Context: Researchers, including a team from the Tata Institute of Fundamental Research in Mumbai, have unveiled the most holistic “three-dimensional” map of the universe, from the observations by the Dark Energy Spectroscopic Instrument, or DESI, measuring how fast the universe expanded over 11 billion years.
Dark Energy Spectroscopic Instrument:
- Dark Energy Spectroscopic Instrument (DESI) is a scientific instrument designed to peer into the distant universe and study dark energy. It is mounted over the Mayall 4-Meter Telescope in Arizona, United States.
- DESI works by collecting the faint light from millions of galaxies and quasars, then splitting that light into its component colours using a technique called spectroscopy. By analysing the spectrum of light from these distant objects, astronomers can learn about their composition, motion, and distance from Earth.
- Through it, the researchers have been able to collect light from six million galaxies (some of which were present around 11 billion years ago) and were able to measure the distances between these galaxies with a very high degree of accuracy. Thus, they were able to unveil a three-dimensional map of the Universe.
- Significance:
- Knowing the precise distances of the galaxies is crucial because that allows us to calculate the expansion rate of the universe.
- This could provide insights into the secrets of dark energy and give insights into new Physics. Eventually, it will offer a vital perspective into the origin and evolution of the universe.
- The DESI collaboration has so far discovered that the expansion rate of the universe was rising by 68.5 km per second after every 3.26 million light-years of distance.
Dark Matter and Dark Energy:
- Dark matter and dark energy together make up 95% of the universe. Around 68% of the Universe is made of dark energy while dark matter makes up 27%.
- Only the remainder (5%) is composed of fermionic matter, i.e., things on the Earth, planets, stars, etc.
Dark Matter:
- Dark matter is completely invisible and has not yet been observed directly. It does not interact with matter, emits no light or energy and thus cannot be detected directly by conventional sensors and detectors.
- Scientists are confident it exists because of the gravitational effects it has on galaxies and galaxy clusters.
Dark Energy:
- The existence of dark energy was theorised 25 years ago, when a team of researchers found that the expansion of the Universe was speeding up or accelerating, instead of slowing down due to gravity (inwards pulling force). Scientists have hypothesised that this is happening due to a mysterious form of energy called dark energy.
Characteristics of Dark Energy:
- Dark energy has been hypothesised as a repulsive force or anti-gravity, i.e. while gravity tends to make objects attract, dark energy would pull them apart by increasing the space between them. Thus, dark energy has an expansionary effect. As our universe is expanding, it indicates that dark energy has a greater abundance than dark matter.
- Dark energy is a property of space, so it does not get diluted as space expands.
- Normally, as the universe expands the density of mass and radiation in it decreases.
- However, the density of dark energy remains constant throughout. This means the dark energy in the universe is ever increasing, in order to keep the energy-density constant. Thus, dark energy should be energy inherent in the fabric of space itself.