Archivi tag: cosmic microwave background

9th International Conference on Interconnections between Particle Physics and Cosmology

Recent advances in observational astronomy and the discovery of 125-GeV Higgs boson have brought paradigm shifts on the potential connections between new fundamental particles and our understanding of their impact on the early universe and its evolution. With the content of the universe well known from astrophysical observations, a key aspect is that 27% of the universe appears to consist of dark matter. If current theories are correct, the particle physics candidate for this matter may well be observed in ongoing direct and/or indirect dark matter detection experiments or at the LHC. In addition, about 69% of the universe, the dark energy, still remains a significant mystery that major theoretical attempts are trying to understand. Continua a leggere 9th International Conference on Interconnections between Particle Physics and Cosmology

Cosmology on Safari

The past decade has seen a significant growth in cosmological observations that have placed increasingly tighter constraints on the cosmological model and the basic parameters that describe it. While we have an excellent phenomenological model a more fundamental picture is largely missing, considering both the very earliest times where high-energy processes are relevant and in the late-time universe, where we are in the curious position of living in a universe that is 95% dark. Continua a leggere Cosmology on Safari

Cosmology and relativistic astrophysics

The 2014 year marks the 100th anniversary of Yakov Zeldovich. The conference will commemorate his contribution to astronomy by concentrating on recent progress in cosmology and high energy astrophysics, the areas where his ideas laid the basis for revolutionary advances. Continua a leggere Cosmology and relativistic astrophysics

BOSS quasars yield a precise determination of cosmic expansion

An artist’s conception of how BOSS uses quasars to measure the distant universe. Light from distant quasars is partly absorbed by intervening gas, which is imprinted with a subtle ring-like pattern of known physical scale. Astronomers have now measured this scale with an accuracy of two percent, precisely measuring how fast the universe was expanding when it was just 3 billion years old. (Illustration by Zosia Rostomian, Lawrence Berkeley National Laboratory, and Andreu Font-Ribera, BOSS Lyman-alpha team, Berkeley Lab.)

La survey del cielo denominata Baryon Oscillation Spectroscopic Survey (BOSS), che rappresenta la parte più grande della terza survey Sloan Digital Sky Survey (SDSS-III), ha osservato i quasar distanti per realizzare una mappatura delle variazioni di densità del gas intergalattico a redshift elevati permettendo così di tracciare la struttura dell’Universo primordiale. BOSS ci fornisce da un lato una carta temporale della storia evolutiva dell’Universo al fine di avere maggiori indizi sulla natura dell’energia scura e dall’altro ci permette di realizzare nuove misure della struttura su larga scala, le più precise mai ottenute sull’espansione cosmica sin dall’epoca in cui si sono formate le prime galassie.

Continua a leggere BOSS quasars yield a precise determination of cosmic expansion

27° Texas Symposium on Relativistic Astrophysics

The 27th Texas Symposium on Relativistic Astrophysics will be held in downtown Dallas December 8 – 13, 2013. It is organized by the Department of Physics at The University of Texas at Dallas (UTD) and is chaired by Wolfgang Rindler and Mustapha Ishak. The Symposium will include both invited and contributed talks and posters. This will be a special and historically meaningful Jubilee meeting, marking the 50th anniversary, almost to the day, of the very first of these Texas Symposia, held in Dallas in December 1963. We are excited to welcome hundreds of international astrophysicists back to Dallas fifty years later, both to celebrate the past 50 years of Texas Symposia and relativistic astrophysics and to kick off the next 50 years of remarkable discoveries.

The Symposium will cover the following topics:


