Archivi tag: active galactic nuclei

Extreme-Astrophysics in an Ever-Changing Universe

Since ancient times, astronomers’ attention has been drawn to changes in the sky. Today we know that most phenomena observed in “time-domain” astronomy are related to extreme astrophysical events or processes. Whether it is the explosion of stars in supernovae or the observations of flare stars, pulsars, gamma-ray bursts, blazars or active galactic nuclei, time-domain astronomy stretches across the whole electromagnetic spectrum and beyond. With increasing technical capabilities, the 21st century will see corresponding new instruments being developed or coming online, revolutionising our view of the ever-changing Universe. Continua a leggere Extreme-Astrophysics in an Ever-Changing Universe

The X-ray Universe

The XMM-Newton Science Operations Centre is organising a major astrophysical symposium from Monday 16th to Thursday 19th of June 2014 in Dublin, Ireland. The symposium is the fourth international meeting in the series “The X-ray Universe”. The intention is to gather a general collection of research in high energy astrophysics. The symposium will provide a showcase for results, discoveries and expectations from current and future X-ray missions. Continua a leggere The X-ray Universe

Seeds of supermassive black holes are quite massive themselves

The galaxy NGC 4395 is shown here in infrared light, captured by NASA’s Spitzer Space Telescope. This dwarf galaxy is relatively small in comparison with our Milky Way galaxy, which is nearly 1,000 times more massive. Image Credit: NASA/JPL-Caltech
Come fa un buco nero supermassiccio ad acquisire una massa che va tipicamente da qualche decina/centinaia di milioni fino a qualche miliardo di masse solari? Ad oggi, non c’è una risposta ben precisa ma alcuni dati ottenuti di recente dal telescopio spaziale Wide-field Infrared Survey Explorer (WISE) stanno facendo luce sulla natura di quei “siti cosmici” dove hanno origine i buchi neri. Inoltre, questi dati forniscono nuovi indizi che hanno lo scopo di comporre insieme il puzzle che descrive l’evoluzione di questi enigmatici oggetti che risiedono nei nuclei delle galassie attive.

Growing a black hole is not as easy as planting a seed in soil and adding water. The massive objects are dense collections of matter that are literally bottomless pits; anything that falls in will never come out. They come in a range of sizes. The smallest, only a few times greater in mass than our Sun, form from exploding stars. The biggest of these dark beasts, billions of times the mass of our Sun, grow together with their host galaxies over time, deep in the interiors. But how this process works is an ongoing mystery. Researchers using WISE addressed this question by looking for black holes in smaller, “dwarf” galaxies. These galaxies have not undergone much change, so they are more pristine than their heavier counterparts. In some ways, they resemble the types of galaxies that might have existed when the Universe was young, and thus they offer a glimpse into the nurseries of supermassive black holes. In this new study, using data of the entire sky taken by WISE in infrared light, up to hundreds of dwarf galaxies have been discovered in which buried black holes may be lurking. Infrared light, the kind that WISE collects, can see through dust, unlike visible light, so it’s better able to find the dusty, hidden black holes. The researchers found that the dwarf galaxies’ black holes may be about 1,000 to 10,000 times the mass of our Sun, larger than expected for these small galaxies. “Our findings suggest the original seeds of supermassive black holes are quite massive themselves“, said Shobita Satyapal of George Mason University, Fairfax, Va.

Daniel Stern, an astronomer specializing in black holes at NASA’s Jet Propulsion Laboratory, Pasadena, California, who was not a part of the new study, says: “The research demonstrates the power of an all-sky survey like WISE to find the rarest black holes. Though it will take more research to confirm whether the dwarf galaxies are indeed dominated by actively feeding black holes, this is exactly what WISE was designed to do: find interesting objects that stand out from the pack“.

The new observations argue against one popular theory of black hole growth, which holds that the objects bulk up in size through galaxy collisions.

