Cluster of Galaxies

Cluster of galaxies are the largest and massive structure in universe which are gravitationally bound together.Each cluster of galaxy contain 10 to 1000 galaxies.Galaxies in cluster have a very large peculiar velocity of 800-1000 km/s to be virialized in cluster.

Beside the galaxies it is found that there is a hot plasma gas in the clusters with the name of ICM "Inter cluster mass" which is approximately 2 times massive that the baryonic matter in galaxies.

The mysterious aspect of clusters is that if this structures are in hydrostatic equilibrium they need Dark matter with mass of 6 times more than baryonic matter in cluster.

So in this case there are three main constituents in each cluster:

1)5% galaxies 2)10% X-ray emitting hot gas 3)Dark matter.

It seems that the dark matter ,galaxies and ICM has approximately the same distribution in clusters.

Cluster of galaxies are the most massive and lately formed structure in the hierarchical structure formation model.They masses vary from 10^14 to 10^ 15 solar masses and the diameter of this clusters are from 2 to 10 Mpc.

The nearby important clusters are Virgo cluster, Hercules cluster and Coma cluster.

The galaxy clusters are a rich regions for observational cosmology and consequently theoretical cosmology.

Accreation disks

Accretion disks arises when materials in universe usually being transformed from one celestial to the other object.Accretion means the collecting of additional matter.

The place that accretion disk take place is Binary stars and active galaxy nuclei.

For example consider a white dwarf that a simple star like ours rotate around it.

because of the conservation of angular momentum and gravitational pull from White dwarf to interstellar medium and sun ,spirals appear in disk.

gas become very hot in disk due to friction and being tugged on by white dwarf and eventually looses angular momentum and falls into WD.

The important of accretion disk is that the first and most common is the growth of a massive object by gravitationally attracting more matter, typically gaseous matter in an accretion disc.

Neutron Star

Collapse of stars,type II supernovae and type Ib and type Ic SN caused to have neutron stars.This stars whic are completely/dominantly/ composed of neutrons have masses between 1.35~2.1 solar mass and radius of 12 km which means that neutron stars have high densities of 3.7~5.9 * 10^17 kg/m^3 .At the very high pressures involved in this collapse, it is energetically favorable to combine protons and electrons to form neutrons plus neutrinos. The neutrinos escape after scattering a bit and helping the supernova happen, and the neutrons settle down to become a neutron star, with neutron degeneracy/Pauli exclusion principle/ managing to oppose gravity.

The neutron stars are formed by high rotation speed because of conservation of angular momentum.Also because of the high speed of stars they can escape from disk of galaxies and can be found in perpendicular direction of disk galaxies.

The high density of neutron star cause to have a escape velocity of about 33% of light speed as a comparison a teaspoon of neutron star has a mass of 5*10^12 kg.

Neutron stars are believed to form in supernovae such as the one that formed the Crab Nebula (or check out this cool X-ray image of the nebula, from the Chandra X-ray Observatory).

up to today there are 2000 known neutron stars are found in milky way and Magellanic clouds.

it is also worth that they appear in binary type with 5%.

Some good links for neutron stars.

http://www.astro.umd.edu/~miller/nstar.html#formation

http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html

6 puzzles for LCDM

Recently a nice review article appeared in arxivarXiv:0811.4684 by Perivolaropoulos from Greece.

The title is 6 puzzles for LCDM .In this article author pay attention to 6 problems /observational ones/that the LCDM model have problem with them.

In literature always we confront with the two problems of fine tuning and coincidence problem for LCDM ,but there are more to confront.

1)Large scale velocity flow: LCDM predicts smaller amplitude and scale for the flow.

2)Brightness of type I SuperNova at high redshifts :LCDM predicts fainter SuperNova in high redshifts.

3)Emptiness of voids:LCDM predicts more dwarf or irregular galaxies in voids.

4)Profile of Halo clusters:LCDM predicts low and shallower concentration and density.

5)Profile of galaxy halos:LCDM predicts cuspy core and low outer density while lensing and other observations predicts central core of constant density.

6)Size able population of disk galaxies:LCDM predicts less disk galaxies.

This are really interesting probes for dark energy problem

Sweet molecule in our galaxy

An interesting article with id number of 0811.3821 in arXiv is uploaded.

A group of astronomers in University Collage of London found the simplest monosacharite ,

"glycolaldehde" in a distant of 9 kpc in a hot molecular cloud in our galaxy.

The discovery is so interesting because this monosacharite is the block for generating Ribose which is the main block of RNA.

lately there are evidence for glycolaldeyde in the center of galaxy ,but because of high interaction rate and density of this part of galaxy it seemed natural to found it there.

But the detection of spectral line of glycolaldehde by IRAM radio telescope in France in region which star forming is probable is an interesting news for exoearth life science.

molecule

News in science daily:

http://www.sciencedaily.com/releases/2008/11/081125090344.htm

arXiv:0811.3821v1

Reionization

Today in IPM/Tehran/There is a lecture talk about the law frequency radio astronomy.

In the conclusion part, the lecturer state that one of the applications of law frequency radio astronomy is detecting objects in reionization era.

Now what is reionization era.

Let me do a little job to describe it.

In the history of universe two major phase transition occurred for hydrogen.