  • Cosmic acceleration/dark energy
  • Cosmic microwave background
  • Early universe (Inflation, Cyclic Model, CCC cosmology …)
  • Galaxy formation and reionization
  • Inhomogeneous cosmologies, averaging, and backreaction
  • Large-scale surveys
  • Quantum gravity/cosmology and string cosmology
  • Weak gravitational lensing
  • Experimental/observational cosmology – other topics
  • Theoretical cosmology – other topics
Compact objects and galactic/cluster scales
  • Black holes, mergers, and accretion discs
  • Galaxy evolution and supermassive black holes
  • Imaging black holes
  • Microlensing and exoplanets
  • Neutron stars, pulsars, magnetars, and white dwarfs
  • Nuclear Equation of State for Compact Objects
  • Singularities
  • Strong gravitational lensing
  • Supermassive black hole binaries
  • Tidal disruption of stars by supermassive black holes
  • Compact object observations – other topics
  • Compact object theory – other topics
High-energy astrophysics and astroparticle physics
  • Active galactic nuclei and jets
  • Cosmological implications of the Higgs and the LHC
  • Dark matter astrophysics
  • Dark matter experiments and data
  • Gamma-ray bursts, SNe connection, and sources
  • High-energy cosmic rays (VHE, UHE, mechanisms, etc.)
  • High-energy gamma-rays
  • Nuclear Astrophysics
  • Supernovae and their remnants
  • High-energy astrophysics/astroparticle physics – other topics
Testing general relativity and modified gravity
  • Alternative theories of gravity
  • Strong-field tests of general relativity
  • Testing general relativity at cosmological scales
  • Testing general relativity – other topics
  • Modified gravity – other topics
Gravitational waves
  • Electromagnetic counterparts of gravitational wave sources
  • Ongoing and planned gravitational wave experiments
  • Gravitational wave theory and simulations
  • Results and progress from gravitational wave searches
  • Supernovae and Gravitational Wave Emission
  • Gravitational waves – other topics
Numerical relativity
  • Computer algebra and symbolic programming
  • Locating black hole horizons
  • Numerical simulations
  • Relativistic magnetohydrodynamics
  • Numerical relativity – other topics
Other ongoing and future experiments and surveys
  • ACT, AMS, BOSS, CFHT, Chandra, DES, Euclid, Fermi, HETDEX, HSC, JWST,
  • (to be completed after abstract submissions)
And also:
History of relativistic astrophysics
History of the Texas Symposium and interface with other anniversaries
The Kerr solution – 50 years later

Anisotropic Universe: from microwaves to ultrahigh energies

The study of anisotropies connects and unravels fundamental issues in various fields of astrophysics and cosmology. With the recent experimental progress, it is now possible to analyze, understand, and cross-correlate the anisotropic skies observed by Planck, 2MASS Redshift Survey, ChandraFermi, AMS-2, HAWC, IceCube, and Auger, – to cite but a few major instruments that scrutinize the Universe from microwaves to ultrahigh energies, in photons, cosmic rays, and neutrinos. Anisotropic features can reveal key information on the structure and the nature of the components of the Universe, and provide hints on the origin of high energy emission.

Instead of focusing on one particular field, we are planning for an interdisciplinary workshop on anisotropies and fluctuations in astrophysics and cosmology. Gathering researchers from various backgrounds, we aim at putting together our tools and our knowledge on anisotropies and fluctuations. Various methods and theories have been developed in parallel but their use has often been restricted to one particular area.

In particular, during the meeting we will be sharing our experience on

1) theoretical predictions of anisotropy signatures, for given configurations of source populations and of the whole Universe,
2) anisotropy analysis and measurement techniques,
3) cross-correlation of data from various wavelengths and messengers, fluctuations in time.

Simulating the evolution of the early Universe

Alcuni fisici dell’Università di Chicago hanno simulato in laboratorio le fasi evolutive primordiali della storia dell’Universo riproducendo in parte la caratteristica struttura della radiazione cosmica di fondo grazie ad un esperimento che utilizza atomi di cesio a bassissime temperature in una apposita camera in cui è stato prodotto il vuoto.

This is the first time an experiment like this has simulated the evolution of structure in the early Universe“, said Cheng Chin, professor in physics.

Chin and his colleagues planned to harness ultracold atoms for simulations of the Big Bang to better understand how structure evolved in the infant Universe.

The cosmic microwave background is the echo of the Big Bang. Extensive measurements of the CMB have come from the orbiting Cosmic Background Explorer in the 1990s, and later by the Wilkinson Microwave Anisotropy Probe and various ground-based observatories, including the UChicago-led South Pole Telescope collaboration. These tools have provided cosmologists with a snapshot of how the Universe appeared approximately 380.000 years following the Big Bang, which marked the beginning of our Universe. It turns out that under certain conditions, a cloud of atoms chilled to a billionth of a degree above absolute zero (-459.67 degrees Fahrenheit) in a vacuum chamber displays phenomena similar to those that unfolded following the Big Bang. “At this ultracold temperature, atoms get excited collectively. They act as if they are sound waves in air“, Chin said. The dense package of matter and radiation that existed in the very early Universe generated similar sound-wave excitations, as revealed by COBE, WMAP and the other experiments. The synchronized generation of sound waves correlates with cosmologists’ speculations about inflation in the early Universe. “Inflation set out the initial conditions for the early Universe to create similar sound waves in the cosmic fluid formed by matter and radiation“, co-author Chen-Lung Hung said. “The sudden expansion of the Universe during its inflationary period created ripples in space-time in the echo of the Big Bang. One can think of the Big Bang, in oversimplified terms, as an explosion that generated sound“, Chin said. “The sound waves began interfering with each other, creating complicated patterns. That’s the origin of complexity we see in the Universe“, he said. These excitations are called Sakharov acoustic oscillations, named for Russian physicist Andrei Sakharov, who described the phenomenon in the 1960s. To produce Sakharov oscillations, Chin’s team chilled a flat, smooth cloud of 10,000 or so cesium atoms to a billionth of a degree above absolute zero, creating an exotic state of matter known as a two-dimensional atomic superfluid. Then they initiated a quenching process that controlled the strength of the interaction between the atoms of the cloud. They found that by suddenly making the interactions weaker or stronger, they could generate Sakharov oscillations.

