Posted February 16, 2019
For decades, astronomers have searched for something that sounds as if it's hard to miss, "Baryonic, matter in the universe. New findings from NASA's Chandra X-ray Observatory could have helped them locate this elusive vastness of missing matter.
From independent, well-established observations, scientists have confidently calculated how much normal matter – that is, hydrogen – means. Helium and other elements – came shortly after the Big Bang. In the time between the first few minutes and the first billion years, much of the normal matter came in cosmic dust, gas, and objects like stars and planets that telescopes can see in the universe today.
The problem is that when astronomers sum up the mass of all normal matter in the universe today, about a third of it can not be found. (This missing matter is different from the still mysterious dark matter.)
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The new version of Hubble's depth field image is shown above. In dark gray you can see the new light that was 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 create this deepest image of the universe ever taken from space by recovering a large amount of "lost" light around the largest galaxies in the iconic Hubble Ultra-Deep Field becomes.
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One idea is that the missing mass accumulated into gigantic strands or filaments of warm (temperature below 100,000 Kelvin) and hot (temperature over 100,000 Kelvin) gas in intergalactic space. These filaments are known by astronomers as "warm-hot intergalactic medium" or "WHIM". They are not visible to optical light telescopes, but part of the warm gas in filaments was detected in ultraviolet light.
Using a new technique, researchers based on data from Chandra have found new and strong evidence for the hot component of WHIM and other telescopes.
"If we find this missing mass, we can solve one of the biggest mysteries in astrophysics," said Orsolya Kovacs of the Center for Astrophysics Harvard & Smithsonian (CfA) in Cambridge, Massachusetts. "Where has the universe hidden so much matter that makes up things like stars, planets, and we?"
Astronomers used Chandra to seek and study threads of warm gas that lay on the way to a quasar Bright Source X-rays are powered by a fast-growing supermassive black hole. This quasar is about 3.5 billion light-years from Earth. If the hot gas component of the WHIM is connected to these filaments, some of the x-rays of the quasar would be absorbed by this hot gas. They were looking for a signature of hot gas that had been imprinted into the Chandra X-ray of the Quasar.
One of the challenges of this method is that the signal of absorption by the WHIM is weak compared to the total amount of X-rays coming from the quasar. By searching the entire spectrum of X-rays at different wavelengths, it is difficult to distinguish such weak absorption features – actual WHIM signals – from random fluctuations.
Kovacs and her team have overcome this problem by focusing their search only on certain parts of the X-ray spectrum, thereby reducing the likelihood of false alarms. They did this by first identifying galaxies near the line of sight of the quasar, which are at the same distance from Earth as hot gas areas detected from ultraviolet data. Using 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 that propagates light, the absorption of X-rays by matter in these filaments is shifted to redder wavelengths. The extent of the shifts depends on the known distances to the filament, so the team knew where to look for WHIM in the spectrum.
"Our technique is basically similar to an efficient search for animals in the vast plains of Africa," said Akos Bogdan, co-author of CfA. "We know that animals need to drink, so it makes sense to search near waterholes first."
Although search narrowed the search, researchers also had to overcome the problem of the powerlessness of X-ray absorption. Therefore, they amplified the signal by adding spectra from 17 filaments, making a 5.5 day observation to a data value of almost 100 days. Using this technique, they discovered oxygen with properties that indicated it was in a gas with a temperature of about one million Kelvin.
By extrapolating these observations of oxygen to the totality of the elements and from the observed region to the local universe, the researchers report that they can explain the total amount of missing material. At least in this particular case, the missing thing had been hidden in WHIM.
"We were thrilled to find some of this missing issue," said fellow author Randall Smith, also CfA. "In the future, we can apply the same method to other quasi-data to confirm that this long-standing mystery has finally been cracked."
The Daily Galaxy via the Chandra X-ray Center