Archivi tag: dark energy

STARS 2013 e SMFNS 2013

The events are the second and third in a series of meetings gathering scientists working on astroparticle physics, cosmology, gravitation, nuclear physics, and related fields. As in previous years, the meeting sessions will consist of invited and contributed talks and will cover recent developments in the following topics:
STARS2013 – New phenomena and new states of matter in the Universe, general relativity, gravitation, cosmology, heavy ion collisions and the formation of the quark-gluon plasma, white dwarfs, neutron stars and pulsars, black holes, gamma-ray emission in the Universe, high energy cosmic rays, gravitational waves, dark energy and dark matter, strange matter and strange stars, antimatter in the Universe, and topics related to these.
SMFNS2013 – Strong magnetic fields in the Universe, strong magnetic fields in compact stars and in galaxies, ultra-strong magnetic fields in neutron star mergers, quark stars and magnetars, strong magnetic fields and the cosmic microwave background, and topics related to these.

Black holes as tools to measure the expansion of the Universe

Black HoleA few years ago, researchers revealed that the Universe is expanding at a much faster rate than originally believed, a discovery that earned in 2011 the Nobel Prize in Physics. But measuring the rate of this acceleration over large distances is still challenging and problematic according to Prof. Hagai Netzer of Tel Aviv University’s School of Physics and Astronomy.

Now, Prof. Netzer, along with other colleagues from the Institute of High Energy Physics of the Chinese Academy of Sciences and from the Observatoire de Paris, has developed a method with the potential to measure distances of billions of light years with a high degree of accuracy. The method uses certain types of active black holes that lie at the center of many galaxies. The ability to measure very long distances translates into seeing further into the past of the Universe and being able to estimate its rate of expansion at a very young age. This system of measurement takes into account the radiation emitted from the material that surrounds black holes before it is absorbed. “As material is drawn into a black hole, it heats up and emits a huge amount of radiation, up to a thousand times the energy produced by a large galaxy containing 100 billion stars. For this reason, it can be seen from very far distances”, explains Prof. Netzer. Using radiation to measure distances is a general method in astronomy, but until now black holes have never been used to help measure these distances. By adding together measurements of the amount of energy being emitted from the vicinity of the black hole to the amount of radiation which reaches Earth, it’s possible to infer the distance to the black hole itself and the time in the history of the Universe when the energy was emitted. Getting an accurate estimate of the radiation being emitted depends on the properties of the black hole. “For the specific type of black holes targeted in this work, the amount of radiation emitted as the object draws matter into itself is actually proportional to its mass”, say the researchers. Therefore, long-established methods to measure this mass can be used to estimate the amount of radiation involved. The viability of this theory was proved by using the known properties of black holes in our own astronomical vicinity, “only” several hundred million light years away. Prof. Netzer believes that his system will add to the astronomer’s tool kit for measuring distances much farther away, complimenting the existing method which uses the exploding stars called supernovae. According to Prof. Netzer, the ability to measure far-off distances has the potential to unravel some of the greatest mysteries of the Universe, which is approximately 14 billion years old. “When we are looking into a distance of billions of light years, we are looking that far into the past“, he explains. “The light that I see today was first produced when the Universe was much younger“. One such mystery is the nature of what astronomers call “dark energy,” the most significant source of energy in the present day Universe. This energy, which is manifested as some kind of “anti-gravity,” is believed to contribute towards the accelerated expansion of the Universe by pushing outwards. The ultimate goal is to understand dark energy on physical grounds, answering questions such as whether this energy has been consistent throughout time and if it is likely to change in the future.

Tel Aviv University: Using Black Holes to Measure the Universe's Rate of Expansion
arXiv: Super-Eddington accreting massive black holes as long-lived cosmological standards

Measuring the Universe More Accurately Than Ever Before

After nearly a decade of careful observations an international team of astronomers has measured the distance to our neighbouring galaxy, the Large Magellanic Cloud, more accurately than ever before. This new measurement also improves our knowledge of the rate of expansion of the Universe, the Hubble constant, and is a crucial step towards understanding the nature of the mysterious dark energy that is causing the expansion to accelerate. The team used telescopes at ESO’s La Silla Observatory in Chile as well as others around the globe. These results appear in the 7 March 2013 issue of the journal Nature.