First of it was in the time of recombination/redshift z~1100 / 400,000years after big bang when the rate of combination of electron to protons became higher than the ionization of hydrogen atom so in consequence of this the hydrogen atoms formed and the universe become transparent for photons.This is the last scattering surface and the photons coming from this redshift are the cosmic microwave background radiation photons.

The second phase transition occurred in reionization era, 150 million to 1 billion year after big band/redshift of 20 to 6/ because of formation of structures high energy became free and the universe /the intergalactic medium /changes it phase and from neutral become ionized and transformed to plasma.In this case the protons and electrons which are not bound can not capture the photons so they become transparent to it.

There are different techniques to found out about this era,which in future posts I will introduce them first of all for my self like.

Techniques are:

Quasars and the Gunn-Peterson trough

CMB anisotropy and polarization

21-cm line

Ph.D.

Now it is November 2008!
I start to plan all the way for my Ph.D. thesis
The general title will be accelerating universe:Theory and phenomenology.
In this work I should take a look and do my research in theoretical models generally Dark energy and modified gravity ones,and also use cosmological observations like Supernova, CMB,large scale structure,local tests of gravity to investigate the mystery of 70% of our universe.
I think that I should finish my work in September 2011!!!
It seems interesting time for me.
Go on...

Scintillation of light curves and Dark matter

In the last two weeks, in physics department of SUT, in our weekly cosmology seminars we have Frahang Habibi as a speaker. In this two sessions he describes for us a general view of his Ph.D thesis. Farhang is a joint Ph.D. student of sharif university and IAP in Paris.
He is working on dark matter detection in form of hydrogen molecule gas.

Now what is the story?
As we know 23% of our universe is composed of dark matter/means no electromagnetism interaction/but gravitationally is resemble to ordinary baryonic matter.
There are many many candidates for Dark matter starting from super symmetric particles to unseen baryonic matter.
Now what is Farhangs and Mark Moniez/his french side supervisor/ idea ?It is about a cloud of hydrogen molecule distrubeted in clusters which are not radiating because of there internal structure of hydrogen molucule ,but can be a candidate of unseen matter.
In this thesis they introduce a type of a test in order to detect them.
If there is a cloud of hydrogen molecules, they can effect optically on the light coming from stars beyond it.This cloud can scatter and diffract the light coming.So if in an experiment / observation/we can see an effect of scintillation in the light curves of the stars., it shows that there is something there that cause the amplification of light and maybe if the characteristics of our observation seems to our models match, it could be a cloud of hydrogen.

This is the good part of the story.But the bitterly hard part remains,the simulation of this effect and then observation of a known cluster and after that data reduction in order to find the best candidate stars which their light curves shows the effect of scintillation is Farhangs hard task.

6+1 lesson from f(R)-gravity

Last Monday 3 of November a nice talk-article was appeared in arXiv with the title of:

6+1 lessons from f(R) gravity with the arxiv address arXiv:0810.5594

In this article Thomas P. Sotiriou a postdoc in Meryland, describe the 7 lessons that we learn from studing the straightforward form of modification of gravity.

Thomas P. Sotiriou received his Ph.D. in SISSA in September 2007 under supervision of Stefano Liberati and John Miller with the title of Modified Actions for Gravity: Theory and Phenomenology with the address of arXiv:0710.4438 .

He is the great expert of modified gravity.Tracking his articles in recent years help me lot even in preparing my Master thesis.

Homepage of Thomas Sotiriou

http://terpconnect.umd.edu/~sotiriou/mysite/About_Me.html

Chameleon mechanism

Tuesday 28 of October I gave a small!!! talk in physics department,in series of cosmology weekly seminars.

The general title of talk is the Accelerating universe,Theory and phenomenology and the subtitle is Chameleon scalars mechanism and modified gravity.

The general title is the field which I want to be engaged in my Ph.D.thesis.

And what about the chameleon theories?

The accelerating universe open a new paradigm in cosmology.

There are many many models trying to describe this phenomena,but generally we can divided all the models in 2 general subdivisions.

If we accept the context of general relativity, which means that we know gravity well, we will come to the realization that new physical entity needed to describe the accelerating universe,such as cosmological constant or scalar fields generally named quintessence.

The second main models come to existence from the assumption that the general relativity needed to be modified in long ranges and small curvatures.This models named Modified gravity.

But what is chameleon?

The point is that we know that general relativity works well in solar system and local tests of gravity.So if we change the action of Einstein -Hilbert to have new effects in cosmological scales also we will affect the local tests of gravity, so we need a mechanism! in order to conceal this effect in local tests and disappear it and bring it back to existence in cosmological scales. This mechanism is called Chameleon mechanism after the name of lizard!!!like animal which changes its skin color with environment.So the scalar field equivalent to modified gravity /We know about the equivalence of modified gravity with scalar field theories/

changes its behaviour with respect of the density of environment like Chameleons.

BUT

in theoretical point of view this mechanism needs more investigations to be reliable,I will study it more...

Ads/CFT

It is about a year that in our physics department in Sharif university, each Tuesday held a seminar among the three active theoretical groups of department.

