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Posted on February 16, 2019
Astronomers have spent decades looking for something that would seem hard to miss: about a third of the "normal", baryonic, material of the universe. The new findings from NASA's Chandra X-ray observatory may have helped them locate this elusive expanse of missing material.
From independent and well-established observations, scientists have confidently calculated how much normal matter – namely hydrogen, helium and other elements – existed right after the Big Bang . Between the first minutes and the first billions of years, much of the normal matter has infiltrated into the dust, gases and cosmic objects, such as stars and planets, that telescopes can see in the current universe.
The problem is that when astronomers add the mass of all the normal matter of the current Universe, we can not find about a third. (This missing material is distinct from the still mysterious dark matter.)
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The new version of the Hubble Deep Field Image is shown above. In dark gray, you can see the new light that has been found around the galaxies in this field. This light corresponds to the brightness of more than a hundred billion suns. It took nearly three years for researchers at the Instituto de Astrofísica de Canarias to produce this deepest image of the Universe ever captured in space, recovering a large amount of "lost" light around the largest galaxies of the famous Hubble Ultra-Deep Field.
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One idea is that the missing mass has accumulated in gigantic strands or filaments of hot gas (temperature lower than 100 000 Kelvin) and hot (temperature higher than 100 000 Kelvin) in an intergalactic space. Astronomers call these filaments the "warm-hot intergalactic medium" or WHIM. They are invisible to optical light telescopes, but some of the hot gas contained in the filaments has been detected in ultraviolet light.
Using a new technique, the researchers found strong new evidence for the warm component of WHIM from data from Chandra and other telescopes.
"If we find this mass missing, we will be able to solve one of the biggest problems of astrophysics," said Orsolya Kovacs of the Center for Astrophysics | Harvard & Smithsonian (CfA) in Cambridge, Massachusetts. "Where did the universe hide so much of its material that makes up objects like stars, planets and us?"
Astronomers have used Chandra to research and study hot gas filaments along the path to a quasar, an X-ray light source powered by a rapidly growing supermassive black hole. This quasar is located about 3.5 billion light years from Earth. If the hot gas component of the WHIM is associated with these filaments, part of the X-rays of the quasar would be absorbed by this hot gas. They searched for a hot gas signature printed in the quasar x-ray light detected by Chandra.
One of the challenges of this method is that the signal of absorption by the WHIM is small compared to the total amount of X-rays from the quasar. When searching for the full spectrum of x-rays at different wavelengths, it is difficult to distinguish these weak absorption characteristics – the actual WHIM signals – from random fluctuations.
Kovacs and his team solved this problem by concentrating their research solely on parts of the X-ray light spectrum, reducing the risk of false positives. To do this, they first identified the galaxies near the line of sight of the quasar, located at the same distance from the Earth as regions of hot gas detected from ultraviolet data. With this technique, they identified 17 possible filaments between the quasar and us and got their distances.
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Due to the expansion of the universe, which stretches the light as it moves, any absorption of X-rays by the material in these filaments will be shifted to shorter wavelengths. . The importance of offsets depends on the known distances to the filament. The team knew where to look in the spectrum for WHIM absorption.
"Our technique is similar in principle to how to conduct efficient animal research in the vast plains of Africa," said Akos Bogdan, also co-author of the CfA. "We know that animals need to drink, so it makes sense to start by looking for water points."
Although the research was reduced, the researchers also had to overcome the problem of weak X-ray absorption. Thus, they amplified the signal by adding the spectra of 17 filaments, transforming a 5.5-day observation. in a quantity of data equivalent to nearly 100 days. With this technique, they detected oxygen with characteristics suggesting that it was in a gas with a temperature of about one million degrees Kelvin.
By extrapolating from these observations of oxygen to all elements and the region observed in the local universe, the researchers indicate that they can explain the complete amount of missing material. At least in this particular case, the missing question was hidden in the SIMD after all.
"We were delighted to be able to find some of this missing question," said co-author Randall Smith, also of the CfA. "In the future, we will be able to apply this same method to other quasar data to confirm that this long-standing mystery has finally been solved."
The Daily Galaxy via Chandra X-Ray Center
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