In this centennial anniversary of General Relativity, we will hold a conference on Hot Topics in General Relativity and Gravitation with the motivation to emphasize the tremendous progresses that have been made in Astrophysics and in Cosmology since Einstein’s discovery of General Relativity (GR) in 1915. This international conference will be held at ICISE as part of the Rencontres du Vietnam. Continua a leggere Hot Topics in General Relativity and Gravitation
Archivi tag: gravitational lensing
A three day workshop on various ways of testing gravity (cosmological, astrophysical and terrestrial). This is a topical theme, in part because of the growing interest in modified gravity theories motivated by the unexplained nature of dark matter and dark energy, and in part by improving technologies that open opportunities for new types of tests. Continua a leggere Testing Gravity
Cosmology after Planck
The Planck Satellite has transformed the accuracy of cosmological observations, which allows to constrain cosmological models with unprecedented precision. The Planck observations have far reaching impact on the possible cosmological models and interpretations. This MIAPP workshop “Cosmology after Planck” will bring together observers and theorists to provide a platform for presenting and discussing the Planck Satellite results in the context of cosmological models. In particular we will discuss the polarization measurements, constraints on primordial Non-Gaussianity, the effect and exploitation of CMB lensing, constraints on inflationary models, probes of the reionization history of the Universe, Sunyaev-Zel’dovich galaxy cluster observations and the future of CMB observations.
Discovered an unusual dynamics of two young galaxies
New Herschel Space Observatory findings have given scientists a remarkable insight into the internal dynamics of two young galaxies. Surprisingly, they have shown that just a few billion years after the Big Bang, some galaxies were rotating in a mature way, seemingly having completed the accumulation of their gas reservoirs.
More at ASU: ASU researchers find young galaxies not behaving as expected
arXiv: Herschel Extreme Lensing Line Observations: Dynamics of two strongly lensed star forming galaxies near redshift z = 2
Discovered a new galaxy lens magnifying a distant supernova
A team of researchers led by Robert Quimby at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) has announced the discovery of a galaxy that magnified a background, Type Ia supernova thirtyfold through gravitational lensing. This is the first example of strong gravitational lensing of a supernova confirms the team’s previous explanation for the unusual properties of this supernova.
More at IPMU: COSMIC ILLUSION REVEALED: GRAVITATIONAL LENS MAGNIFIES SUPERNOVA
arXiv: Detection of the Gravitational Lens Magnifying a Type Ia Supernova
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
First image from Hubble’s Frontier Fields
Quella di Abell 2744 è la prima di una serie di spettacolari immagini che saranno realizzate dal programma Hubble’s Frontier Fields attraverso il fenomeno della lente gravitazionale causata dagli ammassi di galassie allo scopo di esplorare le regioni più remote dell’Universo (post). Noto anche come Pandora’s Cluster, si ritiene che Abell 2744 abbia avuto un passato violento dato che la sua formazione è emersa in seguito ad un processo di ammassamento di più ammassi di galassie.
Astronomers previously observed Abell 2744 with the NASA/ESA Hubble Space Telescope back in 2011, exploring the cluster’s history. They found that at least four galaxy clusters had crashed into one another to form Abell 2744, causing some weird and wonderful effects. This mix of cosmic phenomena, some of which had never been seen before, led to the nickname of Pandora’s Cluster (heic1111). A mix of hazy elliptical galaxies and colourful spirals can be seen clumping together in the centre of this image. The effects of the cluster’s gravity can be seen in the blue arcs and distorted shapes that are scattered across the frame, including galaxies that seem to be bleeding into the surrounding space. The arcs are actually the distorted images of galaxies far in the distance. Abell 2744 is the first of six targets for an observing programme known as Frontier Fields.
This three-year, 840-orbit programme will yield our deepest views of the Universe to date, using the power of Hubble to explore more distant regions of space than could otherwise be seen, by observing gravitational lensing effects around six different galaxy clusters.
Gravitational lensing is a phenomenon caused by an object’s influence on the space-time around it. Massive objects like galaxy clusters warp and distort this space-time. This causes light from more distant objects hidden behind this makeshift lens to be deflected and bent, leading to a bizarre array of optical effects, for example, it caused a cosmic space invader to appear around cluster Abell 68 (heic1304) by creating mirror images of one galaxy, as well as smearing galaxies out into arcs, and creating multiple images of individual objects. As well as creating these weird shapes, lensing also magnifies the images so that astronomers can see more detail. This means that distant objects that otherwise would be too distant and faint to be seen become visible, something that Frontier Fields aims to exploit over the coming years. Some results from this programme are already starting to emerge, with Abell 2744 as the first target. In a new paper submitted to The Astrophysical Journal on 29 November 2013 (available on the ArXiv Preprint Server), a group of astronomers detected a large number of distant, gravitationally lensed galaxy candidates, all viewed through Abell 2744, with the galaxy cluster acting as a lens. They also found that five of these candidates are part of distant systems that appear to have been imaged multiple times due to the cluster’s gravitational lensing effects. These deep surveys using massive galaxy clusters like Abell 2744 show that looking through cosmic lenses can be an effective and useful way to study the distant Universe. For more information on gravitational lensing see Hubblecast 70: Peering around cosmic corners.
