These dwarf galaxies don’t appear to have dark matter and make no sense

Ask astronomers about dark matter, and one of the things they talk about is this invisible, mysterious “thing” that permeates the universe. In particular, it exists in halos around most galaxies.

The halo’s mass exerts a strong gravitational influence on the galaxy itself, as well as other nearby galaxies. This is pretty much the standard view of dark matter and its effects on galaxies.

However, there are problems with the idea of ‚Äč‚Äčthese halos. Apparently, there are some oddly shaped dwarf galaxies that don’t appear to have halos. how can that be? Do they represent an observational challenge to the prevailing view of dark matter halos?

Looking for disturbed dwarf galaxies

In the so-called “Standard Model” of cosmology, a shell or halo of dark matter protects galaxies from the gravitational pull of their nearby galactic neighbors.

However, when astronomers from the Universities of Bonn and St Andrews in Scotland looked at the nearby Fornax star cluster, some 62 million light-years away, they saw something strange.

It contains many dwarf galaxies with distorted, perturbed shapes. That’s odd, especially if they’re supposed to be surrounded by dark matter halos.

Fornax galaxy cluster. (ESO/J. Emerson/VISTA)

Let’s take a quick look at dwarf galaxies. They are small and faint, and are usually found in galaxy clusters or near larger companions. There is a group of dwarf galaxies around the Milky Way.

In fact, it is cannibalizing the Sagittarius dwarf sphere, etc. Interestingly, recent research has shown that at least one dwarf galaxy in our neighborhood, an ancient dwarf galaxy called Tucana II, has a surprisingly large dark matter halo.

So, what happened to Fornax differently?

There, dwarf galaxies may be “disturbed” by gravitational tides from larger nearby galaxies in the cluster. Tides occur when the gravity of one body exerts different pulls on different parts of the other body. These are similar to tides on Earth, when the moon pulls harder on the side of Earth that faces it.

The distorted shapes of dwarf galaxies the team saw suggest problems with our understanding of dark matter.

“According to the Standard Model, furnace dwarfs do not exhibit such perturbations,” said Pavel Krupa, a professor at the University of Bonn and Charles University in Prague.

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

Explaining twisted dwarf galaxies

Kroupa and doctoral student Elena Ascencio analyzed observations of disturbed dwarf stars in Fornax. They wanted to understand how much gravitational distortion these galaxies exhibit and what causes them.

The expected level of distortion depends on several factors. One is the internal features of dwarf galaxies. Also, their distance from the cluster center is important. This is where the gravitational influence is stronger.

Typically, large galaxies with few stars are easily disturbed by strong gravitational tides. The same is true for galaxies close to the cluster’s core.

Team members compared what they saw in the cluster with observations from the European Southern Observatory’s VLT survey telescope. Asencio points out that their findings appear to indicate a problem with the Standard Model.

“The comparison suggests that, if the observations in the Standard Model are to be explained,” she said, “even when it is rising at 64 times the tide on the dwarf, the Fornax dwarf should have been destroyed by the gravitational force at the center of the cluster. Its own gravity is even weaker.”

Not only is this counterintuitive, she says, it contradicts previous research. The team also found that the force required to perturb a dwarf galaxy is about the same as its own gravity.

What does this mean for the Standard Model?

If the dwarf galaxies in Fornax were surrounded by dark matter, it would be difficult to explain these perturbed, perturbed shapes, the team noted. In other words, if they do have halos, they shouldn’t be deformed.

However, their shape looks messy. This means that there are no dark matter halos around these galaxies.

Clearly, the Standard Model needs some tweaking if the astronomers’ findings are confirmed. And, there is at least another explanation for the strange galaxy shape. It’s called the MOND model (short for Modified Newtonian Dynamics).

It suggests that Newton’s law of gravity should be modified to account for the observed properties of galaxies. It could be used to explain why misshapen galaxies look the way they do.

According to Hongsheng Zhao, a member of the research team at the University of St Andrews, the search for disturbed dwarf stars without dark matter halos is a major challenge to current views.

It points out that galaxies have halos. He noted that not everyone seems to be doing this.

“Our results have major implications for fundamental physics,” he said. “We hope to find more disturbed dwarfs in other clusters, and this is a prediction that other teams should verify”.

This article was originally published by Universe Today. Read the original text.

Leave a Comment

Your email address will not be published.