March 1, 2024

Webb can see far enough to test dark matter theories

This is a composition by the Stephan Quintet made up of almost 1,000 separate images. It was one of the first James Webb Space Telescope images released to the public. | Credit: NASA, ESA, CSA and STScI

The Hubble Space Telescope (HST) overturned beliefs about the fundamental nature of the Universe, providing evidence that the Universe was not slowing down, as gravity apparently suggested it should be, but rather expanding. 25 years later, the James Webb Space Telescope (JWST) could help scientists make another breakthrough.

Where Hubble showed, through its observations of extremely distant supernovae, that the Universe once expanded more slowly than it is today, demonstrating that it is no continually slowing down, Webb is trying to show why that is.

There are countless theories about why the Universe expands at an accelerating rate, but at the center of the most compelling is “dark energy.” In the years since Hubble shattered beliefs, physicists have learned a lot about dark matter and energy, but much more remains mysterious.

Current beliefs hold that approximately 68% of the Universe is so-called dark energy and 27% is dark matter. The other 5%? All this is common business; all that humans can observe and interact with.

Numerous theories could explain dark energy and matter and how they interact with the structure of the Universe and everything in it, and Webb may be able to test one of the leading theories.

As Space reports, since JWST can see so far back — it has already detected a galaxy just a few hundred million years after the Big Bang — astrophysicists can gather new data to create significantly more accurate simulations of the early Universe.

“Over the past year and a half, the James Webb Space Telescope has provided astonishing images of distant galaxies formed not long after the Big Bang, giving scientists their first glimpses of the infant universe. Now, a group of astrophysicists has upped the ante: Find the smallest, brightest galaxies near the beginning of time, or scientists will have to completely rethink their theories about dark matter,” explains the University of California, Los Angeles (UCLA) in a press release.

The team, led by UCLA astrophysicists, implemented interactions between gas and dark matter in new simulations, events that have typically been ignored, and found that the resulting galaxies are tiny, significantly brighter and formed more quickly than in previous simulations. .

Scientists believe that all galaxies are surrounded by a “vast halo of dark matter”, which was fundamental to their formation. However, dark matter is impossible to observe using optics, electricity or magnetism. Ultimately, it’s still hypothetical. However, dark matter interacts with gravity, so its existence can be inferred through the effects observed in ordinary (observable) matter.

The “standard cosmological model” that underpins the collective understanding of galaxy formation relies on dark matter in the early days of the Universe to attract ordinary matter through gravity, allowing the formation of stars and galaxies.

However, it is believed that many dark matter particles, called “cold dark matter”, move significantly slower than the speed of light, so the accretion process described would have to occur gradually.

The small dwarf galaxies believed to be the oldest in the Universe don’t always appear as expected. Some spin very quickly, others have inexplicably low densities. Dark matter can fill these problematic gaps between cosmological theory and real-world observations.

Webb in search of small, bright, ancient galaxies that could overturn cosmological theory.
About a year ago, an international team of astrophysicists used Webb to detect ancient, massive galaxies that are unexplained within current cosmological theory. The proposition that Webb will find more galaxies that don’t make sense is not at all unlikely. | Image credit: NASA, ESA, CSA, I. Labbe (Swinburne University of Technology). Image processing: G. Brammer (Cosmic Dawn Center of the Niels Bohr Institute at the University of Copenhagen).

“But more than 13 billion years ago, before the first galaxies formed, ordinary matter, made up of hydrogen and helium gas from the Big Bang, and dark matter moved relative to each other. The gas flowed at supersonic speeds past dense thickets of slower-moving dark matter that should have pulled it to form galaxies,” explains UCLA.

“In fact, in models that don’t take streaming into account, this is exactly what happens,” says Claire Williams, a UCLA doctoral student and first author on the research paper. “The gas is attracted by the gravitational pull of dark matter, forms clumps and knots so dense that hydrogen fusion can occur, and thus forms stars like our Sun.”

Williams and the study’s co-authors are part of the Supersonic Project team, an international collaboration of astrophysicists from the United States, Italy and Japan. UCLA physics and astronomy professor Smadar Naoz leads the team.

The Supersonic Project coalition discovered that if they incorporated the effect of the flow of varying speeds between dark and ordinary matter into simulations of the early Universe, the gas (hydrogen and helium) would end up far from the dark matter and therefore could not immediately form stars. . When this accumulated gas fell back into a galaxy millions of years later, there was an explosion of star formation.

Because the galaxies in this adjusted simulation have many more young, luminous stars than ordinary small galaxies, they are relatively brighter than other galaxies.

“Although the flow suppressed star formation in the smallest galaxies, it also boosted star formation in the dwarf galaxies, causing them to outshine the no-flow zones of the Universe,” explains Williams. “We predict that the Webb telescope will be able to find regions of the Universe where galaxies will be brighter, magnified by this speed. The fact that they are so bright could make it easier for the telescope to discover these small galaxies, which are normally extremely difficult to detect just 375 million years after the Big Bang.”

By searching for bright patches of galaxies in the early Universe using Webb, scientists can test theories about dark matter.

“The discovery of patches of small, bright galaxies in the early Universe would confirm that we are on the right track with the cold dark matter model because only the velocity between two types of matter can produce the type of galaxy we are looking for,” says Naoz. “If dark matter does not behave like standard cold dark matter and the outflow effect is not present, then these bright dwarf galaxies will not be found and we will have to go back to the drawing board.”

The research is described in detail in a new research paper published in The letters from the astrophysical journal. NASA and the National Science Foundation supported the research.

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