2023-06-25 17:19:59
An illustration shows the evolution of a white dwarf pulsar (Image credit: Dr Mark Garlick//University of Warwick)
This week astronomers have discovered what is only the second example of a white dwarf pulsar, following the one discovered in 2016.
White dwarfs are small, dense stars, typically the size of a planet, that form when a low-mass star has burned up all its fuel, losing its outer layers. Sometimes called “stellar fossils”, they offer information regarding different aspects of stellar formation and evolution.
Astronomers from the University of Warwick in the United Kingdom have published this discovery in the journal Nature Astronomy, and confirm that this rare stellar remnant is spinning rapidly, and in doing so, spews powerful beams of electrical particles and radiation at a red dwarf companion star, causing the entire system to fade and brighten dramatically during regular periods.
A high-speed propeller star is the fastest-spinning confirmed white dwarf (UNIVERSITY OF WARWICK/MARK GARLICK)
This pulsar activity is thought to be driven by strong magnetic fields, but scientists aren’t sure what causes them. One explanation is a model that suggests that white dwarfs have dynamos at their cores like Earth’s, which generates its magnetosphere, albeit in a much more powerful version. Studying the system might confirm this mechanism and might also give scientists new insights into stellar evolution.
“The origin of magnetic fields is a big open question in many fields of astronomy, and this is particularly true for white dwarf stars,” said Ingrid Pelisoli, a researcher at the University of Warwick’s Department of Physics. “The magnetic fields on white dwarfs can be more than a million times stronger than the sun’s magnetic field, and the dynamo model helps explain why. The discovery of J1912-4410 was a fundamental step in this field,” she stated.
White dwarfs form when stars with masses similar to that of the Sun and up to seven times greater run out of nuclear fuel, and their cores can no longer hold up once morest gravitational collapse. As stellar cores collapse, these stars shed their outer shell of material that swells up to 100 times the width of the parent star. This is known as the red giant phase. The core cools over millions of years as this outer material spreads out and disperses, leaving behind a stellar remnant called a white dwarf.
Artistic recreation of the pulsar by expert astronomers
Our sun will undergo this process in regarding 4.5 billion years, expanding around the orbit of Mars, consuming the inner planets, including Earth. Our star will then end its life as a smoky white dwarf in a dying solar system.
Some white dwarfs are found in systems that remain dynamic even following the stellar death throes that created them, especially when they have a companion star. An example of this is the recently detected white dwarf pulsar, J191213.72–441045.1 (J1912–4410), the second such system to be found following the discovery of AR Scorpii (AR Sco) in 2016.
Located regarding 773 light-years from our solar system, this white dwarf pulsar is regarding the mass of the Sun across a width regarding that of Earth. It is spinning around 300 times faster than our planet. Just a teaspoon of material from this white dwarf would weigh 15 tons, regarding four times as much as a hippopotamus. White dwarfs lose heat as they age, and the relatively cool temperature of this J1912-4410 indicates that it is of advanced age.
08-18-2010 One in four white dwarfs will end their life crossed by a strong magnetic field. (ESO/L. CALCADA)
“The origin of magnetic fields is a big open question in many fields of astronomy, and this is particularly true for white dwarf stars. Fields on white dwarfs can be more than a million times stronger than the Sun’s magnetic field, and the dynamo model helps explain why. The discovery of J1912-4410 was a fundamental step in this field,” said Pelisoli.
He added: “We used data from a few different surveys to find candidates, focusing on systems that had similar characteristics to AR Sco. We tracked the candidates with Ultracam, which detects the very fast light variations expected of white dwarf pulsars. After looking at a couple dozen candidates, we found one that showed very similar light variations to AR Sco. Our follow-up campaign with other telescopes revealed that every five minutes or so, this system was sending a radio signal and X-rays in our direction.”
“This confirmed that there are more pulsar white dwarfs out there, as previous models predicted. The dynamo model made other predictions, which were confirmed by the discovery of J1912-4410″, she contended.
Our solar system will also collapse next to the Sun
And he concluded: “Due to their old age, white dwarfs in the pulsar system should be cool. Its companions should be close enough that the white dwarf’s gravitational pull in the past was strong enough to capture the mass of the companion, and this causes them to spin rapidly.”
All of those predictions were confirmed by J1912-4410, with the white dwarf having a temperature below 13,000 degrees Celsius, which is much cooler than the average white dwarf temperature of around 100,000 degrees Celsius.
The team also found that J1912–4410 spins on its axis once every five minutes, and the white dwarf’s gravitational pull has a strong effect on the companion star, also in line with what scientists expected to see. “This research is an excellent demonstration that science works: we can make predictions and test them, and that is how any science progresses,” Pelisoli concluded.
Keep reading:
Why one extra planet in the Solar System might end life on Earth NASA’s Curiosity rover found clues to Mars’ aquatic past The Perseverance robot finished collecting samples on Mars that another spacecraft will bring to Earth
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