It would be a scientific sensation: A U.S. research team has stumbled upon an object that is more than a thousand times farther away from Earth than any planet known so far. Only one problem remains.
About the size of Saturn, it could be the object U.S. astronomers have discovered in the M51-ULS-1 star system, which they believe is a potential planet. The special feature: It does not revolve its orbits around a star in the Milky Way, as all known planets do, but around one in the spiral galaxy Messier 51 – 28 million light-years from Earth. So writes the research team from the Center for Astrophysics at Harvard and Smithsonian in Cambridge in its report. That would be more than a thousand times farther from Earth than the previous record holders, which spin their orbits 22,000 light-years away, according to the German Aerospace Center.
According to the scientists, the object so far away was discovered because it is located in an X-ray binary star system: These are millions of times brighter than the sun, but the source of the radiation is confined to a comparatively small space, they said. The passage of a planet could therefore completely block the intense X-ray radiation for an observer on Earth.
The team had systematically searched the night sky for such systems with Nasa’s Chandra X-ray telescope – they found them at M51-ULS-1: For more than three hours, X-ray emission in the system dropped to zero. “Our discovery of the planet candidate gives us the first insight into external populations of planetary systems and extends the reach of planet searches to distances about 10,000 times farther away,” said study leader Rosanne Di Stefano.
Verification as a planet likely to be difficult
It might be difficult, however, to finally verify the putative exoplanet as such: That would require observing another passage of the object in front of the binary star – but that will be about 70 years away because of its wide orbit. “And because of the uncertainties about exactly how long it will take, we wouldn’t know when to look,” said co-author Nia Imara of the University of California at Santa Cruz.
There has been criticism from colleagues of the researchers’ conclusion that they are dealing with a presumed exoplanet. Physicist Hugh Osborne, for example, pointed out that Nasa’s TESS telescope has observed more than 100 million star systems a day over a long period of time, but has never detected one with a comparably long orbital period.
