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Astronomers have made the first discovery of its kind – a white dwarf with two completely different faces.
White dwarfs are the remains of stars that died and burned. Our sun will become a white dwarf around us 5 billion years After swelling into a red giant star, it exploded its outer matter and, with only its core remaining, shrank back into a smoldering remnant.
The newly discovered white dwarf has two faces, one made of hydrogen and the other made of helium. Researchers named the star Janus after the two-faced Roman god of transition. A detailed study of the results was published July 19 in the journal Nature alam.
“The surface of the white dwarf shifts completely from side to side,” study lead author Ilaria Caiazzo, a postdoctoral research fellow in astronomy at Caltech, said in a statement. “When I showed the note to people, they were stunned.”
White dwarfs are incredibly dense, compressing a mass similar to our Sun into something equivalent to an Earth-sized planet.
The strong gravitational effects during a star’s death mean that the remaining heavy elements move toward the center while lighter elements such as hydrogen or helium rise to the upper layers. Given the scorching temperatures of white dwarfs, the hottest ones have a hydrogen atmosphere. As stars cool over time, they tend to have helium atmospheres.
But a typical white dwarf doesn’t have one side of the star dedicated to one element, and the other side dominated by the other element.
This unusual stellar remnant was first detected by the Zwicky Transit Facility, located at Caltech’s Palomar Observatory. Caiazzo used the instrument, which scans the sky every night, to conduct a recent survey of a highly magnetic white dwarf when an object of rapidly changing brightness appeared.
Follow-up observations were made by Caiazzo and his team using Palomar’s CHIMERA instrument HiPERCAM located at Gran Telescopio Canarias in the Spanish Canary Islands and the WM Keck Observatory on Maunakea, Hawaii.
All three observatories showed that Janus rotates on its axis every 15 minutes – and demonstrates the nature and composition of multiple stars. Astronomers used a spectrometer to separate the white dwarf’s light into different wavelengths, which revealed the chemical signatures of hydrogen on one side and helium on the other.
The star has a temperature of 62,540 degrees Fahrenheit (34,726 degrees Celsius), which the researchers determined with help from the Neil Gehrels Swift Observatory.
Researchers aren’t entirely sure why a star has two very different sides. It is possible that Janus is undergoing a rare form of evolution.
“Not all, but some white dwarfs transition from hydrogen to helium which dominates their surface,” said Kiazo. “We might catch a white dwarf in action.”
As the white dwarf cools over time, heavier and lighter materials can mix together. During this transition, it is possible for hydrogen to become diluted on the inside, allowing helium to become the dominant element.
If this happened on Janus, then one side of the star evolved before the other.
K. Miller, Caltech/IPAC
The magnetic field, shown here as lines around the star, may explain Janus’ unusual appearance.
“The magnetic fields around cosmic objects tend to be asymmetrical, or stronger on one side,” said Kaizu. The magnetic field can prevent the mixing of materials. So if the magnetic field is stronger on one side, that side will have less mixing and therefore more hydrogen. ”
Another possibility is that the magnetic field shifts the pressure and density of these atmospheric gases on Janus.
“Magnetic fields can lead to lower gas pressure in the atmosphere, and this may allow hydrogen oceans to form where the magnetic field is strongest,” study co-author James Fuller, professor of theoretical astrophysics at Caltech, said in a statement. “We don’t know which theory is correct, but we can think of no other way to explain the asymmetrical aspect without a magnetic field.”
The team will continue to search for more white dwarfs like Janus using the Zwicky Transient Facility because the instrument is “so good at finding strange objects,” Kayazu said.
2023-07-24 23:59:48
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