HST: Pandora's magnifying glass arXiv: Probing the z>6 Universe with the first Hubble Frontier Fields cluster Abell 2744
A subtle distortion in the oldest light of the Universe
La rivista Physics World ha pubblicato le 10 notizie più importanti del 2013 nel campo della fisica tra le quali viene menzionata la scoperta ottenuta dagli scienziati che hanno rivelato per la prima volta delle piccole distorsioni relative alla luce più antica dell’Universo, un risultato che potrebbe fornire nuovi indizi sulle fasi primordiali della storia dell’Universo (post). Le misure si riferiscono alla polarizzazione della radiazione cosmica di fondo, all’epoca durante la quale cioè la luce interagì per l’ultima volta con la materia, circa 380.000 anni dopo il Big Bang. Queste distorsioni, note come “modi-B“, sono dovute al fenomeno della lente gravitazionale che si ha quando la luce viene deflessa da oggetti di grande massa. Nel 2014, si attendono con grande interesse i nuovi dati dal satellite Planck che ci darà delle informazioni ancora più dettagliate sulla polarizzazione della radiazione cosmica di fondo e quindi sulla presenza dei modi-B (vedasi L’Universo Infante).
A multi-institutional collaboration of researchers led by John Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics at the University of Chicago, made the discovery. They announced their findings in a paper published in the journal Physical Review Letters, using the first data from SPTpol, a polarization-sensitive camera installed on the telescope in January 2012. “The detection of B-mode polarization by South Pole Telescope is a major milestone, a technical achievement that indicates exciting physics to come”, said Carlstrom, who also is deputy director of the Kavli Institute for Cosmological Physics. The cosmic microwave background is a sea of photons (light particles) left over from the Big Bang that pervades all of space, at a temperature of minus 270 degrees Celsius, a mere 3 degrees above absolute zero.
Measurements of this ancient light have already given physicists a wealth of knowledge about the properties of the Universe. Tiny variations in temperature of the light have been painstakingly mapped across the sky by multiple experiments, and scientists are gleaning even more information from polarized light.
Light is polarized when its electromagnetic waves are preferentially oriented in a particular direction. Light from the cosmic microwave background is polarized mainly due to the scattering of photons off of electrons in the early Universe, through the same process by which light is polarized as it reflects off the surface of a lake or the hood of a car. The polarization patterns that result are of a swirl-free type, known as “E modes,” which have proven easier to detect than the fainter B modes, and were first measured a decade ago by a collaboration of researchers using the Degree Angular Scale Interferometer, another UChicago-led experiment. Simple scattering can’t generate B modes, which instead emerge through a more complex process, hence scientists’ interest in measuring them.
Gravitational lensing, it has long been predicted, can twist E modes into B modes as photons pass by galaxies and other massive objects on their way toward earth. This expectation has now been confirmed.
To tease out the B modes in their data, the scientists used a previously measured map of the distribution of mass in the Universe to determine where the gravitational lensing should occur. They combined their measurement of E modes with the mass distribution to provide a template of the expected twisting into B modes. The scientists are currently working with another year of data to further refine their measurement of B modes. The careful study of such B modes will help physicists better understand the Universe. The patterns can be used to map out the distribution of mass, thereby more accurately defining cosmologically important properties like the masses of neutrinos, tiny elementary particles prevalent throughout the cosmos. Similar, more elusive B modes would provide dramatic evidence of inflation, the theorized turbulent period in the moments after the Big Bang when the Universe expanded extremely rapidly. Inflation is a well-regarded theory among cosmologists because its predictions agree with observations, but thus far there is not a definitive confirmation of the theory. Measuring B modes generated by inflation is a possible way to alleviate lingering doubt. “The detection of a primordial B-mode polarization signal in the microwave background would amount to finding the first tremors of the Big Bang”, said the study’s lead author, Duncan Hanson, a postdoctoral scientist at McGill University in Canada.
B modes from inflation are caused by gravitational waves. These ripples in space-time are generated by intense gravitational turmoil, conditions that would have existed during inflation. These waves, stretching and squeezing the fabric of the Universe, would give rise to the telltale twisted polarization patterns of B modes.
