Astronomers have found 65 evenly spaced rocks orbiting a white dwarf star in its habitable zone, hinting that a planet’s gravity may be holding them there
A distant white dwarf is surrounded by space rocks marching in perfect time. This observation offers hints of what may be the first planet we have detected in the habitable zone of one of these stellar corpses, suggesting that they might be just as good for life as bigger, younger stars.
“A lot of people think of a white dwarf as a dead system or a dead end, but this tells us that there is a lot of stuff going on around white dwarfs,” says Jay Farihi at University College London.
He and his colleagues spotted these hints while observing a star called WD 1054-226, which lies about 118 light years away, using several powerful telescopes. They found that something appeared to be regularly passing in front of the star, causing dips in its light. The biggest dip happened every 23.1 minutes, in a pattern that repeated every 25 hours.
The measurements indicate that the star is surrounded by a ring of 65 comet-sized or moon-sized objects, remarkably evenly spaced in their orbits. “The structures that are transiting are so highly regular that you can’t really do that accidentally,” says Farihi. That doesn’t mean it is aliens, though. “Regular structures in space do invoke this idea of planetary engineering, but I favour the more mundane explanation,” he says.
This is that the bits of cosmic debris are kept in order by the gravitational pull of a planet orbiting slightly further away from the star. “If we’re correct that there is a planet causing this order, my guess would be that it would be around the size of Mercury or Mars,” says Farihi.
The researchers calculated that the orbiting objects are about 2.6 million kilometres from the star – about 4 per cent of the distance between Mercury and the sun – putting their temperatures at around 50°C, which is right in the middle of the range for liquid water. This means that if there is a planet there, it could have the right temperature for oceans and maybe even life.
Journal reference: Monthly Notices of the Royal Astronomical Society, DOI: 10.1093/mnras/stab3475
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Article amended on 11 February 2022
We corrected the distance comparison of the orbiting objects in relation to Mercury’s distance from the sun
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