Possible explanation for Hubble tensión

 

Cosmologists attribute Hubble’s tension -discrepancies in the speed at which the Universe expands- to irregularities in the distribution of 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 is proportional to the distance between them. For example, if galaxy A is twice as far away from Earth as galaxy B, its distance to us also grows twice as fast. American astronomer Edwin Hubble was one of the first to recognize this connection.

Therefore, to calculate at what speed two galaxies are left one from each other, it is necessary to know how far they are. However, this also requires constant by which this distance must be multiplied. This is the constant call of Hubble-Lemaitre, a fundamental parameter in cosmology. Its value can be determined, for example, by observing regions far from the universe. This gives a speed of almost 244000 kilometers per megaparsec away (a megaparsec equals just over three million light years).

But you can also see celestial bodies that are much closer to us, the so-called category 1a supernovae, which are a certain type of exploding star” explains Professor Pavel Kroupa of the Helmholtz Institute of Radiation and Nuclear Physics at the University of Bonn, co-author of the study. It is possible to determine with great precision the distance of a supernova 1a to Earth. We also know that bright objects change colour when they move away from us and the faster they move, the stronger the change. This is similar to an ambulance, whose siren sound deeper as it moves away from us.

If we now calculate the speed of supernovae 1a from their colour change and correlate it with its distance, we reach a different value for the constant of Hubble-Lemaitre, that is, just under 264,000 kilometres per hour per megaparsec distance. “Therefore, the universe seems to expand faster in our environment, that is, up to a distance of about three billion light-years, than in its entirety” says Kroupa. “And that shouldn’t really be the case”.

Recently, however, there has been a comment that could explain this. According to this, the Earth located in a region of space where there ir relatively litter matter, comparable to an air bubble on a cake. The density of matter is higher around the bubble. From this surrounding matter emanate gravitational forces that attract the galaxies from the bubble to the edges of the cavity.

This is because the standard model does not provide for such sub densities or “bubbles”; in reality, they should not exit. On the other hand, matter should be evenly distributed in space. However, if this were the case, it would be difficult to explain which forces propel galaxies at 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 can behave differently from what Einstein expected”. The working groups of the universities of Bonn and St. Andrews used a modified gravity theory in a computer simulation. This “modified Newtonian dynamic (MOND) was proposed four decades ago by Israeli physicist Mordehai Milgrom. Even today it is considered an external theory. “However, in our calculations, MOND accurately predict the existence of this type of bubble” says Kroupa.

If it were assumed that gravity actually behaves according to the assumptions of Milgrom, Hubble’s tension would disappear: in reality there would be only one constant for the expansion of universe and the observed deviations were due to irregularities in the distribution of matter.