Astronomers survey the scale of the Universe by first measuring the distances to close-by objects and then using them as standard candles to pin down distances further and further out into the cosmos. But this chain is only as accurate as its weakest link. Up to now finding an accurate distance to the Large Magellanic Cloud (LMC), one of the nearest galaxies to the Milky Way, has proved elusive. As stars in this galaxy are used to fix the distance scale for more remote galaxies, it is crucially important. But careful observations of a rare class of double star have now allowed a team of astronomers to deduce a much more precise value for the LMC distance: 163 000 light-years. “I am very excited because astronomers have been trying for a hundred years to accurately measure the distance to the Large Magellanic Cloud, and it has proved to be extremely difficult,” says Wolfgang Gieren (Universidad de Concepción, Chile) and one of the leaders of the team. “Now we have solved this problem by demonstrably having a result accurate to 2%.” The improvement in the measurement of the distance to the Large Magellanic Cloud also gives better distances for many Cepheid variable stars. These bright pulsating stars are used as standard candles to measure distances out to more remote galaxies and to determine the expansion rate of the Universe, the Hubble constant. This in turn is the basis for surveying the Universe out to the most distant galaxies that can be seen with current telescopes. So the more accurate distance to the Large Magellanic Cloud immediately reduces the inaccuracy in current measurements of cosmological distances. The astronomers worked out the distance to the Large Magellanic Cloud by observing rare close pairs of stars, known as eclipsing binaries. As these stars orbit each other they pass in front of each other. When this happens, as seen from Earth, the total brightness drops, both when one star passes in front of the other and, by a different amount, when it passes behind. By tracking these changes in brightness very carefully, and also measuring the stars’ orbital speeds, it is possible to work out how big the stars are, their masses and other information about their orbits. When this is combined with careful measurements of the total brightness and colours of the stars remarkably accurate distances can be found. This method has been used before, but with hot stars. However, certain assumptions have to be made in this case and such distances are not as accurate as is desirable. But now, for the first time, eight extremely rare eclipsing binaries where both stars are cooler red giant stars have been identified. These stars have been studied very carefully and yield much more accurate distance values — accurate to about 2%. “ESO provided the perfect suite of telescopes and instruments for the observations needed for this project: HARPS for extremely accurate radial velocities of relatively faint stars, and SOFI for precise measurements of how bright the stars appeared in the infrared,” adds Grzegorz Pietrzyński (Universidad de Concepción, Chile and Warsaw University Observatory, Poland), lead author of the new paper in Nature. “We are working to improve our method still further and hope to have a 1% LMC distance in a very few years from now. This has far-reaching consequences not only for cosmology, but for many fields of astrophysics,” concludes Dariusz Graczyk, the second author on the new Nature paper.

ESO: Measuring the Universe More Accurately Than Ever Before
Research paper in Nature: An eclipsing binary distance to the Large Magellanic Cloud accurate to 2 per cent

Planck reveals an almost perfect Universe

Acquired by ESA’s Planck space telescope, the most detailed map ever created of the cosmic microwave background – the relic radiation from the Big Bang – was released today revealing the existence of features that challenge the foundations of our current understanding of the Universe.

The image is based on the initial 15.5 months of data from Planck and is the mission’s first all-sky picture of the oldest light in our Universe, imprinted on the sky when it was just 380 000 years old. At that time, the young Universe was filled with a hot dense soup of interacting protons, electrons and photons at about 2700ºC. When the protons and electrons joined to form hydrogen atoms, the light was set free. As the Universe has expanded, this light today has been stretched out to microwave wavelengths, equivalent to a temperature of just 2.7 degrees above absolute zero. This ‘cosmic microwave background’ – CMB – shows tiny temperature fluctuations that correspond to regions of slightly different densities at very early times, representing the seeds of all future structure: the stars and galaxies of today. According to the standard model of cosmology, the fluctuations arose immediately after the Big Bang and were stretched to cosmologically large scales during a brief period of accelerated expansion known as inflation. Planck was designed to map these fluctuations across the whole sky with greater resolution and sensitivity than ever before. By analysing the nature and distribution of the seeds in Planck’s CMB image, we can determine the composition and evolution of the Universe from its birth to the present day.