When our Universe was young, galaxies were more likely to crash into others and merge. It is possible the galaxies’ black holes merged too, accumulating more mass. In this scenario, supermassive black holes grow in size through a series of galaxy mergers. The discovery of dwarf galaxy black holes that are bigger than expected suggests that galaxy mergers are not necessary to create big black holes. Dwarf galaxies don’t have a history of galactic smash-ups, and yet their black holes are already relatively big. Instead, supermassive black holes might form very early in the history of the Universe. Or, they might grow harmoniously with their host galaxies, feeding off surrounding gas.”We still don’t know how the monstrous black holes that reside in galaxy centers formed“, said Satyapal. “But finding big black holes in tiny galaxies shows us that big black holes must somehow have been created in the early Universe, before galaxies collided with other galaxies“.

NASA: The Search for Seeds of Black Holes

arXiv: Discovery of a Population of Bulgeless Galaxies with Extremely Red Mid-IR Colors: Obscured AGN Activity in the Low Mass Regime?

 

 

Testing Bell’s theorem with distant quasars

Illustrazione artistica del concetto del disco di accrescimento attorno al buco nero nella galassia Mrk 231. Il flusso di radiazione è rappresentato in alto sopra il disco (in blu) ma non è ciò che si vede da Terra. Si nota inoltre un getto, molto stretto e localizzato che era noto prima delle osservazioni di Gemini.  Credit:Gemini Observatory/AURA, Lynette Cook

Alcuni ricercatori del MIT hanno pubblicato un articolo in cui viene proposto un esperimento che potrebbe risolvere un teorema vecchio di 50 anni, noto come teorema di Bell, che se violato potrebbe implicare che il nostro Universo non è strutturato secondo le leggi della fisica classica bensì secondo quelle meno tangibili ed estremamente probabilistiche della meccanica quantistica.

Such a quantum view would allow for seemingly counterintuitive phenomena such as entanglement, in which the measurement of one particle instantly affects another, even if those entangled particles are at opposite ends of the Universe. Among other things, entanglement, a quantum feature Albert Einstein skeptically referred to as “spooky action at a distance”, seems to suggest that entangled particles can affect each other instantly, faster than the speed of light. In 1964, physicist John Bell took on this seeming disparity between classical physics and quantum mechanics, stating that if the Universe is based on classical physics, the measurement of one entangled particle should not affect the measurement of the other, a theory, known as locality, in which there is a limit to how correlated two particles can be. Bell devised a mathematical formula for locality, and presented scenarios that violated this formula, instead following predictions of quantum mechanics. Since then, physicists have tested Bell’s theorem by measuring the properties of entangled quantum particles in the laboratory.

Essentially all of these experiments have shown that such particles are correlated more strongly than would be expected under the laws of classical physics, findings that support quantum mechanics.

However, scientists have also identified several major loopholes in Bell’s theorem. These suggest that while the outcomes of such experiments may appear to support the predictions of quantum mechanics, they may actually reflect unknown “hidden variables” that give the illusion of a quantum outcome, but can still be explained in classical terms. Though two major loopholes have since been closed, a third remains; physicists refer to it as “setting independence,” or more provocatively, “free will.” This loophole proposes that a particle detector’s settings may “conspire” with events in the shared causal past of the detectors themselves to determine which properties of the particle to measure, a scenario that, however far-fetched, implies that a physicist running the experiment does not have complete free will in choosing each detector’s setting. Such a scenario would result in biased measurements, suggesting that two particles are correlated more than they actually are, and giving more weight to quantum mechanics than classical physics. “It sounds creepy, but people realized that’s a logical possibility that hasn’t been closed yet”, says MIT’s David Kaiser, the Germeshausen Professor of the History of Science and senior lecturer in the Department of Physics. “Before we make the leap to say the equations of quantum theory tell us the world is inescapably crazy and bizarre, have we closed every conceivable logical loophole, even if they may not seem plausible in the world we know today?” Now Kaiser, along with MIT postdoc Andrew Friedman and Jason Gallicchio of the University of Chicago, have proposed an experiment to close this third loophole by determining a particle detector’s settings using some of the oldest light in the Universe: distant quasars, or galactic nuclei, which formed billions of years ago.

The idea, essentially, is that if two quasars on opposite sides of the sky are sufficiently distant from each other, they would have been out of causal contact since the Big Bang some 14 billion years ago, with no possible means of any third party communicating with both of them since the beginning of the Universe, an ideal scenario for determining each particle detector’s settings.

