What is Dark Matter?

Dark Matter is a mysterious substance that makes up about 27% of the universe. Unlike ordinary matter (like atoms), dark matter does not emit, absorb, or reflect light, making it invisible to telescopes. Scientists know it exists because of its gravitational effects on galaxies and galaxy clusters.

Key Properties

  • Invisible: Cannot be seen directly with any telescope.
  • Non-luminous: Does not emit electromagnetic radiation.
  • Interacts Weakly: Rarely interacts with normal matter, except through gravity.
  • Massive: Has mass and exerts gravitational force.

Evidence for Dark Matter

1. Galaxy Rotation Curves

Galaxies spin faster than expected based on visible matter. The extra gravity needed to hold them together comes from dark matter.

Galaxy Rotation Curve

Image: Rotation curves show stars moving faster than predicted by visible matter alone.

2. Gravitational Lensing

Light from distant galaxies bends more than expected as it passes near massive objects, suggesting extra invisible mass.

Gravitational Lensing Diagram

Image: Gravitational lensing caused by dark matter.

3. Cosmic Microwave Background (CMB)

Measurements of the CMB show patterns that can only be explained if dark matter exists.

Timeline: Discovery & Study of Dark Matter

  • 1933: Fritz Zwicky notices missing mass in galaxy clusters.
  • 1970s: Vera Rubin studies galaxy rotation curves, confirming dark matter’s presence.
  • 2006: Bullet Cluster observation provides strong evidence for dark matter.
  • 2012: Large Underground Xenon (LUX) experiment begins searching for dark matter particles.
  • 2020: New research suggests dark matter may interact with itself (see citation below).

Types of Dark Matter Candidates

  • WIMPs (Weakly Interacting Massive Particles): Most popular candidate, predicted by particle physics.
  • Axions: Hypothetical particles with very low mass.
  • Sterile Neutrinos: A type of neutrino that doesn’t interact via the weak force.
  • MACHOs (Massive Compact Halo Objects): Includes black holes, neutron stars, and brown dwarfs; now less favored.

Surprising Facts

  1. Dark matter is six times more abundant than ordinary matter in the universe.
  2. Dark matter may influence the formation of galaxies and stars, acting as a cosmic scaffold.
  3. Some experiments suggest dark matter could interact with itself, not just through gravity (see Nature, 2020).

Controversies & Unsolved Mysteries

  • What is dark matter? No one knows its exact nature or what particles make it up.
  • Does dark matter interact with normal matter? Most experiments have found no interaction except gravity.
  • Alternatives: Some scientists propose changing the laws of gravity (Modified Newtonian Dynamics) instead of invoking dark matter.
  • Direct Detection: Despite decades of searching, no dark matter particle has been detected directly.

Dark Matter and Health

While dark matter itself does not affect human health directly, research into dark matter has led to advances in technology and science that benefit medicine:

  • Particle detectors used in dark matter experiments have been adapted for medical imaging (like PET scans).
  • Data analysis techniques developed for astrophysics are used in genetics and epidemiology.
  • Understanding extreme environments (like deep space) helps scientists learn how life—including bacteria—can survive in harsh conditions, which may lead to new treatments or drugs.

Extreme Environments: Bacteria and Dark Matter

Some bacteria survive in deep-sea vents and radioactive waste, places with little ordinary matter and high radiation. Studying these organisms helps scientists understand how life could exist in the universe, even in places dominated by dark matter.

Recent Research

A 2020 study published in Nature (Nature, 2020) found evidence that dark matter might interact with itself, not just through gravity. This could change how scientists search for dark matter and improve our understanding of the universe’s structure.

Summary Table

Property Ordinary Matter Dark Matter
Visible Yes No
Emits Light Yes No
Interacts Strongly Yes No
Mass Yes Yes
Role in Universe Forms stars, planets Holds galaxies together

Study Questions

  1. What evidence supports the existence of dark matter?
  2. Name two dark matter candidates.
  3. How does dark matter relate to galaxy formation?
  4. What are some controversies about dark matter?
  5. How has dark matter research helped health science?

Additional Resources

End of Study Guide