Scientists discover the first planets outside the Milky Way – and there may be trillions
A cluster of planets in a galaxy 3.8 billion light years away have been found with a novel technique that reaches far beyond the gaze of any telescope
The truth is out there. And past that is a cluster of planets 3.8 billion light-years away, a recent discovery that if confirmed could extend the boundary of what we know about the universe.
Using data from a Nasa X-ray laboratory in space, Xinyu Dai, an astrophysicist and professor at the University of Oklahoma, detected, for the first time ever, a population of planets beyond the Milky Way galaxy. The mass of the planets range in size from Earth’s moon to the massive Jupiter, our solar system’s biggest planet.
There are few methods to determine the existence of distant planets. They are so far away that no telescope can observe them, Dai said. So Dai and his postdoctoral researcher Eduardo Guerras relied on a scientific principle to make the discovery: Albert Einstein’s Theory of Relativity.
Einstein’s theory suggests light bends when tugged by the force of gravity. In this case, the light is coming from a quasar – the nucleus of a galaxy with a swirling black hole – which emits powerful radiation in the distance.
Between that quasar and the space-based laboratory is the galaxy of newly discovered planets. The gravitational force of the galaxy bends the light heading toward the Milky Way, illuminating the galaxy in an effect called microlensing. In that way, the galaxy acts as a magnifying glass of sorts, bringing a previously unseen celestial body into X-ray view.
The technique was first used to first identify planets outside of our Solar System but inside the galaxy, known as exoplanets.
“Microlensing is probably the only way,” Dai said.
In a university news release, Guerras had a less formal way to describe the complicated process: very cool science.
“This is an example of how powerful the techniques of analysis of extragalactic microlensing can be. This galaxy is located 3.8 billion light years away, and there is not the slightest chance of observing these planets directly, not even with the best telescope one can imagine in a science fiction scenario,” said Guerras. “However, we are able to study them, unveil their presence and even have an idea of their masses. This is very cool science.”
The photo that emerged is a modest image of the extraordinary find that Dai said will advance the study of planetary science. The central elliptical object is the galaxy where the planets reside. The linked white dots at the top and solo white mark at the bottom are the lensed images of active radiation pulsating from a black hole.
Dai estimated the distant galaxies contains 2,000 planets for every star, many of them free-floating and not bound in orbit like the Earth is around the Sun. That means trillions of planets likely reside beyond our own galaxy, he said, consistent with the ratio found in free-floating planets in the Milky Way that itself contains billions of planets.
“This discovery, if the interpretation of the data holds up, looks very exciting indeed,” Dr. Priyamvada Natarajan, a theoretical astrophysicist at Yale University, told NBC.
But other experts stressed scepticism. David Bennett, a gravitational lensing expert at Nasa, said the research was “interesting” but the data could be interpreted in a way to suggest the objects were not extragalactic, NBC reported.
Microlensing can reveal surprising things, like the same star exploding four times, but objects in space are not static, and will not always have the perfect quasar backdrop to bathe a given object with arcing light. That gives limited time for a discovery to be made with nearly boundless galaxies in the sky.
That might make this discovery all the more remarkable: the fact that it might not have happened at all. Dai was simply looking to study the environment in and around a black hole. He may have found something more.
“It was serendipity,” he said.