The immensity of the universe; new measurement (The nature of a \'Creator\')

by David Turell , Wednesday, January 30, 2019, 01:51 (2123 days ago) @ David Turell

Astronomers are now using quasars as standard candles, as very bright objects have always been used to estimate distances:

https://phys.org/news/2019-01-galaxies-physics-cosmic-expansion.html

"A new study, led by Guido Risaliti of Università di Firenze, Italy, and Elisabeta Lusso of Durham University, UK, points to another type of cosmic tracer – quasars – that would fill part of the gap between these observations, measuring the expansion of the universe up to 12 billion years ago.

"Quasars are the cores of galaxies where an active supermassive black hole is pulling in matter from its surroundings at very intense rates, shining brightly across the electromagnetic spectrum. As material falls onto the black hole, it forms a swirling disc that radiates in visible and ultraviolet light; this light, in turn, heats up nearby electrons, generating X-rays.

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"Astronomical sources whose properties allow us to gauge their distances are referred to as 'standard candles'.

"The most notable class, known as 'type-Ia' supernova, consists of the spectacular demise of white dwarf stars after they have over-filled on material from a companion star, generating explosions of predictable brightness that allows astronomers to pinpoint the distance. Observations of these supernovas in the late 1990s revealed the universe's accelerated expansion over the last few billion years.

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"Digging into the XMM-Newton archive, they collected X-ray data for over 7000 quasars, combining them with ultraviolet observations from the ground-based Sloan Digital Sky Survey. They also used a new set of data, specially obtained with XMM-Newton in 2017 to look at very distant quasars, observing them as they were when the universe was only about two billion years old. Finally, they complemented the data with a small number of even more distant quasars and with some relatively nearby ones, observed with NASA's Chandra and Swift X-ray observatories, respectively.

"'Such a large sample enabled us to scrutinise the relation between X-ray and ultraviolet emission of quasars in painstaking detail, which greatly refined our technique to estimate their distance," says Guido.

"The new XMM-Newton observations of distant quasars are so good that the team even identified two different groups: 70 percent of the sources shine brightly in low-energy X-rays, while the remaining 30 percent emit lower amounts of X-rays that are characterised by higher energies. For the further analysis, they only kept the earlier group of sources, in which the relation between X-ray and ultraviolet emission appears clearer.

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"After skimming through the data and bringing the sample down to about 1600 quasars, the astronomers were left with the very best observations, leading to robust estimates of the distance to these sources that they could use to investigate the universe's expansion.

"When we combine the quasar sample, which spans almost 12 billion years of cosmic history, with the more local sample of type-Ia supernovas, covering only the past eight billion years or so, we find similar results in the overlapping epochs," says Elisabeta.

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"'However, in the earlier phases that we can only probe with quasars, we find a discrepancy between the observed evolution of the universe and what we would predict based on the standard cosmological model."

"Looking into this previously poorly explored period of cosmic history with the help of quasars, the astronomers have revealed a possible tension in the standard model of cosmology, which might require the addition of extra parameters to reconcile the data with theory.

"'One of the possible solutions would be to invoke an evolving dark energy, with a density that increases as time goes by," says Guido.

"Incidentally, this particular model would also alleviate another tension that has kept cosmologists busy lately, concerning the Hubble constant – the current rate of cosmic expansion. This discrepancy was found between estimates of the Hubble constant in the local universe, based on supernova data – and, independently, on galaxy clusters – and those based on Planck's observations of the cosmic microwave background in the early universe.

Comment: This should help in getting a finer measurement of the Hubble Constant and how it has sped up during the life of the universe. Hopefully dark matter may be better understood.

Read more at: https://phys.org/news/2019-01-galaxies-physics-cosmic-expansion.html#jCp