Astronomers have detected a previously unknown type of stellar explosion called a micronova involving thermonuclear explosions in the polar regions of a type of scorched star called a white dwarf after siphoning material from a companion star.
Researchers said Wednesday that a micronova is by far the least powerful type of star explosion currently known – less energetic than an explosion called a nova, in which the entire surface of a white dwarf explodes, and tiny by compared to a supernova that occurs upon death. pangs of some giant stars.
How are micronovae?
Micronovae are observed from Earth as bursts of light lasting about 10 hours. They have been documented on three white dwarfs – one 1,680 light-years from Earth, one 3,720 light-years away, and one 4,900 light-years away. A light year is the distance traveled by light in one year, or 9.5 trillion kilometres.
“The discovery was an unexpected surprise. It shows how dynamic the universe is. These events are fast and sporadic. Finding them requires looking in the right place at the right time,” said astronomer Simone Scaringi of the University of Durham in England, lead author of the study published in the journal Nature.
What is a white dwarf?
White dwarfs, among the densest objects in the universe, result from the collapse of the core of a dying star. They have the mass of our sun but are about the size of the Earth in diameter. Most stars, including the sun, are destined to end their lives in this form.
Some white dwarfs are part of what is called a binary system, orbiting another star.
Where do micronovae occur?
Micronovae occur in very specific binary systems – with a white dwarf star possessing a strong magnetic field and a low mass normal star. The gravitational pull of the white dwarf can pull hydrogen gas from the surface of the companion star. The hydrogen then flows to the magnetic poles of the white dwarf, much like the Earth’s magnetic field channels the solar wind to our planet’s magnetic poles, causing the auroras.
At the base of the columns of gas which accumulate at the poles of the white dwarf, the pressure and the temperature increase, causing a thermonuclear fusion which transforms the hydrogen into helium.
“Under the conditions in which this is triggered, this merger is explosive and the micronova occurs: a thermonuclear ‘bomb’ goes off,” said astronomer and study co-author Paul Groot, who splits his time between Radboud University in the Netherlands and the University of Cape Town and the South African Astronomical Observatory.
1/ Thanks to our Very Large Telescope, astronomers have discovered a new phenomenon: micronovae, stellar explosions lasting only a few hours.
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Why micronovae can happen again and again on the same star
The explosion is localized and does not destroy the white dwarf. In fact, the micronova cycle can repeat itself.
“Only a very small percentage of the white dwarf is participating in this explosion, about one millionth of the surface. Translated to Earth, that would be an area of about, say, the city of London,” Groot said.
Each micronova event burns through matter the equivalent of a large asteroid, or just over a millionth the mass of Earth, Scaringi said.
How a micronova is different from a nova
A micronova is similar to a nova, a thermonuclear explosion engulfing the entire surface of a white dwarf. With novae, the white dwarf does not have a strong magnetic field, which means the hydrogen stolen from the companion star is distributed globally rather than concentrated at the poles. Novae can last for weeks or months, burning up about a million times more mass than micronovae, Scaringi said.
The researchers discovered the micronovae while analyzing data from NASA’s TESS space telescope. They used the Chile-based European Southern Observatory’s Very Large Telescope to confirm that the outbursts involved white dwarfs.
Some other types of stellar explosions include: a kilonova, when two neutron stars or a neutron star and a black hole merge; a hypernova, a kind of supernova involving a massive star exploding at the end of its life cycle and collapsing to form a black hole; and a bright red nova involving the merger of two stars.