DARK MATTER & DARK ENERGY

UNIVERSE IS EXPANDING

EDWIN HUBBLE

 OBSERVED DOPPLER RED SHIFTS IN VARIOUS SPECTRAL LINES OF LIGHT COMING FROM DIFFERENT GALAXIES.  FURTHER RED SHIFTS FOR LIGHT COMING FROM VERY FAR DISTANT GALAXIES WAS LESSER IN COMPARISON WITH THOSE OF NEARBY GALAXIES.

FORCES IN NATURE  ELECTROMAGNETIC FORCE  STRONG FORCE  WEAK FORCE  GRAVITATIONAL FORCE  FOR HEAVY MASSES WE HAVE ONLY GRAVITATIONAL FORCE WHICH IS ATTRACTIVE

SO WHICH ENERGY IS CAUSING THE EXPANSION?  ANSWER IS DARK ENERGY HYPOTHESIS

 In physical cosmology and astronomy, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted hypothesis to explain observations since the 1990s that indicate that the universe is expanding at an accelerating rate. In the standard model of cosmology, dark energy currently accounts for 74% of the total mass energy of the universe.

DARK MATTER  That matter which radiate any electromagnetic radiation is called LUMINOUS MATTER.  Dark Matter neither emits nor absorbs light or other electromagnetic radiation at any significant level, cannot be seen directly with telescopes.  NOTE- HUMAN BODY IS A LUMINOUS BODY AS IT RADIATES INFRA RED DUE TO IT’S TEMPERATURE.

 Dark matter came to the attention of astrophysicists due to discrepancies between the mass of large astronomical objects determined from their gravitational effects, and the mass calculated from the "luminous matter" they contain; such as stars, gas and dust. It was first postulated by Jan Oort in 1932 to account for the orbital velocities of stars in the Milky Way and Fritz Zwicky in 1933 to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters

CONDITON FOR ESCAPING PROJECTILE FROM GRAVITATIONAL FORCE  E = ½ mv^2 – GMm/r  Where E is total energy of body ;1 st term is kinetic energy & 2 nd is potential energy  Now if E > 0, Then body can escape if E = 0, Both forces are balanced if E < 0, Body can’t escape from field

PROJECTILE CASE IS ANALOGOUS TO UNIVERSE  IF THE K.E OF UNIVERSE EXCEEDS THE GRAVITATIONAL ENERGY, THEN EXPANSION WILL BE UNSTOPPABLE.  BUT IF GRAVITATIONAL ENERGY WILL EXCEEDS K.E THEN EXPANSION WILL BE STOPPED.  CORRESPONDING TO TOTAL ENERGY (DENSITY ) VALUES UNIVERSE IS ALSO CATEGORIZED AS  OPEN UNIVERSE  FLAT UNIVERSE  CLOSED UNIVERSE

CONCEPT OF CRITICAL DENSITY  Friedmann equations The Friedmann equations are a set of equations in physical cosmology that govern the expansion of space in homogeneous and isotropic models of the universe within the context of general relativity

 H is the Hubble parameter, G, Λ, and c are universal constants (G is Newton's gravitational constant, Λ is the cosmological constant, c is the speed of light in vacuum). k is constant throughout a particular solution, but may vary from one solution to another. a, H, ρ are functions of time.  Using integration we can find the solution of above equation  Using it’s solution we can also find a very important quantity known as CRITICAL DENSITY

 CRITICAL DENSITY: IT IS DEFINED AS THAT PARTICULAR DENSITY OF UNIVERSE WHOSE GRAVITATIONAL FORCE CAN STOP THE EXPANSION OF UNIVERSE.  AFTER SOLVING FRIED MANN EQUATION, CRITICAL DENSTY IS GIVEN AS  WE ALSO DEFINE DENSITY FACTOR Ώ, WHICH IS DEFINED AS RATIO OF DENSITY OF A STELLAR BODY TO CRITICAL DENSITY

CLOSED,FLAT & OPEN UNIVERSE OUR UNIVERSE IS FLAT

IN TERMS OF CRITICAL DENSITY, TOTAL ENERGY DENSITY OF UNIVERSE IS FOUND TO BE 4% FROM LUMINOUS MATTER, 22% FROM DARK MATTER & 74% FROM DARK ENERGY TOTAL ENERGY DENSITY = 0.74ρc^ ρc^ ρc^2

