What are Dark Matter and Dark Energy?

what are dark matters and dark energy

Context: The European Space Agency (ESA) has unveiled the first images captured by the Euclid space telescope designed to unlock the secrets of dark matter and dark energy. The primary objective of the telescope is to create the largest cosmic 3D map of the universe to better understand the distribution of dark matter and influence of dark energy in the early universe.

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.
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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. 

Practice Question: 

Q. Consider the following statements with reference to dark energy:

    1. Dark energy consists of more than 90% of the Universe.
    2. Dark energy has been hypothesised as a repulsive force or anti-gravity.

Which of the statements given above is/are correct?

(a)    1 only

(b)    2 only

(c)    Both 1 and 2

(d)    Neither 1 nor 2

Answer: (b) 

UPSC 2019 (Advancements in the field of Space) 

Q. Recently, scientists observed the merger of giant ‘blackholes‘ billions of light-years away from the Earth. What is the significance of this observation?

(a)     ‘Higgs boson particles’ were detected.

(b)    ‘Gravitational waves‘ were detected.

(c)     Possibility of intergalactic space travel through Wormhole’ was confirmed.

(d)     It enabled scientists to understand ‘singularity’.

Answer: (b)

Source: The Hindu

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