1)Particle physics 2)Cosmology 3)Conformal field theory group

The idea and the motivation of seminars is nice:it is to be connected and aware of the work of each other.Last Tuesday particle group talk about really complex subject.I want to respell the ideas of it in order to have a snapshot of this.

The talk is given by Mohsen Alishahia and is about about Ads/CFT correspondence more vastly Anti de sitter space/Conformal field theory correspondence which is also called after Maldacena the Argentinian physicists MAldacena duality.What is all about?

The theory shows that the string theory in a Anti desitter space plus a sphere or orbifold is physically equivalent to a conformal field theory with out gravity defined in its boundary.

It seems complicated anyhow it is interesting because of presenting a way to solve the quantum gravity theory and also it is inspired by the holographic principle which claim that you can extract the physics of a volume from its boundary.Holographic principle is a a speculative idea about quantum gravity originally proposed by Gerard 't Hooft and improved and promoted by Leonard Susskind.

Finally the lecturer imposed the probability that maybe this correspondence first of all can be used to describe the gravitational effects on inflationary models.

Let me show up some important papers on this genius work.

Reminding you that In about five years, Maldacena's article had 3000 citations and became one of the most important conceptual breakthroughs in theoretical physics of the 1990s, providing stark new insight into both quantum gravity and QCD.

1)Maldacena, The Large N Limit of Superconformal Field Theories and Supergravity, arΧiv:hep-th/9711200.
2)Witten, Anti-de Sitter Space and Holography, arΧiv:hep-th/9802150.
3)Gubser, Klebanov and Polyakov, Gauge Theory Correlators from Non-Critical String Theory, arΧiv:hep-th/9802109.
4)Aharony et al, Large N Field Theories, String Theory and Gravity, arΧiv:hep-th/9905111.
AdS/CFT correspondence on arxiv.org.

2008 Physics Nobel Prize

Finally the 2008 Physics Nobel prize goes to Japanese.

Yoichiro Nambu from Chicago University /http://physics.uchicago.edu/research/areas/particle_t.html#Nambu /for his contribution to the finding of the mechanism of spontaneous broken symmetry in subatomic physics get 1/2 of the Nobel prize and the other half goes to Makoto Kobayashi and Toshihide Maskawa for for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature.

One another Nobel prize goes to particle physicists campaign,although their are hope to see the prize in cosmology for the discovery Accelerating universe by Supernovas but ...

Anyhow in the upcoming posts I will try to describe the work of Nobel prize winners...

MOND vs Dark Matter

A couple of weeks ago, there was a Ph.D. thesis defence in Sharif University of Technology by Hossein Haghi **,***under supervision of Dr. Sohrab Rahvar/He is my supervisor too!:)/, in physics department with the title of MOND* in ... : Modified Newtonian Dynamics.

What is it about?and what is the story of modification...

During last century, in physics history usually we observed new phenomenas in experiments which could not be described by approved and used models and physical laws of the day.So what happened? Immediately the situation is divided in two ways

1)In the same frame of our known laws and models, we defined new physical entities to describe the experiment. or

2)We concluded that we do not know the laws well, and we start to change and modify them.

This scenario was happened several times, as a famous example is the problem of missing mass in beta decay in late 20's and beginning of 30's ,as I mentioned there were two solution 1)The law of conservation of energy is not correct or

2)there is a new mysterious unseen particle that we do not know about it and can not detect in experiment.

The history in this case shows that the second solution, the famous Neutrino predicted by Pauli was the right answer.

Now we have such a situation in galactic scale cosmology too.

The rotation curves of stars rotating in galaxy contradict with the prediction of Newtonian Mechanic, and we get flat rotational curves.

Immediately there is two solutions to the problem

1)Modifying the Newtonian law:Which means we do not understand it well,or there is more complete theory standing there.MOND as an example.

2)There is a new mysterious,only gravitationally interacting particle which named DARK MATTER ,which is responsible for this new missing mass in galaxy.

Finally what I want to mention is about the always existing two perspectives as a solution of the problem.

1)Modifying the laws or 2)Introducing New physical entity, are always teasing physicists minds.

But which one is seems more plausible is not yet well established but it will be fair to mention that the DARK MATTER campaign is so large /because of its success in cosmological model for structure formation models as CDM and there is a huge Hope to find light supersymmetric particles (LSP) in LHC arXiv:0807.2244 as a candidate for this entities as DARK MATTER.

But the story is not happy ended yet .Anyhow let us see what experiments unreveal for us.

*Nice web site about MOND related papers: http://www.astro.umd.edu/~ssm/mond/

**arXiv:astro-ph/0606246

***arXiv:astro-ph/0504171

Timeline of General Relativity and Cosmology from 1905

The new semester in Sharif university begins.This term Dr. Reza Mansouri,/ http://en.wikipedia.org/wiki/Reza_Mansouri /one of the prominent scientists of Iran teach General relativity and gravitation. Dr. Mansouri which recieved his Ph.D. in Austria in begining of 1970s is the first one who taught general relativity in Iran.
In first session he take a look on history of general relativity and cosmology.
The below is a more complete list of the happenings since the foundation of Special relativity in 1905.


1905 - Albert Einstein , special relativity

1907 - Albert Einstein introduces the principle of equivalence of gravitation and inertia

1915 - Albert Einstein - general relativity.

