Archivi tag: cosmic background radiation

Secrets of the Universe’s First Light

The  first definite proof that the Universe underwent an almost unimaginably fast expansion when it was only a trillionth of a trillionth of a trillionth of a second old has taken the world by storm. This sudden growth spurt was first theorized more than three decades ago. Yet only last month did astrophysicists reveal what may be “smoking gun” evidence that the Universe swelled from microscopic to cosmic size in an instant, an announcement that’s being compared to the discovery of the Higgs boson.

More at The Kavli Foundation: Secrets of the Universe’s First Light

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Observing the Universe with the Cosmic Microwave Background

The Planck satellite mission has provided a multifrequency detailed view of the Universe at millimeter waves, exploring the cosmic microwave background (CMB) and the relevant foregrounds with an unprecedented combination of sensitivity, angular resolution and frequency coverage. Meanwhile, a number of ground based and balloon-borne experiments are exploring the tiniest details of the CMB (anisotropy, polarization, spectral anisotropy, etc.) providing a wealth of new knowledge on our universe. New space mission concepts have also been proposed, involving significant technology improvements, and are actively investigated.

This school will provide an up to date review of the latest results and of their impact on cosmology and on fundamental physics. Experimental, interpretation and theoretical activities will be weighted to provide a well balanced understanding of the current status and of the forthcoming efforts in this field.

Some physicists doubt on inflation evidence

Circa una settimana fa, la notizia della presunta scoperta delle “tracce” impresse nella radiazione cosmica di fondo dovute al passaggio delle onde gravitazionali primordiali ha preso d’impatto come una tempesta improvvisa il mondo dei media (post). Non solo, ma si vocifera già la nomination per il Premio Nobel al gruppo di ricercatori di Harvard che non solo avrebbero trovato la “prima evidenza diretta” del processo dell’inflazione cosmica ma anche degli indizi a supporto dell’esistenza di altri universi. Nonostante ciò, alcuni fisici stanno suggerendo di “rimettere nel frigo lo champagne”, almeno per ora.

Theoretical physicists and cosmologists James Dent, Lawrence Krauss, and Harsh Mathur have submitted a brief paper (arXiv:1403.5166 [astro-ph.CO]) stating that, while groundbreaking, the BICEP2 Collaboration findings have yet to rule out all possible non-inflation sources of the observed B-mode polarization patterns and the “surprisingly large value of r, the ratio of power in tensor modes to scalar density perturbations.”

“However, while there is little doubt that inflation at the Grand Unified Scale is the best motivated source of such primordial waves, it is important to demonstrate that other possible sources cannot account for the current BICEP2 data before definitely claiming inflation has been proved”, as stated by the authors in the paper

Inflation may very well be the cause, and Dent and company state right off the bat that “there is little doubt that inflation at the Grand Unified Scale is the best motivated source of such primordial waves“, but there’s also a possibility, however remote, that some other, later cosmic event is responsible for at least some if not all of the BICEP2 measurements. (Hence the name of the paper: “Killing the Straw Man: Does BICEP Prove Inflation?”). Not intending to entirely rain out the celebration, Dent, Krauss, and Mathur do laud the BICEP2 findings as invaluable to physics, stating that they “will be very important for constraining physics beyond the standard model, whether or not inflation is responsible for the entire BICEP2 signal, even though existing data from cosmology is strongly suggestive that it does“.

The Physics arXiv Blog: Cosmologists Say Last Week’s Announcement About Gravitational Waves and Inflation May Be Wrong
arXiv: Killing the Straw Man: Does BICEP Prove Inflation?

 

Alan Guth commenta i risultati di BICEP2

E’ ancora vivo il fermento che ha generato in questi giorni l’annuncio dei ricercatori dell’Harvard CMB Group sull’esperimento BICEP2 in merito alla rivelazione di un segnale presente nella radiazione cosmica di fondo associato al passaggio di onde gravitazionali primordiali, una forte evidenza indiretta dell’inflazione cosmica (post). Il modello inflazionistico fu inizialmente proposto negli anni ’80 da Alan Guth, oggi Victor F. Weisskopf Professor of Physics presso il MIT, che commenta qui di seguito il significato scientifico dei dati ottenuti da BICEP2.

