Dark matter

 By Mr_dad_divijay



Definition: Dark Matter is referred to the hypothetical matter that scientists have not been able to locate in the universe - either through telescopes or using any other technological method. 27% of the matter in the universe is said to be dark matter. Its existence came to the fore because of its gravitational effects on matters that are visible in the universe.



Description: Scientists have been unable to directly observe dark matter since they do not emit light or energy.



The universe is made up of baryonic matter. This consists of electrons, protons, and neutrons. Dark matter on the other hand, could be made of both baryonic and non-baryonic matter. Despite many speculations regarding the existence of dark matter, no one can clearly define what dark matter is made of.



Dark matter can be classified into three main categories - cold, warm, and hot. These categories have no conjunction with actual temperatures. Instead, they describe the rate at which particles randomly moved within the universe before slowing down, which in turn leads to the expansion of the universe as a whole.

Dark matter has never been identified under any scientific instrument. In fact, its existence is only gauged by its effect on the gravitational pull. But scientists have recently discovered that dark matter - which was considered to be non-interactive with other structures or forces in the universe - is actually slowing down to interact with other dark matter.

IS real despite recent discovery of galaxies that appear to exist without it, scientists argue in new study they claim 'removes doubts on the existence' of the elusive material


explosion kicked off a rapid expansion of space. The universe is still expanding. The speed with which celestial bodies move to achieve this expansion is a mystery that has driven scientists up the wall. Scientists have for decades been trying to figure out the evolution of galaxiesthe most active research area in astrophysics. Several postulates have surfaced to explain what drives these inanimate objects to defy the laws of physics.


One hypothesis that is a favourite among scientists is dark matter. It is an invisible force that cannot be detected easily but whose presence can be inferred from effects on visible matter. It is the force that makes stars run 299,792,458 metres per second (light year speed)a speed that is envied by space scientists and so far has only been replicated in science fiction movies. But that is just the tip of the iceberg.Dark matter, along with dark energy, is the dominating component that is supposed to constitute 95 per cent of the universe. Only 5 per cent of the mystery has been unravelled so far.

Dark matter


In the 1930s Fritz Zwicky, an eminent astrophysicist from the California Institute of Technology in usa studied the speed of Coma Galaxy clusters, a collection of 1,000 identified galaxies. Zwicky was the first scientist to talk about the existence of dark matter; he was not taken seriously.


As technology progressed astronomers continued with their space vigil and 40 years later they had to agree to the presence of dark matter as a logical explanation to the motion of stars. Further proof was provided by the Arcminute Cosmology Bolometer Array Receiver (acbar) and the Wilkinson Microwave Anisotropy Probe (wmap) that are trying to make sense of the cosmic afterglow left behind by Big Bang, called the cosmic microwave background radiation.


Researchers from the school of physics and astronomy at Cardiff University at Wales in the UK and Kavli Institute for Particle Astrophysics and Cosmology at Stanford in usa used QUaD to study the afterglow. QUaD is an extragalactic surveyor located at the South Pole in Antarctica. This team has further strengthened the belief that dark matter does make up 95 per cent of everything in existence. Detailed maps of the cosmic microwave background were released in the November 1 issue of The Astrophysical Journal.


The team has been able to investigate not just where the dark matter existed but also how it was moving and thus how the universe looked shortly after cosmic bodies came into existence following the Big Bang.




The instruments used are highly sensitive and the observations though difficult to interpret very closely match the results hypothetically predicted by the existence of dark matter. Walter Gear of Stanford, one of the principal scientists, said: This reinforces the view that researchers are on the right track and need to learn more about the strange nature of dark energy and dark matter if we are to fully understand the workings of the universe. He, however, cautioned these are findings of the universe 400,000 years after it was formed and so understanding what happened in that crucial moment of the Big Bang needs patience and more research.




Pijushpani Bhattacharjee, head of the Centre for Astro Particle Physics at the Saha Institute of Nuclear Physics in Kolkata, said It is a very important development. It has strengthened our view that dark matter dominates the dynamics of individual galaxies and clusters of galaxies, while the evolutionary dynamics of the universe as a whole in the present epoch is dominated by the dark energy.

LONDON: The elusive dark energy, thought to make up 68 per cent of the universe, may not exist at all, scientists have claimed.


They believe that standard models of the universe fail to take account of its changing structure, but that once this is done the need for dark energy disappears.From the 1920s, mapping the velocities of galaxies led scientists to conclude that the whole universe is expanding, and that it began life as a vanishingly small point.


In the second half of the twentieth century, astronomers found evidence for unseen 'dark' matter by observing that something extra was needed to explain the motion of stars within galaxies.




This discovery could greatly change the course of many theories related to this invisible force that guides the universe.

In the new work, researchers led by PhD student Gabor Racz of Eotvos Lorand University in Hungary, question the existence of dark energy and suggest an alternative explanation.


They argue that conventional models of cosmology (the study of the origin and evolution of the universe), rely on approximations that ignore its structure, and where matter is assumed to have a uniform density.


In practice, normal and dark matter fill the universe with a foam-like structure, where galaxies are located on the thin walls between bubbles, and are grouped into superclusters.


The insides of the bubbles are in contrast almost empty of both kinds of matter.


Using a computer simulation to model the effect of gravity on the distribution of millions of particles of dark matter, scientists reconstructed the evolution of the universe.


Unlike conventional simulations with a smoothly expanding universe, taking the structure into account led to a model where different regions expand at different rates.


The average expansion rate though is consistent with present observations, which suggest an overall acceleration.


"Our findings rely on a mathematical conjecture which permits the differential expansion of space, consistent with general relativity, and they show how the formation of complex structures of matter affects the expansion," researchers said.


"These issues were previously swept under the rug but taking them into account can explain the acceleration without the need for dark energy," they said.


If this finding is upheld, it could have a significant impact on models of the universe and the direction of research in physics.




For the past 20 years, astronomers and theoretical physicists have speculated on the nature of dark energy, but it remains an unsolved mystery.


The research was published in the Monthly Notices of the Royal Astronomical Society.