Wang et al., 2024 / Pennsylvania State University
These fresh and compact objects found in deep space images are the most surprising discovery of James Webb.
Astronomers of the Center for Astrophysics / Harvard & Smithsonian (CFA / HS) proposed a new explanation for some of the most intriguing galaxies in the primitive universe, nicknamed “small red dots” (LRDs).
In a new one, published this week in The Astrophysical Journal LettersAstronomers Fabio Pacucci e Avi counts suggest that these galaxies are the result of Halos of dark matter which run very slowly, an extremely rare cosmic structure.
These fresh and compact objects, in images of the deep space of the James Webb space telescope (JWST), challenged understanding of scientists about how black galaxies and holes form in the primitive universe.
The new article now offers a physical explanation for properties distinctive of these points.
“The small red dots They are very compact distant galaxies and red completely unnoticed before From the James Webb Space Telescope, ”says Pacucci in from CFA/HS.
“They are arguably most surprising discovery from JWST to date. Our work shows that these could naturally form in dark matter hales with very low rotation. ”
A puzzle in the primitive universe
These galaxies are mainly visible when the universe had only about billionbut probably formed much earlier, during a period known as the cosmic dawn.
Despite having about one tenth the size of the typical galaxiesastronomical observations show that they seem unusually bright. Astronomers believe that their striking red color suggests that they are wrapped in dust or full of older stars.
For years, astronomers have debated if the light we observe of these objects is generated by stars or supermassive black holes Centrals.
“It is a fundamental mystery“Says Pacucci.“ Black holes contain, these black holes They are huge for such small galaxies. But if they only contain stars, the galaxies are too compact to contain them allreaching central star densities that are unthinkable. ”
Instead of focusing on the lighting points, Pacucci and Loeb adopted A DIFFERENT APPROACH: They examined how such objects could, first of all, form.
Wang et al., 2024 / Pennsylvania State University
Color images, composed from three Nircam filter bands aboard the James Webb space telescope. They are remarkably compact in red wavelengths (which earned them the term “small red dots”) with some evidence of spatial structure in blue wavelengths.
The low rotation cycle
The hales of dark matter are the invisible and rotating structure around which the galaxies form. In their article, the authors show that the bright points have formed in halos that are in the lower 1% of the rotation distribution. In other words, 99% of all halos run faster than these.
These low rotation halos would naturally create extremely compact galaxies. Like the swings at a popular fairthe faster the halo runs, the farther the riders extend, causing the galaxy that forms in its center expands; Similarly, a slow rotation keeps the smaller ride of swing.
This hypothesis It also explains Why the light points are relatively rare: they represent only 1% of the abundance of typical galaxies, but are more common than quasars, extremely brilliant centers of supermassive black holes that shine at the center of some galaxies.
In addition, the theory helps to clarify why the bright points are observed only for a brief period billions of years in the primitive universe. As the universe evolves, the hales of dark matter become larger and earn more angular momentmaking it more difficult to form compact galaxies of low rotation.
“The halos of dark matter are characterized by their speed of rotation: some of them run very slowly, and others run faster,” says Loeb. “We showed that if we assume that the small red dots are typicallythe first percentile of the rotation distribution of the hales of dark matter, So we explain all its properties observational ”.
Privileged environments for black holes
Although the article does not solve if the small red dots are fed by black stars or holes, suggests thatprivileged environments for rapid growth of stars or black holes.
“The low rotation halos tend to concentrate mass in the centerwhich facilitates the accretion of matter by a black hole or the rapid formation of stars, ”explains Pacucci.
Some of the points show wide emission lines in its spectrawhich are possible signs of active black holes, but lack the emission of X-ray typically associated with them.
Pacucci is leading new programs to better understand the nature of these peculiar astrophysical sources. For example, Find nearby galaxies Similarly will clarify what they evolve further in space.
“Our work is a step in understanding these mysterious objects,” he said. “They can help us understand how the first black holes formed and co-evolved with the galaxies in the primitive universe.”
