These systems would contain either a white dwarf, neutron star, or black hole pulling in material from a companion star. So, in order to find this first extragalactic planet, scientists opted to search for passing planets within X-ray binaries. That's still well within the boundaries of our Milky Way galaxy, which is about 100,000 light-years across. Even though planets are much smaller than their stars, researchers can measure these small but recognizable fluctuations in brightness.ДЄlthough both the radial velocity and transit methods are clearly effective, they are only useful for finding planets out to about 3,000 light-years from Earth. This briefly dims the starlight by a detectable amount. The transit method, on the other hand, takes advantage of a planet crossing in front of its star. Even though stars hold considerably more mass than the planets around them, even a petite world can cause its star to move around a bit, leaving an imprint in the star's light. The radial velocity method measures how a star slightly wobbles when an orbiting planet around it gently tugs on its stellar host. Researchers have mainly used two methods to spot the over 4,000 confirmed exoplanets so far. Within all those systems, they found only one exoplanet. The team targeted more than 200 total star systems within these galaxies using the Chandra X-ray Observatory and the European Space Agency's XMM-Newton.

The new research, published in Nature Astronomy, examined three galaxies: M51, M101, and M104.

'We are trying to open up a whole new arena for finding other worlds by searching for planet candidates at X-ray wavelengths, a strategy that makes it possible to discover them in other galaxies,' said study lead Rosanne Di Stefano of the Harvard-Smithsonian Center for Astrophysics in a press release. To find the distant planet hiding in this system, astronomers relied on X-ray data rather than more standard visual observations. Residing some 28 million light-years away near the heart of the Whirlpool Galaxy (M51), the binary system M51-ULS-1 consists of either a neutron star or a black hole that's tangoing with a more standard companion star. Astronomers believe they've spotted the first extragalactic exoplanet beyond our own galaxy.

Back to saturn x episode 3