Earth), making it difficult to identify individual stars.
With X-rays, she explained, “there may only be a few dozen sources all over the galaxy spread out, so we can define them. Also, a part of them is so bright on X-rays that we can measure their light curves.”
“Finally, the huge emission of X-rays come from a small region that can be substantially or (as in our case) full It is blocked by a passing planet.”
Researchers openly admit that more data is needed to verify this interpretation. planet means it would not cross in front of its binary companion again for about 70 years, nullifying any attempt to make a short-term follow-up observation.
Another possible explanation is that astronomers considered that the darkening was caused by a cloud of gas and dust passing in front of the X-ray source.
However, they believe this is unlikely, because of the characteristics do not correspond to the properties of an event gas cloud.
“We know we are making an exciting and bold statement, so that other astronomers will examine it very carefully,” we hope, said study co-author Julia Berndtsson, from Princeton University, USA.
“We think we have a strong argument, and this process as science works.”
Di Stefano said that the new generation of optical and infrared telescopes would not be able to compensate for the clumping and dimming problems, so observations at X-ray wavelengths would likely follow. being the main method for detecting planets in other galaxies.
However, she stated that a method known as microlensing may also be promising for identifying planets outside our galaxy.
*)The study was published in the scientific journal Nature Astronomy.