Neil deGrasse Tyson hosts this StarTalk Cosmic Queries episode on cosmology with comedian Chuck Nice and guest expert Katherine Freese, Director of the Weinberg Institute for Theoretical Physics at UT Austin. Freese, who spent 10 years at Stockholm University with a $15 million grant for cosmoparticle theory research, is known for her work on dark matter detection and her popular 2014 book The Cosmic Cocktail Three Parts Dark Matter.

The conversation covers cutting-edge cosmology topics including dark stars, paleo detectors, and recent James Webb Space Telescope discoveries. Freese discusses her theoretical work on dark energy, WIMP detection methods, and the possibility of invisible dark matter galaxies. The episode explores fundamental questions about the nature of dark matter and dark energy, including recent debates about whether dark energy changes over time based on DESI experiment results.

Dark Stars: The Universe's First Stellar Giants

Dark stars are hypothetical first stars powered by dark matter annihilation rather than nuclear fusion, starting at one solar mass but growing to 'a million times as massive as the sun and a billion times as bright' - Katie

These objects would be cool and enormous, with radii '10 times the distance between the Earth and the Sun,' allowing continuous matter accretion unlike hot fusion-powered stars that blow material away

James Webb Space Telescope has identified candidates for dark stars among unexpectedly bright early universe objects called 'blue monsters' and 'little red dots' that current models cannot explain

Dark stars could solve multiple cosmological puzzles: explaining supermassive black holes in the early universe after they die, and accounting for anomalously bright objects in the cosmic dawn

Paleo Detectors: Billion-Year Dark Matter Archaeology

Paleo detectors use ancient rocks from deep underground that have been 'collecting dark matter tracks for a billion years,' replacing detector volume with time - Katie

The approach emerged because xenon dark matter experiments 'have bought the entire world supply' of xenon, making the element extremely expensive and necessitating alternative detection methods

Olivine crystals, found in pallasite meteorites, are the preferred target material, requiring rocks from at least five kilometers underground to avoid cosmic ray contamination

These detectors could also track neutrinos from historical supernovae, allowing scientists to 'figure out how many supernova went off in the galaxy' at different times in the past

Dark Energy's Deepest Mystery: The 10^120 Problem

Dark energy represents 'one of the biggest unsolved problems in all of physics' with theoretical calculations off by '10 to the 120 in the exponent' from observations - Katie

The DESI experiment suggests dark energy may be changing over time, but Freese's simpler analysis with collaborator Yoon Wang finds 'we do not find that evidence to be very strong'

Vacuum energy from particle-antiparticle pairs can be measured through the Casimir effect, but scaling this up to cosmic levels produces the massive theoretical discrepancy

Dark energy causes repulsion rather than attraction, fundamentally different from ordinary matter and energy, leading to the universe's accelerating expansion

WIMP Detection: Make It, Shake It, or Break It

WIMPs (Weakly Interacting Massive Particles) can be detected three ways: 'make it' in particle accelerators like the Large Hadron Collider, 'shake it' in underground detectors, or 'break it' through annihilation

Underground detectors look for WIMPs hitting xenon atoms and depositing energy, with 'billions going through your body every second' but 'only one a month hits you' - Katie

Indirect detection searches for WIMP annihilation products, with neutrino detectors like IceCube at the South Pole looking for signals from dark matter collisions

Other dark matter candidates include axions that can convert to photons in magnetic fields, and primordial black holes that could explain some gravitational wave detections

Invisible Dark Matter Galaxies and Cosmic Structure

'Without dark matter, we wouldn't exist' because it had to collapse first to create proto-galaxies before ordinary matter could follow - Katie

Pure dark matter galaxies may exist with no stars, detectable only through gravitational lensing effects that bend light from background objects

Dark matter doesn't coalesce like ordinary matter because it only interacts through gravity and the weak force, preventing the formation of compact dark matter planets or stars

Redshift measurements must account for both Doppler effects from cosmic expansion and gravitational redshift from dark matter, but spectral line shifts confirm the expansion interpretation