A new possible explanation for the Hubble tension

The universe is increasing. How briskly it does so is described by the so-called Hubble-Lemaitre fixed. However there’s a dispute about how massive this fixed truly is: Totally different measurement strategies present contradictory values.

This so-called “Hubble pressure” poses a puzzle for cosmologists. Researchers from the Universities of Bonn and St. Andrews at the moment are proposing a brand new resolution: Utilizing an alternate idea of gravity, the discrepancy within the measured values could be simply defined—the Hubble pressure disappears. The examine has now been printed within the Month-to-month Notices of the Royal Astronomical Society (MNRAS).

The expansion of the universe causes the galaxies to maneuver away from one another. The pace at which they do that is proportional to the gap between them. As an example, if galaxy A is twice as distant from Earth as galaxy B, its distance from us additionally grows twice as quick. The US astronomer Edwin Hubble was one of many first to acknowledge this connection.

To be able to calculate how briskly two galaxies are shifting away from one another, it’s, due to this fact, essential to know the way far aside they’re. Nonetheless, this additionally requires a relentless by which this distance should be multiplied. That is the so-called Hubble-Lemaitre fixed, a elementary parameter in cosmology. Its worth could be decided, for instance, by wanting on the very distant areas of the universe. This offers a pace of virtually 244,000 kilometers per hour per megaparsec distance (one megaparsec is simply over three million light-years).

244.000 kilometers per hour per megaparsec—or 264,000?

“However you may as well take a look at celestial bodies which can be a lot nearer to us—so-called class 1a supernovae, that are a sure kind of exploding star,” explains Prof. Dr. Pavel Kroupa from the Helmholtz Institute of Radiation and Nuclear Physics on the College of Bonn. It’s doable to find out the gap of a 1a supernova to Earth very exactly. We additionally know that shining objects change coloration once they transfer away from us—and the sooner they transfer, the stronger the change. That is much like an ambulance, whose siren sounds deeper because it strikes away from us.

If we now calculate the pace of the 1a supernovae from their coloration shift and correlate this with their distance, we arrive at a unique worth for the Hubble-Lemaitre fixed—particularly, just below 264,000 kilometers per hour per megaparsec distance. “The universe, due to this fact, seems to be increasing sooner in our neighborhood—that’s, as much as a distance of round three billion gentle years—than in its entirety,” says Kroupa. “And that should not actually be the case.”

Nonetheless, there has just lately been an remark that might clarify this. In line with this, the Earth is positioned in a area of space the place there may be comparatively little matter—corresponding to an air bubble in a cake. The density of matter is increased across the bubble. Gravitational forces emanate from this surrounding matter, which pulls the galaxies within the bubble towards the sides of the cavity. “That is why they’re shifting away from us sooner than would truly be anticipated,” explains Dr. Indranil Banik from St. Andrews College. The deviations may, due to this fact merely be defined by a neighborhood “under-density.”

In reality, one other analysis group just lately measured the common pace of numerous galaxies which can be 600 million gentle years away from us. “It was discovered that these galaxies are shifting away from us 4 instances sooner than the standard model of cosmology permits,” explains Sergij Mazurenko from Kroupa’s analysis group, who was concerned within the present examine.

Bubble within the dough of the universe

It’s because the usual mannequin doesn’t present for such under-densities or “bubbles”—they need to not truly exist. As a substitute, matter needs to be evenly distributed in space. If this had been the case, nevertheless, it could be troublesome to elucidate which forces propel the galaxies to their excessive pace.

“The usual mannequin relies on a idea of the character of gravity put ahead by Albert Einstein,” says Kroupa. “Nonetheless, the gravitational forces could behave in another way than Einstein anticipated.” The working teams from the Universities of Bonn and St. Andrews have used a modified idea of gravity in a pc simulation.

This “modified Newtonian dynamics” (abbreviation: MOND) was proposed 4 a long time in the past by the Israeli physicist Prof. Dr. Mordehai Milgrom. It’s nonetheless thought-about an outsider idea right now. “In our calculations, nevertheless, MOND does precisely predict the existence of such bubbles,” says Kroupa.

If one had been to imagine that gravity truly behaves in keeping with Milgrom’s assumptions, the Hubble pressure would disappear: There would truly solely be one fixed for the growth of the universe, and the noticed deviations could be because of irregularities within the distribution of matter.