The Universe simulated in Chin’s laboratory measured no more than 70 microns in diameter, approximately the diameter as a human hair.

It turns out the same kind of physics can happen on vastly different length scales“, Chin explained. “That’s the power of physics“. The goal is to better understand the cosmic evolution of a baby Universe, the one that existed shortly after the Big Bang. It was much smaller then than it is today, having reached a diameter of only a hundred thousand light years by the time it had left the CMB pattern that cosmologists observe on the sky today. In the end, what matters is not the absolute size of the simulated or the real universes, but their size ratios to the characteristic length scales governing the physics of Sakharov oscillations. “Here, of course, we are pushing this analogy to the extreme“, Chin said. “It took the whole Universe about 380,000 years to evolve into the CMB spectrum we’re looking at now“, Chin said. But the physicists were able to reproduce much the same pattern in approximately 10 milliseconds in their experiment. “That suggests why the simulation based on cold atoms can be a powerful tool“, Chin said. None of the Science co-authors are cosmologists, but they consulted several in the process of developing their experiment and interpreting its results. The co-authors especially drew upon the expertise of UChicago’s Wayne Hu, John Carlstrom and Michael Turner, and of Stanford University’s Chao-Lin Kuo. Hung noted that Sakharov oscillations serve as an excellent tool for probing the properties of cosmic fluid in the early Universe. “We are looking at a two-dimensional superfluid, which itself is a very interesting object. We actually plan to use these Sakharov oscillations to study the property of this two-dimensional superfluid at different initial conditions to get more information“. The research team varied the conditions that prevailed early in the history of the expansion of their simulated universes by quickly changing how strongly their ultracold atoms interacted, generating ripples. “These ripples then propagate and create many fluctuations“, Hung said. He and his co-authors then examined the ringing of those fluctuations. Today’s CMB maps show a snapshot of how the Universe appeared at a moment in time long ago (post). “From CMB, we don’t really see what happened before that moment, nor do we see what happened after that“, Chin said. But, Hung noted, “In our simulation we can actually monitor the entire evolution of the Sakharov oscillations“. Chin and Hung are interested in continuing this experimental direction with ultracold atoms, branching into a variety of other types of physics, including the simulation of galaxy formation or even the dynamics of black holes. “We can potentially use atoms to simulate and better understand many interesting phenomena in nature“, Chin said. “Atoms to us can be anything you want them to be“.

University of Chicago: Ultracold Big Bang experiment successfully simulates evolution of early Universe 

arXiv: From Cosmology to Cold Atoms: Observation of Sakharov Oscillations in Quenched Atomic Superfluids

Ripples in the Cosmos

An international cosmology conference entitled “Ripples in the Cosmos” will be held at Durham University, England, on 22-26 July 2013. The agenda includes Baryon Acoustic Oscillations (BAO) and other cosmological probes from ground-based redshift surveys such as BOSS and WiggleZ. We shall also be reviewing results from the Planck satellite, as well as the latest results from the LHC. The intent is to make a broad review of the crucial issues in cosmology from the identity of dark matter to the nature of dark energy by coupling the very latest results from astronomy and particle physics.

All the light in the Universe since the Big Bang

Vi siete mai chiesti quanta luce è stata emessa da tutte le galassie da quando è nato l’Universo? Pensate un attimo a ciascun fotone di qualsiasi lunghezza d’onda, dall’ultravioletto all’infrarosso, che sta viaggiano ancora nello spazio fino a raggiungere i nostri rivelatori. Se riuscissimo a misurare in maniera accurata il numero e l’energia di tutti i fotoni, non solo quelli dei nostri giorni ma anche quelli più antichi, potremmo ricavare indizi fondamentali sulla natura e l’evoluzione dell’Universo e comprendere come le galassie più antiche siano differenti rispetto a quelle che vediamo oggi.