Q: Can you explain the theory of cosmic inflation that you first put forth in 1980?

A: I usually describe inflation as a theory of the “bang” of the Big Bang: It describes the propulsion mechanism that drove the universe into the period of tremendous expansion that we call the Big Bang. In its original form, the Big Bang theory never was a theory of the bang. It said nothing about what banged, why it banged, or what happened before it banged. The original Big Bang theory was really a theory of the aftermath of the bang. The universe was already hot and dense, and already expanding at a fantastic rate. The theory described how the universe was cooled by the expansion, and how the expansion was slowed by the attractive force of gravity. Inflation proposes that the expansion of the universe was driven by a repulsive form of gravity. According to Newton, gravity is a purely attractive force, but this changed with Einstein and the discovery of general relativity. General relativity describes gravity as a distortion of spacetime, and allows for the possibility of repulsive gravity. Modern particle theories strongly suggest that at very high energies, there should exist forms of matter that create repulsive gravity. Inflation, in turn, proposes that at least a very small patch of the early universe was filled with this repulsive-gravity material. The initial patch could have been incredibly small, perhaps as small as 10-24 centimeter, about 100 billion times smaller than a single proton. The small patch would then start to exponentially expand under the influence of the repulsive gravity, doubling in size approximately every 10-37 second. To successfully describe our visible universe, the region would need to undergo at least 80 doublings, increasing its size to about 1 centimeter. It could have undergone significantly more doublings, but at least this number is needed. During the period of exponential expansion, any ordinary material would thin out, with the density diminishing to almost nothing. The behavior in this case, however, is very different: The repulsive-gravity material actually maintains a constant density as it expands, no matter how much it expands! While this appears to be a blatant violation of the principle of the conservation of energy, it is actually perfectly consistent. This loophole hinges on a peculiar feature of gravity: The energy of a gravitational field is negative. As the patch expands at constant density, more and more energy, in the form of matter, is created. But at the same time, more and more negative energy appears in the form of the gravitational field that is filling the region. The total energy remains constant, as it must, and therefore remains very small. It is possible that the total energy of the entire universe is exactly zero, with the positive energy of matter completely canceled by the negative energy of gravity. I often say that the universe is the ultimate free lunch, since it actually requires no energy to produce a universe. At some point the inflation ends because the repulsive-gravity material becomes metastable. The repulsive-gravity material decays into ordinary particles, producing a very hot soup of particles that form the starting point of the conventional Big Bang. At this point the repulsive gravity turns off, but the region continues to expand in a coasting pattern for billions of years to come. Thus, inflation is a prequel to the era that cosmologists call the Big Bang, although it of course occurred after the origin of the universe, which is often also called the Big Bang.

Q: What is the new result announced this week, and how does it provide critical support for your theory?

A: The stretching effect caused by the fantastic expansion of inflation tends to smooth things out — which is great for cosmology, because an ordinary explosion would presumably have left the universe very splotchy and irregular. The early universe, as we can see from the afterglow of the cosmic microwave background (CMB) radiation, was incredibly uniform, with a mass density that was constant to about one part in 100,000. The tiny nonuniformities that did exist were then amplified by gravity: In places where the mass density was slightly higher than average, a stronger-than-average gravitational field was created, which pulled in still more matter, creating a yet stronger gravitational field. But to have structure form at all, there needed to be small nonuniformities at the end of inflation. In inflationary models, these nonuniformities — which later produce stars, galaxies, and all the structure of the universe — are attributed to quantum theory. Quantum field theory implies that, on very short distance scales, everything is in a state of constant agitation. If we observed empty space with a hypothetical, and powerful, magnifying glass, we would see the electric and magnetic fields undergoing wild oscillations, with even electrons and positrons popping out of the vacuum and then rapidly disappearing. The effect of inflation, with its fantastic expansion, is to stretch these quantum fluctuations to macroscopic proportions. The temperature nonuniformities in the cosmic microwave background were first measured in 1992 by the COBE satellite, and have since been measured with greater and greater precision by a long and spectacular series of ground-based, balloon-based, and satellite experiments. They have agreed very well with the predictions of inflation. These results, however, have not generally been seen as proof of inflation, in part because it is not clear that inflation is the only possible way that these fluctuations could have been produced. The stretching effect of inflation, however, also acts on the geometry of space itself, which according to general relativity is flexible. Space can be compressed, stretched, or even twisted. The geometry of space also fluctuates on small scales, due to the physics of quantum theory, and inflation also stretches these fluctuations, producing gravity waves in the early universe. The new result, by John Kovac and the BICEP2 collaboration, is a measurement of these gravity waves, at a very high level of confidence. They do not see the gravity waves directly, but instead they have constructed a very detailed map of the polarization of the CMB in a patch of the sky. They have observed a swirling pattern in the polarization (called “B modes”) that can be created only by gravity waves in the early universe, or by the gravitational lensing effect of matter in the late universe. But the primordial gravity waves can be separated, because they tend to be on larger angular scales, so the BICEP2 team has decisively isolated their contribution. This is the first time that even a hint of these primordial gravity waves has been detected, and it is also the first time that any quantum properties of gravity have been directly observed.

