A new kind of thermonuclear starburst

A team of astronomers with the help of the European Southern Observatory very large telescope (ESOVLT) a new type of stellar explosion – a micronova. These explosions occur on the surface of some stars, and each can burn up through about 3.5 billion Great Pyramids of Giza from stellar material in just a few hours.

“We have detected and identified for the first time what we call a micronova,” explains Simon Scaringi, an astronomer at Durham University in the UK who led the study on these eruptions published today in Nature. “This phenomenon challenges our understanding of how thermonuclear explosions occur in stars. We thought we knew, but this discovery suggests an entirely new way to achieve them,” he adds.

Astronomers have discovered a new type of explosion occurring in white dwarf The stars are in two star systems. This video summarizes the discovery.

Micronovae are very powerful events, but small on astronomical scales; They are much less energetic than starbursts known as novas, which astronomers have known for centuries. Both types of explosions occur on white dwarfs, dead stars whose masses are the same as our sun, but as small as Earth.

A white dwarf in a two star system can steal matter, mostly hydrogen, from its companion star if they are close enough to each other. When this gas falls on the super-hot surface of the white dwarf star, it causes hydrogen atoms to fuse into helium explosively. In supernovae, these thermonuclear explosions occur over the entire stellar surface. “Such explosions cause the entire surface of the white dwarf to burn and shine brightly for several weeks,” explains co-author Nathalie Degenar, an astronomer at the University of Amsterdam in the Netherlands.

This artist’s impression shows a two star system where micronovas can occur. The blue disk orbiting the bright white dwarf in the center of the image is made of material, mostly hydrogen, that has been stolen from its companion star. Toward the center of the disk, the white dwarf uses its strong magnetic fields to direct hydrogen toward its poles. When matter falls on the star’s hot surface, it causes a micronova explosion, contained by magnetic fields at one of the white dwarf’s poles. Credit: ESO/M. Kornmeiser, El Calcada

Micronovae are similar explosions that are smaller and faster, lasting only several hours. They occur in some white dwarfs with strong magnetic fields, which direct material toward the star’s magnetic poles. For the first time, we have now seen that hydrogen fusion can also occur in a local manner. Hydrogen fuel can be contained at the base of the magnetic poles of some white dwarfs, so fusion occurs only at these magnetic poles,” says Paul Grote, an astronomer at Radboud University in the Netherlands and co-author of the study.

“This leads to the explosion of micronova fusion bombs, which have about a millionth the force of a nova explosion, hence the name micronova,” continues Groot. Although “partial” might suggest that these events are small, don’t be mistaken: just one of these eruptions could burn through about 20,000,000 trillion kilograms, or about 3.5 billion of the Great Pyramids of Giza.^[1]

This artist’s impression shows a two star system, with a white dwarf (in the foreground) and a companion star (in the background), where micronovas can occur. The white dwarf steals the material from its companion, which is directed towards its poles. When matter falls on the hot surface of the white dwarf, it causes a micronova explosion, located at one of the star’s poles. Credit: Mark Garlick

This new microstructure is challenging astronomers’ understanding of starbursts and they may be more abundant than previously thought. “It just shows how dynamic the universe is. These events may actually be very common, but because they are so fast it’s hard to catch them in action,” explains Scaringi.

The team first encountered these mysterious micro-eruptions when analyzing data from NASATransiting Exoplanet Survey Satellite (he-goat). “Looking at astronomical data collected by NASA’s TESS, we discovered something unusual: a bright flash of optical light that lasts for a few hours. For further research, we found several similar signals,” says Degenar.

This video shows an animation of a Micronova explosion. The blue disk orbiting the bright white dwarf in the center of the image is made of material, mostly hydrogen, that has been stolen from its companion star. Toward the center of the disk, the white dwarf uses its strong magnetic fields to direct hydrogen toward its poles. When matter falls on the star’s hot surface, it causes a micronova explosion, contained by magnetic fields at one of the white dwarf’s poles. Credit: ESO/L. Calsada, M. Cornmeiser

The team observed three micronovae using TESS: two are known white dwarfs, but the third required further observations using the X-shooter instrument on ESO’s VLT to confirm the white dwarf’s state.

