Some three hundred light years from ours, a gas giant keeps its rapid vigil around a dead star, and astronomers now suspect it was not born with the star's youth but raised from the scattered remains of the star's last violent exhalations. If this reading holds, it would mark a rare kind of beginning: a world that comes into being only after its sun has already gone out. Such a story, in which death becomes the material of new creation, has long lived in human myth, and here it appears to be playing out in the quiet arithmetic of gravity and chemistry.
Scientists Find a 'Phoenix Planet' Born from the Ashes of a Dying Star
Born again from the ashes of its dying host star
Mark
So what's actually new here? Planets around dead stars aren't unheard of.
Mimi
Planets around pulsars have been proposed before, a small number. This would be the first formed around a white dwarf, which is a far more common kind of remnant.
Luke
Worth saying that 'formed after the star died' is the researchers' interpretation. It isn't directly observed.
Mark
What's the evidence for it?
Mimi
Chemistry. The planet is rich in niobium, copper and zinc, elements certain dying stars shed as they expand. That suggests it grew from that expelled material.
Luke
Right, but the team itself wants James Webb to confirm. So it's a strong clue, not a settled case.
Mark
And the planet's condition now?
Mimi
Brutal. It orbits at 4% of the Earth-sun distance every 4.4 days, and ultraviolet radiation is boiling off its outer atmosphere, some of which falls onto the star.
Mark
Why does the habitable-zone idea matter?
Mimi
Williams said a rocky planet could form too, and because white dwarfs cool slowly, it could stay habitable for billions of years.
Luke
That's a 'could'. Nothing like that has been found. The only planet here is a gas giant, inhospitable to life.
Mark
And the Taurus system?
Mimi
A separate study: a red dwarf and a brown dwarf orbiting every 87 minutes, with a hot spot where stolen material lands.
Luke
Distance is a range, 300 to 500 light years, so that one isn't pinned down precisely either.
O Pulso
- A gas giant races around its white dwarf every 4.4 days, so close that its outer atmosphere is being stripped away and falling onto the star.
- Its chemistry carries the signature of a dying star's ejected material, unsettling the assumption that planets only form around newborn suns.
- Researchers are gathering evidence from Hubble, TESS and FUSE and preparing James Webb observations to test whether the second-generation origin truly holds.
- Because white dwarfs are so common, the discovery opens the possibility that many more such worlds exist, and that one may someday be rocky and habitable.
Some three hundred light years from ours, a gas giant keeps its rapid vigil around a dead star, and astronomers now suspect it was not born with the star's youth but raised from the scattered remains of the star's last violent exhalations. If this reading holds, it would mark a rare kind of beginning: a world that comes into being only after its sun has already gone out. Such a story, in which death becomes the material of new creation, has long lived in human myth, and here it appears to be playing out in the quiet arithmetic of gravity and chemistry.
Roughly 250 light years from Earth, near the constellation Cetus, a gas giant circles a dead star every 4.4 days. Astronomers now believe the planet may have been born after its star died, assembled from the debris of the star's final convulsions. If confirmed, it would be the first known planet to form around a white dwarf, the compact remnant of a star a little larger than our sun.
When such a star nears its end, it swells and flings material into space. The researchers propose that this expelled matter formed a disk around the stellar corpse, and the planet coalesced within it. Jamie Williams, the University of Warwick doctoral student who leads the study in Nature Astronomy, reached for the myth of the phoenix to describe a system reborn from its own ashes.
The planet, perhaps a little heavier than Jupiter, orbits so tightly that the white dwarf's ultraviolet light is evaporating its atmosphere. The strongest clue to its origin is its chemistry: it is rich in niobium, copper and zinc, the elements dying stars cast off. The team hopes the James Webb Space Telescope will confirm the picture.
Similar candidates have appeared around pulsars, but white dwarfs are far more numerous, and Williams noted that more than 95% of Milky Way stars will end as one. If a gas giant can form this way, a rocky world might too, and since white dwarfs cool predictably, such a planet could remain in the habitable zone for billions of years.
Roughly 250 light years from Earth, near the constellation Cetus, a gas giant circles a dead star every 4.4 days. Astronomers now say that planet may have been born after the star died, assembled from the debris of its host's final convulsions. If the finding holds, it would be the first known planet to have formed around a white dwarf.
The white dwarf is the compact remnant of a star somewhat larger than the sun. When such a star nears its end, it expands and throws off material into space. The researchers propose that a disk of this expelled matter surrounded the stellar corpse and that the planet coalesced from it. That makes it a second generation planet, as opposed to first generation worlds like Earth, which formed from the disk around a newborn star. Jamie Williams, a doctoral student in astrophysics at the University of Warwick in England and lead author of the study in Nature Astronomy, called it the first example of a planet forming around a white dwarf. He reached for the myth of the phoenix, reborn from its own ashes, to describe a planetary system reborn after its star's death.
The planet itself is a gas giant, perhaps slightly more massive than Jupiter. It sits only 4% of the Earth-sun distance from its star. At that range, the white dwarf's extreme ultraviolet radiation is stripping away the planet's outer atmosphere, and some of that gas falls onto the star.
The strongest clue to its origin is chemical. The planet is rich in niobium, copper and zinc, elements of the kind certain dying stars cast off as they swell in their death throes. That pattern points to a birth from expelled stellar material. The team drew on data from the Hubble, TESS and FUSE space telescopes, and hopes to use the James Webb Space Telescope to confirm its conclusions.
There is precedent of a sort. A small number of possible second generation planets have been identified around pulsars, a rare kind of neutron star and another type of stellar remnant. White dwarfs are a far larger population, Williams noted: more than 95% of stars in the Milky Way will end up as one. That suggests many more second generation planets may orbit white dwarfs than pulsars.
This particular world would be hostile to life, but Williams said a different one might not be. If a gas giant can form around a white dwarf, a rocky planet could too. White dwarfs cool predictably, and their cooling slows with time, so a rocky planet formed close enough could stay in the habitable zone for billions of years.
The same journal carried a second, unrelated discovery from the constellation Taurus, 300 to 500 light years away. Using the Zwicky Transient Facility at Palomar Observatory in California, researchers found a red dwarf with about 8% of the sun's mass in a tight orbit with a brown dwarf, an object too small to be a star and too large to be a planet. The brown dwarf is about 30 times Jupiter's mass and a third of the star's mass.
The pair orbit each other every 87 minutes, at slightly more than half the Earth-moon distance. The star's gravity appears to be pulling material from the brown dwarf, and the team detected a hot spot on the star's surface where it seems to land. Aaron Householder, an MIT graduate student in astrophysics and lead author, called it the first observed example of this phenomenon. The two objects are so close, he said, that their entire orbit would fit inside the sun.
For the phoenix planet, the next test is the James Webb observations the team hopes to make.
Citações Notáveis
This is the first example of a planet forming around a white dwarf.— Jamie Williams, University of Warwick doctoral student and lead author
The two objects are so close together that the entire orbit would fit inside the sun.— Aaron Householder, MIT graduate student and lead author
Quer a matéria completa?
Leia o original em The Star ↗