Micronova – Still going strong
Researchers discover a new type of starburst
04/22/2022, 10:25 AM
So far, astronomers have known of nova explosions. A team of researchers has now mistakenly detected a micronova for the first time: thermonuclear explosions at the poles of white dwarf stars. According to them, microwaves occur on white dwarfs with strong magnetic fields.
Don’t let the name fool you: a “micronova” is what astronomers call a new type of starburst that an international team of researchers accidentally discovered while searching for planets from distant stars. In fact, macronovas only emit about one-thousandth the energy of ordinary supernovae – but by Earth standards, they are still gigantic explosions: the amount of hydrogen burned is about 40,000 times the mass of Mount Everest. These flashes of radiation are caused by thermonuclear explosions at the poles of white dwarf stars, Write for researchers in the journal Nature..
“These events challenge our understanding of how stars experience thermonuclear explosions,” said Simon Scaringi of Durham University in the United Kingdom. “We previously thought we knew, but this discovery reveals an entirely new mechanism.” Astronomers have known about nova explosions for centuries: some stars shine unusually frequently for several weeks.
Hydrogen theft from partner star
These are white dwarfs – the last stages of the evolution of stars similar to our Sun, which have used up nuclear energy supplies and have shrunk to almost the size of the Earth. If such a compact white dwarf forms a double system with an ordinary star, it can snatch matter—particularly hydrogen—from the partner star through its gravity.
If enough hydrogen accumulates on the surface of the white dwarf, a thermonuclear reaction occurs, the fusion of hydrogen into helium, which explosively spreads over the entire surface of the dwarf star: the star shines as brightly as a nova.
But in data from the US space telescope TESS, which specializes in searching for planets close to other stars, researchers have encountered starbursts that cannot be explained using this model. Similar to a supernova, the brightness of the star here also increases, but not to the same extent and only for several hours. Scaringi and colleagues were able to identify a total of three such events in the TESS data.
It was already known that two of the affected stars were white dwarfs. Observations using the European Southern Observatory’s Very Large Telescope in Chile showed that the third object is also a white dwarf. So astronomers assumed that this was a phenomenon similar to that of brighter nova explosions. As the researchers’ observations show, microspheres occur on white dwarfs with strong magnetic fields. “This observation was crucial to the interpretation and discovery of micronova,” Scaringi says.
It is clear that these magnetic fields preferentially direct the shredded matter from the partner star to the magnetic poles of the white dwarf. “Hydrogen can be trapped at the base of magnetic poles,” explains co-author Paul Grote of Radboud University in the Netherlands. As a result, nuclear fusion occurs only at these electrodes. We have seen for the first time that hydrogen fusion can also occur locally.
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