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)
- 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. Dark matter seems to outweigh visible matter roughly six to one, making up about 27% of the universe.
- 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.
Possible Explanations of Dark Energy:
- Fifth Fundamental Force: There are four fundamental forces in the universe(Gravitational force, weak nuclear force, electromagnetic force, and nuclear force), and speculative hypotheses have postulated a fifth force — something that the four forces cannot explain. Many dark energy models include unique technologies to conceal or screen this fifth factor. Some theories have dubbed this “quintessence,” after the Greek philosophers’ fifth element.
- Property of Space: Albert Einstein was the first to recognise that empty space is not insignificant. One form of Einstein’s gravity theory, the one with a cosmological constant, suggests that “empty space” can have its own energy. This energy would not be diminished as space expanded since it is a characteristic of space itself. More of this energy-of-space would arise as more space was created. As a result, this type of energy would cause the cosmos to expand at an increasing rate.
- Quantum Theory of Matter: The quantum theory of matter provides another explanation for how space obtains energy. According to this idea, “empty space” is actually filled with transitory (“virtual”) particles that form and then disappear all the time.
None of the hypotheses, however, have been proven. As a result, Dark energy has been dubbed “the most profound mystery in all of science.”
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