Recently, scientists have discovered what they think is the first planet ever to be found outside our galaxy. This possible exoplanet, meaning a planet outside our solar system, was discovered in the Whirlpool Galaxy (the spiral galaxy Messier 51 (M51)) by NASA’s Chandra X-ray observatory, according to NASA. All other exoplanets ever discovered have been found in the Milky Way Galaxy, until now. Most of them are less than 3,000 light-years from Earth. This new exoplanet could be up to 28 million light-years away, thousands of times farther than the others.
Although this discovery marks a major milestone in astrophysics, the planet’s existence cannot be confirmed for another 70 years. This is because the possible extragalactic exoplanet has a large orbit; it will not cross in front of the binary path for another 70 years with a large margin of error. This means scientists must wait to see another transit. The team of scientists who made the discovery used X-ray wavelengths, which are undetectable to the human eye.
The team used dips in the brightness of X-rays from X-ray bright binaries, which contain a neutron star or black hole. A black hole is essentially sucking material off of a small host star (usually a neutron star). The stellar material being sucked up by the black hole radiates X-rays. The brightness of this event is well-known and can be used to measure distances relative to other events (like the transit of this mystery extragalactic exoplanet).
If this discovery is proven, experts say that it would have had to survive a supernova explosion, which is an explosion of stellar materials at speeds up to several percent of the speed of light. There is a dying star very near the system of interest. This supernova would drive an expanding shock wave into the surrounding interstellar medium, obliterating the exoplanet.
Scientists believe that the companion star could explode as a supernova and blast the planet with high levels of radiation. The Harvard-Smithsonian Center of Astrophysics’ lead researcher Rosanne Di Stefano has contributed to this finding and the new process to discover far away objects through X-ray technology.
Other scientists say these X-ray techniques are brilliant and clever, but “unlikely that it could be used to find hundreds of thousands of planetary candidates because it also relies on luck.” This is because the viewer can only view these objects when the bodies in space line up perfectly, which happens for only a few minutes to hours. Nevertheless, Di Stefano said that it is gratifying that the new method for searching for extragalactic exoplanets, which she and her colleagues first theorized in 2018, has produced an “enticing result.”
These results are monumental to the laboratory which made the discovery, but also the astrophysics world. The technique and result will lead to a whole new area of astrophysics data that can be collected and analyzed.