21 November 2019

Extremely energetic particles coupled with the violent death of a star for the first time

The death of a star:

Researchers at the Niels Bohr Institute, University of Copenhagen and DTU Space in Lyngby have determined the emission of extremely energetic light particles during the death of a very heavy star for the first time. The discovery was made in collaboration with a large, international team of scientists. The light particles were measured with the telescope MAGIC, situated on the Canary Islands.

How the observations of a GRB in the time after the initial explosion
The gamma ray burst after 37.5 minutes, after 4.3 hours and after 9.02 days.

The researchers at the Niels Bohr Institute subsequently measured the particles with the neighboring Nordic Optical Telescope. The scientific perspective – the source detection of the emission of particles – is to gain basic insights into the extreme physical processes in the death of the heaviest stars. The study is now published in the journal Nature.

Gamma Ray Burst – what is that?

When a heavy star dies or collapses, it happens in the form of a supernova – a gigantic explosion. In about a ten thousandth of the supernovae it is even more violent.

“Presumably a black hole or an extremely magnetic neutron star is formed”, Johan Fynbo from the Cosmic DAWN Center at the Niels Bohr Institute explains. The matter is compressed to form an enormously compact object, spinning extremely fast. The magnetic field along the rotational axis can become intense and emit energetic particles in the direction of the axis in what the researchers names as a “jet”.

If it points in our direction, we see a gamma ray burst.

Extremely energetic particles in the gamma ray burst reach us on Earth.

The particles (electrons) emitted in the jet, strike light (photons) in their path and transfer the energy to the photons. The photons travel through the Universe, eventually to be detected and measured on Earth.

Johan Fynbo and his colleagues, Daniele Malesani, Jonatan Selsing, Kasper Heintz and Luca Izzo observed the gamma ray burst only 29 minutes after its arrival on Earth and succeeded in measuring the distance to it. The distance is crucial in order to identify the source, which you have to know to understand the processes emitting a gamma ray burst this energetic into space.

“It is extremely relativistic, which means that the jet emitted from the gamma ray burst travels with 99.999% of the speed of light, the fastest possible speed. And the basic understanding of the most extreme processes in space are at the center of the subsequent research. The discovery of a gamma ray burst also shows us that on this position in the Universe, the conditions for this extreme situation exist.

In other words, we can use the gamma ray burst to learn more about these conditions as well”, Daniele Malesani explains.

The Sun is born – and an old star dies

The distance is important for a number of reasons: The intensity of any radiation, including the light from the gamma ray burst, fades with the distance it travels, so the energy-calculation of its source tells us it must have been a very energy packed event indeed.

When we know the distance, we can calculate the time of the explosion as well: It took place 4.5 billion years ago. When we look into space, we also look back in time.

The supernova happened almost simultaneously with the forming of our own sun. Since then, the light from the gamma ray burst has travelled through space and reached Earth on 14th of January 2019. The gamma ray burst is in the constellation “Fornax”.

International collaboration – and an important upgrade of The Nordic Optical Telescope

The scientific article is the result of a collaboration between many researchers from all over the world, and the important distance measurement and positioning of the gamma ray burst were made by the team at the Niels Bohr Institute.

This particular task it is expected to be solved with more ease at the Niels Bohr Institute in the future, thanks to a grant from the Carlsberg Foundation for a scientific instrument added to the Nordic Optical Telescope.

“Within 5 years, we should become much better at following up on this type of transients or violent, short lived, astrophysical events with The Nordic Optical Telescope. Several research projects are under way, and they should enable us to discover many more of the energetic light particles from dying stars and other extreme objects, in order to be able to study this type of physics in much better detail”, Johan Fynbo explains.