Astronomers spot first planet outside of Milky Way galaxy: ‘It’s a beautiful thing’

There’s a possible new planet on the universal scene.

The newly uncovered planet, minted M51-ULS-1b, resides in the Whirlpool galaxy, our Milky Way’s neighbor, located 28 million light-years from Earth. It orbits two hosts: a massive star, with a mass at least eight times larger than our sun, and one dead star.

There are no less than 4,800 exoplanets in our home galaxy, the Milky Way. However, planet-hunting technology has yet to reliably extend outward toward further galaxies, which surely boast a variety of their own planets.

“We probably always assumed there would be planets [in other galaxies],” said Harvard-Smithsonian Center astrophysicist Rosanne Di Stefano, whose new report — with help from the University of California, Santa Cruz — was published in Nature Astronomy on Monday. “But to actually find something, it’s a beautiful thing. It’s a humbling experience,” she told Science News.

A relatively novel method helped scientists search for planets outside our galaxy by pointing their telescopes in the direction of binary star systems containing one living and one dead star, called X-ray binaries, named for the X-rays emitted as the collapsing star sucks some of the life from the remaining living star.

If astronomers’ radar shows hiccups in X-ray emission of these particular binary systems, they may deduce that an orbiting planet has caused the brief pause.

Researchers perused data from NASA’s Chandra X-ray telescope for evidence of sporadic X-ray emissions throughout three galaxies: the M101 Pinwheel galaxy, M104 Sombrero galaxy and the M51 Whirlpool galaxy.

Out of a possible 2,624 sources in the data, and ruling out for other potential causes of fluctuations in X-rays, just one suggested a planetary presence.

“We said, ‘Wow. Could this be it?’ ” said Di Stefano.

It’s a hostile environment for Saturn-sized M51-ULS-1b, which fields an onslaught of X-rays and ultraviolet radiation, according to DiStefano.

While some scientists called the research “speculative,” Di Stefano told Science News that the rarity of the observation — out of thousands of potential planetary passes — is a testament to the validity of their findings.

“The real test is finding more planets,” said Di Stefano. And it could be decades before we see M51-ULS-1b transit its host stars again.

“Maybe we were lucky,” she said. “But I think it’s very likely that we were not special. We looked and we found something because there was something to find.”