Q: How would you describe the significance of these new findings, and your reaction to them?

A: The significance of these new findings is enormous. First of all, they help tremendously in confirming the picture of inflation. As far as we know, there is nothing other than inflation that can produce these gravity waves. Second, it tells us a lot about the details of inflation that we did not already know. In particular, it determines the energy density of the universe at the time of inflation, which is something that previously had a wide range of possibilities. By determining the energy density of the universe at the time of inflation, the new result also tells us a lot about which detailed versions of inflation are still viable, and which are no longer viable. The current result is not by itself conclusive, but it points in the direction of the very simplest inflationary models that can be constructed. Finally, and perhaps most importantly, the new result is not the final story, but is more like the opening of a new window. Now that these B modes have been found, the BICEP2 collaboration and many other groups will continue to study them. They provide a new tool to study the behavior of the early universe, including the process of inflation. When I (and others) started working on the effect of quantum fluctuations in the early 1980s, I never thought that anybody would ever be able to measure these effects. To me it was really just a game, to see if my colleagues and I could agree on what the fluctuations would theoretically look like. So I am just astounded by the progress that astronomers have made in measuring these minute effects, and particularly by the new result of the BICEP2 team. Like all experimental results, we should wait for it to be confirmed by other groups before taking it as truth, but the group seems to have been very careful, and the result is very clean, so I think it is very likely that it will hold up.

Courtesy MIT: 3 Questions: Alan Guth on new insights into the ‘Big Bang’

Primordial gravitational waves: a possible major discovery could be announced today

Alle ore 17 di oggi, alcuni astronomi dell’Harvard-Smithsonian Center for Astrophysics potrebbero annunciare una scoperta clamorosa in cosmologia, il che darebbe enfasi e valore ad un modello che descrive le primissime fasi iniziali della storia cosmica e che risale tra la fine degli anni ’70 e gli inizi degli anni ’80: l’inflazione cosmica. L’obiettivo è quello di rivelare le onde gravitazionali “primordiali” che rappresentano una sorta di residuo fossile del Big Bang da cui si è originato l’Universo circa 14 miliardi di anni fa. Dunque, se saranno mostrate forti evidenze della presenza di onde gravitazionali primordiali, allora si potrà parlare di una scoperta sensazionale che potrebbe modificare le nostre conoscenze fondamentali in cosmologia e fisica delle particelle.

Per saperne di più:

The Harvard-Smithsonian Center for Astrophysics (CfA) will host a press conference at 12:00 noon EDT (16:00 UTC) on Monday, March 17th, to announce a major discovery.

