Dark matter powered the universe’s first stars – new study

Dark matter powered the universe’s first stars – new study

Dark matter is not really do a lot of anything in the current universe. But in the early days of the cosmos, there may have been pockets of dark matter with a high enough density to provide a heat source for newly formed stars. Welcome to the weird and wonderful world of “black stars”.

A dark matter dance

The simplest models of dark matter are incredibly boring. It’s just…sitting there, gravitating. We only know of its existence through its subtle gravitational influence on galaxies and larger structures in the universe. It does not interact with light, with ordinary matter, or even with itself. Right now, you could be swimming in a vast sea of ​​dark matter particles, and you wouldn’t even know it.

But this simplistic picture of dark matter has some problems. When astrophysicists run computer simulations of galaxy formation, including dark matter, they find that if dark matter particles are too boring, it doesn’t quite match reality. The cores of galaxies become much denser than what we observe, and typical galaxies have far too many satellites than we see.

So maybe dark matter is just a little complicated. Maybe he still doesn’t interact with light or with ordinary matter, but maybe he sometimes interacts with himself. This self-interaction cannot be too strong; however, otherwise the dark matter would have clumped together into tiny little balls or simply annihilated long ago.

This “interact but not much” assumption makes it difficult for astronomers to find ways to test the scenario. Fortunately, astronomers are very smart people.

Dark Matter: Youth and Darkness

The extremely early universe, when it was only a few hundred million years old, was very different from what it is today. On the one hand, it was much denser, with all the material of the cosmos crammed into a much smaller volume. Second, it was much darker because the stars and galaxies hadn’t formed yet.

Back then, the universe was made up of dark matter (whatever it was) and neutral hydrogen and helium. Slowly, over the eternities, all of this material began to gravitationally collapse, forming larger and larger structures. The first protostars began as dense clusters no larger than one thousandth the size of the Sun. In the traditional picture of the formation of the first stars, these clusters gradually transformed into behemoths a hundred times larger than the Sun, fueled by nuclear fusion in their cores.

The first stars were made of only hydrogen and helium. NASA/WMAP science team

But a team of astrophysicists realized the traditional story might be different, as they reported in a new article that appeared recently in the preprint journal arXiv. If dark matter interacts with itself, then when dark matter particles collide, they release some energy. Each collision doesn’t produce much, but in the early days of the universe, star formation sites may have had densities high enough that dark matter annihilation was a major player.

In this scenario, the first stars are not fueled by nuclear fusion but rather by the annihilation of dark matter in their cores. The research team calls them “dark stars,” even though the stars themselves are still made up of mostly normal matter. These stars do not exist in the modern universe because dark matter densities are too low, so we cannot see them in the galaxy today.

But researchers hope that the James Webb Space Telescope, specially designed to study the early universe and the formation of the first stars, will be able to see these dark stars directly.

This article was originally published on Universe today by Paul M. Sutter. Read the original article here.

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