by A new theory that suggests that dark matter is made up of particles that interact strongly with each other through the so-called “dark force”. If true, this could finally explain the large densities we see in haloes of dark matter surrounding galaxies.
Particles called self-interacting dark matter (SIDM) act as an alternative to cold dark dark theories which suggest that the elusive stuff is made up of massive, slow-moving (and therefore cold) particles, which interact weakly and do not collide. The problem with those cold dark matter models is that they struggle to explain two puzzles related to something called a dark matter halo.
“The first is a high-density dark matter halo in a giant elliptical galaxy. The halo was detected by observing strong gravitational lensing, and its density is so high that it is highly unlikely in cold dark matter theory prevailing,” Hai-Bo Yu, team leader and professor of physics and astronomy at the University of California, Riverside, said in a statement.
“The second,” he continued, “is that the dark matter halos of ultra-diffuse galaxies have very low densities, and are difficult to explain by the cold dark matter theory.”
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The Hales
Dark matter poses a major challenge to scientists because, despite making up about 85% of the matter in the cosmos, it does not interact with light and is therefore almost invisible to us. This suggests to researchers that dark matter cannot be conglomerates of matter made up of electrons, protons and neutrons – so-called baryonic matter that includes stars, planets, our bodies and almost everything we see around us on us from day to day. – daily base. Must, must do dark stuff something else.
The only way researchers can conclude that dark matter actually exists at all is that it has mass and therefore interacts with gravity. This effect can be “felt” with baryonic matter that we can actually see and with the light, which astronomers are certainly able to observe.
Specifically, when light travels past these dark matter-wrapped galaxies from background sources, the impact of the matter on the fabric of space redirects the path of light and, in turn, the background sources appear to “shift” to new locations in space.
It is this effect, known as gravitational lensing, that first allowed scientists to determine that most, if not all, galaxies are surrounded by halos of dark matter in the first place. And these haloes are believed to extend far beyond the limits of the visible matter of those galaxies such as stars, gas and dust. Gravitational lensing also allowed astronomers to measure the density of dark matter haloes. Dense haloes are responsible for stronger lensing than denser haloes around ultradiffuse galaxies — low-brightness galaxies containing scattered gas and stars. However, researchers have struggled to explain the extremes in dark matter halo densities.
Enter, artificial intelligence
To address this question, Yu and his colleagues, including University of Southern California postdoctoral researchers Ethan Nadler and Daneng Yang, performed high-resolution simulations of cosmic structures based on real astronomical observations.
They included the strong self-interactions of dark matter in those simulations on massive scales of strongly lensed haloes and ultra-diffuse galaxies.
“These self-interactions are the result of heat transfer in the halo, which diversify the halo density in the central regions of galaxies,” explained Nadler. “In other words, some haloes have higher central densities, while others have lower central densities, compared to their cold dark matter counterparts, with details depending on the cosmic evolution history and environment of individual halos.”
The team concluded that SIDM could interact through “dark force”, just as baryonic particles interact through electromagnetism and the strong and weak nuclear forces, offering a solution that cold dark matter theories do not deliver.
“Cold dark matter is challenged to explain these puzzles. SIDM is arguably the strong candidate to solve the other two extremes,” Yang said. “Now there is an intriguing possibility that dark matter may be more complex and vibrant than we expected.”
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The team thinks their research also provides an example of the analytical power of uniting real-world observations, which increase in detail with each new generation of telescopes, with the increasing power of artificial intelligence.
“We hope our work inspires more studies in this promising area of research,” said Yu. “It will be a very timely development given the influx of data expected in the near future from astronomical observatories, including the James Webb Space Telescope and the upcoming Rubin Observatory.”
The team’s research was published in November i The Astrophysical Journal Letters.
