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In 2017, astronomers noticed a star emerging from the Milky Way at nearly 2 million mph (3.2 million km / h) – about four times faster than our solar orbits – and flying against the direction in which most stars revolve around the galactic center. It’s also made of completely different, mostly heavy, “metallic” star stuff. atoms rather than the usual light items. The LP 40-365, as it was called, was as eye-catching as a wooden car cruising up the freeway against traffic at hundreds of miles an hour.
“It’s unusually strange in many ways,” said lead author JJ Hermes, astronomer at Boston University.
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The star is moving so quickly that it is definitely heading out of our galaxy, which astronomers have taken as evidence that the Metallic Explorer was launched here by a cosmic catastrophe – a supernova. But they couldn’t tell how the supernova had sent it flying. Was LP 40-365 a piece of the exploded star itself? Or was it a partner star clearly projected by the shock wave associated with star explosions? New analysis of old data reveals that the star – called a white dwarf – rotates around its axis at a leisurely pace – a clue that it is indeed a piece of stellar debris (not a partner star ) who managed to survive one of the most violent and mysterious events.
“We can now connect this star to the shrapnel of an exploded white dwarf with a lot more confidence,” Hermes said.
Witness of a cosmic catastrophe
Shortly after the discovery, astronomers realized that the white dwarf star’s unique characteristics likely meant that it had witnessed a supernova. It was fast and his whole composition seemed altered. Most stars are made almost entirely of hydrogen and helium. In LP 40-365, however, astronomers detected only heavy elements like oxygen, neon and magnesium – atoms fused together in a supernova furnace. A supernova had infused the entire star with these “metals”. (Unlike chemists, astronomers consider anything heavier than helium be a metal.)
Astronomers concluded that the star had once been a member of a pair of white dwarfs – the typical fate of small sun-like stars – which explode after siphoning enough mass from their partner. These explosions are so powerful that the elements merge their nuclei into completely new elements. Two scenarios were possible. In the first, a star exploded cleanly, exploding its partner with heavy metals and sending him into space. In the second, a fragment of the exploding star escaped from the supernova, charged with the metals forged during the explosion.
“A big question is: what part of the binary star are we observing,” Saurabh Jha, an astronomer at Rutgers University in New Jersey, who was not involved in the research, told Live Science in an e- mail. “Both are exciting, giving us a new way of understanding exploding white dwarfs.”
A survivor who turns slowly
To better understand the bizarre star, Hermes and his colleagues sifted through data collected by NASA’s Transiting Exoplanet Survey satellite, which searches for distant planets passing by and darkening their host stars. LP 40-365 does not have a planet, but it darkens and lights up every 8.9 hours, data from TESS has revealed. The team found the same clockwork in existing data from the Hubble Space Telescope, which they say means the star is spinning, causing sunspots to appear and disappear. Blinking could also indicate a heartbeat, but stellar pulsations tend to be irregular. “The most likely scenario,” Hermes said, is “that there are a few small warts on the surface”.
They published their findings online on June 7 in Letters from the astrophysical journal.
Knowing the rotational speed of the LP 40-365 is useful because it helps researchers understand what the white dwarf likely experienced about 5 million years ago during the supernova. The pair initially went into orbit once every 30 to 60 minutes, the group estimated. If LP 40-365 were the clear companion star, it should still turn almost as fast.
But his relatively relaxed rotation suggests he’s undergone a more dramatic transformation. The white dwarf that exploded is said to have swelled further, its rate of rotation plummeting as much as a figure skater’s rotation slows down when he extends his arms. The rotation period of more than a week suggests that the white dwarf is a diffuse fragment of the star that exploded.
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“I find this to be a very good job of observation, and assuming their calculations are correct for the predictions of both scenarios, it certainly strengthens the case for the [incomplete supernova] scenario, ”Jha wrote.
The calculation assumes that the star has essentially held together, without producing too many large chunks that could significantly affect its revolution. (If a figure skater throws one of their skates, it could change their rotation.)
While astronomers frequently observe white dwarf supernovas, using them to synchronize the accelerated expansion of the universe due to dark energy, researchers do not fully understand how such events unfold. Until recently, few theorists would have predicted that it would be possible to survive a supernova. An off-center ignition may not blow up the whole star, but the debate is far from settled. “There is a lot of unknown physics,” Hermes said.
In search of more “partly burned” stars
Finding LP 40-365 as a supernova survivor is the scenario the researchers hoped for, because it means that, compared to the companion star, the fragment is more intimately linked to the stellar catastrophe. By studying the amount of magnesium, neon, and other elements inside the fast star, the researchers were able to get a glimpse inside the supernova’s black box itself. “We just can’t simulate that on Earth. The conditions are so extreme it’s the only lab we have, finding stars like this,” Hermes said.
LP 40-365 is one of a handful of extremely metallic and swift white dwarfs that astronomers have recently spotted, the flagship member of a group they call “partly burnt stellar remains.” Collecting data on more stars that supernovas failed to completely burn out could help researchers get a better idea of what these systems are doing before the explosive lightning bolts appear in astronomers’ telescopes.
“This star really came out with a bang,” Hermès said. “We can use it to learn more about these violent endings.”
Originally posted on Live Science.
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