Video > live streaming at 11:55 a.m. EDT from the link at http://www.cfa.harvard.edu/news/news_conferences.html

Press release > it will be available here: http://www.cfa.harvard.edu/news/2014-05

More at viXra log: “first direct evidence of cosmic inflation” BICEP2 results

Paper: http://bicepkeck.org/b2_respap_arxiv_v1.pdf

BICEP2 2014 Results Release

Using the Universe as ‘tool’ to detect gravitons

La gravità è l’unica tra le quattro forze fondamentali per la quale gli scienziati non hanno ancora rivelato la sua unità fondamentale. Infatti, secondo il modello standard delle particelle elementari si ritiene che l’interazione gravitazionale venga trasmessa attraverso il gravitone, allo stesso modo con cui l’interazione elettromagnetica viene trasmessa dai fotoni. Oggi, nonostante esistano delle basi teoriche a favore dell’esistenza dei gravitoni rimane, però, il problema di rivelarli, almeno sulla Terra dove le possibilità sono estremamente basse se non quasi nulle.

For example, the conventional way of measuring gravitational forces, by bouncing light off a set of mirrors to measure tiny shifts in their separation, would be impossible in the case of gravitons. According to physicist Freeman Dyson, the sensitivity required to detect such a miniscule distance change caused by a graviton requires the mirrors to be so massive and heavy that they’d collapse and form a black hole. Because of this, some have claimed that measuring a single graviton is hopeless. But what if you used the largest entity you know of, in this case the Universe, to search for the telltale effects of gravitons. That is what two physicists are proposing. In the paper, “Using cosmology to establish the quantization of gravity”, published in Physical Review D (Feb. 20, 2014), Lawrence Krauss, a cosmologist at Arizona State University, and Frank Wilczek, a Nobel-prize winning physicist with MIT and ASU, have proposed that measuring minute changes in the cosmic background radiation of the Universe could be a pathway of detecting the telltale effects of gravitons.

Krauss and Wilczek suggest that the existence of gravitons, and the quantum nature of gravity, could be proved through some yet-to-be-detected feature of the early Universe.

This may provide, if Freeman Dyson is correct about the fact that terrestrial detectors cannot detect gravitons, the only direct empirical verification of the existence of gravitons”, Krauss said. “Moreover, what we find most remarkable is that the Universe acts like a detector that is precisely the type that is impossible or impractical to build on Earth”. It is generally believed that in the first fraction of a second after the Big Bang, the Universe underwent rapid and dramatic growth during a period called “inflation.” If gravitons exist, they would be generated as “quantum fluctuations” during inflation. Ultimately, these would evolve, as the Universe expanded, into classically observable gravitational waves, which stretch space-time along one direction while contracting it along the other direction. This would affect how electromagnetic radiation in the cosmic microwave background (CMB) radiation left behind by the Big Bang is produced, causing it to become polarized. Researchers analyzing results from the European Space Agency’s Planck satellite are searching for this “imprint” of inflation in the polarization of the CMB.

Krauss said his and Wilczek’s paper combines what already is known with some new wrinkles.

While the realization that gravitational waves are produced by inflation is not new, and the fact that we can calculate their intensity and that this background might be measured in future polarization measurements of the microwave background is not new, an explicit argument that such a measurement will provide, in principle, an unambiguous and direct confirmation that the gravitational field is quantized is new”, he said. “Indeed, it is perhaps the only empirical verification of this very important assumption that we might get in the foreseeable future”. Using a standard analytical tool called dimensional analysis, Wilczek and Krauss show how the generation of gravitational waves during inflation is proportional to the square of Planck’s constant, a numerical factor that only arises in quantum theory. That means that the gravitational process that results in the production of these waves is an inherently quantum-mechanical phenomenon. This implies that finding the fingerprint of gravitational waves in the polarization of CMB will provide evidence that gravitons exist, and it is just a matter of time (and instrument sensitivity) to finding their imprint. “I’m delighted that dimensional analysis, a simple but profound technique whose virtues I preach to students, supplies clear, clean insight into a subject notorious for its difficulty and obscurity”, said Wilczek. “It is quite possible that the next generation of experiments, in the coming decade or maybe even the Planck satellite, may see this background”, Krauss added.

ASU: Researchers propose a new way to detect the elusive graviton

arXiv: Using Cosmology to Establish the Quantization of Gravity

Massive or massless neutrinos?

Gli scienziati avrebbero risolto uno dei problemi aperti dell’attuale modello cosmologico standard combinando i dati del satellite Planck e quelli ottenuti grazie al fenomeno della lente gravitazionale allo scopo di determinare la massa dei neutrini.

