If our sun one day end of their life cycle reached, this means the end for the earth and its neighboring planets. Because as soon as the sun swells into a red giant, they are destroyed and swallowed up. Then, when the dying Sun has become a white dwarf, all that remains of the inner solar system is a great void. But what regarding the outer planets? Can Jupiter, Saturn and the ice giants Uranus and Neptune survive the death of our star?
Planetary death at the white dwarf
Several white dwarfs, around which astronomers have already discovered rings of dust and planetary debris, provide clues to the fate of planets at star death. In the case of a stellar remnant 410 light-years away, the debris disk might even contain the remnant of a planetary core hide. It’s likely only survived the tremendous tidal forces near the white dwarf because it’s made of solid metal.
How the gravitational pull of a white dwarf acts on nearby planetary remnants is something astronomers have seen for the first time with the white dwarf G29-38, which is only 44 light-years away observed directly. Images from NASA’s Chandra X-ray Telescope have shown multiple X-ray flares on the white dwarf’s surface. From the spectrum of this radiation, the researchers conclude that it comes from planetary debris that hit the white dwarf. “This detection gives us the first direct evidence that white dwarfs are consuming what is left of their planetary system,” says Tim Cunningham of the University of Warwick.
There are survivors too
But there can also be survivors. This is demonstrated, for example, by the white dwarf MOA-2010-BLG-477Lb, which is around 6,500 light-years away and is orbited by a planetary companion – a gas giant with 1.4 times the mass of Jupiter. “This confirms for the first time that planets can survive the death of their star if they orbit at a sufficiently large distance,” says Joshua Blackman from the University of Tasmania.
What is strange, however, is that the gas giant orbits only 2.8 astronomical units away from the white dwarf. This roughly corresponds to the position of the asteroid belt in our solar system and is therefore much too close, according to current theory, to have survived star death. However, the astronomers suspect that the planet used to orbit further outwards and was only pulled further inwards with the formation of the white dwarf.
This is how planet MOA-2010-BLG-477Lb might have survived the end of its star.© W. M. Keck Observatory/ Adam Makarenko
Life-friendly world at the rest of the stars
And there might even be potentially habitable planets around white dwarfs, as a team led by Jay Farihi of University College London recently discovered. When observing the white dwarf WD1054-22, 117 light-years away, with telescopes from the La Silla Observatory in Chile and the TESS space telescope, they encountered an anomaly: Every 25 hours, the light of this stellar remnant is dimmed by 26 debris clouds lined up like a string.
According to astronomers, this regular arrangement suggests that this debris is being influenced by an as yet unseen actor – a planet. This might be regarding the size of the earth and should orbit the white dwarf at a distance of around 2.5 million kilometers. This would put the planet exactly in the habitable zone of this stellar remnant.
The team suspects that this celestial body originally orbited far out of the star and thus survived its demise. However, it is also conceivable that the planet only emerged from the debris disk following the death of the star. “This is the first time astronomers have detected a planetary body in the habitable zone of a white dwarf,” says Farihi. However, the existence of this planet around WD1054-22 has yet to be confirmed by further analysis.
A second life for planetary systems?
But the very possibility that there might be habitable planets around such stellar remnants is as exciting as it is unexpected. Because then white dwarfs might not only be planet destroyers, but also potential hoards of life. For billions of years, these stellar remnants might provide light, warmth, and stable conditions to the surviving or newly formed worlds in their orbit.
For our solar system and many other planetary systems in the cosmos, this means that they may experience a kind of second life following the end of their star – a renaissance around a small, hot white dwarf.