Thursday , January 28 2021

Cosmological rulers: how large cosmic distances were measured by analyzing gamma-ray bursts



The measurement of large cosmic distances is supported by various “rulers” – phenomena whose properties, such as light, are well known. By comparing the well-known property or function of several properties with the observed properties, we can then determine how far the phenomenon is from us.

© ESO / L. Sidewalk (CC BY 4.0) |  commons.wikimedia.org
© ESO / L. Sidewalk (CC BY 4.0) | commons.wikimedia.org

One of the best rulers for determining distances to distant galaxies is type Ia supernovae, whose maximum brightness is almost always the same. Rulers can also become gamma-ray spots, but there is a greater range of both their properties and types, which makes it difficult to find the right ratio for distance measurement. In a new study, this was done by analyzing the largest set of gamma-ray bursts that occurred at known distances.

Gamma ray flashes also emit radiation from other sections, and X-rays initially have a plateau phase – they have remained virtually unchanged for some time. For all gamma flashes, there is a relationship between three parameters: maximum gamma radiation light, X-ray light in the plateau phase and plateau phase duration.

The relationship can be represented as a plane in a three-dimensional space consisting of these parameters. But not all individual flashes are on this plane – their X-ray plateau sometimes differs several tens of times from the predicted ratio.

By examining the sample in detail, the researchers found three subpopulations whose members are very equally distant from the planet, making them more suitable to be cosmic distance rulers. The best set are short gamma-ray bursts that occur along with kilowatt explosions. One such event occurred in August 2017 and was also the first fusion of neutron stars caught in the gravitational wave region. All of these flashes are weaker in the X-ray range than predicted by the overall ratio, but using them alone can predict the flash’s actual X-ray platform with better than 1% accuracy.

This discovery may also help to better understand the nature of the different types of gamma-ray bursts.

The results of the study “arXiv”.


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