1915 - Karl Schwarzschild - Schwarzschild metric ,first solution to the Einstein field

1916 - Albert Einstein - field equations of general relativity admit wavelike solutions

1917 - Willem de Sitter derives an isotropic static cosmology with a cosmological constant, as well as an empty expanding cosmology with a cosmological constant, termed a de Sitter universe.

1918 - J. Lense and Hans Thirring find the gravitomagnetic precession of gyroscopes GR

1919 - Arthur Eddington -solar eclipse expedition- detection gravitational deflection of light

1921 - Theodor Kaluza 5-dimensional version of GR equations unifies gravitation and EM

1922 - Alexander Friedmann finds a solution to the Einstein field equations which suggests a general expansion of space

1927 - Georges Lemaître discusses the creation event of an expanding universe governed by the Einstein field equations.

1929 - Edwin Hubble demonstrates the linear redshift-distance relation and thus shows the expansion of the universe

1933 - Edward Milne names and formalizes the cosmological principle 1934 - Georges Lemaître interprets the cosmological constant as due to a vacuum energy with an unusual perfect fluid equation of state

1937 - Fritz Zwicky states that galaxies could act as gravitational lenses

1937 - Albert Einstein, Leopold Infeld, and Banesh Hoffmann -geodesic equations of GR can be deduced from its field equations

1938 - Paul Dirac suggests the large numbers hypothesis, that the gravitational constant may be small because it is decreasing slowly with time.

1948 - Hermann Bondi, Thomas Gold, and Fred Hoyle propose steady state cosmologies based on the perfect cosmological principle.

1948 - George Gamow predicts the existence of the cosmic microwave background radiation by considering the behavior of primordial radiation in an expanding universe

1950 - Fred Hoyle derisively coins the term "Big Bang".

1957 - John Wheeler discusses the breakdown of classical general relativity near singularities and the need for quantum gravity.

1960 - Robert Pound and Glen Rebka test the gravitational redshift predicted by EP the approximately 1%

1961 - Robert Dicke argues that carbon-based life can only arise when the gravitational force is small, because this is when burning stars exist; first use of the weak anthropic principle

1962 - Robert Dicke, Peter Roll, and R. Krotkov use a torsion fiber balance to test the weak equivalence principle to 2 parts in 100 billion

1964 - Irwin Shapiro predicts a gravitational time delay of radiation travel as a test GR

1965 - Joseph Weber puts the first Weber bar gravitational wave detector into operation

1965 - Martin Rees and Dennis Sciama analyze quasar source count data and discover that the quasar density increases with redshift.

1965 - Arno Penzias and Robert Wilson, astronomers at Bell Labs discover the 2.7 K microwave background radiation, which earns them the 1978 Nobel Prize in Physics. Robert Dicke, James Peebles, Peter Roll and David Todd Wilkinson interpret it as relic from the big bang.

1966 - Stephen Hawking and George Ellis show that any plausible general relativistic cosmology is singular

1966 - James Peebles shows that the hot Big Bang predicts the correct helium abundance

1967 - Andrei Sakharov presents the requirements for baryogenesis, a baryon-antibaryon asymmetry in the universe

1968 - Irwin Shapiro presents the first detection of the Shapiro delay

1968 - Kenneth Nordtvedt studies a possible violation of the weak equivalence principle for self-gravitating bodies and proposes a new test of the weak equivalence principle based on observing the relative motion of the Earth and Moon in the Sun's gravitational field.

1969 - Charles Misner formally presents the Big Bang horizon problem 1969 - Robert Dicke formally presents the Big Bang flatness problem.

1974 - Robert Wagoner, William Fowler, and Fred Hoyle show that the hot Big Bang predicts the correct deuterium and lithium abundances

1976 - Robert Vessot and Martin Levine use a hydrogen maser clock on a Scout D rocket to test the gravitational redshift predicted by the equivalence principle to approximately 0.007%

1976 - Gravity Probe A experiment confirmed slowing the flow of time caused by gravity matching the predicted effects to an accuracy of about 70 parts per million.

1979 - Dennis Walsh, Robert Carswell, and Ray Weymann discover the gravitationally lensed quasar Q0957+561

1981 - Viacheslav Mukhanov and G. Chibisov propose that quantum fluctuations could lead to large scale structure in an inflationary universe 1981 - Alan Guth proposes the inflationary Big Bang universe as a possible solution to the horizon and flatness problems

1982 - Joseph Taylor and Joel Weisberg show that the rate of energy loss from the binary pulsar PSR B1913+16 agrees with that predicted by the general relativistic quadrupole formula to within 5%

1990 - Preliminary results from NASA's COBE mission confirm the cosmic microwave background radiation is an isotropic blackbody to an astonishing one part in 105 precision, thus eliminating the possibility of an integrated starlight model proposed for the background by steady state enthusiasts.

1990s - Ground based cosmic microwave background experiments measure the first peak, determine that the universe is geometrically flat

1998 - Controversial evidence for the fine structure constant varying over the lifetime of the universe is first published.

1998 - Adam Riess, Saul Perlmutter and others discover the cosmic acceleration in observations of Type Ia supernovae providing the first evidence for a non-zero cosmological constant.

