Dwarf galaxies seem to be devoid of dark matter, and it doesn’t make sense

(ORDO NEWS) — Ask astronomers about dark matter, and one of the things they talk about is that this invisible, mysterious “stuff” pervades the universe. In particular, it exists in the halos surrounding most galaxies.

The mass of the halo has a strong gravitational effect on the galaxy itself, as well as other galaxies in the neighborhood. This is pretty much the standard view of dark matter and how it affects galaxies.

However, there are problems with the idea of ​​these halos. Apparently, there are oddly shaped dwarf galaxies that look like they don’t have a halo. How could this happen? Do they represent an observational challenge to the prevailing concept of dark matter halos?

Search for perturbed dwarf galaxies

In such a “Standard Model” of cosmology, shells or halos of dark matter protect galaxies from the gravitational influence of their nearest galactic neighbors.

However, when astronomers from the University of Bonn and St. Andrews in Scotland looked into the nearby Fornax cluster, which is about 62 million light-years away, they saw something strange.

It contains a number of dwarf galaxies with distorted, perturbed shapes. This is strange, especially if they should be surrounded by dark matter halos.

Let’s take a look at dwarf galaxies. They are small and dim and are usually found in galaxy clusters or near much larger moons. The Milky Way galaxy is surrounded by a group of dwarf galaxies.

In fact, it engulfs galaxies such as the dwarf spheroidal Sagittarius. Interestingly, recent research suggests that at least one of our closest dwarf galaxies, the ancient Tucana II, has a startlingly massive dark matter halo.

So, what is so unusual going on in Fornax?

There, dwarf galaxies can be “perturbed” by the gravitational tides of nearby larger galaxies in the cluster. Tides occur when the gravity of one body affects different parts of another body differently. This is similar to the tides on Earth, when the Moon pulls harder on the side of the Earth that faces it.

The distorted shapes of dwarf galaxies observed by the team point to a problem with our understanding of dark matter.

“According to the Standard Model, such perturbations are not expected in Fornax dwarfs,” said Pavel Krupa, a professor at Bonn and Charles University in Prague.

“This is because, according to this model, the dark matter halos of these dwarfs should partially protect them from the tides created by the cluster.”

Explaining distorted dwarf galaxies
Krupa and Ph.D. student Elena Asensio analyzed observations of perturbed dwarfs at Fornax. They wanted to understand the degree of gravitational distortion these galaxies exhibit and what causes them.

The expected levels of distortion depend on several factors. One of them is the internal characteristics of a dwarf galaxy. In addition, their distance from the center of the cluster is important. This is where the gravitational influences are much stronger.

As a rule, galaxies with large sizes, but with a small number of stars, can be easily disturbed by strong gravitational tides. The same applies to galaxies located closer to the core of the cluster.

The team members compared what they saw in the cluster with observations made by the VLT survey telescope at the European Southern Observatory. Asensio pointed out that what they found seemed to point to problems with the Standard Model.

“The comparison showed that if one wants to explain the observations in the standard model,” she said, “the Fornax dwarfs should already be destroyed by the gravity of the center of the cluster, even if the tides it raises on the dwarf are sixty-four times weaker than its own gravity. dwarf.”

Not only does this defy common sense, she said it also defies previous research. The team also found that the force needed to perturb a dwarf galaxy is roughly equal to its own gravity.

What does this mean for the Standard Model?

The research team notes that it is difficult to explain these distorted shapes of dwarf galaxies in Fornax if they are surrounded by dark matter. In other words, they should not be deformed if they have halos.

However, they are distorted. This means that there are no dark matter halos around these galaxies.

Obviously, if what the astronomers have found is confirmed, then the Standard Model needs some tweaking. And there is at least one alternative explanation for the strange shapes of galaxies. It is called the MOND model (short for Modified Newtonian Dynamics).

It suggests that Newton’s law of universal gravitation should be modified to account for the observable properties of galaxies. It can be used to explain why deformed galaxies look the way they do.

Finding perturbed dwarfs without dark matter halos is a major challenge, said Hongsheng Zhao, a member of the research team at the University of St. Andrews. challenges the current view.

It says that galaxies have halos. It seems that not all, he notes.

“Our results have great implications for fundamental physics,” he said. “We expect to find more disturbed dwarfs in other clusters, and this prediction should be confirmed by other teams.”


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