The team, from the universities of Nottingham and Manchester, used observations of the Big Bang and the curvature of spacetime to accurately measure the mass of these elementary particles for the first time. The recent Planck spacecraft observations of the Cosmic Microwave Background (CMB), the fading glow of the Big Bang, highlighted a discrepancy between these cosmological results and the predictions from other types of observations. The CMB is the oldest light in the Universe, and its study has allowed scientists to accurately measure cosmological parameters, such as the amount of matter in the Universe and its age. But an inconsistency arises when large-scale structures of the Universe, such as the distribution of galaxies, are observed. Dr Adam Moss, from The University of Nottingham’s School of Physics and Astronomy said: “We observe fewer galaxy clusters than we would expect from the Planck results and there is a weaker signal from gravitational lensing of galaxies than the CMB would suggest. A possible way of resolving this discrepancy is for neutrinos to have mass. The effect of these massive neutrinos would be to suppress the growth of dense structures that lead to the formation of clusters of galaxies.” Neutrinos interact very weakly with matter and so are extremely hard to study. They were originally thought to be massless but particle physics experiments have shown that neutrinos do indeed have mass and that there are several types, known as flavours by particle physicists. The sum of the masses of these different types has previously been suggested to lie above 0.06 eV (much less than a billionth of the mass of a proton). Dr Moss and Professor Richard Battye from The University of Manchester have combined the data from Planck with gravitational lensing observations in which images of galaxies are warped by the curvature of spacetime.

They conclude that the current discrepancies can be resolved if massive neutrinos are included in the standard cosmological model.

They estimate that the sum of masses of neutrinos is 0.320 +/- 0.081 eV (assuming active neutrinos with three flavours). Professor Battye added: “If this result is borne out by further analysis, it not only adds significantly to our understanding of the sub-atomic world studied by particle physicists, but it would also be an important extension to the standard model of cosmology which has been developed over the last decade”.

Nottingham University: Massive neutrinos solve a cosmological conundrum

arXiv: Evidence for massive neutrinos from CMB and lensing observations

New hints on the primordial gravitational waves in the CMB

Grazie ad una serie di osservazioni realizzate mediante il telescopio del Polo Sud in Antartide e l’osservatorio spaziale Herschel, gli astronomi sono stati in grado di rivelare per la prima volta un segnale molto debole nella radiazione cosmica di fondo che potrebbe fornire informazioni di vitale importanza sui primi momenti della creazione dell’Universo. Le misure di questo segnale elusivo sono state realizzate studiando il modo con cui la luce viene deflessa nel suo viaggio cosmico prima di arrivare sulla Terra, passando attraverso gli ammassi di galassie e la distribuzione della materia scura. La scoperta permette di fornire nuovi indizi su come rivelare le onde gravitazionali che si sono originate durante l’epoca dell’inflazione cosmica, un risultato cruciale anticipato dalla missione Planck (post).

The relic radiation from the Big Bang, the Cosmic Microwave Background, or CMB, was imprinted on the sky when the Universe was just 380 000 years old. Today, some 13.8 billion years later, we see it as a sky filled with radio waves at a temperature of just 2.7 degrees above absolute zero. Tiny variations in this temperature, around a few tens of millionths of a degree, reveal density fluctuations in the early Universe corresponding to the seeds of galaxies and stars we see today. The most detailed all-sky map of temperature variations in the background was revealed by Planck in March (post). But the CMB also contains a wealth of other information. A small fraction of the light is polarised, like the light we can see using polarised glasses. This polarised light has two distinct patterns: E-modes and B-modes. E-modes were first found in 2002 with a ground-based telescope. B-modes, however, are potentially much more exciting to cosmologists, although much harder to detect. They can arise in two ways. The first involves adding a twist to the light as it crosses the Universe and is deflected by galaxies and dark matter, a phenomenon known as gravitational lensing. The second has its roots buried deep in the mechanics of a very rapid phase of enormous expansion of the Universe, which cosmologists believe happened just a tiny fraction of a second after the Big Bang, namely the ‘inflation’.

