Observations of a hot cocoon around exploding supernova

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Remotely-controlled telescope RBT/PST2 in Arizona, which was used by astronomers from the Poznań observatory to observe the explosion of a very massive star, and the resulting gamma-ray burst GRB171205A. The inset shows a picture taken by the telescope at which a gamma-ray burst (shown by the arrow) and its host galaxy (a more extended structure to the right) can be seen
Remotely-controlled telescope RBT/PST2 in Arizona, which was used by astronomers from the Poznań observatory to observe the explosion of a very massive star, and the resulting gamma-ray burst GRB171205A. The inset shows a picture taken by the telescope at which a gamma-ray burst (shown by the arrow) and its host galaxy (a more extended structure to the right) can be seen

Astronomers from Poznań, working in an international team, have observed a gamma-ray burst and an associated hot cocoon of gas. This allowed them for the first time to confirm the existence of such cocoons in supernova explosions. The observations were led by dr. hab. Michał Michałowski from the Astronomical Observatory Institute at the Adam Mickiewicz University in Poznań and executed using the Roman Baranowski Telescope. This is a robotic telescope owned by the university, located in Arizona (USA) and operated remotely via internet from Poznań. The results were published in Nature on 17 January 2019.

When we look at the stars shining in the sky, we do not immediately notice that the Universe is like a minefield. Every now and then huge explosions of massive stars, called supernovae, take place. They shine as bright as entire galaxies, which are composed of hundreds of millions of stars. The brightest explosions in the Universe are called gamma-ray burst, and happen when the most massive stars die.

Generally accepted theoretical model of a gamma-ray burst involves three components: a narrow jet of particles, hot cocoon of gas surrounding the star and emission connected with supernova – a radioactive decay of heavy elements. This event resembles therefore a combination of a bulb (supernova) and a powerful torch shining in both directions (jet).

Artistic representation of a gamma-ray burst composed of a supernova (in the middle), jet of charged particles moving in opposite directions, and a hot cocoon of gas (Copyright NASA/D. Berry)
Artistic representation of a gamma-ray burst composed of a supernova (in the middle), jet of charged particles moving in opposite directions, and a hot cocoon of gas (Copyright NASA/D. Berry)
If we look at this system perpendicularly to the jet, then we see the supernova (the bulb). If we happen to be within the jet, then we are blinded by the gamma-ray burst. To complete the picture, there is also a ring of hot gas, which is being expelled from a rapidly rotating core of the star.

While the connection between gamma-ray bursts and supernovae type Ic has been proved in the past, the existence of the cocoon predicted by the theoretical model was a mystery. On the 5th of December 2017 a gamma-ray burst GRB 171215A exploded in a nearby galaxy 500 millions light years away. The team of astronomers from 13 countries started an intensive observational campaign using many telescopes around the world. This allowed the first confirmation of the existence of the hot cocoon surrounding the exploding star and its connection with the gamma-ray burst.

The Poznań team led by dr. hab. Michał Michałowski includes prof. Tadeusz Michałowski, dr. Krzysztof Kamiński, dr. hab. Tomasz Kwiatkowski, and Mikołaj Krużyński.

Full text of article.


The research of dr. hab. Michał Michałowski is supported by the National Science Centre, Poland through the POLONEZ grant 2015/19/P/ST9/04010; this project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 665778.

 
 

2019-01-16 19:00, MM