1999 - Measurements of the cosmic microwave background radiation (most notably by the BOOMERanG experiment see Mauskopf et al., 1999, Melchiorri et al., 1999, de Bernardis et al. 2000) provide evidence for oscillations (peaks) in the anisotropy angular spectrum as expected in the standard model of cosmological structure formation. These results indicates that the geometry of the universe is flat. Together with large scale structure data, this provides complementary evidence for a non-zero cosmological constant.

2002 - The Cosmic Background Imager (CBI) in Chile obtained images of the cosmic microwave background radiation with the highest angular resolution of 4 arcmin. It also obtained the anisotropy spectrum at high-resolution not covered before up to l ~ 3000. It found a slight excess in power at high-resolution (l > 2500) not yet completely explained, the so-called "CBI-excess".

2003 - NASA's WMAP obtained full-sky detailed pictures of the cosmic microwave background radiation. The image can be interpreted to indicate that the universe is 13.7 billion years old (within one percent error) and confirm that the Lambda-CDM model and the inflationary theory are correct. 2003 - The Sloan Great Wall is discovered.

2004 - The Cosmic Background Imager first obtained the E-mode polarization spectrum of the cosmic microwave background radiation.

2006 - The long-awaited three-year WMAP results are released, confirming previous analysis, correcting several points, and including polarization data.

2007 - End of Gravity Probe B experiment.

Primordial non-gaussianity in cosmology

Couple of days ago Niayesh Afshordi from Perimeter Institute visited to Sharif university of technology, physics department.He had a talk about primordial non Gausianity in cosmology.It seems that will be interesting and hot topic of research in upcoming decade, because of new and exact experiments that we will have.

This is the title and abstract of his talk.

Title: Primordial non-gaussianity in cosmology
Abstract: "Modern cosmological observations seem to indicate that theinitial conditions of the universe obey gaussian statistics withremarkable accuracy, as predicted by simple inflationary models.Nevertheless, any possible signature of primordial non-gaussianity will provide a unique window into physics of the very early universe. In this talk, I will outline the various ways through which these signatures could be observed, and what they may imply for the early universe physics. Inparticular, I will talk about recent developments that show primordialnon-gaussianity will affect large scale structure of galaxy distribution significatntly, and already provides comparable constraints to the cosmicmicrowavebackground anisotropies."

Article of Niayesh about primordial non gusianity:

http://arxiv.org/abs/0806.1046

GRB in z=6.7

Gamma ray bursts (GRB)/are the most luminous electromagnetic events occurring in the universe since the Big Bang. They are flashes of gamma rays emanating from seemingly random places in deep space at random times/, are lately in focus of great attention.The speculation that maybe they would be possible standard candles make their importance more.

If there are standard candles then we can track the expansion history of universe in higher redshifts,cause they founded farther than supernovas.The farthest Gamma ray burst is founded in z=6.7 the report of this GCN is reported in work of Fynbo et al.This is the report.

"

TITLE: GCN CIRCULAR NUMBER: 8225

SUBJECT: GRB 080913:

VLT/FORS spectrum

DATE: 08/09/13 17:28:26 GMT

J.P.U. Fynbo (DARK/NBI), J. Greiner, T. Kruehler (both MPE),A. Rossi (Tautenburg Obs), P. Vreeswijk, D. Malesani (both DARK/NBI)report on behalf of a larger collaboration

Based on the rapid determination of an "i-band" drop out we triggered VLT/ToO observations (program-ID 081.A-0135; PI Greiner) and obtained spectroscopy with FORS2+Gris600z of the afterglow of GRB080913(Schady et al. 2008, GCN #8217; Stamatikos et al. 2008, GCN #8222*.

Observations started at 8:30, about 100 min after the GRB, and continueduntil morning twilight. We detect a red continuum that disappears bluewards of a break around 9400 AA. Interpreting this break as the onset of the Lyman-alpha forest we infer a redshift of about z=6.7 consistent with the photometric redshift determined by GROND (Greiner et al., GCN #8223)."

*http://gcn.gsfc.nasa.gov/gcn3_archive.html#tc1

But the physics of GRB is undiscovered yet.,further investigations may assure us about their physics.

footnote:

Thanks to Amir a Gamma ray burst investigator in Michigan tech physics department.

M. Dominik In Tehran & Microlensing method for exoplant finding

One of the hottest topics in Astronomy is EXOPLANETS founding.

Finding exoplanets are the first steps in order to find life in our universe!!!

There are many methods in order to find the exoplanets,like astometry, spectroscopy, straight observation and...

A new physical method is gravitational microlensing mainly become in attention after founding of OGLE group by Alcock et al . published in Nature which they found and exoplanet by this method for the first time.

The story is the old one of Einstein's bending light story.When a light ray pass by from a massive object /in this case the gravitational lens a star a galaxy or cluster of galaxies/ light beams bend, consequently the shape and flux magnitude of images of the source are altered,this phenomena is named as gravitational lensing.

In 1919 Eddington's observation of gravitational lensing is the first stone like prove of general relativity view of nature.

But what is gravitational microlensing. When the lens is a star which magnify the energy flux of a distant source caused to microlensing effect.The naming comes after the situation that the effect of light bending produce new images of source which are separated in sky by micro seconds angle,which with our nowadays technology is hard to detect. So the only effect we will see is the magnification of light.

