Cosmic rays help supernovae explosions pack a bigger punch

Image of a supernova remnant, with different areas of gas and dust highlighted in different colours
Composite X-ray and optical image of the remnant of Kepler's supernova. The red, green and blue colours show low, intermediate and high energy X-rays observed with NASA's Chandra X-ray Observatory, and the star field is from the Digitized Sky Survey.
NASA / CXC / NCSU / JPL-Caltech / M. Burkey et al.

The final stage of cataclysmic explosions of dying massive stars, called supernovae, could pack an up to six times bigger punch on the surrounding interstellar gas with the help of cosmic rays, according to a new study led by researchers at the University of Oxford.  The work will be presented by PhD student Francisco Rodríguez Montero today (19 July) at the virtual National Astronomy Meeting (NAM 2021).

When supernovae explode, they emit light and billions of particles into space. While the light can freely reach us, particles become trapped in spiral loops by magnetic shockwaves generated during the explosions. Crossing back and forth through shock fronts, these particles are accelerated almost to the speed of light and, on escaping the supernovae, are thought to be the source of the mysterious form of radiation known as cosmic rays.

Due to their immense speed, cosmic rays experience strong relativistic effects, effectively losing less energy than regular matter and allowing them to travel great distances through a galaxy.  Along the way, they affect the energy and structure of interstellar gas in their path and may play a crucial role in shutting down the formation of new stars in dense pockets of gas. However, to date, the influence of cosmic rays in galaxy evolution has not been well understood.

In the first high-resolution numerical study of its kind, the team ran simulations of the evolution of the shockwaves emanating from supernovae explosions over several million years. They found that cosmic rays can play a critical role in the final stages of a supernova’s evolution and its ability to inject energy into the galactic gas that surrounds it. 

Rodríguez Montero explains: “Initially, the addition of cosmic rays does not appear to change how the explosion evolves. Nevertheless, when the supernova reaches the stage in which it cannot gain more momentum from the conversion of the supernova’s thermal energy to kinetic energy, we found that cosmic rays can give an extra push to the gas, allowing for the final momentum imparted to be up to 4-6 times higher than previously predicted.”  

The results suggest that gas outflows driven from the interstellar medium into the surrounding tenuous gas, or circumgalactic medium, will be dramatically more massive than previously estimated.

Contrary to state-of-the-art theoretical arguments, the simulations also suggest that the extra push provided by cosmic rays is more significant when massive stars explode in low-density environments. This could facilitate the creation of super-bubbles powered by successive generations of supernovae, sweeping gas from the interstellar medium and venting it out of galactic disks. 

Rodríguez Montero adds: “Our results are a first look at the extraordinary new insights that cosmic rays will provide to our understanding of the complex nature of galaxy formation.


Media contacts

Anita Heward
Royal Astronomical Society
Mob: +44 (0)7756 034 243

Dr Morgan Hollis
Royal Astronomical Society
Mob: +44 (0)7802 877 700

Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)7802 877 699

Vittoria D'Alessio
PR and Media Manager
University of Bath
Tel: +44 (0)1225 383 135


Science contacts

Francisco Rodríguez Montero
University of Oxford


Images and captions

A blue star showing white/green hot and cold patches of gas on the surface, and blue cosmic rays around the edge
False colour image of a supernova simulation showing hot and cold patches of gas (white/green) in the bubble and the filamentary structure of cosmic rays (blue) around the shell of the supernova remnant.

F. Rodríguez Montero


Image of a supernova remnant, with different areas of gas and dust highlighted in different colours
Composite X-ray and optical image of the remnant of Kepler's supernova. The red, green and blue colours show low, intermediate and high energy X-rays observed with NASA's Chandra X-ray Observatory, and the star field is from the Digitized Sky Survey.
NASA / CXC / NCSU / JPL-Caltech / M. Burkey et al.


Notes for editors

About the National Astronomy Meeting

The Royal Astronomical Society National Astronomy Meeting (NAM 2021) will take place online from 19 - 23 July 2021. Bringing together around 800 astronomers and space scientists, the conference is the largest annual professional astronomy and space science event in the UK, and sees leading researchers from around the world presenting their latest work.

NAM 2021 incorporates the annual meetings of the Magnetosphere Ionosphere Solar-Terrestrial (MIST) and UK Solar Physics (UKSP) groups. The conference is principally sponsored by the Royal Astronomical Society (RAS), the Science and Technology Facilities Council (STFC) and the University of Bath.

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The University of Bath is one of the UK's leading universities both in terms of research and our reputation for excellence in teaching, learning and graduate prospects.

The University is rated Gold in the Teaching Excellence Framework (TEF), the Government’s assessment of teaching quality in universities, meaning its teaching is of the highest quality in the UK. 

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Submitted by Morgan Hollis on Mon, 19/07/2021 - 15:25