Why is it in the News?

An international team of researchers has just released the most comprehensive “three-dimensional” map of the universe, which, scientists hope, could reveal some clues about dark energy, the mysterious force that is believed to be causing the universe to expand uncontrollably.

Context:

• An international team of researchers has unveiled an extensive 3D map of the universe, aiming to unlock secrets about dark energy, the enigmatic force thought to be driving the universe's rapid expansion.
• Led by Shadab Alam from the Tata Institute of Fundamental Research in Mumbai, the team collaborated on this groundbreaking project, utilizing the Dark Energy Spectroscopic Instrument (DESI), a specialized tool capable of simultaneously gathering light from 5,000 galaxies when attached to a telescope.
• The DESI collaboration has measured that the expansion rate of the universe was increasing by 68.5 km per second after every 3.26 million light-years of distance, a unit astronomers define as megaparsec.

About Dark Energy Spectroscopic Instrument (DESI):

• The Dark Energy Spectroscopic Instrument (DESI) is a remarkable tool designed to capture light from an impressive 5,000 galaxies simultaneously when attached to a telescope.
• This collaborative effort involves over 900 researchers from institutions worldwide, with the Tata Institute of Fundamental Research (TIFR) representing India's sole participating institution.
• DESI, stationed atop the Mayall 4-Meter Telescope in Arizona, United States, has enabled researchers to analyze light emissions from an astounding six million galaxies, some dating as far back as 11 billion years ago.
• This wealth of data has facilitated the creation of the most intricate map of the universe to date.

Dark Energy Vs Dark Matter:

• Dark energy and dark matter are two distinct yet mysterious components of the universe, with vastly different properties and effects on cosmic structures.

Nature and Composition:

• Dark Energy: Dark energy is a hypothetical form of energy that permeates all of space and is responsible for the accelerated expansion of the universe.
  • It is often associated with a cosmological constant or Einstein's "cosmological antigravity."
  • Dark energy is thought to exert a repulsive force that counteracts gravity on cosmic scales, driving galaxies away from each other at an accelerating rate.
  • However, its precise nature remains one of the greatest mysteries in modern physics.
  • It's important to note that dark energy does not matter; rather, it's an energy density inherent in space itself.
• Dark Matter: Dark matter is a form of matter that does not emit, absorb, or reflect electromagnetic radiation, making it invisible and detectable only through its gravitational effects.
  • Unlike dark energy, dark matter exerts an attractive gravitational force, influencing the motion of galaxies and other cosmic structures.
  • It interacts with ordinary matter and with itself only through gravity and possibly through weak nuclear force, but not through electromagnetic forces like photons.
  • Various astrophysical observations strongly suggest the existence of dark matter, but its precise composition and particle nature are still unknown.

Effects on the Universe:

• Dark Energy: The primary effect of dark energy is to drive the accelerated expansion of the universe.
  • This expansion results in the increasing separation between galaxies over time. Dark energy is thought to dominate the energy density of the universe, comprising approximately 68% of the total mass-energy content.
• Dark Matter: Dark matter plays a crucial role in the formation and structure of galaxies and larger cosmic structures.
  • Its gravitational influence binds galaxies together and provides the framework for the large-scale cosmic web.
  • While dark matter does not emit or interact with light, its presence can be inferred from gravitational lensing, galaxy rotation curves, and the large-scale distribution of matter in the universe.
  • Dark matter is estimated to constitute about 27% of the total mass-energy content of the universe.

Detectability:

• Dark Energy: Dark energy is challenging to detect directly because it does not interact with electromagnetic radiation.
  • Its existence is inferred from the observational data related to the accelerating expansion of the universe, such as measurements of distant supernovae and the cosmic microwave background radiation.
• Dark Matter: Dark matter is also challenging to detect directly due to its non-interaction with light.
  • However, its gravitational effects on visible matter and radiation allow astronomers to indirectly infer its presence.
  • Various experimental efforts, such as those involving particle accelerators and underground detectors, aim to detect dark matter particles directly, though success has not yet been achieved.