A team of astrophysicists has mapped the “Lyman-Alpha Forest” and provided new evidence that the formation of galaxies and galaxy clusters is better explained by the theory of the existence of dark matter than by other alternative theories.
During astronomical observations, researchers have discovered that galaxies and clusters of galaxies do not behave as we would expect. In short, stars at the edges of galaxies are moving so fast (in most but not all galaxies) that they should be thrown out into intergalactic space given the visible mass we can observe in those galaxies.
There are alternative explanations, such as Modified Newtonian Dynamics (MOND), which proposes that gravity works differently at low accelerations. There are problems with the MOND theory, however, and the hypothesis preferred by most physicists today is that space is filled with invisible “dark matter” that interacts with other baryonic matter (the matter we can see) only through gravity.
The theory of the existence of dark matter, supported by “forests” of hydrogen
What is the theory of the existence of dark matter? To explain the dynamics of galaxies and clusters of galaxies, it is estimated that dark matter should be about ten times more massive than ordinary baryonic matter. However, so far we have not found any direct evidence of its existence.
Candidates for dark matter range from weakly interacting massive particles (WIMPS) and axions to primordial black holes, although the latter option is becoming increasingly unlikely. It has also been suggested that dark matter could be caused by supermassive black holes that behave in ways we do not yet fully understand, writes IFL Science.
In the new study, astrophysicists from the University of California, Riverside (USA) used the “Lyman-Alpha Forest” to try to indirectly map dark matter. Basically, they analyzed light from distant sources and mapped the light decays along the hydrogen wavelength. These drops of light correspond to the matter that the light encountered along the way.
“It’s a bit like shadow theater, where we guess the character placed between the light and the screen based on their silhouette,” explained Simeon Bird, associate professor of physics and astronomy and lead author of the study.
“Because each type of atom has a specific way of absorbing light, leaving a kind of signature in the spectrogram, it’s possible to trace its presence, particularly hydrogen, the most abundant element in the Universe,” added Bird.
Like dye in a river
The result of mapping this light is the “forest”, which looks like many small trees. The team claims that using hydrogen spectrograms can be used to track dark matter indirectly, similar to pouring dye into a stream.
“The dye will go where the water goes. Dark matter has a gravitational potential. Hydrogen gas falls into this potential and you use it as an indicator of dark matter. Where it is denser, there is more dark matter. You can think of hydrogen as the dye and dark matter as water,” Bird said.
The team suggests that the structures seen in the resulting map indicate an unknown influence or that dark matter is a particle. However, this does not “solve the mystery” as we have yet to detect such a particle.
“It’s not completely convincing yet. But if this is confirmed in subsequent data sets, then it’s much more likely to be a new particle or a new type of physics than black holes messing up our calculations,” added Bird.
The study was published in Journal of Cosmology and Astroparticle Physics.
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Source: www.descopera.ro