Overall, the information extracted from Planck’s new map provides an excellent confirmation of the standard model of cosmology at an unprecedented accuracy, setting a new benchmark in our manifest of the contents of the Universe. But because precision of Planck’s map is so high, it also made it possible to reveal some peculiar unexplained features that may well require new physics to be understood. “The extraordinary quality of Planck’s portrait of the infant Universe allows us to peel back its layers to the very foundations, revealing that our blueprint of the cosmos is far from complete. Such discoveries were made possible by the unique technologies developed for that purpose by European industry,” says Jean-Jacques Dordain, ESA’s Director General. “Since the release of Planck’s first all-sky image in 2010, we have been carefully extracting and analysing all of the foreground emissions that lie between us and the Universe’s first light, revealing the cosmic microwave background in the greatest detail yet,” adds George Efstathiou of the University of Cambridge, UK. One of the most surprising findings is that the fluctuations in the CMB temperatures at large angular scales do not match those predicted by the standard model – their signals are not as strong as expected from the smaller scale structure revealed by Planck. Another is an asymmetry in the average temperatures on opposite hemispheres of the sky. This runs counter to the prediction made by the standard model that the Universe should be broadly similar in any direction we look. Furthermore, a cold spot extends over a patch of sky that is much larger than expected. The asymmetry and the cold spot had already been hinted at with Planck’s predecessor, NASA’s WMAP mission, but were largely ignored because of lingering doubts about their cosmic origin. “The fact that Planck has made such a significant detection of these anomalies erases any doubts about their reality; it can no longer be said that they are artefacts of the measurements. They are real and we have to look for a credible explanation,” says Paolo Natoli of the University of Ferrara, Italy. “Imagine investigating the foundations of a house and finding that parts of them are weak. You might not know whether the weaknesses will eventually topple the house, but you’d probably start looking for ways to reinforce it pretty quickly all the same,” adds François Bouchet of the Institut d’Astrophysique de Paris. One way to explain the anomalies is to propose that the Universe is in fact not the same in all directions on a larger scale than we can observe. In this scenario, the light rays from the CMB may have taken a more complicated route through the Universe than previously understood, resulting in some of the unusual patterns observed today. “Our ultimate goal would be to construct a new model that predicts the anomalies and links them together. But these are early days; so far, we don’t know whether this is possible and what type of new physics might be needed. And that’s exciting,” says Professor Efstathiou.

New cosmic recipe

Beyond the anomalies, however, the Planck data conform spectacularly well to the expectations of a rather simple model of the Universe, allowing scientists to extract the most refined values yet for its ingredients. Normal matter that makes up stars and galaxies contributes just 4.9% of the mass/energy density of the Universe. Dark matter, which has thus far only been detected indirectly by its gravitational influence, makes up 26.8%, nearly a fifth more than the previous estimate. Conversely, dark energy, a mysterious force thought to be responsible for accelerating the expansion of the Universe, accounts for less than previously thought. Finally, the Planck data also set a new value for the rate at which the Universe is expanding today, known as the Hubble constant. At 67.15 kilometres per second per megaparsec, this is significantly less than the current standard value in astronomy. The data imply that the age of the Universe is 13.82 billion years. “With the most accurate and detailed maps of the microwave sky ever made, Planck is painting a new picture of the Universe that is pushing us to the limits of understanding current cosmological theories,” says Jan Tauber, ESA’s Planck Project Scientist. “We see an almost perfect fit to the standard model of cosmology, but with intriguing features that force us to rethink some of our basic assumptions. “This is the beginning of a new journey and we expect that our continued analysis of Planck data will help shed light on this conundrum.”

A series of scientific papers describing the new results will be published on 22 March.
arXiv: Planck 2013 results. I. Overview of products and scientific results

See also in arXiv: Planck 2013 results (29 papers)

arXiv: Planck 2013 results support the simplest cyclic models

arXiv: Inflationary paradigm in trouble after Planck2013

More info: Planck ESA

The biggest accelerators in Space and on Earth – COST/CERN conference

This Workshop is jointly organized by the COST programme on “Black Holes in a Violent Universe”, the CERN TH group and the LPCC. The focus of the workshop are the phenomena taking place at the highest-energies available in the cosmos and in the laboratory, spanning the whole range from the most luminous events in space (extragalactic jets from active black holes, gamma ray bursts, cosmic rays, etc) to the exploration, theoretical and at the LHC, of new particles and quantum gravity phenomena (searches for black holes, extra dimensions, dark matter; theoretical understanding of the information properties of black holes, gravitational scattering at high energy, properties of the event horizon, etc.). The goal of the meeting is to bring together experts from the two communities of astrophysics and particle physics, and share with each other the latest developments and open issues in their respective field.

More info: The biggest accelerators in Space and on Earth

Cosmology, Large Scale Structure and First Objects

Cosmology, Large Scale Structure and First Objects – This USP Conference shall cover the key issues of Cosmology, from particle physics, fundamental gravitation, cosmic background radiation, dark matter and dark energy, large-scale structure, simulations of the formation of structure in the Universe, as well as comparisons to observations.  Continua a leggere Cosmology, Large Scale Structure and First Objects