In a Wild Twist, Physicists Have Revived an Alternative Theory of Gravity

Our models of the universe get chaotic in the furthest reaches of space. A recent study of the super-diffused dwarf galaxy AGC 114905 has resurrected a contentious idea (or, more correctly, a hypothesis) concerning gravity, leaving us with more questions than answers about what makes our galaxies tick.

Everything begins with dark matter – or, in this case, the lack thereof. Even though most cosmologists agree that "dark matter" causes spiral galaxies to spin faster than they should, dark matter does not explain all of our issues.

As a result, considering alternative possibilities is not a good idea. Just in case we can't discover anything.

Dark matter Modified Newton Dynamics (MOND) or Milgromian dynamics framework is an alternate hypothesis. If we compute the gravitational forces that stars in the outer galactic regions experience differently from Newton's laws, we don't need dark matter to fill the gravitational voids in the universe, according to this concept, initially proposed by physicist Mordihai Milgrom in 1983.

We need to consider the velocities of galaxies—specifically exotic galaxies like Ultra-widespread galaxies—to test this theory, which includes working in proportion to a star's radius or centripetal acceleration.

The galaxy's dim, ugly ducklings have a habit of not acting like a galaxy. Some super-diffuse galaxies, for example, appear to be almost totally made up of dark matter, while other materials appear to be nearly empty of dark matter.

That's where AGC 114905 enters the picture. This dwarf galaxy has a lot of light. 250 million light-years In a recently published study in 2021, Look into how fast it revolves.

However, this researchers discovered that the galaxy's rotation was too sluggish — so slow that they need not only dark matter to corroborate the models, but also the galactic rotation curve, which calls into question the MOND framework. Neither hypothesis fits.

“The reported extremely low rotational velocity of this galaxy is incompatible with both MOND and the standard dark matter approach,” says Hong-Sheng Zhao, a physicist from the University of St Andrews and one of the authors of the new work.

“But only Mond is able to get around this apparent contradiction.”

The 2021 discovery was published in a recent publication, suggesting that the problem is not with MOND, but rather with the galaxy's tilt.

It can be difficult to establish the angle we perceive when looking at faraway galaxies in the depths of space. The initial researchers discovered that AGC 114905 looked to be elliptical, indicating that we are viewing the galaxy from a different perspective.

However, models show that the galaxy could appear elliptical even when squarely facing us, according to the astronomers. Changing the galaxy's angle for us changes the galaxy's rotation speed, which makes all the MOND calculations add up in the end.

“Our simulations show that the tilt of AGC 114905 may be much lower than what has been reported, which means that the galaxy is in fact rotating much faster than people think, in line with MOND’s predictions,” the lead author of the new paper, physicist Indranil Panek, says: also from the University of St Andrews.

This is still a question. We don't sure if this new card or the 2021 card will emerge victorious – or at the very least, the healthiest.

Meanwhile, if this new discovery continues, it appears that the MOND architecture may have a future. With dark matter still a mystery and so many other mysteries unanswered, we need all the alternatives we can get.