Astronomers observed the signals of the first-ever planet outside our Milky Way galaxy. Till now, at least 5,000 exoplanets are planets are discovered but within the Milky Way. Its estimated size is comparable to the Saturn and Chandra X-Ray Telescope used for the study. This planet outside our milky way galaxy is located in the Messier 51 galaxy which is around 28 million light-years away from the Milky Way.
Team leader Rosanne Di Stefano of the Harvard & Smithsonian Center for Astrophysics after studying thousands of signals found that a big dip in X-ray light from the Whirlpool Galaxy is evidence of an extragalactic planet. M51-ULS-1b, the name given to this exoplanet.
Di Stefano said, “We feel proud of our ability to contribute to such work. It tells new methods to explore new planets in the Milky way and even in other galaxies. And we are humble about the fact that the discovery of exoplanets in other galaxies connects our work with history.”
Discovering exoplanets in our galaxy is very difficult. The transit method is widely used for detection. In this method, when an exoplanet passes between the earth and the star it revolves, the change in the star brightness can be observed as a light curve.
Di Stefano and her colleague Nia Imara in the year 2018 said that exoplanets may impart different effects on a type of binary star called an X-ray binary. The pairs of stars are so close that one of them attracts materials of another which then produce X-radiation. Such stars have great brightness but are small like neutron stars or stellar-mass black holes.
“Obviously we do not know whether planets specifically orbit X-ray binaries, but there are reasons that make sense to study and observe them”, Di Stefano adds.
Basically, the team observed three galaxies named the Whirlpool Galaxy (M51), the Pinwheel Galaxy (M101), and the Sombrero Galaxy (M104), and for which X-ray observatories, Chandra and XMM-Newton are used. Researchers figured out 2,624 X-ray binary light curves from their observations and started finding extraplanetary eclipses. And interestingly out of thousands, only one was continuous. It was an ultra-bright X-ray binary which was then called M51-ULS-1 and consisted of a hot, bright B-type star.
The star’s brightness remained somewhat constant during observation but it went dark for three hours afterward. However, brightness levels were the same before and after the dip in light. It showed that the dimming was due to an external agent, and not due to interaction with binary relationships.
Dr. Di Stefano said that the upcoming generation’s optical and infrared telescopes would not have the ability to resolve the problems of crowding and dimness, and thus observations at X-ray wavelengths will be very helpful for tracing planets in other galaxies. However, microlensing methods can be useful for identifying extragalactic planets.
The next step is to figure out that external agent. The team is also looking at other small stars, dwarfs, gas clouds which are basically the common X-ray binaries. moreover, this study has been published in the journal Nature Astronomy.