by A major discrepancy between different measurements of the expansion rate of our universe could be explained if our Milky Way galaxy lies in a void two billion light years wide. This is the conclusion of scientists who maintain that a modified theory of gravity can replace the standard model of cosmology. However, this hypothesis is strongly questioned by many astronomers.
He standard model of cosmology describes how we live in a universe dominated by dark energy and dark matter. Dark energy is a mysterious force that is apparently causing the expansion of the universe accelerate, while dark matter provides most of the universe’s gravity and is thought to surround galaxies in halo-like shapes while preventing them from falling apart. Together, these elusive phenomena describe how matter is distributed in the cosmos and how galaxies move relative to each other.
However, one of the biggest challenges the Standard Model of cosmology must overcome is known as the “Hubble tension.” This concept is not named after space telescope as you can imagine, but his namesake, the astronomer Edwin Hubble. In 1929, Edwin Hubble discovered that the more distant a galaxy is, the faster it appears to move away from us. He was able to derive a relation to describe this connection, which later became known as the Hubble-Lemaître law (in honor of the Belgian theoretical physicist and priest Georges Lemaître, who also discovered it independently). He says that the speed with which a galaxy is moving away from us is the product of its distance multiplied by the expansion rate of the universe, which is given by a parameter called the Hubble constant.
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Since the time of Edwin Hubble, astronomers have strived to measure the Hubble constant with increasing precision. Knowing the Hubble constant and, therefore, precisely the speed at which the universe is expanding, we can calculate how old the universe must be for it to have reached its current size. Our best current measurements put the the age of the universe to 13.8 billion years.
However, there is a problem.
Measurements of the expansion of the universe created by measuring type Ia redshifted light supernovas have resulted in a Hubble constant value of 73.2 kilometers per second per megaparsec. In other words, it says that each volume of space one megaparsec in diameter (a parsec is 3.26 light years and a megaparsec is one million parsecs, that is, 3.26 million light years) expands 73.2 kilometers (45.5 miles) per second.
However, the expansion rate of the universe is also included in the physics of the universe. cosmic microwave background (CMB) radiation. CMB measurements by European Space AgencyThe Planck mission gives a value for the Hubble constant of 67.4 kilometers per second per megaparsec. Both measurements have been made with great precision, but it is not possible for both to be correct.
This strange dichotomy, known as the Hubble tension, is possibly the most perplexing problem in cosmology today. While some astronomers suspect it is the product of a measurement error at some point, others think it could be hinting at new physics.
That’s exactly what a new paper by scientists from Germany, Scotland and the Czech Republic proposes.
“The universe… appears to be expanding faster in our vicinity – that is, to a distance of about three billion light years – than as a whole,” says one of the paper’s authors, Pavel Kroupa of the University of Bonn in Germany. in a Press release. “And that really shouldn’t be the case.”
Their hypothesis centers on an astrophysical oddity called the Keenan-Barger-Cowie supervoid, named after the trio of astronomers who studied it. The supervoid is the so-called “underdensity” of matter in the universe, a region where there are statistically fewer galaxies on average, and our Milky Way It turns out it’s right in the middle, scientists say.
Outside of this supervoid, galaxies are slightly denser on average, resulting in greater gravity that can pull objects within the supervoid toward them. This could give the impression that space The team suggests that it is expanding more rapidly in our vicinity, as galaxies are pulled by the gravity of matter beyond the supervoid.
“That’s why they are moving away from us faster than you would really expect,” said co-author Indranil Banik of the University of St Andrews in Scotland.
The standard model of cosmology says that matter should be distributed fairly evenly throughout the universe and that voids should not grow beyond a certain size. Therefore, it has some difficulty explaining a supervoid as large as the Keenan-Barger-Cowie vacuum. Some astronomers, including Kroupa and Banik, believe that the Standard Model cannot explain it, while others such as Martin Sahlén, Iñigo Zubeldía and Joseph Silk of the University of Oxford have has been registered saying that it is possible.
In the hypothesis of Kroupa, Banik and their co-authors (Sergij Mazurenko of Universität Bonn and Moritz Haslbauer of Charles University in the Czech Republic), our current theory of gravity, and therefore of dark matter, is replaced by a new theory called Modified Newtonian Dynamics. or MOND for short. This postulates that at low accelerations, gravity behaves differently than described. Einstein and Newton, and that additional gravity can replace the need for dark matter. In the MOND paradigm, the universe could more easily create large voids like the Keenan-Barger-Cowie supervoid.
However, the idea that the presence of a vacuum can affect measurements of the expansion rate of the universe has been highly questioned in the past. Nobel laureate Adam Riess of Johns Hopkins University in Baltimore, who is leading efforts to measure the Hubble constant with type Ia supernovae, along with W. D’Arcy Kenworthy of Johns Hopkin and Dan Scolnic of Duke University in the United States United, they demonstrated that type Ia Supernovae observed beyond the limit of the supervacuum had the same expansion rate like those inside the void. In response, Kroupa, Banik, Mazurenko and Haslbauer argue that the effect of the supervacuum would be felt far beyond the vacuum itself, so we would expect to measure a greater expansion rate in supernovae beyond the confines of the vacuum.
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Other methods for measuring the Hubble constant, which are independent of the supervacuum and the Standard Model of cosmology, also maintain that the Hubble strain cannot be explained. By tracking the angular distance in the sky that water masers in molecular clouds orbit supermassive black holes in distant galaxies, and from this, deriving their physical distance from the geometry, a value of the Hubble constant of 73.9 kilometers per second per megaparsec has been obtained, which is close to the measurements of type Ia supernovae, given the uncertainty in maser measurements. There is also the H0LiCOW (H0 refers to the Hubble constant), which studies how light from quasars in the early universe can take different paths of different lengths through the foreground gravitational lenses. Quasars often have fluctuations in their brightness; As it traverses the different paths through the gravitational lens, the universe is still expanding and the speed of this expansion is imprinted on the different images of the quasar’s brightness variations. This project finds that the expansion rate is 73.3 kilometers per second per megaparsec, almost identical to the value of the type Ia supernova.
These measurements conflict with the CMB measurement and are independent of the hypothesis that the supervacuum can create the Hubble strain. So ultimately, for that hypothesis to have traction, it looks like Kroupa, Banik, Mazurenko and Haslbauer will have to convince a lot more people.
The hypothesis was published in November in the magazine. Monthly Notices of the Royal Astronomical Society.
For any readers interested in reading more, you can find a list of articles on the topic of the Hubble voltage and their measured values of the Hubble constant. here.