The new study has combined data from the South Pole Telescope and Herschel to make the first detection of B-mode polarisation in the CMB due to gravitational lensing.

This measurement was made possible by a clever and unique combination of ground-based observations from the South Pole Telescope, which measured the light from the Big Bang, with space-based observations from Herschel, which is sensitive to the galaxies that trace the dark matter which caused the gravitational lensing,” says Joaquin Vieira, of the California Institute of Technology and the University of Illinois at Urbana-Champaign, who led the Herschel survey used in the study. By using Herschel’s observations, the scientists mapped the gravitational lensing material along the line of sight, and then searched for correlations between that pattern and the polarised light coming from the CMB, as measured by the South Pole Telescope. “It’s an important checkpoint that we’re able to detect this small lensing B-mode signal and it bodes well for our ability to ultimately measure an even more elusive type of B-mode created during the inflationary Big Bang”, adds Duncan Hanson of McGill University, Montreal, Canada. Scientists believe that during inflation, violent collisions between clumps of matter and between matter and radiation, should have created a sea of gravitational waves. Today, those waves would be imprinted in a primordial B-mode component of the CMB.

Finding such a signal would yield crucial information about the very early Universe, well before the time when the CMB itself was generated, and would provide confirmation of the inflation scenario.

In 2014, new results will be released from ESA’s Planck, and the most eagerly anticipated is whether primordial B-modes have been detected. In the meantime, Herschel has helped to point the way.

ESA: HERSCHEL THROWS NEW LIGHT ON OLDEST COSMIC LIGHT

arXiv: Detection of B-mode Polarization in the Cosmic Microwave Background with Data from the South Pole Telescope

arXiv: A CMB lensing mass map and its correlation with the cosmic infrared background

Large galaxy clusters contain the right proportion of visible matter

Grazie ad uno studio recente condotto da alcuni ricercatori della University of Alabama in Huntsville (UAH) guidati da Massimiliano Bonamente, i barioni, che costituiscono la materia visibile nell’Universo e che si riteneva un tempo assente dagli ammassi di galassie, sono presenti in accordo alle proporzioni attese dal modello cosmologico standard negli ammassi di galassie più grandi e luminosi.

The new research studied very large galaxy clusters and concludes that they indeed contain the proportion of visible matter that is being worked out as part of the Big Bang Theory.

The work may prompt new efforts to explain past research findings that some clusters have a deficit in baryons from what is expected.

The Universe is composed of about 75 percent dark energy and 25 percent matter. Of the portion that is matter, about 16 percent is the familiar visible matter that is all around us and the remaining 84 percent is dark matter. “We call it dark matter because we don’t know what it is made of, but it is made of some type of particles and it doesn’t seem to emit visible energy”, said Bonamente. Together dark energy, dark matter and ordinary baryonic matter form a pie chart of the mass of the Universe, where everything has to add up to 100 percent. “We don’t know what dark matter is”, he said, “but we have the means to put the pie together”. While dark energy has a repulsive energy, dark matter and baryonic matter have an attractive force where “everything likes to clump together” to form stars and planets and galaxies. Using x-rays, astrophysicists discovered that there is a diffuse hot plasma gas that fills the space between galaxies. “Basically, the space between galaxies is filled with this hot plasma that is 100 million degrees in temperature”, said Bonamente. Because the gas is so diffuse, it has very low heat capacity. “It is like if I posed this question to you: Which would you rather put your finger in, a boiling cup of water or a room that had been heated to 212 degrees Fahrenheit? You choose the room because the temperature inside it is more diffused than it would be in the concentrated cup of water, and so you can tolerate it”. So why doesn’t the hot gas simply escape? “It is bound to the cluster by gravity”, said Bonamente. “With hot gas, you can do two things. You can measure the regular matter, which is the baryon content. And two, since the hot gas is bound, you can measure how much matter it would take to hold the gas and therefore you can tell how much dark matter there is. “All of a sudden, there is something really wonderful about the hot gas”, he said. “You can have your cake and eat it, too”. Theoretically, the Universe should contain the same proportions of visible and dark matter regardless of where it is sampled. Using cosmic microwave radiation readings, astrophysicists have been able to do a type of forensics of the Universe’s past, and those findings have shown the proportions that were present at the Big Bang or shortly thereafter (post). “Because it started in the Big Bang, that ratio should persist”, Bonamente said. “It is like if I go to the ocean with a scoop. The scoop of water I get should have the same concentration of salt as the rest of the ocean, no matter where I get it”.