That bath of ancient and young photons suffusing the Universe today is called the extragalactic background light (EBL). An accurate measurement of the EBL is as fundamental to cosmology as measuring the heat radiation left over from the Big Bang, the cosmic microwave background, at radio wavelengths. A new paper, called “Detection of the Cosmic γ-Ray Horizon from Multiwavelength Observations of Blazars”, by Alberto Dominguez at University of California at Riverside and six coauthors, based on observations spanning wavelengths from radio waves to very energetic gamma rays, obtained from several NASA spacecraft and several ground-based telescopes, describes the best measurement yet of the evolution of the EBL over the past 5 billion years. Directly measuring the EBL by collecting its photons with a telescope, however, poses towering technical challenges, harder than trying to see the dim band of the Milky Way spanning the heavens at night from midtown Manhattan. Earth is inside a very bright galaxy with billions of stars and glowing gas. Indeed, Earth is inside a very bright Solar System: sunlight scattered by all the dust in the plane of Earth’s orbit creates the zodiacal light radiating across the optical spectrum down to long-wavelength infrared. Therefore ground-based and space-based telescopes have not succeeded in reliably measuring the EBL directly. So, astrophysicists developed an ingenious work-around method: measuring the EBL indirectly through measuring the attenuation of, that is, the absorption of, very high energy gamma rays from distant blazars. Blazars are supermassive black holes in the centers of galaxies with brilliant jets directly pointed at us like a flashlight beam. Not all the high-energy gamma rays emitted by a blazar, however, make it all the way across billions of light-years to Earth; some strike a hapless EBL photon along the way. When a high-energy gamma ray photon from a blazar hits a much lower energy EBL photon, both are annihilated and produce two different particles: an electron and its antiparticle, a positron, which fly off into space and are never heard from again. Different energies of the highest-energy gamma rays are waylaid by different energies of EBL photons. Thus, measuring how much gamma rays of different energies are attenuated or weakened from blazars at different distances from Earth indirectly gives a measurement of how many EBL photons of different wavelengths exist along the line of sight from blazar to Earth over those different distances. Observations of blazars by NASA’s Fermi Gamma Ray Telescope spacecraft for the first time detected that gamma rays from distant blazars are indeed attenuated more than gamma rays from nearby blazars, a result announced on November 30, 2012, in a paper published in Science, as theoretically predicted. Now, the big news is that the evolution of the EBL over the past 5 billion years has been measured for the first time. That’s because looking farther out into the Universe corresponds to looking back in time. Thus, the gamma ray attenuation spectrum from farther distant blazars reveals how the EBL looked at earlier eras. This was a multistep process. First, the coauthors compared the Fermi findings to intensity of X-rays from the same blazars measured by X-ray satellites Chandra, Swift, Rossi X-ray Timing Explorer, and XMM/Newton and lower-energy radiation measured by other spacecraft and ground-based observatories. From these measurements, Dominguez and collaborators were able to calculate the blazars’ original emitted, unattenuated gamma-ray brightnesses at different energies. The coauthors then compared those calculations of unattenuated gamma-ray flux at different energies with direct measurements from special ground-based telescopes of the actual gamma-ray flux received at Earth from those same blazars. When a high-energy gamma ray from a blazar strikes air molecules in the upper regions of Earth’s atmosphere, it produces a cascade of charged subatomic particles. This cascade of particles travels faster than the speed of light in air, which is slower than the speed of light in a vacuum. This causes a visual analogue to a “sonic boom”: bursts of a special light called Čerenkov radiation. This Čerenkov radiation was detected by imaging atmospheric Čerenkov telescopes (IACTs), such as HESS (High Energy Stereoscopic System) in Namibia, MAGIC (Major Atmospheric Gamma Imaging Čerenkov) in the Canary Islands, and VERITAS (Very Energetic Radiation Imaging Telescope Array Systems) in Arizona. Comparing the calculations of the unattenuated gamma rays to actual measurements of the attenuation of gamma rays and X-rays from blazars at different distances allowed Dominquez and colleagues to quantify the evolution of the EBL, that is, to measure how the EBL changed over time as the Universe aged, out to about 5 billion years ago, corresponding to a redshift of about z = 0.5. “Five billion years ago is the maximum distance we are able to probe with our current technology”, Domínguez said. “Sure, there are blazars farther away, but we are not able to detect them because the high-energy gamma rays they are emitting are too attenuated by EBL when they get to us, so weakened that our instruments are not sensitive enough to detect them”. This measurement is the first statistically significant detection of the so-called “Cosmic Gamma Ray Horizon” as a function of gamma-ray energy. The Cosmic Gamma Ray Horizon is defined as the distance at which roughly one-third or, more precisely, 1/e, that is, 1/2.718 where “e” is the base of the natural logarithms, of the gamma rays of a particular energy have been attenuated. This latest result confirms that the kinds of galaxies observed today are responsible for most of the EBL over all time. Moreover, it sets limits on possible contributions from many galaxies too faint to have been included in the galaxy surveys, or on possible contributions from hypothetical additional sources, such as the decay of hypothetical unknown elementary particles.

UCR: Astronomers Measure the Elusive Extragalactic Background Light
arXiv: Detection of the cosmic γ-ray horizon from multiwavelength observations of blazars