TYPES OF DARK MATTER  BARYONIC DARK MATTER  NON BARYONIC DARK MATTER  A small proportion of dark matter may be baryonic dark matter; astronomical bodies, such as massive compact halo objects, that are composed of ordinary matter but which emit little or no electromagnetic radiation. Study of nucleosynthesis in the Big Bang produces an upper bound on the amount of baryonic matter in the universe,  The non baryonic dark matter includes neutrinos, and possibly hypothetical entities such as axions, or supersymmetric particles. Unlike baryonic dark matter, nonbaryonic dark matter does not contribute to the formation of the elements in the early universe

Acco. to Mass NON BARYONIC DARK MATTER IS OF THREE TYPES  COLD DARK MATTER  HOT DARK MATTER  WARM DARK MATTER  COLD DARK MATTER : "Cold" dark matter is dark matter composed of constituents with a free-streaming length much smaller than the ancestor of a galaxy-scale perturbation. This is currently the area of greatest interest for dark matter research, as hot dark matter does not seem to be viable for galaxy and galaxy cluster formation, The composition of the constituents of cold dark matter is currently unknown. Possibilities range from large objects like MACHOs (such as black holes) or RAMBOs, to new particles like WIMPs and axions. Possibilities involving normal baryonic matter include brown dwarfs or perhaps small, dense chunks of heavy elements. Many supersymmetric models naturally give rise to stable dark matter candidates in the form of the Lightest Supersymmetric Particle (LSP).

WARM DARK MATTER  Warm dark matter refers to particles with a free- streaming length comparable to the size of a region which subsequently evolved into a dwarf galaxyA challenge for this model is that there are no very well- motivated particle physics candidates with the required mass ~ 300 eV to 3000 eV.  There have been no particles discovered so far that can be categorized as warm dark matter. There is a postulated candidate for the warm dark matter category, which is the sterile neutrino: a heavier, slower form of neutrino which does not even interact through the Weak force unlike regular neutrinos.

HOT DARK MATTER  An example of hot dark matter is already known: the neutrino. Neutrinos were discovered quite separately from the search for dark matter, and long before it seriously began: they were first postulated in 1930, and first detected in Neutrinos have a very small mass: at least 100,000 times less massive than an electron. Other than gravity, neutrinos only interact with normal matter via the weak force making them very difficult to detect (the weak force only works over a small distance, thus a neutrino will only trigger a weak force event if it hits a nucleus directly head-on). This would classify them as Weakly Interacting Light Particles, or WILPs, as opposed to cold dark matter's theoretical candidates, the WIMPs  Using cosmic microwave background data and other methods, the current conclusion is that their average mass probably does not exceed 0.3 eV/c 2 Thus, the normal forms of neutrinos cannot be responsible for the measured dark matter component from cosmology.  Hot dark matter was popular for a time in the early 1980s, but it suffers from a severe problem: since all galaxy-size density fluctuations get washed out by free-streaming, the first objects which can form are huge supercluster-size pancakes, which then were theorised somehow to fragment into galaxies. Deep-field observations clearly show that galaxies formed at early times, with clusters and superclusters forming later as galaxies clump together, so any model dominated by hot dark matter is seriously in conflict with observations.

EVIDENCES IN FAVOUR OF DARK MATTER(RUBIN & FORD EXPT.) VELOCITY PROFILE OF GALAXIES

Using newton’s & kepler’s law theory predicts that Inside the galaxy: V (rotation ) ∝ r Outside galaxy: V (rotation) ∝ r−1/2  But the experimental results were contrary to the above predictions  Above discrepency was sort out by using dark matter hypothesis, it was proposed that whole galaxy has a huge amount of dark matter, whose mass was the cause of variation in gravitational force & hence velocity of galaxies

BENDING OF SPACE TIME CONTINUUM

GRAVITATIONAL LENSING ACCO TO G.T.R ALL HEAVY MASSES CREATE A BUMP IN SPACE TIME CONTINUUM, WHICH LEADS TO BENDING O F LIGHT RAYS. BUT OBSERVED BENDING WAS MUCH MORE THAN EXPECTED. SO WHICH MEANS THAT LARGE AMOUNT OF INVISIBLE MASS IS PRESENT IN THE UNIVERSE.

