A unusual star that explodes repeatedly appears to be producing the Universe's most intense form of light.

The shock wave stretching out into space functions as a particle accelerator, generating gamma radiation, according to an analysis of an outburst from the binary system RS Ophiuchi. This means that the conditions under which this radiation is produced do not have to be as harsh as previously thought.

As a result, it's possible that larger explosions, such as supernovae, are much more powerful particle accelerators, generating cosmic rays with strengths exceeding a quadrillion electronvolts.

Astrophysicist Ruslan Konno of the German Electron Synchrotron (DESY) and the HESS Collaboration noted, the discovery that the theoretical limit for particle acceleration can be reached in genuine cosmic shock waves has huge ramifications for astronomy.

It implies that the acceleration mechanism in their even more extreme relatives, supernovae, could be just as efficient.

The star in question is a type of binary star that is extremely rare. Its designation is RS Ophiuchi, and it's a recurring nova, one of just around 10 known in the Milky Way galaxy. It's located 4,566 light-years away. The object occasionally bursts in an explosion known as a nova, which occurs every 15 years or so, as you can imagine from the category name.

Stellar vampirism is what produces these eruptions (yep, you read that correctly).

A white dwarf is in close orbit with a red giant in this binary system. The smaller, denser white dwarf syphons material – chiefly hydrogen – from the red giant as the two spin around one other.

In this binary system, a white dwarf is in tight orbit with a red giant. As the two spin around one other, the smaller, denser white dwarf syphons material – primarily hydrogen – from the red giant.

The most recent nova was discovered in August of last year, and it was so bright that RS Ophiuchi was visible with the human eye for a short time.

"The stars in the system are about the same distance apart as Earth and the Sun," said Alison Mitchell, chief investigator of the HESS Nova programme and astronomer at Friedrich-Alexander University Erlangen-Nürnberg in Germany.

"When the nova occurred in August 2021, we were able to see a galactic explosion in very-high-energy gamma rays for the first time thanks to the HESS telescopes."

The HESS array, which is made up of five telescopes in Namibia and was recently modified with a new, very sensitive camera, detects Cherenkov radiation when a high-energy gamma ray contacts Earth's atmosphere, causing a shower of supercharged particles. Due to the fact that light travels slower in air than it does in a vacuum, these particles briefly travel faster than light, resulting in a blue flash.

Scientists can use this radiation to figure out how much energy the gamma ray that caused it had. The gamma rays emitted by RS Ophiuchi surpassed 100 giga electronvolts, or 100 billion electronvolts.

While these aren't the most powerful gamma rays ever discovered, they do disclose the mechanism that produces them in a nova.

The researchers reconstructed the event that produced the gamma rays by watching the nova unfold in real time. According to their calculations, the shockwave from the white dwarf's nova slams against the wind of the red giant, propelling protons to extremely high energies where they can collide and produce gamma ray photons.

"This is the first time we've ever been able to conduct observations like this, and it will allow us to obtain even more precise future insights into how cosmic explosions function," says Rikkyo University's theoretical astrophysicist Dmitry Khangulyan.

We might find, for example, that novae contribute to the ever-present sea of cosmic rays and hence have a significant impact on the dynamics of their local environment.

The next-generation Cherenkov Telescope Array, which is ten times more sensitive than current ground-based Cherenkov telescopes, should aid scientists in determining the frequency of this process in novas.

The Research is Published in Science.