An exotic dark matter model suggests that the first stars may have formed not as individuals, but as tiny pockets embedded in gigantic pancake-like sheets. This would have led to the formation of truly gigantic stars that the James Webb Space Telescope may be able to detect, according to a research team.
Astronomers have a wealth of evidence to suggest that the vast majority of all matter in the universe is black matter, meaning it does not interact with light or normal matter. For example, stars revolve around the center of their galaxies far too quickly considering the gravity of all we can see. The same thing happens when we observe the movements of galaxies within clusters. And the cosmic web, the large-structured arrangement of galaxies throughout the universe, appeared and grew far too quickly considering the small amount of gravity provided by all visible objects.
A large part of our universe is therefore invisible, but we do not yet know what this dark part is made of. A popular suggestion is known as cold dark matter, which means that dark matter is made up of some kind of exotic particle that generally moves much slower than light. speed of light. Although this model is a huge success – it can explain all the weird observations of galaxies and structures – it has some shortcomings.
Related: Dark matter can form tiny cold “clusters”. Scientists have found the smallest yet.
For one thing, the cold dark matter model struggles at scales smaller than galaxies. For example, the model predicts far more matter at the center of galaxies than we observe and predicts far more small satellite galaxies than we can detect.
One idea to get around this problem is to make the cold dark matter a bit “fuzzy”. If dark matter consists of an incredibly tiny particle – say, 10^22 times smaller than an electron – then it would be light enough for its quantum mechanical wave nature to show up on a large scale. So instead of these particles existing as point objects, they would be blurred and their identities would be spread over regions as large as 1,000 light-years.
A new recipe
By making dark matter fuzzy, this wave-like nature of the particle effectively spreads it out over great distances, solving many of the accumulation problems faced by cold dark matter. In other words, this model prevents dark matter from building structures less than 1,000 light-years away.
Because this model was designed to explain existing observations, to do the work of science, we have to go out and find a new way to test the idea. That’s the motivation behind a new paper submitted for publication to The Astrophysical Journal Letters and available for preprint via arXiv.
In the article, the astronomers developed computer simulations of the early universe and the appearance of the first stars. They allowed dark matter to be “fuzzy” and observed how this altered the evolution of normal matter and the development of stars.
Stars and galaxies need dark matter to form. Because the universe is constantly expanding, you need a lot of gravity to pull together a clump of gas to get high enough densities to trigger fusion and the start of star formation. And there just isn’t enough normal matter in the universe for that to happen. But clumps of dark matter in the early universe serve as gravitational incubators, attracting enough normal matter to form stars and galaxies.
So if you change the properties of dark matter, like blurring it, you change the way stars and galaxies evolve.
lumps in the dough
In their simulations, the researchers found that when dark matter becomes fuzzy, it alters the narrative of star formation. In ordinary cold dark matter, stars first shine deep within tiny individual pockets scattered throughout the cosmos. But with fuzzy dark matter, gigantic two-dimensional pancake-like sheets form first.
The crepe then quickly fragments into individual pockets that eventually turn into stars. So no matter what, you fill a universe with a collection of stars, just like in normal cold dark matter scenarios. But the researchers found a key observable difference.
Because two-dimensional pancakes have so much mass and collapse so quickly, the first generation of stars is much larger than cold dark matter scenarios predict. These early stars in fuzzy dark matter models can reach up to a million times the mass of the sunwhere cold dark matter can produce, at best, stars a few hundred times larger than the Sun.
Due to their enormous sizes, the stars would not live long. And in the blink of an eye, the first generation of stars would disappear in a furious storm of supernova explosions. From there, once the pancakes dissipated, normal star formation would begin and the universe would begin to look more like our own.
Although the James Webb Space Telescope will not be able to directly observe the first stars that appeared in the universe, it is able to image some of the first galaxies, which could contain some remnants of the primordial generation of stars. The researchers predict that if Webb sees no first-generation stars, that could be evidence of the team’s scenario, because in their model, all first-generation stars die quickly.
Alternatively, Webb might be able to detect remnants of radiation from the intense supernova round.
When it comes to dark matter, however, it’s impossible to say what the universe might be cooking up.
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