2023-12-01 17:56:17
Distribution of matter in space (blue; yellow dots represent galaxies. The Milky Way (green) is located in an area with little matter. Galaxies in the bubble move in the direction of greater matter density (red arrows) – AG KROUPA/UNIVERSITY OF BONN
MADRID, 1 Dic. (EUROPA PRESS) –
Cosmologists attribute Hubble tension -discrepancies in the speed at which the Universe expands- to irregularities in the distribution of the matter and not to an error in the calculation method.
The study, which uses an alternative theory of gravity, has been published in Monthly Notices of the Royal Astronomical Society (MNRAS).
The expansion of the universe causes galaxies to move away from each other. The speed at which they do so is proportional to the distance between them. For example, if galaxy A is twice as far from Earth as galaxy B, its distance from us also grows twice as fast. American astronomer Edwin Hubble was one of the first to recognize this connection.
Therefore, to calculate how fast two galaxies are moving away from each other, it is necessary to know how far away they are. However, this also requires a constant by which this distance must be multiplied. This is the so-called Hubble-Lemaitre constant, a fundamental parameter in cosmology. Its value can be determined, for example, by observing very distant regions of the universe. This gives a speed of almost 244,000 kilometers per hour per megaparsec away (one megaparsec is equivalent to just over three million light years).
“But you can also observe celestial bodies that are much closer to us, the so-called category 1a supernovae, which are a certain type of exploding star,” he explains. it’s a statement Professor Pavel Kroupa from the Helmholtz Institute for Radiation and Nuclear Physics at the University of Bonn, co-author of the study. It is possible to determine very precisely the distance of a 1a supernova from Earth. We also know that bright objects change color when they move away from us and the faster they move, the stronger the change. This is similar to an ambulance, whose siren sounds deeper as it moves away from us.
If we now calculate the speed of supernovae 1a from their color change and correlate it with their distance, we arrive at a different value for the Hubble-Lemaitre constant, i.e. just under 264,000 kilometers per hour per megaparsec away. “Therefore, the universe appears to be expanding faster in our environment, that is, up to a distance of about three billion light years, than in its entirety,” says Kroupa. “And that really shouldn’t be the case.”
However, there has recently been an observation that could explain this. According to this, the Earth is in a region of space where there is relatively little matter, comparable to an air bubble in a cake. The density of matter is greater around the bubble. From this surrounding matter gravitational forces emanate that attract the galaxies in the bubble towards the edges of the cavity. “That’s why they are moving away from us faster than we would expect,” explains co-author Dr. Indranil Banik from the University of St. Andrews. Therefore, the deviations could simply be explained by a local “underdensity.”
This is because the standard model does not provide for such underdensities or “bubbles”; In reality, they should not exist. Instead, matter should be uniformly distributed in space. However, If this were the case, it would be difficult to explain what forces drive galaxies to their high speed.
“The Standard Model is based on a theory about the nature of gravity proposed by Albert Einstein,” says Kroupa. “However, gravitational forces may behave differently than Einstein expected.” Working groups from the universities of Bonn and St. Andrews used a modified theory of gravity in a computer simulation. This “modified Newtonian dynamics” (MOND) was proposed four decades ago by Israeli physicist Mordehai Milgrom. It is still considered an external theory today.. “However, in our calculations, MOND accurately predicts the existence of these types of bubbles,” says Kroupa.
If it were assumed that gravity actually behaves according to Milgrom’s assumptions, the Hubble tension would disappear: actually there would only be one constant for the expansion of the universe and the observed deviations would be due to irregularities in the distribution of the matter.
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