DARK MATTER&

DARK ENERGY

Submitted By: Sandeep Kaur

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WHAT IS DARK MATTER?

Dark matter is a kind of matter hypothesized in astronomy and cosmology to account for gravitational effects that appear to be the result of invisible mass.

Dark matter cannot be seen directly with telescopes; evidently it neither emits nor absorbs light or other electromagnetic radiation at any significant level. If we can't see it,How do we know it exists??

The existence and properties of dark matter are inferred from its gravitational effects on visible matter.

OBSERVATIONAL EVIDENCE :

SOMETHING IS NOT RIGHT WITH….. Galactic Rotation Curves Galactic Clusters Appearance of far away Galaxies Cosmic Microwave Background

What's the solution?Lets find out.

GALAXIES ROTATEGalaxies are collections of billions of stars. Most of the light from a galaxy comes from its center. This indicated that most of the galaxies stars and most of its mass is concentrated at its center. Under this scenario, we should expect the stars in the outer part of the galaxy to rotate about the center, and this is just what we observe.

GALAXY ROTATION CURVESo In the late 1960s and early 1970s, Vera

Rubin at the Department of Terrestrial Magnetism at the Carnegie Institution of Washington was the first to both make robust measurements indicating the existence of dark matter and attribute them to dark matter.

o Rubin worked with a new sensitive spectrograph that could measure the velocity curve of edge-on spiral galaxies to a greater degree of accuracy .

o Rubin's observations and calculations showed that most galaxies must contain about six times as much “dark” mass as can be accounted for by the visible stars.

GALAXY CLUSTERS

Galaxies have been called the atoms of the universe. Nearly all the visible matter in the universe is found in galaxies which are distributed throughout space. Galaxies are often found in groups called clusters.

GALAXY CLUSTERS Radio astronomers have found hot gas

in the space between galaxies in a cluster. This gas produces a pressure that pushes the galaxies apart.

The galaxies’ mutual gravitational attraction causes them to cling together. The heavier the galaxies, the stronger the gravitational attraction.

So, are galaxies massive enough to hang together??

From X-rays emitted by very hot gas within the clusters. The temperature and density of the gas can be estimated from the energy and flux of the X-rays, hence the gas pressure; assuming pressure and gravity balance, this enables the mass profile of the cluster to be derived.

Chandra X-ray Observatory use this technique to independently determine the mass of clusters.

“It turns out that galaxies do not have enough visible mass to stay grouped in clusters. The extra mass they need must come from dark matter.”

WHO SQUASHED THE GALAXIES?

In 1995, the Hubble Space Telescope focused its attention on a very small patch of sky. It was able to see farther away than any other optical telescope in history. It saw thousands of new galaxies. Many appeared squashed or stretched out.

A gravitational lens is formed when the light from a more distant source is "bent" around a massive object (such as a cluster of galaxies) between the source object and the observer. The process is known as Gravitational Lensing.

GRAVITATIONAL LENSING

The observed distortion of background galaxies into arcs when the light passes through a gravitational lens, has been observed around Abell 1689 By measuring the distortion geometry, the mass of the cluster causing the phenomena can be obtained.

Weak gravitational Lensing looks at minute distortions of galaxies observed in vast galaxy surveys due to foreground objects through statistical analyses. By examining the apparent shear deformation of the adjacent background galaxies, astrophysicists can characterize the mean distribution of dark matter by statistical means.

BULLET CLUSTER

X-ray observations show that much of the baryonic matter in the system is concentrated in the center of the system.

Weak Gravitational Lensing observations of the same system show that much of the mass resides outside of the central region of baryonic gas.

COSMIC MICROWAVE BACKGROUND:

The cosmic microwave background (CMB) is the thermal radiation assumed to be left over from the "Big Bang" of cosmology.

In older literature, the CMB is also variously known as cosmic microwave background radiation (CMBR) or "relic radiation."

The CMB is a cosmic background radiation that is fundamental to observational cosmology because it is the oldest light in the universe, dating to the epoch of recombination.

BIG BANG

• The night sky presents the viewer with a picture of a calm and unchanging Universe. So the 1929 discovery by Edwin Hubble that the Universe is in fact expanding at enormous speed was revolutionary.

• Hubble noted that galaxies outside our own Milky Way were all moving away from us, each at a speed proportional to its distance from us.

• He quickly realized what this meant that there must have been an instant in time when the entire Universe was contained in a single point in space. The Universe must have been born in this single violent event which came to be known as the "Big Bang."

BACKGROUND RADIATION

According to the theories of physics, if we were to look at the Universe one second after the Big Bang, what we would see is a 10-billion degree sea of neutrons, protons, electrons, anti-electrons (positrons), photons, and neutrinos.

Then, as time went on, we would see the Universe cool, the neutrons either decaying into protons and electrons or combining with protons to make deuterium (an isotope of hydrogen).

As it continued to cool, it would eventually reach the temperature where electrons combined with nuclei to form neutral atoms.

