How to weigh Dark matter?

Syllabus:

GS 3: Space Technology India

Why in the News?

Recently, physicists revised the minimum possible mass of dark matter particles, increasing it by an order of magnitude, using advanced computational techniques, this updates fundamental cosmic theories.

How to weigh Dark matter?

What is a Dark matter?

  • Dark matter is a mysterious, invisible substance that makes up about five-sixths of the total mass of the universe.
  • Unlike photons (particles of light), dark particles must have zero mass to form the complex and stable cosmic structure we see today

How can a dark object be light?

  • For decades, scientists believed that the minimum mass of a dark matter particle is 10−31 times that of a proton.
  • However, in May 2024, theoretical physicists updated this value and increased the limit to reach 2.3 × 10−30 proton masses.

Why is this important?

  • This new discovery marks a major step forward in understanding the nature of dark matter.
  • The revised limit narrows the possibilities of research and gives scientists a clear road map to unravel this mystery of the universe.

Exploring the mysteries of dark matter

  • Black matter plays a central role in the formation and organization of the universe, however, its true nature remains unclear.
  • First studied in 1922 by Dutch astronomer Jacobus Kapteyn, dark matter was introduced to explain the motion of stars near the sun.
  • Kapteyn calculated its density to be about 0.0003 solar energy per cubic light year.
  • Despite decades of detailed measurements, his findings have held up remarkably well.

Is there a dark matter in our homes?

  • Dark matter is thought to exist everywhere in the universe. But does that mean it’s in our homes?
  • By Kapteyn’s measurement, dark matter density is equivalent to the mass of two protons per teaspoon.
  • By this calculation, the amount of dark matter in the house could be millions of protons.
  • However, this approximation only works for large scales such as millions of cubic light years.
  • Looking at small areas, such as the size of a house, makes the distribution of dark matter uncertain.
  • The motions of stars used to calculate dark matter involve large cosmic scales, not small ones.
  • Whether we have dark matter in our homes depends on how it is spatially distributed—whether it is evenly spread out or clustered.

Uniform Or Lump Distribution?

  • If dark matter is uniformly distributed, as predicted by standard cosmological theories, then it can be compared to fine grains spread uniformly in space.
  • In this case, particles of dark matter would come home perhaps even among us.
  • But if dark matter accumulated into massive objects separated by a few light years, there would be no dark matter on our rooftops.
  • In this case, the dark matter would be much less delayed, making it far more likely to occur in small areas.

Separation between particles

  • The distance between dark particles depends on their mass.
  • If the mass of the black matter is 100 times the mass of the proton, the distance between neighboring objects would be 7 cm.
  • On the other hand, if the mass of the dark matter is 10¹⁹ times the mass of the proton, they are 30 kilometers apart.
  • When dark matter accumulates into massive 10²⁰ gram particles, the separation between them can exceed the size of the solar system.
  • In such a scenario, the probability of encountering dark matter in small areas would have been greatly reduced.

How small can a particle of dark matter be?

  • When the mass of a dark matter particle exceeds the mass of a proton by about 10−11 times, quantum physics becomes important.
  • At this level, each red cell in the human body could theoretically be a tiny unit.
  • But due to quantum effects, dark matter behaves more like a liquid than discrete particles.
  • Each black matter in this mass has a wavelength of 2 cm.

Narrow limit of mass limitation

  • If the mass of a dark matter particle is reduced to 10⁻³¹ times the mass of a proton, its wavelength will extend to 200 light years, comparable to the mass of a dwarf galaxy.
  • Small galaxies like Leo II are mainly composed of dark matter, with only about 1% of their mass coming from stars.
  • This raises the physical constraint that if a dark particle had a mass less than 10⁻³¹ proton masses and a wavelength greater than the mass of a dwarf galaxy, such particles would not be able to form massive systems such as galaxies.

Recent advances in dark matter research

  • In May 2024, scientists revised the theoretical lower limit on dark matter particles using advanced computational techniques.
  • Study focused on Leo II, a dwarf galaxy orbiting the Milky Way, and examined the density of dark matter.
  • The researchers matched this with theoretical predictions by analyzing Leo II data by solving the modified Schrödinger equation to calculate the gravitational field
  • The results showed that dark matter was more abundant than previously estimated in the Leo II regions.
  • This observation suggests that dark matter particles with mass proton size 10⁻³¹ are insufficient to account for the observed abundance.
  • Heavy particles are needed to define the “solid center” of mass.

A technical milestone

  • This improvement indicates a substantial improvement in particle size, while significantly altering the lower limit of the dark matter mass.
  • Unlike traditional methods of theoretical table calculation, this development has been made possible by sophisticated computer simulations and numerical analysis.

Conclusion

The revised lower limit for dark particles highlights advances in statistical methods, reshapes our understanding of cosmic systems and highlights the fundamental link between theory and observation.

Source: The Hindu

Mains Practice Question:

Presence and distribution of dark matter at macroscopic and microscopic scales has implications for scientific research. Explain the challenges of searching for dark matter and the role of quantum physics in studying its properties.