Measuring the resulting polarization would not only confirm the theory of inflation, a huge scientific achievement in itself, but would also give scientists information about physics at very high energies, much higher than can be achieved with particle accelerators. The measurement of B modes from gravitational lensing is an important first step in the quest to measure inflationary B modes. In inflationary B mode searches, lensing B modes show up as noise. “The new result shows that this noise can be accounted for and subtracted off so that scientists can search for and hopefully measure the inflationary B modes underneath”, Hanson said. “The lensing signal itself can also be used by itself to learn about the distribution of mass in the Universe”.
University of Chicago: Swirls in remnants of Big Bang may hold clues to universe’s infancy physicsworld.com: Cosmic neutrinos named Physics World 2013 Breakthrough of the Year
The Frontier Fields: the deepest space exploration program
La NASA utilizzerà i telescopi spaziali Hubble, Spitzer e Chandra in un ‘tour-de-force’ per esplorare le regioni più remote dell’Universo. Grazie alla tecnica della lente gravitazionale, gli astronomi saranno in grado di studiare le galassie più distanti la cui luce è almeno 100 volte più debole di quella che riescono a catturare oggi con i grandi osservatori.
This ambitious collaborative program is called The Frontier Fields. Astronomers will spend the next three years peering at six massive clusters of galaxies. Researchers are interested not only as to what’s inside the clusters, but also what’s behind them. The gravitational fields of the clusters brighten and magnify distant background galaxies that are so faint they would otherwise be unobservable. The clusters themselves are among the most massive assemblages of matter known.
Astronomers anticipate that these observations will reveal populations of never-before-seen galaxies that existed when the Universe was only a few hundred million years old.
The Hubble and Spitzer data will be combined to measure the galaxies’ distances and masses more accurately than either observatory could measure alone, demonstrating the synergy of these Great Observatories for such studies. The Chandra X-ray Observatory will also peer deep into the fields, imaging them at X-ray wavelengths to help determine the masses and lensing power of the clusters, as well as identify background galaxies with massive black holes. “The idea is to use nature’s natural telescopes in combination with the Great Observatories to look much deeper than before and find the most distant and faint galaxies we can possibly see“, said principal investigator Jennifer Lotz of the Space Telescope Science Institute (STScI) in Baltimore, Md. “We want to understand when and how the first stars and galaxies formed in the universe, and each Great Observatory gives us a different piece of the puzzle. Hubble tells you which galaxies to look at and how many stars are being born in those systems. Spitzer tells you how old the galaxy is and how many stars have formed“, said Peter Capak, the Spitzer principal investigator of the Frontier Fields program. The high-resolution Hubble data from the Frontier Fields program will also be used to trace the distribution of dark matter within the foreground clusters. Accounting for the bulk of the Universe’s mass, dark matter is the underlying, invisible scaffolding attached to galaxies. “The apparent positions of those lensed galaxies then tell you what’s happening with the cluster itself, where the dark matter is in that cluster“, Lotz said. “We’ll use that information to make a better model of the cluster to better understand its lensing power“. The Hubble and Spitzer observations will be much more challenging for researchers than previous deep fields that have been studied by this powerful pair of observatories with great success. “With a deep image, you’ve got a direct image, what you see is what you get. But when we use a gravitational lens, background galaxies appear distorted and brighter“, Lotz said. “In order to understand the true properties of a background galaxy, you have to understand how it is distorted and how it is magnified. This depends on the distribution of dark matter in the gravitational lens, the foreground cluster“. What’s more, the galaxies seen in previous ultra-deep fields are just the most massive at those epochs. “They are the tip of the iceberg. If you want to see the galaxies that will turn into ones like our Milky Way, you have to go much fainter“, Lotz said. Without using the big natural telescopes in space, astronomers would have to wait for the James Webb Space Telescope. In fact, the Frontier Fields offer a sneak peek of what the Webb telescope will routinely see anywhere it points in space, when it is launched in 2018. The Hubble Frontier Fields initiative grew out of high-level discussions at STScI concerning what important, forward-looking science Hubble should be doing in upcoming years. Despite several deep field surveys, astronomers realized that a lot was still to be learned about the distant Universe. And, such knowledge would help in planning the observing strategy for the Webb telescope. To get a better assessment of whether doing more deep field observations was scientifically interesting or urgent, STScI chartered a “Hubble Deep Field Initiative” working group, which included U.S. and European astronomers who were expert users of the Great Observatories. The astronomers also considered synergies with other observatories, such as Spitzer, Chandra, and the new Atacama Large Millimeter Array. STScI Director Matt Mountain allocated his director’s discretionary time to the program. The first object to be looked at this month is called Pandora’s Cluster (Abell 2744), which has been previously observed by all three Great Observatories but not to the depth of the new observations. The giant galaxy cluster appears to be the result of a simultaneous pile-up of at least four separate, smaller galaxy clusters that took place over a span of 350 million years.
HST: NASA's Great Observatories Begin Deepest Ever Probe of the Universe
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