by Astronomers may have finally solved the mystery of how dead superblack stars known as white dwarfs keep their heavy metal shells fresh – by cannibalizing what’s left of their planetary systems.
Our sun is destined to turn into a white dwarf in about five billion years, having run out of the hydrogen fueling nuclear fusion at its core. So the new research may give us a clue as to what might happen to the rest of the solar system after this transformation has taken place.
White dwarfs form when stars like the sun die, creating stellar remnants with masses about the size of the sun and widths about that of Earth. They are the most common stars in the Milky Way, accounting for 97% of the stellar bodies. But, despite the fact that they are common in our galaxy, the chemical composition of white dwarfs is a problem. That’s because the surfaces of these stellar remnants are decorated with elements heavier than helium, which astronomers call “metals.”
Now, a team of scientists has discovered that heavier metals such as silicon, magnesium and calcium find their way to the surface of white dwarfs when these zombie stars eat small rocky bodies that orbit them, such as comets and asteroids . The researchers also showed the mechanism that white dwarfs use to feed themselves by helping planetary animals.
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“Most of the planets in the universe will be orbiting a white dwarf,” said study team member Ann-Marie Madigan, professor of astrophysical and planetary sciences at the University of Colorado Boulder, in a statement. “Its star could eat up 50% of these systems, including our own solar system. Now, we have a mechanism to explain why this would happen.”
How white dwarfs stay heavy metal
The initial discovery of heavy metals on the surface of a white dwarf was shocking. That is because, through the collapse of these stars, when they transform from main sequence stars to white dwarfs, heavy metals should enter the interior of these stellar remnants.
“We know that if these heavy metals are present on the surface of the white dwarf, the white dwarf is dense enough that these heavy metals should penetrate very quickly towards the core,” said a member of the team. studies Tatsuya Akiba, PhD candidate at the University. of Colorado. “So you shouldn’t see any metals on the surface of a white dwarf unless the white dwarf is actively eating something.”
This begs the question: How are these zombie stars snacking on their environment in such a way that their surface is constantly being replenished with heavy metals?
To investigate this, the team created computer simulations that recreated a white dwarf that receives the “prenatal kick” that these remnants receive during their formation as a result of material loss in the chosen direction. This changes the motion of the white dwarf and the dynamics of the material around it.
“Simulations help us understand the dynamics of various astrophysical objects,” said Akiba. “So in this simulation, we throw a bunch of asteroids and comets around the white dwarf, which is much bigger, and see how the simulation evolves and which of the asteroids and comets eat the white dwarf.”
In 80% of the team’s tests, the white dwarf natal kick changed the orbits of asteroids and comets out to a distance 240 times the distance between Earth and the sun. These altered orbits became more elongated and aligned with each other. They also found that 40% of the planetesimals that ate a white dwarf had retrograde orbits, meaning they circled the stellar remnant in a direction opposite to its rotation.
The team allowed the simulation to run for 100 million years, finding that the planets near the white dwarf, about 30 times the distance between Earth and the sun – about the length of Neptune’s orbit – remained on elongated orbits and they began to move as a unit. .
“I think this is something unique about our theory: we can explain why the accreditation events last so long,” Madigan said. “While other mechanisms could explain the original event of accretion, our simulations with the kick show why it still occurs hundreds of millions of years later.”
The results suggest that heavy metals are found on the surfaces of white dwarfs because these zombie stars, like undead creatures from a George Romero film, mindlessly move forward and continuously eat whatever is in their path.
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In the future, the team hopes to increase the scale of their simulations to see what happens when objects larger than comets and asteroids, such as planets, interact with white dwarfs.
Until then, these results show what’s going on around the Milky Way’s most common stars and serve as a peer-reviewed crystal ball for the future of the solar system.
“Planesimals can give us insight into other solar systems and planetary composition beyond where we live in our solar region,” McIntyre concluded. “White dwarfs are not just a lens of the past. They are also a lens of the future.”
The team’s research was published last month in The Astrophysical Journal Letters.
