SAHA INSTITUTE OF NUCLEAR PHYSICS
Department of Atomic Energy, Govt. of India
What is dark matter?
Most of the universe is made of "invisible" dark matter – which we can only detect through its gravitational effects. Galaxies in our universe are rotating with such speed that the gravity generated by their observable matter could not possibly hold them together and they should have torn themselves apart. For the galaxies in clusters it is believed that we have some interplay which we cannot visualize. Physicists feel that something we have yet to detect directly is giving these galaxies extra mass and also causing the extra gravity which they need to stay together. This strange and unknown matter is known as “dark matter” since it is not visible.
Dark matter and the universe
Dark matter does not interact with the electromagnetic force and hence does not absorb, reflect or emit light, and therefore, 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 make up about 27% of the universe. The matter we know that makes up all stars and galaxies only adds upto 5% of the content of the universe!
But how should we explain dark matter?
The familiar material of the universe, known as baryonic matter, is composed of protons, neutrons and electrons. Dark matter composition can be baryonic or non-baryonic matter. If baryonic then the most potential candidates which can be included are brown dwarfs, white dwarfs and neutrino stars. Also Supermassive black holes could also be part, but these difficult-to-indentify objects would need to play a more significant role than scientists have observed to make up the missing mass, while other studies suggest that dark matter can be more exotic.
Scientists think that dark matter is mostly composed of non-baryonic matter. The lead candidate, WIMPS (weakly interacting massive particles) which have mass of the order of ten to a hundred times the mass of a proton, interact weakly with "normal" matter and thus make them difficult to detect. Massive hypothetical particles termed as Neutralinos which are heavier and slower than neutrinos, are other candidates, though they have yet to be discovered.
Dark Energy
Approximately 68% of the universe is made of Dark Energy which appears to be associated with the vacuum in space. One explanation for dark energy is that it is a property of space where it is distributed evenly throughout the universe, not only in space but also in time. Here the even distribution means that dark energy does not have any local gravitational effects, but on the other hand has a global effect on the universe as a whole. Thus causing 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 scientific measurements and other measured data, have confirmed the existence of dark energy and furthermore provide an estimate of just how much of this dark energy exists.
Most of the universe is made of "invisible" dark matter – which we can only detect through its gravitational effects. Galaxies in our universe are rotating with such speed that the gravity generated by their observable matter could not possibly hold them together and they should have torn themselves apart. For the galaxies in clusters it is believed that we have some interplay which we cannot visualize. Physicists feel that something we have yet to detect directly is giving these galaxies extra mass and also causing the extra gravity which they need to stay together. This strange and unknown matter is known as “dark matter” since it is not visible.
Dark matter and the universe
Dark matter does not interact with the electromagnetic force and hence does not absorb, reflect or emit light, and therefore, 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 make up about 27% of the universe. The matter we know that makes up all stars and galaxies only adds upto 5% of the content of the universe!
But how should we explain dark matter?
The familiar material of the universe, known as baryonic matter, is composed of protons, neutrons and electrons. Dark matter composition can be baryonic or non-baryonic matter. If baryonic then the most potential candidates which can be included are brown dwarfs, white dwarfs and neutrino stars. Also Supermassive black holes could also be part, but these difficult-to-indentify objects would need to play a more significant role than scientists have observed to make up the missing mass, while other studies suggest that dark matter can be more exotic.
Scientists think that dark matter is mostly composed of non-baryonic matter. The lead candidate, WIMPS (weakly interacting massive particles) which have mass of the order of ten to a hundred times the mass of a proton, interact weakly with "normal" matter and thus make them difficult to detect. Massive hypothetical particles termed as Neutralinos which are heavier and slower than neutrinos, are other candidates, though they have yet to be discovered.
Dark Energy
Approximately 68% of the universe is made of Dark Energy which appears to be associated with the vacuum in space. One explanation for dark energy is that it is a property of space where it is distributed evenly throughout the universe, not only in space but also in time. Here the even distribution means that dark energy does not have any local gravitational effects, but on the other hand has a global effect on the universe as a whole. Thus causing 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 scientific measurements and other measured data, have confirmed the existence of dark energy and furthermore provide an estimate of just how much of this dark energy exists.