If theories about cold dark matter are correct, the Webb Space Telescope will discover tiny, bright galaxies of the early universe. For the past year and a half, the James Webb Space Telescope has been producing spectacular images of distant galaxies that formed shortly after the Big Bang, giving scientists the first glimpses into the birth of the universe. Now a group of astrophysicists has raised the bar: Find the smallest, brightest galaxies at the beginning of time, or scientists will have to completely revise their theories about dark matter.

A team led by astrophysicists from the University of California, Los Angeles, has run simulations that trace the formation of small galaxies after the Big Bang and include, for the first time, previously neglected interactions between gas and dark matter. They found that the galaxies formed were much smaller, much brighter, and formed faster than typical simulations that ignore these interactions, revealing much dimmer galaxies instead.

The importance of dwarf galaxies in space exploration

Small galaxies, also called dwarf galaxies, exist throughout the universe and are generally considered the oldest types of galaxies. For this reason, small galaxies are of particular interest to scientists studying the origin of the universe. But the small galaxies they find don’t always match the galaxies they think they should find. Those closest to the Milky Way are spinning faster or are not as dense as in the simulation; This suggests that the models may have missed some things, such as gas and dark matter interactions.

A new study has been published Astrophysics Journal Letters, He improves the simulation by adding the interaction of dark matter with gas and finds that these faint galaxies can be much brighter than expected early in the history of the universe, when they were just beginning to form. The authors suggest that scientists are trying to find small galaxies that are much brighter than expected with telescopes such as the Webb Telescope. If they only find faint ones, some of their ideas about dark matter may be wrong.

The elusive nature of dark matter

Dark matter is a type of hypothetical matter that does not interact with electromagnetism or light. Therefore, it is impossible to make observations with optics, electricity or magnetism. But dark matter interacts with gravity, and its existence was made possible thanks to its gravitational effect on the ordinary matter that makes up the entire observable universe. Although dark matter is believed to make up 84% of the matter in the universe, it has never been directly detected.

All galaxies are surrounded by a massive halo of dark matter, and scientists believe dark matter is important in their formation. The “Standard Cosmological Model,” which astrophysicists use to understand galaxy formation, explains how clumps of dark matter in the very early universe gravitationally attracted ordinary matter, triggering star formation and creating the galaxies we see today. This accretion process will occur gradually, as most dark matter particles, called cold dark matter, are thought to move much slower than the speed of light.

Theoretical advances in understanding galaxy formation

But more than 13 billion years ago, before the first galaxies formed, ordinary matter and dark matter, composed of hydrogen and helium produced in the Big Bang, moved relative to each other. The gas flows at supersonic speeds through dense thickets of slower-moving dark matter, which should pull it toward the galaxies.

“This is essentially what happens with models that don’t take flow into account,” said Claire Williams, a postdoctoral researcher at UCLA and first author of the paper. “The gas is pulled by the gravity of dark matter, forming clusters and knots so dense that hydrogen fusion can occur, forming stars like our Sun.”

But Williams and co-authors from the Supersonic Project team, a group of astrophysicists from the United States, Italy and Japan led by UCLA physics and astronomy professor Smadar Naoz, found that if you add in the effect of the flow of different velocities between dark and dark, it’s a matter of ordinary. According to the simulations, the gas landed too far from the dark matter and could not form stars immediately. When gas accumulated over millions of years re-entered the galaxy, a powerful burst of star formation immediately occurred. These galaxies once shone much brighter because they contained many more young, hot, bright stars than ordinary small galaxies.

“While the flow suppressed star formation in the smallest galaxies, it also accelerated star formation in dwarf galaxies, causing them to eclipse the non-flowing regions of the Universe,” Williams said. “With this speed, we predict that the Webb telescope will be able to find regions of the universe where galaxies will be brighter. The fact that they are this bright may make it easier for the telescope to detect these small galaxies, which are normally extremely difficult to detect just 375 million years after the Big Bang.”

Because dark matter cannot be studied directly, probing the bright regions of galaxies in the early universe could offer a powerful test of dark matter theories that have so far remained inconclusive.

“Finding regions of small bright galaxies in the early universe will confirm that we are on the right track with the cold dark matter model, because only the velocity between two types of matter can create the type of galaxy we are looking for.” Naoz is the Howard and Astrid Preston Professor of Astrophysics. “If dark matter does not behave like standard cold dark matter and has no flux effect, then these bright dwarf galaxies will not be found and we will have to go back to the drawing board.”