ABC of Dark Matter and Dark Energy


By: Vivek Kumar


Universe, we all know created by a huge explosion and all matter in it is bounded by a gravitational pull. But all these theories are to be proved by various discoveries and their analysis lead to the certain conclusion. But the enigma of the space beyond the human reach is still a hypothesis. Recently the discovery of some foot prints of dark matter by International Space Station’s Cosmic ray Detector is being carried out. It has detected the footprints of dark matter that considered being the 2nd major part of universe.

dark energy

The standard model of cosmology given my Planks Mission team explained the total mass energy of the universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy.

So, now what exactly this DARK ENERGY is? The expansion of Universe is well known by all of us and that energy released through it considered being as Dark Energy. Einstein was the first scientist who throw light on the matter of dark energy that the universe is not empty as a dark but consists some energy which is yet unknown to the humanity. The first property that Einstein discovered is that it is possible for more space to come into existence. Then one version of Einstein’s gravity theory, the version that contains a cosmological constant ( the repulsive force) makes a second prediction: “empty space” can possess its own energy. He propounded that as it is the energy of space then it is not possible that it would be diluted after its expansion. Thus, as more the space came into existence more the universe is “Expanding”. The new value for the expansion rate, known as the Hubble constant, or H0 (after Edwin Hubble (1923) who first measured the expansion of the universe nearly a century ago), is 74.2 kilometers per second per megaparsec (error margin of ± 3.6).

Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space homogeneously and scalar fields such as quintessence (purest form) or moduli (a specified property is possessed by a specified substance), dynamic quantities whose energy density can vary in time and space. Contributions from scalar fields that are constant in space are usually also included in the cosmological constant. The cosmological constant is physically equivalent to vacuum energy. Scalar fields which do change in space can be difficult to distinguish from a cosmological constant because the change may be extremely slow. Thus the recent attempts also have been made to formulate universe as a cyclic entity.

DARK MATTER, The matter separated to the matter what we see and what we can figure out. It composed of nothing but still there as darkness. It was propounded that the Universe is not only made up of atoms but there is something which is beyond atom or can say no atom. It is nonbaryonic i.e not made up of photons, electrons, atoms. It was the nucleosynthesis of matter that explained that the baryonic compounds are massive compact halo objects and the nucleosynthesis of BigBang lead to the conclusion that majority in the universe cannot be baryons.

Where it all starts that we suddenly started thinking about dark matter or certain that kind of substance in the universe.  But it was not so sudden because in 1920 Edwin hubble first began with the detecting of masses of galaxies that are expanding. The measure of the luminosity of the galaxy leads to its weight like greater the luminosity and greater the mass of that shining body and another approach is to calculating the rotation of the bodies of that galaxy. But when they started calculating all the variations there was something puzzling. They expected to see stars near a galaxy’s center, where the visible matter is more concentrated, move faster than stars at the edge. What they saw instead was that stars at the edge of a galaxy had the same rotational velocity as stars near the center. This observation was first made with the Milky Way, and then, in the 1970s, Vera Rubin confirmed the phenomenon when she made detailed quantitative measurements of stars in several other galaxies, including Andromeda (M31). The implication of all of these results pointed to two possibilities. First, Something was fundamentally wrong with our understanding of gravity and rotation, which seemed unlikely given that Newton’s laws had withstood many tests for centuries. Or, second more likely, galaxies and galactic clusters must contain an invisible form of matter or dark matter responsible for the observed gravitational effects. As astronomers focused their attention on dark matter, they began to collect additional evidence of its existence. Then the discovery of galactic cluster by X-Ray telescopes ( like Chandra observatory) lead to some more clear picture about dark matter.

evolution of matter

[[In 2000, Chandra observed a gigantic cloud of hot gas enveloping the galaxy cluster Abell 2029, leading astronomers to estimate that the cluster must hold an amount of dark matter equivalent to more than a hundred trillion suns! If other clusters have similar characteristics, then 70 to 90 percent of the mass of the universe could be attributed to dark matter]]

Now why it was in news –

Nobel laureate and MIT physicist Samuel C.C. Ting — has detected tantalizing, though preliminary, evidence of a signal that might be caused by dark matter, the long-sought, mysterious substance that makes up about a quarter of the universe. This discovery also felt so enthusiastic as the 7.5-ton, $2 billion instrument was carried to the international space station in 2011 aboard the last flight of space shuttle Endeavour is proven to be conclusive in the initial result and certainly provided the experiment would definitively answer the question of whether the signal was caused by the collision of dark matter particles. The signal could also be generated by a less interesting source — spinning stars called pulsars.



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