Potential planet may have been discovered outside the Milky Way galaxy

2021-10-26

Astronomers say they may have detected a potential planet outside of our galaxy — although the chances of it being confirmed in the next 70 years are slim.

Key points:

• Astronomers have detected dips in X-rays coming from in front of a pair of bright stars in the Whirlpool Galaxy

• They believe it may be a planet the size of Saturn

• But not everyone’s convinced and much more work — and time — will be needed to confirm the observation

The international team of astronomers spotted what they believe is a planet in an arm of the spectacular Whirlpool Galaxy, some 28 million light-years away.

The potential planet, dubbed M51-ULS-1b, was detected using the Chandra X-ray Observatory, the team reported on Tuesday in the journal Nature Astronomy.

“This work demonstrates a new method with the potential to discover planets in a wide range of systems hosting [X-ray sources],” they report.

But it is not the first time potential planets have been reported in other galaxies.

And not everyone is convinced this observation is a planet either.

Dips in X-rays detected in the Whirlpool

The object, which is roughly the size of Saturn, orbits around a massive star and a smaller dense core of a dead star known as a neutron star, or a black hole.

As it passed in front of its binary stars, it caused a dip in X-ray emissions produced by the neutron star or black hole sucking gas off its companion.

The transit lasted about three hours.

Astronomers use dips in visible light — known as the transit method — to detect alien planets in our own galaxy, but the team said using X-rays could allow them to find objects that are hard to spot.

“We are trying to open up a whole new arena for finding other worlds by searching for planet candidates at X-ray wavelengths, a strategy that makes it possible to discover them in other galaxies,” said the study’s lead author Rosanne Di Stefano of the Center for Astrophysics Harvard & Smithsonian in a statement.

Is it really a planet?

But while the team say they’ve picked up tantalising hints of a potential planet, much more work will be needed to confirm if it is one, and not a patch of dust.

Jonti Horner, an astrophysicist who studies alien planets, is sceptical that they’ve captured either.

“There’s something going on, and it could be a planet, but we’d have to be incredibly fortunate to have captured it at just the right time,” Professor Horner of the University of Southern Queensland said.

That’s because the potential planet takes 70 years to orbit its suns, travelling at a distance that is twice that of Saturn to our sun.

“A planet going around every 70 years means it’s bonkers far away [from its suns].”

For us to see it, it would also have to line up in the right position, at the right time.

“If you took observations a million times at random over that 70 years, only on four of those times would you see this thing transiting it,” Professor Horner said.

The only confirmed planets that we’ve spotted within our own galaxy, the Milky Way, using the same technique have orbits of around 10 years, he added.

“It seems too much an outlier, especially with a new technique,” he said.

To make things even harder, it is extremely difficult to spot objects orbiting binary targets blasting off high energy.

“In the past I’ve looked at a number of proposed planets in circumbinary systems and killed them because they didn’t make sense,” Professor Horner said.

“There’s always a chance they got lucky, but I think it’s more likely that there’s something else going on causing this signal.”

abc.net.au, 26 October 2021
; https://www.abc.net.au