For many years, scientists have been unable to find a piece of matter in the universe. Recently published materials show where she is hiding.
Astronomers have finally found the last missing pieces of the universe. They have been in hiding since the mid-1990s, and at some point the researchers decided to take an inventory of all "ordinary" matter in space, including stars, planets, gas - that is, everything that consists of atomic particles. (This is not "dark matter", which is a separate mystery.) Scientists had a fairly clear idea of how much this matter should be, based on the conclusions of theoretical studies about its origin at the time of the Big Bang. Studies of the cosmic microwave background (the remnants of light from the Big Bang) later confirmed these initial estimates.
They put together all the matter they could see: stars, gas clouds and the like. That is, all the so-called baryons. They accounted for only 10% of what should have been. And when scientists came to the conclusion that ordinary matter accounts for only 15% of all matter in the Universe (the rest is dark matter), by that time they had inventoried only 1.5% of all matter in the Universe.
After conducting a series of studies, astronomers recently found the last pieces of ordinary matter in the universe. (They are still perplexed, not knowing what dark matter is made of.) And although it took a very long time to search, scientists found it exactly where they expected to find it: in the huge curls of hot gases that occupy the voids between galaxies. More precisely, they are called the warm-hot intergalactic environment (WHIM).
The first indications that vast regions of essentially invisible gas could exist between galaxies came from computer simulations in 1998. “We wanted to see what was happening with all this gas in the universe,” said cosmologist Jeremiah Ostriker of Princeton University, who built one such model with his colleague Renyue Cen. These scientists have modeled the movement of gas in the universe under the influence of gravity, light, supernova explosions, and all the forces that move matter through space. “We found that gas builds up in detectable filaments,” Ostricker said.
But they could not find these threads - then.
"From the first days of cosmological modeling, it became clear that a significant part of baryonic matter exists in a hot diffuse form outside galaxies," said an astrophysicist at the University of Liverpool. John Moores Ian McCarthy. Astronomers thought these hot baryons would correspond to a cosmic superstructure made of invisible dark matter that fills the giant voids between galaxies. The force of attraction of dark matter should attract gas and heat it to a temperature of several million degrees. Unfortunately, finding hot and rarefied gas is extremely difficult.
To discover the hidden threads, two teams of scientists independently began to look for precise distortions of the relic radiation (afterglow from the Big Bang). Since light from the early universe streams through outer space, it can be affected by the regions it passes through. In particular, electrons in a hot ionized gas (which makes up a warm-hot intergalactic medium) should interact with protons from the relict radiation, and in such a way that this will give the protons additional energy. Consequently, the spectrum of the CMB should be distorted.
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Unfortunately, even the best CMB maps (obtained from the Planck satellite) did not show such distortions. Either there was no gas, or the impact was too weak and imperceptible.
But scientists from the two teams were determined to make it visible. They knew from computer models of the universe, in which more and more details appeared, that gas should stretch between massive galaxies like a spider web on a windowsill. The Planck satellite has nowhere been able to see the gas between pairs of galaxies. So the researchers devised a way to amplify a weak signal a million times.
They first scanned catalogs of known galaxies in an attempt to find the pairs they were looking for, that is, galaxies that are massive enough and spaced far enough apart that a fairly dense web of gas could appear between them. The astrophysicists then went back to the satellite data, located each pair of galaxies, and essentially carved that region out of space with digital scissors. With more than a million clippings in their hands (this is how much the team of the University of Edinburgh graduate student Anna de Graaff had), they began to rotate, enlarge and reduce them so that all pairs of galaxies were visible in the same position. After that they superimposed a million galactic pairs Each other.(A team of researchers led by Hideki Tanimura of the Institute for Space Astrophysics in Orsay has assembled 260,000 pairs of galaxies.) And then the individual filaments, representing ghostly filaments of hot rarefied gas, suddenly became visible.
This method has its drawbacks. According to astronomer Michael Shull of the University of Colorado Boulder, interpretation of the results requires certain assumptions about the temperature and distribution of hot gas in space. And with overlapping signals, “there is always concern about the 'weak signals' that result from the combination of a huge amount of data. "As is sometimes the case with sociological surveys, you can get erroneous results when outliers or random sampling errors appear in the breakdown that distort the statistics."
Based in part on these considerations, the astronomical community refused to consider this issue as settled. An independent method was needed to measure hot gases. This summer he appeared.
Beacon effect
While the first two groups of researchers were overlapping signals, the third team began to act in a different way. These scientists began observing a distant quasar, as they call a bright object billions of light-years away, to detect gas in the supposedly empty intergalactic space through which its light passes. It was like examining a beam from a distant beacon to analyze the fog that had accumulated around it.
Usually, when astronomers make such observations, they look for light absorbed by atomic hydrogen, since this element is the most in the universe. Unfortunately, in this case, this option was excluded. The warm-hot intergalactic medium is so incandescent that it ionizes hydrogen, depriving it of its only electron. The result is a plasma of free protons and electrons that do not absorb light at all.
Therefore, scientists decided to look for another element - oxygen. Oxygen in a warm-hot intergalactic medium is much less than hydrogen, but atomic oxygen has eight electrons, while hydrogen has one. Due to the heat, most of the electrons fly away, but not all. This research team, led by Fabrizio Nicastro of Rome's National Institute of Astrophysics, tracked the light absorbed by oxygen, which has lost six of its eight electrons. They discovered two regions of hot intergalactic gas. “Oxygen gives a cue that indicates the presence of a much larger volume of hydrogen and helium,” said Schull, who is on Nikastro's team. The scientists then compared the amount of gas they found between the Earth and the quasar to the universe as a whole. The result showed that they found the missing 30%.
These figures are also quite consistent with the conclusions of the study of the CMB. “Our teams looked at different pieces of the same puzzle and came to the same conclusion, which gives us confidence given the difference in research methods,” said astronomer Mike Boylan-Kolchin at the University of Texas at Austin.
The next step, Shull said, should be to observe more quasars with a new generation of X-ray and ultraviolet telescopes with higher sensitivity. “The quasar we watched was the best and brightest lighthouse we could find. Others will be less bright and observations will last longer,”he said. But for today the conclusion is clear. “We conclude that the missing baryonic matter has been found,” the scientists wrote.
Katya Moskvich (KATIA MOSKVITCH)