Now this method is used to finding exoplanets. If the lens is consisting of a star and planet the magnification curve which is called after Paszynski is lost its symmetry and a bump appear in it

which is a first clue of an binary lens, maybe a exoplanet!!!

This method is fine in order to find planets of less mass which will be suitable for finding life there. Anyhow this method needs tremendous effort in computer work, curve analysis and data management.

But the news is that Martin Dominik professor of physics from Saint Andrews which is a really expert in gravitational microlensing and exoplant finding/see the second link/ visiting Tehran, and has nice couple of lectures in IPM in 10-11 September.

http://exoplanets.org/

http://calvin.st-andrews.ac.uk/external_relations/news_article.cfm?reference=888

LHC Starts!!!

Finally after a two decade scientific planning and work, today the Cern Large Hadron Collider /near Geneva in the border of France and Switzerland/starts it works.

This tremendous,huge scientific projects, I think, must be included in the new eras one of world 7 wonders list.This super collider in energy and dimensions /27 km in circumstance tunnel /is the biggest one ever build, reaching to energy scales of TeV,which will be suitable for physicist to trace the physics beyond standard model.

There is a great hope to find the missing golden part of standard model the higgs boson.

Although there is chances in finding light supersymmetric particles/LSP/ which theoretically are presented as Dark Matter candidates.

The opening experiment excitement of LHC is reflected well in cosmic variance live blog.

Even today the Google changes its logo in honor of this human achievement.

Now there will be opened a golden era for particle physics phenomenologists to grasp the next decades Nobel prizes.

official website of LHC

Cern Page

What is LHC?

Cosmology a monumental work by Weinberg

Steven Weinberg is really a great TITAN standing in the edge of new physics.

In April 2008, Steven's new book in cosmology which named briefly COSMOLOGY is printed by Oxford university press.

What a huge ,tremendous work,like his last decade Quantum field theory books ,this one is an encyclopedia too.

Weinberg claims that he tried to cover the most advanced research areas of cosmology up to 2007 also in the introduction he mentioned that after 1999 as he finished the QFT 3 volume work he had a plenty of time studying cosmology,he read the review articles but not satisfied with them,He drives all the cosmology by himself!!!

It starts from Accelerating universe to Gravitational microlensing,what a work!

Andrei Linde from Stanford declare:

"A monumental book written by a leading authority in particle physics and cosmology. Since publication of Weinberg's famous book Gravitation and Cosmology 35 years ago, there has been a real revolution both in cosmological theory and observations. A major effort of a great expert has been required to summarize the main developments in one book, and to make this presentation both highly accurate and accessible. This book will be greatly appreciated by a broad readership, ranging from students who just enter the field to experts in modern cosmology. It should be on the desk of every actively working cosmologist."

Robert Kirshner from Harvard

"This book tackles the main events of today's cosmology: cosmic acceleration observed with supernovae, the exquisite structure of the cosmic microwave background, and the evidence for dark matter. Weinberg pays close attention to the historical development and summarizes the observations with care. He brings deep knowledge of the underlying physics and weaves these threads together into a rich text that will be of great value to astronomers and physicists. The first half of this book is a wonderful introduction to cosmology, suitable for a graduate course or for someone coming into the field from a neighboring region of the scientific forest. The second half is an original development of the theory for the growth of inhomogeneities in the Universe. Everyone who works on cosmology will find something to learn in this book."

http://en.wikipedia.org/wiki/Steven_Weinberg

Product Details
Hardcover: 544 pages
Publisher: Oxford University Press, USA (April 28, 2008)
Language: English
ISBN-10: 0198526822
ISBN-13: 978-0198526827
Product Dimensions: 10 x 7 x 1.5 inches

Anyhow today I start my journey through Weinbergs Cosmology!!!

Barion Acoustic Oscillations

pic1:Final distribution of baryonic matter and its two peaks in density profile

pic2:Photon start to stream/the right panel/ but baryonic matter remain in its place.The graph shows the distribution of baryonic(blue line) matter and photons(red line)
Pictures from personal page of Prof.Martin White

In dark energy model approaches to solve the accelerating universe puzzle,in the first step we confront a problem.The problem is that we measure the effect of dark energy indirectly through its effect on expansion rate of universe H=H(z).

So generally there are three main cosmological tools/probes/ to address this problem.

1)Standard candle:Use to find the relation between luminosity distance and redshift.In process of finding this we need to integrate the inverse of Hubble parameter.

2)Standard rulers:Standard rulers are object that we know their measure in some epoch of universe history,so looking at them through a specific angle give us the opportunity to calculate the angular diameter distance, which like the luminosity distance,once more we are able to calculate the integral of expansion rate of universe.

3)Growth of structure,also permit us to put constraint on the expansion rate and consequently on Dark energy model./This probe is useful for determine the difference between modified gravity models with dark energy models./

Although the cosmological objects in general does not have a specific shape to use them as standard rules but in early universe we will found one.

Baryon acoustic oscillation is a standard ruler from the last scattering epoch.

What is the story?

In early universe when the density and the temperature of universe were high ,there was

a plasma of baryons, electrons, photons, neutrinos and Dark matter.

