GS-2: Science and Technology- developments
Key phrases: Dark matter, Dark energy, neutrinos, protons, Gravitational lancing
Why in News:
- Astronomers led by researchers from the Netherlands have found no trace of dark matter in the galaxy AGC 114905. An ultra-diffuse dwarf galaxy, AGC 114905, is about 250 million light-years away. The word dwarf here refers to its luminosity (MNRAS).
What is Dark Matter?
- Unlike normal matter, dark matter does not interact with the electromagnetic force. This means it does not absorb, reflect or emit light, making it extremely hard to spot. In fact, researchers have been able to infer the existence of dark matter only from the gravitational effect it seems to have on visible matter..
How have Scientists Known Dark Matter Exists?
- The first real evidence for dark matter came in 1933, when Caltech’s Fritz Zwicky used the Mount Wilson Observatory to measure the visible mass of a cluster of galaxies and found that it was much too small to prevent the galaxies from escaping the gravitational pull of the cluster.
- Something else, concluded Zwicky, was acting like glue to hold clusters of galaxies together. He named the substance dunkle Materie, or dark matter in German.
- In the 1970s, Vera Rubin and Kent Ford, while based at the Carnegie Institution for Science, measured the rotation speeds of individual galaxies and found evidence that, like Zwicky’s galaxy cluster, dark matter was keeping the galaxies from flying apart. Other evidence throughout the years has confirmed the existence of dark matter and shown how abundant it is in the universe.
- In fact, dark matter is about five times more common than normal matter.
What is the Universe made of?
- The Universe is thought to consist of three types of substance: normal matter, ‘dark matter’ and ‘dark energy’.
- Normal matter consists of the atoms that make up stars, planets, human beings and every other visible object in the Universe.
- As humbling as it sounds, normal matter almost certainly accounts for the smallest proportion of the Universe, somewhere between 1% and 10%.
- In the currently popular model of the Universe, 70% is thought to be dark energy, 25% dark matter and 5% normal matter.
Techniques to detect Dark Matter:
- Scientists are using a variety of techniques across the disciplines of
astronomy and physics to detect dark matter:
- Particle colliders such as the Large Hadron Collider.
- Cosmology instruments such as WMAP and Planck.
- Direct detection experiments including CDMS, XENON, Zeplin, WARP, ArDM and others.
- Indirect detection experiments including: Gamma ray detectors (Fermi from space and Cherenkov Telescopes from the ground); neutrino telescopes (IceCube, Antares); antimatter detectors (Pamela, AMS-02) and X-ray and radio facilities.
Dark Energy
• Dark energy makes up approximately 68% of the universe and appears to be associated with the vacuum in space. It is distributed evenly throughout the universe, not only in space but also in time – in other words, its effect is not diluted as the universe expands. The even distribution means that dark energy does not have any local gravitational effects, but rather a global effect on the universe as a whole. This leads to a repulsive force, which tends to accelerate the expansion of the universe. The rate of expansion and its acceleration can be measured by observations based on the Hubble law. These measurements, together with other scientific data, have confirmed the existence of dark energy and provide an estimate of just how much of this mysterious substance exists.
Gravitational lensing
- The phenomenon of gravitational lensing occurs when a huge amount of matter, such as a massive galaxy, cluster of galaxies or a black hole, creates a gravitational field that distorts and magnifies the light from objects behind it.
- Gravitational lensing is based on Einstein's theory of general relativity (Mass bend light).
- It can help astronomers to know about black holes, dark matter, etc.
- Normal lenses such as the ones in a magnifying glass work by bending light rays that pass through them in a process known as refraction, in order to focus the light somewhere else.
Source: The Hindu
Mains Question:
Q. What is Dark Matter? How it help to understand the origin of universe and its expansion?
