A New Kind of Thermonuclear Stellar Explosion

Micronovae are similar explosions that are smaller in scale and faster, lasting just several hours. They occur on some white dwarfs with strong magnetic fields, which funnel material towards the star’s magnetic poles. “For the first time, we have now seen that hydrogen fusion can also happen in a localized way. The hydrogen fuel can be contained at the base of the magnetic poles of some white dwarfs, so that fusion only happens at these magnetic poles, ”says Paul Groot, an astronomer at Radboud University in the Netherlands and co-author of the study.

“This leads to micro-fusion bombs going off, which have about one millionth of the strength of a nova explosion, hence the name micronova,” Groot continues. Although ‘micro’ may imply these events are small, do not be mistaken: just one of these outbursts can burn through about 20,000,000 trillion kg, or about 3.5 billion Great Pyramids of Giza, of material.^[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 micronovae may occur. The white dwarf steals materials from its companion, which is funneled towards its poles. As the material falls on the hot surface of the white dwarf, it triggers a micronova explosion, contained at one of the star’s poles. Credit: Mark Garlick

These new micronovae challenge astronomers’ understanding of stellar explosions and may be more abundant than previously thought. “It just goes to show how dynamic the Universe is. These events may actually be quite common, but because they are so fast they are difficult to catch in action, ”Scaringi explains.

The team first came across these mysterious micro-explosions when analyzing data from
This video shows an animation of a micronova explosion. The blue disc swirling around the bright white dwarf in the center of the image is made up of material, mostly hydrogen, stolen from its companion star. Towards the center of the disc, the white dwarf uses its strong magnetic fields to funnel the hydrogen towards its poles. As the material falls on the hot surface of the star, it triggers a micronova explosion, contained by the magnetic fields at one of the white dwarf’s poles. Credit: ESO / L. Calçada, M. Kornmesser

The team observed three micronovae with TESS: two were from known white dwarfs, but the third required further observations with the X-shooter instrument on ESO’s VLT to confirm its white dwarf status.

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

This artist’s animation shows a two-star system where one of the components is a normal star and the other is a white dwarf, which appears surrounded by a disc of gas and dust. A white dwarf in a two-star system can make steal material, mostly hydrogen, from its companion star if they are close enough together. Credit: ESO / M. Kornmesser

The discovery of micronovae adds to the repertoire of known stellar explosions. The team now wants to capture more of these elusive events, requiring large scale surveys and quick follow-up measurements. “Rapid response from telescopes such as the VLT or ESO’s New Technology Telescope and the suite of available instruments will allow us to unravel in more detail what these mysterious micronovae are,” concludes Scaringi.

Reference: “Localized thermonuclear bursts from accreting magnetic white dwarfs” by S. Scaringi, PJ Groot, C. Knigge, AJ Bird, E. Breedt, DAH Buckley, Y. Cavecchi, ND Degenaar, D. de Martino, C. Done, M. Fratta, K. Iłkiewicz, E. Koerding, J.-P. Lasota, C. Littlefield, CF Manara, M. O’Brien, P. Szkody and FX Timmes, 20 April 2022, Nature.
DOI: 10.1038 / s41586-022-04495-6

Notes

1. We use trillion to mean a million million (1,000,000,000,000 or 10)¹²) and billion to mean a thousand million (1,000,000,000 or 10)⁹). The weight of the Great Pyramid of Giza in Cairo, Egypt (also known as the Pyramid of Khufu or Pyramid of Cheops) is about 5,900,000,000 kg.

More information

This research was presented in a paper titled “Localized thermonuclear bursts from accreting magnetic white dwarfs” to appear in Nature. A follow-up letter, titled “Triggering micronovae through magnetically confined accretion flows in accreting white dwarfs” has been accepted for publication in Monthly Notices of the Royal Astronomical Society.

The team on the Nature paper is composed of S. Scaringi (Center for Extragalactic Astronomy, Department of Physics, Durham University, UK) [CEA]), PJ Groot (Department of Astrophysics, Radboud University, N? Megen, the Netherlands [IMAPP] and 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]), AJ 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, Moxico), ND Degenaar (Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, the Netherlands), D. de Martino (INAF-Osservatorio Astronomic , Italy), C. Done (CEA), M. Fratta (CEA), K. Ilkiewicz (CEA), E. Koerding (IMAPP), J.-P. Lasota (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw, Poland and Institut d’Astrophysique de Paris, CNRS et Sorbonne Universités, Paris, France), C. Littlefield (Department of Physics, University of Notre Dame, USA and Department of Astronomy, Related