Baryons and electrons are coupled to photons through Thompson scattering /electromagnetism interaction/ and Dark matter is only coupled by gravitational interaction.Then the universe was expanding and becoming cool until the last scattering epoch /approximately 300000 years after big-bang/ when the photons decoupled from matter.This is because the energy of photons are not enough to ionized the hydrogen atoms, so electrons were bound by protons.

At this epoch the photons free stream to the universe but the baryonic matter distribution was maintain in the same radius of 100 Megaparsec.As the universe continues its expansion, photons

spread uniformly through universe, while there was a potential well constructed in the middle of the 100Mps shell which the baryonic matter is distributed in its shell uniformly .

This is the sound horizon.Now the gravitational potential cause the final configuration of Acoustic peaks as two peaks in mass profile, one in the middle and one in 100Mps.

This imprint remains in large scale structure.

If we compute 2-point correlation function in LSS,we will found the effect of sound horizon.

Baryon Oscillations are well used in order to:

1)For firm prediction of models with baryons

2)prediction of dark matter and baryonic matter density in CMB3)Using in order to determine 3)angular diameter size and put constraints on Dark Energy models.

Anyhow the ruler of BAO is inconveniently large.Probe of gigaparsec volume is required to mark a precision measurement of the BAO.

A nice internet pages on BAO:

http://astro.berkeley.edu/~mwhite/bao/

http://www.lsst.org/Science/BAO.shtml/

A course and a book.

In 2008-autumn there will be a course in cosmology in Perimeter Institute thought by

Niayesh Afshordi, and Mark Wyman, from Perimeter Institute.

The course is based upon the T. Padmanabhan great book

Cosmology and astrophysics through problems ,published by Cambridge University press.

Although the course presenters change the place of astrophysics and cosmology in title, but they

describe in their course description that:

"This course is aimed at advanced undergraduate and beginning graduate students, and is inspired by a book by the same title, written by Padmanabhan. Each session consists of solving one or two pre-determined problems, which is done by a randomly picked student. While the problems introduce various subjects in Astrophysics and Cosmology, they do not serve as replacement for standard courses in these subjects, and are rather aimed at educating students with hands-on analytic/numerical skills to attack new problems."

Anyhow I take this book from library too and try to keep my paste harmonised with the course

presented in Perimeter and Waterloo physics department.

For website of the course,click here.

SuperStructure Imprint & ISW

" An Imprint of Super-Structures on the Microwave Background due to the Integrated Sachs-Wolfe Effect"

is the name of article published by IFA Hawaii university physics department collegues Benjamin R. Granett, Mark C. Neyrinck, István Szapudi (IFA, Hawaii).

the lanel address is : arXiv:0805.3695

This physicist use Integrated Saches Wolfe effect first introduced by RainerKurt Saches and Arthur Michael Wolfe in 1968 to show the imprint of superclusters and supervoid on photons energy , coming from Last scattering surface.

This imprint which is detected by founding the correlation of CMB temprature fluctuations and galaxy number densities/from SDSS galaxy catalouge/ is a key observation for accelerating universe.

This imprint is in good agreement with the dark Energy assumption and accelerating universe.

Ok what is the story.

The story is easy to grasp.

If the photons travel to the gravitational potentials, they gain energy and have a blue shift in wavelenght in contrast ,if photons come up from potentiel well,they loss energy and has a reshift.Now the point is that ,if the universe is filled with dark matter in linear regime,there is no difference between the change of energy of photons when they are going in and coming outside a gravitational well/cluster/.BUT...

the interesting part of the story is when the universe is accelerating,so in meanwhile that photons live in the potential well,Dark energy -cosmological constant or ...causes the well to be shallowed and become less deep.So there is a difference between energy gain and loss for photons so we can see this imprint on CMB photons and that is the evidence of Accelerating universe.

Good and joyful part of the story is this that the ISW can be used as one of the probes of Dark energy because oit is measuring some quantity/fluctuation of tempreture and it's coreelation/in two different stage of universe.So it can tell us about the dynamic of this exotic dark component of the universe.

IFA team launch a website about the superclusters/over dense regions/, super voids as a tool to exploring the dark matter and dark energy in the universe also explaining the ISW effect and their work on last paper.The site is : http://ifa.hawaii.edu/cosmowave/supervoids/

Dark Energy models

As mentioned in the last blog: "There are many models trying to describe the Accelerating universe problem", the most popular ones are listed as below.

1)Vacuum Energy-Cosmological constant

From Quantum field theory we know that we can relate harmonic oscillator to the vacuum state of QFT(Quantum field Theory)and as we know from the classical mechanics,the ground state of harmonic oscillator has non-zero energy which can contribute to the Dark energy.

In the other way we can easily interpret the energy momentum of vacuum energy as an cosmological constant/which Einstein first proposed before Hubble's discovery to get the static universe and later call it his life's biggest blunder/.

2)Dark Energy models

a)Quintessence

b)k-essence

c)phantom-ghost like fields

d)Pseudo-Nambo-Goldstone bosons

e)Oscillating dark energy models

Dark energy models containing all the subdivisions mention about,are physical models.All proposed a new kind of constitute of universe that has ridiculous equation of state.Usually this exotic entity is related to a scalar field.