“With the help of ESO’s Very Large Telescope, we found that all of these flashes of light were produced by white dwarfs,” says Degenar. “This observation was crucial in interpreting our result and the discovery of Micronova,” Scaringi adds.

This artist’s animation shows a two star system where one component is an ordinary star and the other is a white dwarf appearing surrounded by a disk of gas and dust. A white dwarf in a two star system can steal matter, mostly hydrogen, from its companion star if they are close enough to each other. Credit: ESO/M. Kornmeiser

The discovery of macronovas adds to the repertoire of known starbursts. The team now wants to capture more of these elusive events, which will require large-scale surveys and rapid follow-up measurements. Scaringi concludes that “the rapid response from telescopes such as the VLT or ESO’s New Technology Telescope and the range of instruments available will allow us to reveal in more detail what these enigmatic microparticles are.”

Reference: “Local thermonuclear explosions from accumulating magnetic white dwarfs” by S. Scaringi, P. J. Groot, C. Knigge, A. J. Bird, E. Breedt, D. H. Buckley, Y. Cavecchi, N. D. Degenaar, D. de Martino, C. Done M. Frata, K. Ikevich, E. Cording, J.B. Lasota, C. Littlefield, C. F. Manara, M. O’Brien, P. Szkody and FX Timmes, 20 April 2022, Available here. temper nature.
DOI: 10.1038 / s41586-022-04495-6

Notes

1. We use trillion to mean one million million (1,000,000,000,000 or 10¹²) and billion means one thousand million (1,000,000,000 or 10⁹). The Great Pyramid of Giza in Cairo, Egypt (also known as the Pyramid of Khufu or the Pyramid of Khufu) weighs about 5,900,000,000 kg.

more information

This research was presented in a paper titled “Local thermonuclear explosions of accumulating magnetic white dwarfs” to appear in temper nature. A follow-up letter titled “Triggering micronovae by magnetically confined accretion fluxes in accreting white dwarfs” has been accepted for publication in Monthly Notices of the Royal Astronomical Society.

team on temper nature The research is made by S. Scaringi (Center for Extragalactic Astronomy, Department of Physics, Durham University, UK [CEA]), P. J. Groot (Department of Astrophysics, Radboud University, N? Megen, The Netherlands [IMAPP] and the South African Astronomical Observatory, Cape Town, South Africa [SAAO] and Department of Astronomy, University of Cape Town, South Africa [Cape Town]), C. Knigge (School of Physics and Astronomy, University of Southampton, Southampton, UK [Southampton]), A.J. Bird (Southampton), E. Breedt (Institute of Astronomy, University of Cambridge, UK), DAH Buckley (SAAO, Cape Town, Department of Physics, University of the Free State, Bloemfontein, South Africa), Y. Cavecchi (Instituto de Astronomía, Universidad Nacional Autónoma de México, Ciudad de México, México), ND Degenaar (Anton Pannekoek Institute of Astronomy, University of Amsterdam, Amsterdam, Netherlands), D. de Martino (INAF-Osservatorio Astronomico di Capodimonte, Naples, Italy), C. Done (CEA), M. Fratta (CEA), K. Ilkiewicz (CEA), E. Koerding (IMAPP), J.-P. Lasota (Nicolas Copernicus Astronomical Centre, Polish Academy of Sciences, Warsaw, Poland, and Institute of Astrophysics in Paris, CNRS and Sorbonne Universities, Paris, France), C. Littlefield (Department of Physics, University of Notre Dame, USA and Department of Astronomy, University of WashingtonSeattle, USA [UW]), CF Manara (European Southern Observatory, Garching, Germany [ESO]), M. O’Brien (CEA), P. Szkody (UW), FX Timmes (School of Earth and Space Exploration, Arizona State University, Arizona, USA, Joint Institute for Nuclear Astrophysics – Center for Element Evolution, USA) .