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Scientists clarify the origin of photons in mysterious gamma-ray bursts



  exploding star
Credit: CC0 Public Domain

Researchers from the RIKEN cluster for pioneering research and business partners have used simulations to show that photons emitted by long gamma ray bursts, among the most energetic events taking place in the universe, originate from the photo sphere ̵

1; the visible part of it "relativistic jet" emitted by exploding stars.


Gamma-ray bursts are the most powerful electromagnetic phenomenon observed in the universe, releasing so much energy in just a second or so as the sun will release over its entire lifetime. Although discovered in 1967, the mechanism behind this huge release of energy remained mysterious for a long time. Decades of research finally revealed that a type of long-term outbreak originates from relativistic rays of material ejected during massive star deaths. Exactly how gamma rays are produced from the rays is still unknown.

Current research, published in Nature Communications began from a discovery called the Yonetoku relationship, which was originally made by one of the authors of the paper. This correlation between GRB's spectral peak energy and peak brightness is the strictest correlation so far found in the properties of GRB emissions. It thus provides the best diagnosis so far to explain the emission mechanism and the strictest test for any gamma ray burst model. Incidentally, this also meant that long gamma ray bursts could be used as a "standard light" for distance measurement, so astronomers could look further into the past than type 1A supernovae commonly used today but are much lighter. This would make it possible to gain insight into the history of the universe and to create insight into mysteries such as dark material and dark energy.

Using computer simulations performed on several supercomputers, including Aterui from the National Astronomical Observatory in Japan, Hokusai of RIKEN and Cray xc40 from Yukawa Institute of Theoretical Physics, the group focused on the so-called "photospheric emission" model, one of the leading models for the emission mechanism for GRBs. This model postulates that photons visible on the ground are emitted from the photo sphere in the relativistic jet. As the beam expands, it becomes easier for photons to escape from within it, as there are fewer objects available to spread the light. Thus, the "critical density" – the place where the photons can escape – is moving downward through the beam to material that was originally at higher and higher densities.

To test the model's validity, to test it in a way that took into account the global dynamics of relativistic rays and radiation transmission. By using a combination of three-dimensional relativistic hydrodynamic simulations and radiation transfer calculations to evaluate photosensitive emissions from a relativistic ray bursting out of massive star envelopes, they could determine that at least in the case of long GRBs, the type there is is associated with such collapsing massive stars – the model worked. Their simulations revealed that the Yonetoku ratio could be reproduced as a natural consequence of the jetstellar interactions. "For us," says Hirotaka Ito from Cluster for Pioneering Research, "it strongly suggests that photospheric emission is the emission mechanism for GRBs."

He continues: "While we have highlighted the origin of photon, there are still mysteries of how the relativistic rays themselves are generated by the coinciding stars. powerful events. "


The ordered chaos of black holes


More Information:
Nature Communications (2019). DOI: 10,1038 / s41467-019-09281-z

Citation :
Scientists determine the origin of photons in mysterious gamma-ray bursts (2019, April 3)
April 3, 2019
from https://phys.org/news/2019-04-photons-mysterious-gamma-ray.html

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