3)Failure of General Relativity

a)Gravitation action is a general function of a Ricci scalar , scalars from Ricci and Riemann tensor

b)Scalar-Vector-tensor theories

d)Brane world cosmologies

this models discuss and propose that maybe we do not understand the gravity well and we should change the Einstein-Hilbert action to more general one.

The Brane world cosmologies suggest that in stead of 4D we live in a brane embedded in 5 Dimensions,in this case the gravity leakage to the 5-dimension in contrast to the matter and other force fields that are constrained to live in 4D.the result of this causes modification to the gravity understanded in 4D and causes the accelerating universe.

4)Chamelon models

This models suggest any exotic component of universe with equation of state that in early times behave like dark matter and in late universe is playing the role of dark energy

5)Dark energy,Dark matter interacting models

6)Failure of FRW-assumption.

In this inhomogeneous models the back reaction of structures cause to alter the distances we measure from standard candle SNIa,,and the dark energy is just a miscalculation.

7)Holographic dark energy

In this models our 4d manifold is a hologram of higher dimensional world

8)String theory landscape

In the framework of string theory the cosmological constant solution for accelerating universe is once again proposed and more, the problems of fine tunning and cosmic coincidence is answered by the landscape interpretation.

9)Quantum Geometry

That the space and time is also quantized and are manifestation of a new field.

10)Anthropic principle models

I will blog about it later...

There are other models too!!It seems that really we do not understand the physics of accelerating universe so so much models come to existing.

Let do more physics to found out the mystery.

Review articles in Accelerating universe

Since the discovery of Accelerating universe many theoretical models were introduced in order to describe the cause of this acceleration.
The models generally, are divided into two main parts.
1)Geometrical ones & 2)Physical ones.
Geometrical models assert that we do not understand the physics of gravity-(geometry)/because of GR/, in long ranges and small curvatures.So we must change the context of general relativity and then consequently we will be able to solve the problem of Accelerating universe ./This models are called generally Modified gravity models/
The other part are standing the physicists that claim the right theory is the physical ones.
They introduce new physical quantities like scalar field (Dark energy models-Quintessence models) with new thermodynamical properties / w<-1/3(Equation of state)/ to describe this problem.
Anyhow many there are many other approaches proposed in last decade that lately, I will post a blog listing the most fav. ones.
But what is the good part of the story is that there are many review papers
"God bless them " , that we can grasp the late happenings in the field of accelerating universe through studying them.
Let me name some :

1) Joshua Frieman (Chicago/Fermilab), Michael Turner (Chicago), Dragan Huterer(Michigan)/2008/
2)Eric V. Linder /2008/
3))Eric V. Linder/2007/
4) T. Padmanabhan /2007/
5)Edmund J. Copeland, M. Sami, Shinji Tsujikawa/2006/
6)Varun Sahni , Alexei Starobinsky/2006/
7)Rachel Bean, Sean Carroll, Mark Trodden /2005/
8) P. J. E. Peebles, Bharat Ratra /2002/
9)Dragan Huterer, Michael S. Turner /2001/
10)Sean M. Carroll /2000/

Hope to enjoy them.

Accelerating Universe

It is just a decade from revolutionary foundings of two SuperNova Suravy teams:

1)Supernova Cosmology Project , at the Lawrence Berkeley National Laboratory and the 2)High-z Supernova Search Team

/Riess(1998) and Perlmutter (1999)/ .They cliam that the SNIa ,which asserted to be standard candels are dimmer than that they seem to be in Standard CDM -model.

So...

What does it mean?

It means that if SNIa are really standard candels, we must wait to something revolutionary in cosmology.

This is because that in the context (becareful about the term used here,it means that we accept the GR and big-bang model ) of general relativity(GR)and Big-Bang model and cosmological principle(Homogenious,Isotropic universe) , we confront with two choises in order to describe the supernova observation:

1)The universe is open- K>0 /k is curvature/

or

2)Universe expansion is accelerating - q<0>

Now day with precise measurement in cosmology like WMAP-5 years result

,we know that curvature of our universe is nearly flat and from Large scale structure measurement the 30% of our known universe is Dark-ordinary Matter.

So ...

Universe is in phase of accelerated expansion and an unknown component of universe which contain 70% of it that may cause this(if we accept GR and cosmological principle) is Dark Energy.

"What is this unknown Dark Energy ,what causes of this acceleration?"

this is one of the greatest questions of physics for new millennium.

Hello TiYezerk

Hello TiYezerk

This is a new blog, specialized in Cosmology, and also other related branches of physics written by Shant Baghram, a Ph.D. Student of physics in Sharif university in Tehran.

The aim of blog first of all is self training to write down about more specialized topics in cosmology in couple of paragraphs, also to keep myself updated to the progress in this fantastic science area .

The start point of this blog is August 25-2008 in last days of my first Ph.D. studying year. Let see where does the train of cosmology go!!!

The name of blog is taken from the Armenian world for "Universe" which is Tiyezerk

Ti : great, big.

Yezerk: boundry .

It seems that the Armenian word of TiYezerk is somehow contains a topological point of view!,the word! believe that the universe has a boundary unless it is great.

Let me keep blogging!

Hello TiYezerk