Recently physicists revised the minimum mass of dark matter to 2.3 × 10-30 proton masses.For decades scientists believed that the minimum mass was about 10-31 times the mass of a proton. In 1922, Dutch astronomer Jacobus Kapteyn concluded that “dark matter” (the first use of the term) had a density of 0.0003 solar masses per cubic light-year.
Dark Matter
- Dark matter is a form of matter that is completely invisible, emitting no light or energy, making it undetectable by conventional sensors and detectors.
- Dark matter does not interact with electromagnetic forces, so it neither absorbs, reflects, nor emits light, making it difficult to detect.
- About 27% of the universe is made up of dark matter, which is six to one times more than visible matter, while visible matter is only 5%.
- Visible matter (baryonic matter) consists of subatomic particles such as protons, neutrons, electrons.
Composition of Dark Matter
- Dark matter is thought to be composed of non-baryonic WIMPs (weakly interacting massive particles), which have a mass 10-100 times that of a proton, but they interact weakly with normal matter, making them difficult to detect. WIMPs include:
- Neutrinos: These are hypothetical particles (not yet observed) that are heavier and slower than neutrinos.
- Sterile neutrinos: Sterile neutrinos have been proposed as a factor in dark matter because they only interact with regular matter through gravity.
Origin of Dark Matter
- Big Bang Theory: It is speculated that dark matter was created during the Big Bang and concentrated in black holes.
- Stellar remnants: Stellar remnants such as white dwarfs and neutron stars also contain high amounts of dark matter.
- Brown dwarfs (failed stars) that could not accumulate enough matter to initiate nuclear fusion in their cores may also be a source of dark matter.
Evidence of Dark Matter
- Galaxy rotation curves: According to Newtonian gravity, objects located at the edges of galaxies should rotate slower than objects near the center.
- Observations show that stars located at the edges of galaxies rotate faster than expected, suggesting that invisible mass – caused by dark matter – provides additional gravitational pull.
- Gravitational lensing: Gravitational lensing occurs when light is bent due to the gravity of a massive object, making it appear more mass than is visible, indicating the presence of dark matter.
- Galaxy formation: The distribution and motion of galaxies over time point to dark matter, as it enables galaxies to cluster together and form the current structures.
- Projects to study dark matter: There are a few major projects designed to shed light on dark matter.
- Alpha Magnetic Spectrometer (AMS): AMS is an experiment on the International Space Station that has detected an excess of positrons (the antimatter equivalent of electrons), which could be a sign of dark matter.
- XENON1T: The XENON1T experiment at the Italian Gran Sasso laboratory aims to detect dark matter by observing the interaction of WIMPs with xenon atoms.
- IceCube Neutrino Observatory, Antarctica: The IceCube Neutrino Observatory is investigating the possibility of sterile neutrinos – hypothetical particles that only interact with regular matter through gravity and could be a form of dark matter.
- Particle collider at CERN, Switzerland: CERN’s Large Hadron Collider (LHC) collides high-energy particles to probe the fundamental components of the universe. In addition, the LHC investigates the aftermath of particle collisions to search for possible signs of dark matter.
- James Webb Space Telescope (JWST): The JWST is expected to provide valuable information about the evolution of galaxies and cosmic structures, which may help us understand the role of dark matter in their formation.
Dark Energy
- Dark energy is a mysterious form of energy that accounts for about 68% of the universe. It is the reason for the rapid expansion of the universe.
- It is evenly distributed throughout the universe, meaning its effect does not decrease as the universe expands.
- The even distribution means that dark energy has no local gravitational effect, but rather a global effect across the entire universe.
- It produces a repulsive force, which accelerates the expansion of the universe.
- The rate of expansion and its acceleration can be measured by observations based on the Hubble Law.
- Hubble’s Law states that the farther away galaxies are from Earth, the faster they are moving away from us, which means the universe is expanding.