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.
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Two strange stars that researchers describe as “freaks” have been spotted in our galaxy. Both are far hotter than stars that are otherwise similar to them, and they seem to be covered in a layer of carbon and oxygen.
Nicole Reindl at the University of Potsdam in Germany and her colleagues found these two stars, using the Large Binocular Telescope in Arizona. When the researchers analysed them, they found two unexpected properties.
First, stars of this size, with masses around half that of the sun, are generally relatively cool, but these stars are far hotter than others of their size. Second, stars of this size and temperature are generally made almost entirely of helium with only small traces of heavier elements, but both of these stars have surface compositions that are about 20 per cent carbon and 20 per cent oxygen – the ashes left behind from burning helium.
This is a very exotic type of star which has never been seen before, and we have two of them,” says Reindl. “There have been other stars that have these high temperatures, but they have different surface compositions.”
Those similar stars are formed when one white dwarf slowly devours another, smaller white dwarf. A second group of researchers led by Marcelo M. Miller Bertolami at the Institute of Astrophysics La Plate in Argentina came up with a variation of this process that could form this new type of star.
In that explanation, the core of the larger of the two white dwarfs must be made mostly of helium, and the smaller one mostly of carbon and oxygen. Then, when the helium white dwarf eats the other one, the resulting object will have carbon and oxygen on its surface.
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