Although there is no definitive confirmation, it may be possible to detect signs that a planet was transiting a star beyond the Milky Way. This fascinating result was obtained using the X-ray Observatory Chandra (NASA) and opens up a new window for searching for exoplanets from further distances than ever before. Due to its unique profile, the possible candidate for an exoplanet is located in the spiral galaxy Messier 51.
Exoplanets can be defined as planets that are not part of the Solar System. Astronomers have so far found almost all of the candidate and known exoplanets within the Milky Way galaxy. They are located approximately 3,000 light years from Earth. A M51 exoplanet would be approximately 28 million light-years away, which would mean that it would be thousands times further than the Milky Way.
Rosanne Di Stefano, of the Harvard Center for Astrophysics, says, “We are trying to open up new fields for finding other planets by searching for candidate planets at X-ray wavelengths. This strategy makes it possible to find them in other galaxies. The study was led by Rosanne Di Stefano, Harvard Center for Astrophysics, and published in Nature Astronomy.
The X-ray method was used by the team to find the exoplanet contender in a binary system called M51-ULS-1, which is located outside of the Milky Way.
The transits are events that occur when a planet passes in front of a star blocking part of its light. This causes a light drop. Ground and space telescopes have been used by astronomers to find gaps in electromagnetic radiation, which can be seen by humans, and this has allowed the discovery of many thousands of planets.
Instead, Di Stefano and his students have been looking for dips in brightness of Xrays received from bright binary X-ray stars. These light systems often contain a neutron Star or a black Hole that draws gas from a companion Star. It orbits nearby. Material close to a neutron star, black hole, overheats, and glows in the X-rays.
The region that emits bright Xrays is very small. A planet passing in front could block all or most of the Xrays. This makes transits easier to detect as Xrays can disappear completely in this area. This could make it possible to detect exoplanets from a greater distance than the current optical light transit studies. These studies are required to detect tiny dips in light, as the planet blocks only a fraction of the star’s light.
This method was used by the team to find the exoplanet candidate within a binary system named M51-ULS-1, which is located at M51. The binary system is composed of a black hole, or neutron star, that orbits a companion Star with a mass about 20 times that the Sun. They found the Xray transit using Chandra data. It lasted for approximately three hours before the Xray emission dropped to zero. The researchers based on this information and others estimate that M51-ULS-1’s candidate exoplanet would be approximately the same size as Saturn and orbit the neutron star/black hole at around twice the distance from Saturn.
To confirm, more data is required
This is an intriguing study. However, it would require more data to confirm the identification as an extragalactic planet. The problem is that the candidate planet orbit is so large that it wouldn’t cross in front its binary partner for approximately 70 years. This would make it impossible to confirm any observation attempts for many decades.
“Unfortunately, in order to confirm that we are actually seeing a planet, it would be necessary to wait for decades before we could see another transit,” says Nia Imara, co-author at the University of California at Santa Cruz. We wouldn’t be able to know when we should look because of uncertainties around the time it takes to orbit.
Does it make sense that there is an attenuation due to a cloud composed of dust and gas passing near the X-ray source. Researchers consider this unlikely because the M51-ULS-1 characteristics do not support the passage of a cloud. The data supports the model of a candidate planet, however.
“We know that we are making bold statements exciting, so we hope other astronomers think carefully,” Julia Berndtsson, co-author at Princeton University in New Jersey, adds. We believe we have a strong argument. This is part of the scientific process.
Unstable system on any planet
This system has likely had a turbulent history and a violent past if there is a planet. A black hole or neutron star would have to be formed if an exoplanet from this system survived a supernova explosion. Your future could also be very dangerous. The companion star could also explode and become a supernova, causing the planet to be blasted with high levels of radiation.
His research team, Di Stefano and colleagues searched for X-ray transits within three galaxies other than the Milky Way using Chandra and the European Space Agency’s XMM–Newton. The search included 55 systems in M51 and 64 systems in Messier 101 (the Pinwheel galaxies), as well as 119 systems within Messier 104 (the Sombrero galaxies). This resulted in the discovery of the exoplanet candidate.
The authors will search Chandra and XMM–Newt archives to find more exoplanet candidates from other galaxies. Important Chandra data sets for at least 20 galaxies are available, including M31 and M33, which are closer than M51. This allows for shorter transits to occur. A fascinating line of research is to search for Xray transits in Xray sources of Milky Way in order to find new planets in unusual environments.