The Hubble Space Telescope has shown that dark matter is concentrated in the core of a nearby dwarf galaxy, a discovery that comes to the aid of the Standard Model of Earth. cosmology. This model basically predicts that dark matter is “cold,” but recent findings seem to indicate that the substance is “warm.” However, these new observations favor the Standard Model.
Dark matter is the invisible substance that is said to exist 85% of the mass of the universebut no one knows what dark matter actually is, or how it behaves. Our best guess is that it is “cold,” meaning that it is expected to consist of a low-energy particle that does not fly back and forth, but rather moves slowly and is able to clump together and form huge halos in which galaxies grow. The concept of cold dark matter (CDM) and its influence on the formation of structure in the universe is a crucial part of our current Standard model of cosmology. That part is known as Lambda–CDM (the lambda refers to dark energy).
In the cold dark matter paradigm, dark matter should accumulate mostly in the core of a dark matter halo, and therefore dark matter should be densest in the core of a dark matter halo. universe that grows within that halo. Astronomers call this the dark matter “cusp” because of the shape it takes on a graph of dark matter density versus its radius from the center of a galaxy.
However, astronomers have been puzzled by some recent observations of dwarf galaxies that suggest dark matter might behave differently than they thought. Instead of behaving like cold dark matter and clumping most densely in the core of the dark matter halo, these observations imply that dark matter might be more evenly distributed throughout a galaxy. This would be a sign that dark matter is “warm,” or has enough energy to not clump together. If true, this would have major implications for our cosmological models, which assume that dark matter can clump together in certain ways.
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Astronomers led by Eduardo Vitral of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, have now put this to the test.
Dwarf galaxies are the best place to study dark matter because they have the highest proportion of dark matter of all galaxies. The Draco dwarf galaxy, chosen for this study, orbits our Milky Way at a distance of 250,000 light years from Soil. Hubble’s archives contain data describing the motions of stars in the Draco Dwarf, spanning 18 years, between 2004 and 2022. Vitral’s team was able to use these motions to calculate a precise measurement of the Draco Dwarf’s gravitational field, and thus the distribution of its mass, including the portion assigned to dark matter.
By the “actual movements” of the stars — that is, their motion across the sky — with their radial motions toward or away from us, detectable as a blueshift or a redshift In the light, Vitral’s team was able to follow the motions of the stars in the Draco dwarf 3D.
“When you measure proper motions, you record the position of a star at a certain time and then many years later you measure the position of that same star. You measure the displacement to determine how much the star has moved,” said team member Sangmo Tony Sohn of STScI in a rack“For these kinds of observations, the longer you wait, the better you can measure the shifts of the stars.”
Certainly, Hubble’s longevity in room is an advantage here, as is the powerful resolution from the vantage point high above The Earth’s turbulent atmosphereThe proper motion of the Draco dwarf stars over the course of 18 years at a distance of a quarter of a million light years is small, equal to less than the width of a golf ball on the moon as seen from EarthHubble’s results are therefore the most detailed measurements of stellar motions in another galaxy ever made.
Using these stellar motions, Vitral’s team was able to conclude that the total mass of the Draco dwarf’s dark matter halo, out to a radius of almost 3,000 light-years, is 120 million times the mass of the Draco dwarf. mass of our sunFurthermore, the results strongly indicate that the dark matter density profile of the Draco Dwarf has a cusp at the core and that dark matter is therefore is probably cold. As the researchers write in their research paper, “The results reduce the tension around the ‘cusp-core’ problem and lend more credibility to the standard lambda-CDM cosmology.”
“Our models seem to be more consistent with a cusp-like structure, which is consistent with cosmological models,” Vitral said in the statement. “While we cannot definitively say that all galaxies contain a cusp-like dark matter distribution, it is exciting to have such well-measured data that surpasses anything we have had before.”
The next step is to repeat the analysis for other dwarf galaxies. Currently, Vitral’s team is working on studies of the dwarf galaxies Sculptor and Ursa Minor, which also orbit our Milky Way.
If the findings can be repeated in this and other galaxies, it would effectively rule out a number of dark matter candidates, such as sterile neutrinos And gravitythe latter being a hypothetical particle predicted by the theory of supersymmetry as the enormous partner of the equally hypothetical (but probably Real) gravitonThe results therefore strengthen the possible models of cold dark matter, mainly weakly interacting massive particles (WIMPs), primordial black holes And axions.
The Draco Dwarf results were published on July 11 in The astrophysical journal.