BACKGROUND RADIATION

• Before this "recombination" occurred, the Universe would have been opaque because the free electrons would have caused light (photons) to scatter the way sunlight scatters from the water droplets in clouds.

• But when the free electrons were absorbed to form neutral atoms, the Universe suddenly became transparent.

• Those same photons - the afterglow of the Big Bang known as cosmic background radiation -can be observed today.

ANISOTROPIES IN CMB:

The anisotropies in the CMB are explained as acoustic oscillations in the photon-baryon plasma (prior to the emission of the CMB after the photons decouple from the baryons at 379,000 years after the Big Bang) whose restoring force is gravity.

Ordinary matter interacts strongly with radiation whereas, by definition, dark matter does not. Both affect the oscillations by their gravity, so the two forms of matter will have different effects.

CANDIDATES OF DARK MATTER:

• There is no shortage of ideas as to what the dark matter could be. Serious candidates have been proposed with masses ranging from 9 x 10^-72 M☉

(axions) up to 104M (black holes). That's ☉a range of masses of over 75 orders of magnitude! It should be clear that no one search technique could be used for all dark matter candidates

CATEGORIZATION (A)

BARYONIC MATTER Massive Compact Halo Object

(Macho) . These include brown dwarf stars and black holes.

Brown dwarfs are spheres of H and He with masses below 0.08 , so they never begin nuclear fusion of hydrogen.

Black holes could be the remnants of an early generation of stars which were massive enough so that not many heavy elements were dispersed .

NON BARYONIC MATTER The Axion is mentioned as a

possible solution to the strong CP problem and is non baryonic candidate of dark matter.

The largest class is the Weakly Interacting Massive Particle (Wimp)which consists of literally hundreds of suggested particles. The most popular of these Wimps is the neutralino from supersymmetry.

CATEGORIZATION (B)

HOT DARK MATTER• A dark matter candidate

is called ``hot" if it was moving at relativistic speeds at the time when galaxies could just start to form.Light neutrinos come under this category.

COLD DARK MATTER• A dark matter candidate

is called ``cold" if it was moving non-relativistically at the time when galaxies could just start to form.

WIMPS

Its name comes from the fact that obtaining the correct abundance of dark matter today by thermal production require a self annihilation cross section of 10^-26 cm cube per sec which is roughly what is expected for a new particle in 100Gev mass range that interacts via electroweak force.This class of natural dark matter candidates is generally called weakly interacting massive particles (WIMPs).

SUPERSYMMETRIC WIMPNEUTRALINO

An extension of the standard model, called Supersymmetry (SUSY) offers a promising framework for the type of particle species that could fit the observed properties of dark matter.

The most promising candidate particle is the lightest supersymmetric particle (LSP). This is a supersymmetric particle that all other supersymmetric particles would decay into, itself being stable. This particle is called the neutralino.

In order to be consistent with an early universe annihilation rate, leaving proper relic abundances, such a particle should have a small but measurable interaction cross-section with ordinary matter. Specifically a cross-section for interaction between a neutralino and a nucleon in ordinary matter is of the order of the electroweak scale .

o The relic density provides a target annihilation cross section

s ~ 3 x 10-26 cm3/s

AXIONS• Axions arise from attempts to explain why the strong

interaction seems to obey a certain symmetry called "CP symmetry". Among other things, CP symmetry would prevent the neutron from having a large electric dipole moment - without it, it's very hard to understand why such a dipole moment has not yet been detected. The best explanation for this is called "Peccei-Quinn symmetry", and predicts a new light neutral particle called the axion.

• The axion is stable in many theories, and can also be produced in the early universe. Though axions are far lighter than WIMPs (often 1 eV or much less), they can be created in the right amount by a non-thermal process which also naturally leaves them slow-moving.

LIST OF DARK MATTER EXPERIMENTS

• Advanced Thin Ionization Calorimeter• Alpha Magnetic Spectrometer• ANAIS• ArDM• Axion Dark Matter Experiment(ADMX)• CERN Axion Solar Telescope• Cryogenic Dark Matter Search(CDMS)• Cryogenic Rare Event Search with

Superconducting Thermometers• DAMA/LIBRA• DAMA/NaI• Dark Matter Time Projection Chamber• DarkSide• DEAP• Directional Recoil Identification from

Tracks• EDELWEISS

• European Underground Rare Event Calorimeter Array

• Korea Invisible Mass Search• Large Underground Xenon

experiment(LUX)• Microlensing Observations in Astrophysics• MultiDark• Optical Gravitational Lensing Experiment• PAMELA detector• PandaX• PICASSO• PVLAS• SIMPLE (dark matter experiment)• SNOLAB• UK Dark Matter Collaboration• WIMP Argon Programme• XENON• ZEPLIN-III

SCDMS

• Utilizing state-of-the-art cryogenic germanium detectors, the SuperCDMS (SCDMS) collaboration is searching for WIMPs

• SuperCDMS is the successor to the CDMS II experiment, which was located deep underground in the Soudan mine in Minnesota, USA.