But past research had indicated that some clusters were short on the expected percentage of baryons, posing the question of where they were.

Since recently, people believed that clusters had less than 16 percent of baryons, so there were missing baryons”, Bonamente said. “We said no, they are there. So, how did we find clusters with this correct ratio? We studied the most luminous ones, because they have more mass and retain more baryons”.

The findings could open new areas of investigation into why the deficits in baryons were recorded in past research.

Bonamente suggests one theory. “We know that some smaller clusters do have lower concentrations of baryons than the larger ones”, he said. Perhaps because of weaker gravitational forces, the hot gases escaped in similar fashion as planets that have no atmosphere. “Maybe the gas can be bound but maybe a little bit can fly off if there is just not quite enough gravity”. For further studies on smaller clusters, Bonamente looks forward to the arrival of new faculty member Ming Sun, formerly at the University of Virginia, who is an expert on groups having less than 16 percent baryons. “I am excited that Ming has decided to join our research group”, says Bonamente. “With him on board, UAH is poised to continue making discoveries on the makeup of the universe, and that is the most exciting question to answer that I can think of”.

UAH: UAH findings on makeup of universe may spawn new research
arXiv: Chandra Measurements of a Complete Sample of X-ray Luminous Galaxy Clusters: the Gas Mass Fraction

SPT detects ‘weak signs’ of primordial gravitational waves in the CMB

spt_polarizationLa ricerca dei modi-B, relativi alla componente della polarizzazione della radiazione cosmica di fondo associata alla propagazione delle onde gravitazionali nella mappa della radiazione cosmica, rappresenta una prova fondamentale che potrebbe dare credito al modello dell’inflazione cosmica. Nonostante i calcoli prevedono una intensità del segnale molto debole, oggi alcuni ricercatori del South Pole Telescope (SPT) hanno pubblicato i dati di uno studio in cui dichiarano di aver rivelato deboli fluttuazioni associate ai modi-B della componente di polarizzazione.

Scientists believe that approximately half a million years after the Big Bang, the Universe began switching from a state of plasma and energy to one where temperatures had dropped to a point where the universe became transparent enough for light to pass through. That light is known as cosmic microwave background (CMB) and is still visible today. Cosmologists studying it have formed the basis of a theory known as inflation, where the Universe came to exist as it does today through a process of very rapid expansion just after the Big Bang. In order to prove that the inflation theory is correct, scientists have been studying minute fluctuations in the temperature of the CMB, they revel fluctuations in density of the early Universe. They also study fluctuations of the polarization of the CMB which is due, it is believed, to radiation being scattered across the Universe by the energy of the Big Bang. Fluctuations in polarization were for a time merely theory, but in 2002, they were actually detected, giving credence to inflation theory. Those fluctuations were given the name E-mode polarizations. Theory has also suggested that there are also B-mode fluctuations in polarization, which are far more subtle, they are thought to describe the rotation of CMB polarization.

Finding evidence of them has been extremely difficult, however, as they exist as just one part in ten million in the CMB temperature distribution. But now it appears the team at SPT has done just that, adding further credence to the inflation theory.

The researchers report that they were able to detect E-mode polarization due mostly to improvements in detector technology. Adding credence isn’t the same as finding proof of a theory, of course, and that’s why scientists believe the detection of E-mode polarizations is so important. Many believe it will ultimately lead to the detection of primordial gravitational waves, immense ripples in spacetime that theory suggests should have come about as a result of the force of inflation. If they can be detected, the theory of inflation would likely become the accepted theory regarding the early formation of the Universe.

Nature: Polarization detected in Big Bang's echo
arXiv: Detection of B-mode Polarization in the Cosmic Microwave Background with Data from the South Pole Telescope