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Dark Matter Particles
Context:
For decades, scientists believed dark matter particles were at least 10^-31 the mass of a proton. In May 2024, physicists raised this minimum to 2.3 × 10^-30 proton masses.
Recent Research Findings (May 2024):
- The research used data from the motion of stars in Leo II, a dwarf galaxy orbiting the Milky Way, to infer the dark matter density profile.
- This density profile, combined with a modified Schrödinger equation (accounting for gravity), led to the discovery that lighter particles (around 10^-31 proton masses) couldn’t explain the high density of dark matter in the inner regions of Leo II.
- The study concluded that heavier dark matter particles are required to explain the observed mass in these regions.
Dark Matter and Its Role:
- Dark matter is a form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects.
- It constitutes about 28% to 32% of the universe’s total mass-energy content. The evidence arises from various astrophysical observations, including Galactic Rotation Curves, and Gravitational Lensing.
- Dark matter particles must have non-zero mass to allow the dense cosmic structures to form, as opposed to light particles (photons).
- Distribution: Dark matter is believed to be spread throughout the universe, with an average density of 0.0003 solar masses per cubic light-year (equivalent to two protons per teaspoon).
- This density was first proposed by astronomer Jacobus Kapteyn in 1922 and remains valid for large cosmic scales (million-cubic-light-year volumes). However, on smaller scales (such as your house), the distribution of dark matter depends on whether it is uniform or clumpy.
Clumpy vs. Uniform Distribution
- If dark matter is uniformly distributed (like fine flour), particles could be as close as 7 cm apart if their mass is 100 proton masses.
- If dark matter is more clumpy, the spacing could be many light years, and no dark matter would be found under your roof.
- For heavier particles (e.g., 10^19 proton masses), the separation would be about 30 km, making dark matter less likely to be detectable in small spaces.
Effect of Mass on Dark Matter:
- Lighter dark matter particles have larger wavelengths, affecting their behaviour.
- For particles with a mass of 10^-11 proton masses, their wavelength would be 2 cm, making dark matter behave more like a fluid.
- For particles lighter than 10^-31 proton masses, their wavelength would exceed the size of a dwarf galaxy, preventing the formation of smaller objects.
Significance of the Findings:
- This work represents a major update in the understanding of dark matter, showing that the minimum mass of dark matter particles is higher than previously thought.
- It is a testament to the power of modern computational techniques that researchers were able to make this breakthrough.
