What percentage of the universe's total energy-mass content is dark matter?

About 5% About 27% About 50% About 68%

Which of the following is a required property of dark matter?

Made of protons, neutrons, and electrons like ordinary matter Electrically neutral — it does not emit, absorb, or reflect light Moving at near the speed of light Concentrated only in the centers of galaxies

What does cold mean when scientists say dark matter must be cold?

Dark matter is at a very low temperature and would freeze any gas near it Dark matter particles move slowly compared to the speed of light, allowing them to clump together and form galaxy-scale structures Dark matter was created at very low temperatures in the Big Bang Cold means it does not emit heat or infrared radiation

What are WIMPs?

Weakly charged photons that travel slower than ordinary light Weakly Interacting Massive Particles — hypothetical particles with masses roughly 10 to 1000 times that of a proton, predicted by supersymmetry White Invisible Matter Particles — a form of baryonic dark matter The same as neutrinos, which already make up dark matter

What are axions?

Massive particles produced in supernovae that travel through galaxies Very light hypothetical particles originally proposed to solve a problem in particle physics, now also considered a dark matter candidate A type of antiparticle that annihilates with ordinary matter Modified neutrinos with extra mass that make up dark matter

What are MACHOs, and why are they ruled out as the primary source of dark matter?

Massive Antimatter Cosmic Halos; ruled out because they would annihilate with nearby matter Massive Compact Halo Objects (brown dwarfs, neutron stars); ruled out because microlensing surveys show too few to account for the observed dark matter Magnetic Atomic Cosmic Halos; ruled out because they interact with radio waves MACHO refers to the dark matter in galactic cores only, not the halo

What are primordial black holes as a dark matter candidate?

Black holes formed by collisions between dark matter particles Black holes at the centers of galaxies that are invisible at large distances Black holes that formed in the early universe from density fluctuations, before any stars existed The remnant cores of stars that exhausted their dark matter fuel

Why does Big Bang nucleosynthesis rule out ordinary (baryonic) matter as the primary dark matter component?

BBN shows that all ordinary matter was destroyed in the Big Bang BBN only works with dark matter present; without it no elements would form BBN calculations precisely predict the abundances of hydrogen, helium, and lithium produced in the early universe, and they only work if baryons make up about 5% of total energy content — far less than the observed dark matter BBN proves dark matter is made of heavy elements like iron and gold

Which of the following best describes a sterile neutrino?

A neutrino that has been neutralized by interacting with dark matter A hypothetical heavier partner to ordinary neutrinos that does not interact via the weak nuclear force, making it a candidate for dark matter An ordinary neutrino that has been frozen and cannot move A type of antineutrino produced in nuclear reactors

Why are ordinary neutrinos ruled out as the main dark matter component?

Neutrinos interact too strongly with ordinary matter to be dark Neutrinos are positively charged and would be detected by X-ray telescopes Neutrinos are hot dark matter — they move so fast that they would smooth out structures and prevent the formation of galaxies in the patterns we observe Neutrinos are too rare in the universe to make up 27% of its energy content

What is the current status of dark matter candidate detection as of 2024?

WIMPs have been detected at the LUX-ZEPLIN detector in 2022 Axions have been confirmed as the primary dark matter particle No candidate has been directly detected — each non-detection rules out more of the possible mass and interaction ranges Dark matter has been produced and observed at the Large Hadron Collider