Nova speeds up to theoretical limit

The white dwarf RS-Ophiuchi turns out to be one of the most efficient particle accelerators in the universe. A nova accelerated protons and heavy atomic nuclei from the remnants of the star to their highest theoretically possible energies, determined, as a team led by Alison Mitchell from the University of Erlangen-Nuremberg. The high-energy radiation emitted by the nova, together with computer models, showed that the particles accelerated by the explosion had several hundred times more energy than previously observed novae, Reports the team in »Science«, The result sheds light on why some novae emit gamma rays and suggests that such periodic novae are an important source of high-energy cosmic rays.

RS-Ophiuchi is part of a binary star system whose components orbit each other at a distance between Earth and the Sun. The very compact white dwarf constantly draws matter from its companion by accumulating on its surface. If this mass exceeds a critical threshold, nuclear fusion ignites and causes a thermonuclear explosion on the surface of the white dwarf. A total of nine such eruptions have taken place since 1898. The last such nova was observed in August 2021 by the Namibian High Energy Stereoscopic System (HESS) Gamma-ray Telescope and the Fermi satellite.

In the case of novae, high-energy gamma rays are also produced by a mechanism that has so far only been partially elucidated. According to the HESS Nova program, which is directed by Michelle, Over the course of a month the working group at NOVA observed Manifesting changes in light curves. The intensity of radiation decreases with time, while the spectrum widens at the same time. Experts interpret this as an indication of the mechanism of the radiation’s origin as recorded by the two telescopes: according to this, the shock wave from the explosion accelerates the particles into enormous energy. The strength of the explosion starts increasing even in the first two days, Because the intensity of the highest-energy gamma rays continues to increase during this periodbefore it starts to fall.