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Quasars are the new "standard candles" for calculating the very longest distances in the universe

Quasars are the new “standard candles” for calculating the very longest distances in the universe

The most distant quasars known to date are dated only 700 million years after the Big Bang, greatly expanding the redshift of standard candles.

Another feature of quasars is that hundreds of thousands of them have been discovered in the past few years. It is also important that physical processes in quasars differ from processes in supernovae, so that quasars provide completely independent measurements of cosmic quantities.

The new system proposed by astronomers is based on the discovery of a close relationship between X-rays and ultraviolet radiation from quasars.

As mentioned, at the center of the quasar is a supermassive black hole surrounded by a super-hot disk of accretion material that emits ultraviolet radiation. The disk, in turn, is surrounded by a hot gas with electrons moving at speeds approaching the speed of light, and when ultraviolet photons – particles of light – come into contact with these electrons, their energy is enhanced in the X-ray spectrum.

Building on their previous work, the team behind the study analyzed X-ray measurements of 2,332 distant quasars in the new Chandra Source Catalog and compared that data with UV measurements from the Sloan Digital Sky Survey.

It’s already known that “local” quasars — the closest ones — have a correlation between UV and X-ray brightness, and the researchers found that this was also true for distant quasars — all the way to more than 85 percent of their age. to the universe – and that the connection becomes tighter in these earlier times.

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It follows that these two quantities – the luminosity in the ultraviolet and the X-ray spectrum – can determine the distance to any quasar, and those distances can then be used to test cosmological models or to calculate, for example, the Hubble constant, which follows from the Hubble-LemaĆ®tre law , to be determined for distant galaxies.

If the results of the new system are confirmed in studies, the researchers say, astronomers will have an amazing new tool for measuring the properties of the evolving universe.

that Pre-publication of the study by researchers from the Harvard-Smithsonian Center for Astrophysics and colleagues from the University of Florence, INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica Milano and INAF – Osservatorio Astrofisico di Arcetri is available at arXiv. This article is based on a press release from the Harvard-Smithsonian Center for Astrophysics.