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Understanding the "cold spot" in the cosmic microwave background by Maxwell Bernstein for FermiLab News Batavia IL (SPX) Jan 14, 2022
After the Big Bang, the universe, glowing brightly, was opaque and so hot that atoms could not form. Eventually cooling down to about minus 454 degrees Fahrenheit (-270 degrees Celsius), much of the energy from the Big Bang took the form of light. This afterglow, known as the cosmic microwave background, can now be seen with telescopes at microwave frequencies invisible to human eyes. It has tiny fluctuations in temperature that provide information about the early universe. Now scientists might have an explanation for the existence of an especially cold region in the afterglow, known as the CMB Cold Spot. Its origin has been a mystery so far but might be attributed to the largest absence of galaxies ever discovered. Scientists used data collected by the Dark Energy Survey to confirm the existence of one of the largest supervoids known to humanity, the Eridanus supervoid, as reported in a paper published in December 2021. This once-hypothesized but now-confirmed void in the cosmic web might be a possible cause for the anomaly in the CMB.
The Eridanus supervoid Between these clusters of galaxies are voids: vast regions of space that contain fewer galaxies, and thus less ordinary matter, and less dark matter than exists within the galaxy clusters. Among the largest structures known to humanity, the supervoid in the constellation Eridanus is a massive, elongated, cigar-shaped void in the cosmic web that's 1.8 billion lightyears wide and has been observed to contain about 30% less matter than the surrounding galactic region. Its center is located 2 billion lightyears from Earth, making it the dominant underdensity of matter in our galactic neighborhood.
Mapping dark matter "This map of dark matter is the largest ever such map that's been created," said Niall Jeffrey, the scientist who worked on the construction of a dark matter map. "We have been able to map out dark matter over a quarter of the Southern Hemisphere." Scientists previously counted the number of galaxies visible in the location of the CMB Cold Spot and found an underdensity of galaxies in that region. The new map shows there is a matching underdensity of invisible dark matter. "It is enough of a new element in the long history of the CMB Cold Spot problem that after this, people will at least be sure that there is a supervoid." - Andras Kovacs
Using voids to understand dark energy The Dark Energy Survey documents hundreds of millions of galaxies, supernovae and patterns within the cosmic web, using a 570-Megapixel digital camera, called the DECam, high in the Chilean Andes. This camera's construction and integration of components was led by the U.S. Department of Energy's Fermi National Accelerator Laboratory. "We were thinking many years ago, a decade and a half at least, how would voids affect the present acceleration of the universe," said Juan Garcia-Bellido, a cosmologist from IFT-Madrid and co-author of the paper. At the largest scales of the universe, there is a tug-of-war between the gravitational forces and the expansion of the universe from dark energy, making some of the voids between galactic clusters deeper. "Photons or particles of light enter into a void at a time before the void starts deepening and leave after the void has become deeper," said Garcia-Bellido. "This process means that there is a net energy loss in that journey; that's called the Integrated Sachs-Wolfe effect. When photons fall into a potential well, they gain energy, and when they come out of a potential well, they lose energy. This is the gravitational redshift effect."
Open questions "Having the coincidence of these two individually rare structures in the cosmic web and in the CMB is basically not enough to prove causality with the scientific standard," said Andras Kovacs, the lead researcher on this project. "It is enough of a new element in the long history of the CMB Cold Spot problem that after this, people will at least be sure that there is a supervoid, which is a good thing because some people have debated that," said Kovacs. In short, there are two ways to think about this problem: Either the Lambda-CDM model is correct, and the CMB Cold Spot is an extreme anomaly that coincidentally has a massive supervoid in front of it, or the Lambda-CDM model is incorrect, and the Integrated Sachs-Wolfe effect is stronger in supervoids than expected. The latter would indicate a greater influence of dark energy on the universe and possibly faster cosmic expansion. Interestingly, this possibility is backed up by evidence from other, more distant supervoids. Moreover, the Dark Energy Survey team observed that the lensing signal from the Eridanus supervoid is slightly weaker than expected. "The trouble is that typical alternative models cannot explain this discrepancy either, so if true, it might mean that we do not understand something very deep about dark energy," said Kovacs.
Gravitational waves could be key to answering why more matter was left over after Big Bang Kashiwa, Japan (SPX) Dec 09, 2021 A team of theoretical researchers have found it might be possible to detect Q-balls in gravitational waves, and their detection would answer why more matter than anti-matter to be left over after the Big Bang, reports a new study in Physical Review Letters. The reason humans exist is because at some time in the first second of the Universe's existence, somehow more matter was produced than anti-matter. The asymmetry is so small that only one extra particle of matter was produced every time ten bil ... read more
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