Supernovae – brilliant explosions of stars at the ends of their lives – have been observed and studied by humanity for hundreds of years. Yet we are still working out which types of stars end up exploding as the different types of supernovae we observe in the night sky.

The answer to this question will impact our understanding of how stars evolve, how they create and spread the elements that comprise the periodic table (and our bodies), and how we use them as tools for other experiments in astrophysics.

Type Ia supernovae, specifically, have famously been used as “standard candles” to measure distances to other galaxies. This use led to the discovery that the Universe’s expansion is accelerating under the influence of something new and mysterious we call “dark energy.” But the use of Type Ia supernovae as standard candles is based on the assumption that the supernovae we see in the nearby Universe are identical in nature to the ones we observe in faraway galaxies.

Until we figure out exactly which stars explode as Type Ia supernovae, and how those explosions take place, we will never be wholly certain that we are using them correctly.

At the University's Institute of Cosmology and Gravitation (ICG), Dr Or Graur and his research group conduct observations of supernovae using the world's leading observatories and surveys in order to reveal their workings.

Our research methods

We use several avenues of research to try and figure out what kinds of stars explode as different types of supernovae, with an emphasis on Type Ia supernovae. Each of these research projects provides a different angle on the physics of the progenitor stars and the way in which the explosions unfurl.

Supernova rates

We use both ground- and space-based surveys to discover supernovae and measure the rates at which different types of supernovae explode throughout cosmic history and in different types of galaxies.

Watch: The Secret Lives (and Deaths) of Stars
In the news: Super-Old Supernovas Spotted Across the Universe

Population studies

We use large supernova surveys to conduct population studies of supernovae, such as examining correlations between properties of the supernovae and those of the galaxies in which they explode.

Observations of old supernovae

We use the Hubble Space Telescope to observe Type Ia supernovae hundreds of days after they explode. These observations provide clues to the physics of the explosion mechanism and the state of the star before it exploded.

Watch: Science Bulletins: Shedding Light on Type Ia Supernovae
In the news: Scientists observe year-long plateaus in decline of Type Ia supernova light curves
In the news: Hubble portrait of a galaxy shows it shines in stellar birth and death
Podcast: Using the Hubble Space Telescope

Supernova archaeology

We use images taken by the Hubble Space Telescope before and after the explosions to search for predicted impacts of the supernovae on their environments.

New methods

We develop new ways to discover supernovae, such as picking out the signatures they leave on the spectra of their host galaxies.

Outputs

Late-time photometry of Type Ia Supernova SN 2012cg reveals the radioactive decay of 57Co

Or Graur, David Zurek, Michael M. Shara, Adam G. Riess, Ivo R. Seitenzahl, Armin Rest
A year-long plateau in the late-time near-infrared light curves of Type Ia supernovae

Graur, O., Maguire, K., Ryan, R., Nicholl, M., Avelino, A., Riess, A. G., Shingles, L., Seitenzahl, I. R. & Fisher, R., 1 Feb 2020, In: Nature Astronomy. 4, p. 188–195 8 p.
Supernova

Or Graur
Type-Ia supernova rates to redshift 2.4 from CLASH: the Cluster Lensing And Supernova survey with Hubble

Graur, O., Rodney, S. A., Maoz, D., Riess, A. G., Jha, S. W., Postman, M., Dahlen, T., Holoien, T. W. -S., McCully, C., Patel, B., Strolger, L. -G., Benitez, N., Coe, D., Jouvel, S., Medezinski, E., Molino, A., Nonino, M., Bradley, L., Koekemoer, A., Balestra, I. & 21 others, , 10 Feb 2014, In: The Astrophysical Journal. 783, 1, 19 p., 28.
Multiple images of a highly magnified supernova formed by an early-type cluster galaxy lens

Kelly, P. L., Rodney, S. A., Treu, T., Foley, R. J., Brammer, G., Schmidt, K. B., Zitrin, A., Sonnenfeld, A., Strolger, L-G., Graur, O., Filippenko, A. V., Jha, S. W., Riess, A. G., Bradac, M., Weiner, B. J., Scolnic, D., Malkan, M. A., Linden, A. V. D., Trenti, M., Hjorth, J. & 11 others, , 6 Mar 2015, In: Science. 347, 6226, p. 1123–1126 4 p.

Resources

Supernova by Or Graur

Supernova: A concise illustrated introduction to the history and physics of supernovae by Dr Or Graur was published by MIT Press in February 2022.

Understanding the science of exploding stars: Listen to this podcast discussing Dr Graur's book.

Cover Image of Or Graur's "Supernova" book

Researchers

Dr Or Graur

Associate Professor in Astrophysics

Or.Graur@port.ac.uk

Faculty of Technology

PhD Supervisor

Astrophysics

We're working to better understand the basic building blocks of our Universe, the origin of stars, the formation and evolution of galaxies, and stellar population models. Explore our astrophysics research

Observational Cosmology

We're mapping the Universe on the largest scales to understand dark energy, studying the clustering of galaxies and dark matter, and observing transient events and supernovae.

Theoretical cosmology

We're exploring the inflation of the very early Universe, the impact of dark energy on its geometry and developing tests to monitor its expansion.

Interested in a PhD in Cosmology and Astrophysics?

Browse our postgraduate research degrees – including PhDs and MPhils – at our Cosmology and Astrophysics postgraduate research degrees page.

The Nature of Supernovae

Supernovae – the Explosions of Stars