Physicists have put forward an alternative theory of gravity

(ORDO NEWS) — In the dark depths of space, our models of the universe become chaotic. A new study looking at the ultra-diffuse dwarf galaxy AGC 114905 has revived a controversial theory (or rather hypothesis) of gravity and has given us more questions than answers about what makes our galaxies move.

It all starts with dark matter – or, in this case, no dark matter. While most cosmologists agree that there is something called “dark matter” causing spiral galaxies to spin faster than they should, even dark matter doesn’t answer all the questions we need.

So it’s a good idea to consider some alternatives. Just in case we still can’t find that stuff.

One alternative hypothesis for dark matter is called Modified Newtonian Dynamics (MOND) or Milgrom’s system of dynamics.

This hypothesis, first published in 1983 by physicist Mordechai Milgrom, suggests that we don’t need dark matter to fill the gravitational gaps in the universe if we calculate the gravitational forces experienced by stars in the outer galactic regions in a different way than Newtonian laws suggest.

To test this idea, which involves working with star radius proportionality or centripetal acceleration, we need to look at the speeds of galaxies – especially strange ones like ultra-diffuse galaxies.

These very weak, “ugly ducklings” of the world of galaxies have a habit of behaving differently from how a galaxy should behave. For example, some ultra-diffuse galaxies seem to be made up almost entirely of dark matter, while others are almost entirely devoid of dark matter.

This is where AGC 114905 resides. Located about 250 million light-years away, this ultra-diffuse dwarf galaxy was recently detailed in a paper published in 2021 that examined its rotation rate.

But this team found that the galaxy’s rotation is extremely slow – so slow that not only is dark matter not needed to confirm the models, but the galaxy’s rotation curve casts a lot of doubt on the MOND system. It does not fit into any of the hypotheses.

“The very low recorded rotation rate of this galaxy is not consistent with either MOND or the standard dark matter approach,” said Hongsheng Zhao, a University of St. Andrews physicist and co-researcher of the new work.

“But only MOND can circumvent this seeming contradiction.”

A new paper has debunked the 2021 findings, suggesting it’s not MOND but the tilt of the galaxy itself.

When we look at galaxies far in the depths of space, it is sometimes difficult to determine which angle we are seeing. Initially, a team of researchers found that AGC 114905 looks elliptical, suggesting that we are looking at the galaxy from an angle.

But using simulations, the researchers now suggest that the galaxy may look elliptical even when it is facing us directly. Changing the angle of the galaxy to us will also change the speed of rotation of the galaxy, as a result of which all the mathematical calculations of MOND still converge.

“Our simulations show that the tilt of AGC 114905 could be significantly smaller than reported, which means that the galaxy is actually rotating much faster than people think, in line with MOND’s expectations,” says physicist Indranil Banik, lead author of the new paper. , also from the University of St. Andrews.

But this question is still open. We don’t know if this new entry, or the 2021 entry, will be declared the winner – or at least the most correct one.

In the meantime, if this new result is confirmed, then it looks like the MOND system could survive another day. As wild as MOND is, dark matter is still elusive and many more questions remain to be answered, we need every possible option.


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