Exploring the history of the universe with a large sample of distant ‘active’ galaxies observed by ESA’s XMM-Newton, a team of astronomers found there may be more to the early expansion of the Universe than anticipated by the standard model of cosmology.
As indicated by the leading scenario, our Universe contains just a couple of percent of ordinary matter. One-fourth of the universe is made of the elusive dark matter, which we can feel gravitationally however not watch, and the rest comprises of the much increasingly strange dark matter that is driving the present acceleration of the Universe’s expansion.
This model depends on a large number of data gathered in the course of the most recent few decades, from the cosmic microwave foundation, or CMB – the primary light ever of universe, discharged just 380 000 years after the big bang and observed in uncommon detail by ESA’s Planck mission – to increasingly local perceptions.
The latter include supernova explosions, galaxy clusters and the gravitational distortion imprinted by dark matter on distant galaxies, and can be used to trace cosmic expansion in recent epochs of cosmic history – across the past nine billion years.
Another investigation, driven by Guido Risaliti of Università di Firenze, Italy, and Elisabeta Lusso of Durham University, UK, focuses to another kind of cosmic tracer – quasars – that would fill some portion of the hole between these perceptions, estimating the development of the Universe up to 12 billion years back.
Quasars are the centers of galaxies where an active supermassive black hole is pulling in matter from its surroundings at extremely exceptional rates, sparkling splendidly over the electromagnetic spectrum. As material falls onto the black hole, it shapes a whirling disc that emanates in noticeable and bright light; this light, thusly, warms up close-by electrons, producing X-rays.
Almost before 3 years, astronomers observed that a well-known relation between the ultraviolet and X-ray brightness of quasars could be used to estimate the distance to these sources – something that is notoriously tricky in astronomy – and, ultimately, to probe the expansion history of the Universe.
Galactic sources whose properties enable us to measure their separations are alluded to as ‘standard candles’.
The most prominent class, known as ‘type-Ia’ supernova, comprises of the spectacular demise of white dwarf stars after they have over-filled on material from a partner star, producing blasts of unsurprising splendor that enables space experts to pinpoint the distance. Observations of these supernovas in the late 1990s uncovered the Universe’s quickened extension in the course of the last few billion years.
Elisabeta said, “Using quasars as standard candles have great potential, since we can observe them out to much greater distances from us than type-Ia supernovas, and so use them to probe much earlier epochs in the history of the cosmos.”
With a sizeable sample of quasars at hand, the astronomers have now put their method into practice, and the results are intriguing.
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, especially 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.
Guido said, “Such a large sample enabled us to scrutinize the relation between X-ray and ultraviolet emission of quasars in painstaking detail, which greatly refined our technique to estimate their distance.”