22 min

Extreme astronomical phenomena

A supernova is a star that explodes. When material from the supernova is ejected into space, elements are dispersed, and can form new stars and planets. Josefin Larsson is an astronomer, and is studying how stars explode and how jets form. Her research may also improve our understanding of the early universe, and of physical processes in extreme environments.

Josefin Larsson

Associate Professor

Wallenberg Academy Fellow 2015

KTH Royal Institute of Technology

Research field:
Studying jets and stellar explosions with the help of data from deep space observations

Numerous supernovae are discovered every year. Traditionally, they are named after the year and the first available letter in the alphabet.

“One object I am studying is Supernova 1987A, which was discovered almost thirty years ago. It is located in a small neighboring galaxy called the Small Magellanic Cloud, which is a mere 160,000 light years away. That’s really close,” Larsson enthuses with a smile.

On her computer screen she displays a series of images taken by the Hubble Space Telescope, and a film clip in which the supernova rotates in 3D. It can be clearly seen how it is evolving year by year, with a growing, asymmetrical nucleus. She is using the pictures to survey the radiation and understand the initial phase of the explosion.

“1987A is unique because it’s so close to our own galaxy, which enables us to obtain a spatially resolved image of this kind. It’s the closest supernova I’m studying.”

Active galaxies

Larsson grew up in Malmö, and studied physics and astronomy at Lund University. Those were her favorite subjects, so she found it an easy choice to make. After completing her master’s in physics she was admitted to the PhD program at University of Cambridge in the U.K., where she worked on observations of active galactic nuclei.

“We believe that all galaxies have a supermassive black hole at the center. “Supermassive” means a mass between one million and one billion times that of the sun. In galaxies termed “active”, matter is drawn into the black holes, creating enormous amounts of radiation. During my time as a PhD student I mainly studied X-ray radiation.”

Back in Sweden again after three years at Cambridge she was admitted as a postdoc at the Oskar Klein Centre for Cosmoparticle Physics (OKC), which is run jointly by KTH Royal Institute of Technology and Stockholm University. She has worked at the Department of Particle and Astrophysics at KTH since 2012. In the same corridor, two doors down, is the office of Christer Fuglesang, Sweden’s first and, so far, only astronaut.

“We also have people here developing instruments. I’m not involved in this myself, but it’s interesting to have this work close by.”

As an assistant professor, Larsson teaches KTH students astrophysics. In her spare time, she enjoys teaching a different, more down-to-earth, skill.

“I’m a figure skating coach. It’s great fun. Right now I don’t have a class of my own – I teach on a stand-in basis”.

Explosions and jets

With the support of the Knut and Alice Wallenberg Foundation, Larsson is attempting to understand how stellar explosions and jets occur. To do this, she is studying space phenomena of various kinds, such as supernovae, active galaxies and gamma ray bursts, as she explains:

“Jets are narrow streams of plasma traveling almost at the speed of light. They occur on vastly different time and length scales. They are found in active galaxies, as well as certain kinds of supernovae, where they are termed gamma ray bursts. They are also formed in other systems that I am not studying.”

Jets may help to explain how stars explode. Jets are also excellent laboratories for studying basic physics and processes that cannot be recreated here on Earth.

“We are studying truly extreme environments, with speeds close to the speed of light, extraordinary amounts of energy, and strong gravitational fields.”

Both supernovae and jets impact their surroundings, and play a major role in the evolution of galaxies. Jets in active galaxies are enormous; they can flow through the entire galaxy and exist for millions of years. Jets in gamma ray bursts are much smaller, and are sometimes only visible for a few seconds.

“Gamma-ray bursts can be recorded over huge distances. This means that these events may indirectly teach us more about the state of the early universe.”

“This funding enables me to adopt a more long-term perspective. Quite simply, I can plan projects that are a little larger and last a little longer. It is also highly beneficial to be able to use the Fellows network to meet and exchange experience with other researchers at the same point in their careers.”

Developing new models

Larsson is using data from space- and ground-based telescopes. There are optical images of Supernova 1987A, but not of gamma ray bursts and supernovae that are further away. In these cases, it is necessary to interpret data and model time series for the radiation in some other way.

“The type of data I need depends on the object and type of wavelength I am studying. The biggest thrill for me is when I get to study completely new observational data and see something for the first time.”

In recent years researchers have begun to better understand how high-energy gamma radiation occurs in jets. As a result, tests can now begin on various models to obtain data on physical properties, including the speed of the jets.

“I want to continue working on these models, but I also want to see how these properties relate to the explosion in the supernova,” says Larsson.

Text Susanne Rosén
Translation Maxwell Arding
Photo Magnus Bergström