• After a brief testing period located at Soudan, SCDMS plans to be located at SNOLAB (Vale Inco Mine, Sudbury, Canada).

• The use of underground facilities provide shielding from cosmogenic events and as a result reduce interference of known background particles.

PROCEDURE SuperCDMS detectors are designed with the primary function of detecting the minute

phonon signals generated within the detector crystal by elastic collisions between detector nuclei and WIMPs. The energy deposited in a detector by an interacting WIMP may be as low as a few tens of keV. Event detection at such energy levels requires a sensitive experimental apparatus. The foremost requirement is that the detector maintained at a very low temperature to distinguish the deposited energy from the thermal energy of the detectors nuclei. The SCDMS project and associated test facilities employ He-3/He-4 dilution refrigerators which, with the appropriate cryostat apparatus are able to achieve detector base temperatures as low as 10mK.

An incident particle collides with a nucleus in the detector, which sets off vibrations throughout the crystal lattice. These vibrations, which are called phonons, propagate through the crystal and some reach the surface. Once there, they are absorbed by the aluminum fins. In the aluminum fins, the phonons transfer their energy to quasi-particle Cooper pair electrons. The incident phonon energy breaks these Cooper pairs and gives the energy to the electrons. These quasi-particle electrons diffuse to the tiny strips of tungsten that are attached to aluminium fins. The change in the TES resitance causes a small change in the current flowing through them

CDMS PARAMETER SPACE

ADMX

The goal of the Axion Dark-Matter eXperiment (ADMX) Gen 2 project is to discover axions that would constitute the dark matter in our Milky Way halo.

ADMX consists of a large microwave cavity resonator located inside a high-field solenoid magnet. Halo dark-matter axions which enter the cavity have a small but finite probability to convert into microwave photons.

This exceedingly weak microwave signal is then detected by a receiver which is capable of near quantum-limited noise performance. This ADMX configuration is currently in operation and taking data over plausible axion masses and couplings.

The Gen 2 configuration of ADMX adds a dilution refrigerator to reduce the temperature of the cavity and receiver front end.

RECENT DATA

• Researchers at Leicester University spotted the curious signal in 15 years of measurements taken by the European Space Agency.They noticed that the intensity of x-rays recorded by the spacecraft rose by about 10% whenever it observed the boundary of Earth’s magnetic field that faces towards the sun.

• Similar signal had been detected by Nasa’s Chandra X-ray Observatory.

• Dark matter axions, or axion-like particles, could be responsible for this as they can convert to photons in the magnetic field of the Earth.

DARK ENERGY

INTRODUCTION

In the early 1990's, one thing was fairly certain about the expansion of the Universe The Universe is full of matter and the attractive force of gravity pulls all matter together. So theoretically,universe had to slow.Then came 1998 and the Hubble Space Telescope (HST) observations of very distant supernovae that showed that, a long time ago, the Universe was actually expanding more slowly than it is today. So the expansion of the Universe has not been slowing due to gravity, as everyone thought, it has been accelerating. No one expected this, no one knew how to explain it. But something was causing it.

WHAT IS DARK ENERGY? One explanation for dark energy is that it is a property of space. Albert

Einstein was the first person to realize that empty space is not nothing. Space has amazing properties, many of which are just beginning to be understood.

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, makes a second prediction: "empty space" can possess its own energy. Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear. As a result, this form of energy would cause the Universe to expand faster and faster.

Unfortunately, no one understands why the cosmological constant should even be there, much less why it would have exactly the right value to cause the observed acceleration of the Universe. 

Another explanation for how space acquires energy comes from the quantum theory of matter. In this theory, "empty space" is actually full of temporary ("virtual") particles that continually form and then disappear. But when physicists tried to calculate how much energy this would give empty space, the answer came out wrong - wrong by a lot. The number came out 10120 times too big. That's a 1 with 120 zeros after it. It's hard to get an answer that bad. So the mystery continues.

Another explanation for dark energy is that it is a new kind of dynamical energy fluid or field, something that fills all of space but something whose effect on the expansion of the Universe is the opposite of that of matter and normal energy. Some theorists have named this "quintessence" . But, if quintessence is the answer, we still don't know what it is like, what it interacts with, or why it exists. So the mystery continues.

A last possibility is that Einstein's theory of gravity is not correct. That would not only affect the expansion of the Universe, but it would also affect the way that normal matter in galaxies and clusters of galaxies behaved.

But if it does turn out that a new theory of gravity is needed, what kind of theory would it be?

How could it correctly describe the motion of the bodies in the Solar System, as Einstein's theory is known to do, and still give us the different prediction for the Universe that we need?

“ So the mystery continues”

SURVEY

According to the Planck mission team, and based on the standard model of cosmology, the total mass–energy of the known universe contains 4% ordinary matter, 21% dark matter and 75% dark energy.

Chart of the matter of the universe. In a way, this chart is an embarrassment for scientists. We are only able to account for 4% of the matter in the universe.

THANK YOU