Dark matter not really do much of everything in today’s universe. But in the early days of the cosmos there may have been pockets of dark matter dense enough to provide a heat source for newly forming stars. Welcome to the weird and wonderful world of “Dark Stars”.
A dance of dark matter
The simplest models of dark matter are incredibly boring. It… just sits there and gets dressed. We only know of its existence through its subtle gravitational influence on galaxies and larger structures in the universe. It doesn’t interact with light, or 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 realize it.
But this simplified picture of dark matter has a few problems. When astrophysicists run computer simulations of the formation of galaxies, including dark matter, they find that dark matter particles that are too boring don’t quite match reality. The cores of galaxies become much denser than we observe, and typical galaxies have far more satellites than we see.
So maybe dark matter is just a little complicated. It may still not interact with light or ordinary matter, but it may sometimes interact with itself. This self-interaction cannot be too strong; otherwise, however, the dark matter would have balled up into tiny globules or would have annihilated itself long ago.
This “interacts, but not very much” hypothesis makes it difficult for astronomers to find ways to test the scenario. Fortunately, astronomers are very smart people.
Dark Matter: The Young and the Dark
The extremely early Universe, when it was only a few hundred million years old, was very different than it is today. For one, it was much denser, since all the matter of the cosmos was crammed into a much smaller volume. Second, it was much dimmer because stars and galaxies had not yet formed.
Back then, the universe was made up of dark matter (whatever that is) and neutral hydrogen and helium. Slowly, over the course of eons, all this material began to collapse under the force of gravity, forming larger and larger structures. The first protostars began as dense clumps no larger than one-thousandth the size of the Sun. In the traditional picture of the formation of the first stars, these clumps steadily grew into giants a hundred times the size of the Sun, powered by nuclear fusion at their cores.
But a team of astrophysicists have recognized that the traditional story could be different, they reported in a new article recently published in the Preprint-Journal arXiv. When dark matter interacts with itself, the dark matter particles release a small amount of energy when they collide. Each collision doesn’t produce much, but in the early days of the universe, star-forming sites may have been dense enough to annihilate dark matter to play an important role.
In this scenario, the first stars are not powered by nuclear fusion, but by the annihilation of dark matter in their cores. The research team calls them “dark stars,” although the stars themselves are still mostly made of normal matter. These stars do not exist in the modern Universe because the dark matter density is too low for us to see them in the galaxy today.
However, the researchers hope that the James Webb Space Telescope, designed specifically to study the early Universe and the formation of the first stars, may be able to see these dim stars directly.
This article was originally published on universe today by Paul M Sutter. Read the original article here.