White dwarf pulsars include a rapidly spinning, burnt-out stellar remnant called a white dwarf, which lashes a companion red dwarf with powerful beams of electrical particles and radiation, causing the entire system to brighten and fade dramatically over regular intervals. This is owing to strong magnetic fields, but astronomers are unsure what causes them. A key theory which explains the strong magnetic fields is the dynamo model — that white dwarfs have dynamos in their core, as does the Earth, but much more powerful. But for this theory to be tested, astronomers needed to search for other white dwarf pulsars to see if their predictions held true.
“White dwarf stars are the most common stellar fossils,” said University of Warwick astronomer Ingrid Pelisoli and her colleagues.
“When in binaries, they make up the dominant form of compact object binary within the Milky Way Galaxy and can offer insight into different aspects of binary formation and evolution.”
“One of the most remarkable white dwarf binary systems identified to date is AR Scorpii.”
“AR Scorpii is composed of a red dwarf and a rapidly spinning white dwarf in a 3.56 h orbit.”
“It shows pulsed emission with a period of 1.97 min over a broad range of wavelengths, which led to it being known as a white dwarf pulsar.”
“Both the pulse mechanism and the evolutionary origin of AR Scorpii provide challenges to theoretical models.”
The newly-discovered white dwarf pulsar, J191213.72-441045.1 (J1912-4410 for short), is a sibling of AR Scorpii.
It resides 773 light-years away from Earth, has a size similar to the Earth, but a mass at least as large as the Sun.
It harbors a white dwarf in a 4.03 h orbit with a red dwarf and exhibits pulsed emission with a period of 5.30 min.
White dwarfs begin their lives at extremely hot temperatures before cooling down over billions of years, and the low temperature of J1912-4410 points to an advanced age.
“The origin of magnetic fields…
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