A brand new examine by College of California, San Diego computational astrophysicist Ethan Nadler reveals that star formation can happen in halos right down to 10 million photo voltaic lots by molecular hydrogen cooling.
Nadler calculated the fraction of darkish matter halos that exceeds a vital mass required for star formation. Picture credit score: Xiaodian Chen.
Each galaxy is believed to type on the heart of a darkish matter halo — a area of gravitationally sure matter that extends far past the seen boundaries of a galaxy.
Stars are fashioned when gravity inside darkish matter halos attracts in fuel, however astrophysicists don’t but know whether or not star-free darkish matter halos exist.
“What’s the halo mass threshold for galaxy formation?” Dr. Nadler mentioned.
“This query underlies key areas of analysis in galaxy formation and cosmology, together with when and the way the primary galaxies fashioned, which galaxies drive cosmic reionization, and whether or not ‘darkish’ (galaxy-free) darkish matter halos exist.”
“Sturdy predictions for the galaxy formation threshold are vital given upcoming observations of faint galaxies and low-mass halos all through cosmic historical past.”
In his new examine, Dr. Nadler calculated the mass under which halos fail to type stars.
His work was carried out utilizing analytic predictions from galaxy formation concept and cosmological simulations.
“Traditionally, our understanding of darkish matter has been linked to its habits in galaxies,” Dr. Nadler mentioned.
“A detection of utterly darkish halos would open up a brand new window to check the Universe.”
Beforehand, this threshold for star formation was regarded as between 100 million to 1 billion photo voltaic lots attributable to cooling of atomic hydrogen fuel.
The present examine reveals that star formation can happen in halos right down to 10 million photo voltaic lots by molecular hydrogen cooling.
“With the Rubin Observatory coming on-line later this yr and Webb already making unprecedented observations of our Universe, there’ll quickly be new information to check these predictions and reveal whether or not utterly darkish halos exist,” Dr. Nadler mentioned.
“This will likely have far-reaching penalties for cosmology and the character of darkish matter.”
The study seems within the Astrophysical Journal Letters.
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Ethan O. Nadler. 2025. The Influence of Molecular Hydrogen Cooling on the Galaxy Formation Threshold. ApJL 983, L23; doi: 10.3847/2041-8213/adbc6e