DETECTION OF DARK MATTER  Direct detection experiments typically operate in deep underground laboratories to reduce the background from cosmic rays. These include: the Soudan mine; the SNOLAB underground laboratory at Sudbury, Ontario (Canada); the Gran Sasso National Laboratory (Italy); the Canfranc Underground Laboratory (Spain); the Boulby Underground Laboratory (UK); and the Deep Underground Science and Engineering Laboratory, South Dakota (US).Soudan mine SNOLABSudburyGran Sasso National LaboratoryCanfranc Underground Laboratory Boulby Underground LaboratoryDeep Underground Science and Engineering Laboratory  The majority of present experiments use one of two detector technologies: cryogenic detectors, operating at temperatures below 100mK, detect the heat produced when a particle hits an atom in a crystal absorber such as germanium. Noble liquid detectors detect the flash of scintillation light produced by a particle collision in liquid xenon or argon. Cryogenic detector experiments include: CDMS, CRESST, EDELWEISS, EURECA. Noble liquid experiments include ZEPLIN, XENON, DEAP, ArDM, WARP and LUX. Both of these detector techniques are capable of distinguishing background particles which scatter off electrons, from dark matter particles which scatter off nuclei. Other experiments include SIMPLE and PICASSO.crystalgermanium Noble liquidscintillationxenonargonCDMS CRESSTEDELWEISSEURECA XENONDEAPArDMWARPLUXSIMPLEPICASSO  The DAMA/NaI, DAMA/LIBRA experiments have detected an annual modulation in the event rate, [81] which they claim is due to dark matter particles. (As the Earth orbits the Sun, the velocity of the detector relative to the dark matter halo will vary by a small amount depending on the time of year). This claim is so far unconfirmed and difficult to reconcile with the negative results of other experiments assuming that the WIMP scenario is cDAMA/NaIDAMA/LIBRA [81]

 Directional detection of dark matter is a search strategy based on the motion of the Solar System around the galactic center.  By using a low pressure TPC, it is possible to access information on recoiling tracks (3D reconstruction if possible) and to constrain the WIMP-nucleus kinematics. WIMPs coming from the direction in which the Sun is travelling (roughly in the direction of the Cygnus constellation) may then be separated from background noise, which should be isotropic. Directional dark matter experiments include DMTPC, DRIFT, Newage and MIMAC.TPCDRIFT  On 17 December 2009 CDMS researchers reported two possible WIMP candidate events. They estimate that the probability that these events are due to a known background (neutrons or misidentified beta or gamma events) is 23%, and conclude "this analysis cannot be interpreted as significant evidence for WIMP interactions, but we cannot reject either event as signal." [83] [83]  More recently, on 4 September 2011, researchers using the CRESST detectors presented evidence [84] of 67 collisions occurring in detector crystals from sub-atomic particles, calculating there is a less than 1 in 10,000 chance that all were caused by known sources of interference or contamination. It is quite possible then that many of these collisions were caused by WIMPs, and/or other unknown particles. CRESST [84]

INDIRECT DETECTION  Indirect detection experiments search for the products of WIMP annihilation. If WIMPs are Majorana particles (the particle and antiparticle are the same) then two WIMPs colliding could annihilate to produce gamma rays or particle-antiparticle pairs. This could produce a significant number of gamma rays, antiprotons or positrons in the galactic halo. The detection of such a signal is not conclusive evidence for dark matter, as the production of gamma rays from other sources are not fully understood. [5][10]Majorana particles annihilategamma rays antiprotonspositrons [5][10]  The EGRET gamma ray telescope observed more gamma rays than expected from the Milky Way, but scientists concluded that this was most likely due to an error in estimates of the telescope's sensitivity. [85] The Fermi Gamma-ray Space Telescope, launched June 11, 2008, is searching for gamma ray events from dark matter annihilation. [86]EGRET [85]Fermi Gamma-ray Space Telescope [86]  At higher energies, ground-based gamma-ray telescopes have set limits on the annihilation of dark matter in dwarf spheroidal galaxies [87] and in clusters of galaxies. [ground-based gamma-ray telescopes [87] [

 The PAMELA experiment (launched 2006) has detected a larger number of positrons than expected. These extra positrons could be produced by dark matter annihilation, but may also come from pulsars. No excess of anti- protons has been observed. [89]PAMELApulsars [89]  A few of the WIMPs passing through the Sun or Earth may scatter off atoms and lose energy. This way a large population of WIMPs may accumulate at the center of these bodies, increasing the chance that two will collide and annihilate. This could produce a distinctive signal in the form of high-energy neutrinos originating from the center of the Sun or Earth. [90] It is generally considered that the detection of such a signal would be the strongest indirect proof of WIMP dark matter. [5] High-energy neutrino telescopes such as AMANDA, IceCube and ANTARES are searching for this signal.SunEarth neutrinos [90] [5] AMANDAIceCubeANTARES  WIMP annihilation from the Milky Way Galaxy as a whole may also be detected in the form of various annihilation products. [91] The Galactic center is a particularly good place to look because the density of dark matter may be very high there. [92] [91]Galactic center [92]