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Dark matter can hit the right note in small galaxies

Astronomers have observed that dark matter does not seem to agglutinate much in small galaxies, but that its density peaks in larger systems such as clusters of galaxies. It has been difficult to understand why different systems behave differently. Credit: Kavli IPMU – Kavli IPMU changed this figure according to the image credited by NASA, STScI

In a new study, researchers in Japan, Germany and Austria can disperse against each other when they reach the right energy. Their idea helps to explain why galaxies from the smallest to the largest have the shapes they have.

Dark matter is a mysterious and unknown form of matter that comprises over 80% of the matter in the universe today. Its nature is unknown, but physicists believe that its gravity is responsible for the formation of stars and galaxies, which has led to our existence.

"The dark matter is actually our mother, who brought us all, but we did not meet her, we separated anyway at birth, who is she? we want to know, "says author of the article Hitoshi Murayama, senior researcher at the University of California at Berkeley and at the Kavli Institute of Physics and Mathematics of the Universe.

Astronomers have already found that dark matter does not seem to agglutinate as much as computer simulations suggest. If gravity is the only force that drives dark matter, only shooting and never pushing, dark matter should become very dense towards the centers of galaxies. However, especially in small, weak galaxies called dwarf spheroids, dark matter does not seem to become as dense as expected towards the galactic centers.

When two particles of dark matter approach one another, they tend to simply cross each other. Credit: Kavli IPMU

This puzzle could be solved if dark matter scattered on itself, like billiard balls, allowing the particles to disperse more evenly after a collision. But a problem with this idea is that dark matter seems to agglutinate in larger systems such as galaxy clusters. What is it that dark matter behaves differently between dwarf spheroids and clusters of galaxies? An international team of researchers has developed an explanation that could solve this puzzle and reveal what dark matter is.

"If dark matter scatters with each other at a low but very special speed, it can often happen in the dwarf spheroids, where it is slowly advancing, but it is rare in galaxy clusters where it moves rapidly. ", explains Chinese physicist Xiaoyong Chu, postdoctoral researcher at the Austrian Academy of Sciences.

Resonance is a common phenomenon: turning the wine in a glass to expose it to oxygen and produce more aroma requires going around the glass at the right speed. Old analog radios must be set to the correct frequency. These are examples of resonance, and the team suspects that this resonance could explain this puzzle of dark matter.

But when they arrive at a special speed, they "resonate" and stick to each other for a brief moment, then move in different directions afterwards, causing them to disperse. In this way dark matter can spread so that we can understand the smooth profile of small galaxies. Credit: Kavli IPMU

"As far as we know, this is the simplest explanation of the puzzle.We are delighted because we may know what dark matter is in the near future," he said. said Murayama.

However, the team was not convinced that such a simple idea would properly explain the data. "First of all, we were a little skeptical about the fact that this idea explains the observation data, but once we tried it, it worked perfectly," said Colombian scientist Camilo Garcia Cely, postdoctoral researcher at the Deutsches Elektronen-Synchrotron (DESY) in Germany.

Using the idea of ​​resonance, the plot demonstrates that we can explain all systems at the same time. Credit: Xiaoyong Chu, Camilo Garcia Cely, Hitoshi Murayama

The team believes that it is not a coincidence that dark matter can hit the exact note. "There are many other systems in nature that exhibit similar accidents: in stars, alpha particles strike a resonance of beryllium, which in turn strikes a carbon resonance, producing the building blocks that gave rise to the A similar process occurs in a subatomic particle called phi ", says Garcia Cely.

"It can also be a sign that our world has more dimensions than we see, if a particle moves in extra dimensions, it has energy." For humans, who do not see the extra dimension , we think that the energy is actually a mass, thanks to Einstein's E = mc2. Maybe some particles move twice as fast in extra dimension, their mass being exactly twice as much as the mass of dark matter, "says Chu.

The next step of the team will be to find observational data that corroborates their theory. "If this is true, future and more detailed observations of different galaxies will reveal that the dark matter's diffusion indeed depends on its speed," said Murayama, who also runs a separate international group Premier Spectrograph under construction. The instrument, with a budget of $ 80 million, will be mounted on the Subaru telescope atop Mauna Kea on Big Island, Hawaii, and will be able to measure the speed of thousands of people. stars in the dwarf spheroids.

The team's document was published online on February 22 by Letters of physical examination.

Explore further:
Dark matter in motion

More information:
Xiaoyong Chu et al. Speed ​​dependence of self-interacting resonant dark matter, Letters of physical examination (2019). DOI: 10.1103 / PhysRevLett.122.071103

Journal reference:
Letters of physical examination

Provided by:
Kavli Institute for Physics and Mathematics of the Universe

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