As Kaiser explains it, an experiment would go something like this: A laboratory setup would consist of a particle generator, such as a radioactive atom that spits out pairs of entangled particles. One detector measures a property of particle A, while another detector does the same for particle B. A split second after the particles are generated, but just before the detectors are set, scientists would use telescopic observations of distant quasars to determine which properties each detector will measure of a respective particle. In other words, quasar A determines the settings to detect particle A, and quasar B sets the detector for particle B. The researchers reason that since each detector’s setting is determined by sources that have had no communication or shared history since the beginning of the Universe, it would be virtually impossible for these detectors to “conspire” with anything in their shared past to give a biased measurement; the experimental setup could therefore close the “free will” loophole. If, after multiple measurements with this experimental setup, scientists found that the measurements of the particles were correlated more than predicted by the laws of classical physics, Kaiser says, then the Universe as we see it must be based instead on quantum mechanics. “I think it’s fair to say this [loophole] is the final frontier, logically speaking, that stands between this enormously impressive accumulated experimental evidence and the interpretation of that evidence saying the world is governed by quantum mechanics”, Kaiser says. Now that the researchers have put forth an experimental approach, they hope that others will perform actual experiments, using observations of distant quasars. Physicist Michael Hall says that while the idea of using light from distant sources like quasars is not a new one, the group’s paper illustrates the first detailed analysis of how such an experiment could be carried out in practice, using current technology. “It is therefore a big step to closing the loophole once and for all”, says Hall, a research fellow in the Centre for Quantum Dynamics at Griffith University in Australia. “I am sure there will be strong interest in conducting such an experiment, which combines cosmic distances with microscopic quantum effects, and most likely involving an unusual collaboration between quantum physicists and astronomers”. “At first, we didn’t know if our setup would require constellations of futuristic space satellites, or 1,000-meter telescopes on the dark side of the Moon”, Friedman says. “So we were naturally delighted when we discovered, much to our surprise, that our experiment was both feasible in the real world with present technology, and interesting enough to our experimentalist collaborators who actually want to make it happen in the next few years”. Adds Kaiser, “We’ve said, ‘Let’s go for broke, let’s use the history of the cosmos since the Big Bang, darn it.’ And it is very exciting that it’s actually feasible”.

MIT: Closing the ‘free will’ loophole

arXiv: Testing Bell's Inequality with Cosmic Photons: Closing the Setting-Independence Loophole

Astrotomography II – Imaging at the micro-arcsecond scale

Astrotomography is a generic term for indirect mapping techniques that can be applied to a huge variety of astrophysical systems, ranging from planets via single stars and binaries to active galactic nuclei. With this workshop we aim at consolidating the success of a previous workshop dedicated to this topic, and plan to bring together people from different communities but who use similar techniques to construct images at very high angular resolution. In the time since the first workshop, the scientific output of the astrotomography methods has been considerable, the range of applications becoming larger and larger with time. It is thus timely to review these methods, the progress in the field, the new harvest of results that were collected, as well as to prepare the next generation of astronomers to use these tools.

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:

Cosmology

  • 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,
  • LHC, LSST, NuSTAR, Pan-STARRS, Planck, SDSS, SKA, SPT, WFIRST, WMAP, …
  • (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

Discovered a new type of black hole quasar-like object

E’ noto che ogni galassia ospita nel suo nucleo un buco nero supermassiccio spesso circondato da un disco di accrescimento super brillante composto di gas a temperature elevate che dà luogo alla fenomenologia tipica dei quasar. Ora, un gruppo di ricercatori della Penn State University hanno individuato con grande sorpresa una nuova classe di quasar distanti la cui esistenza non è prevista dagli attuali modelli che descrivono le proprietà e la fenomenologia dei nuclei galattici attivi.

The gas in this new type of quasar is moving in two directions: some is moving toward Earth but most of it is moving at high velocities away from us, possibly toward the quasar’s black hole“, said study co-author Niel Brandt, Distinguished Professor of Astronomy and Astrophysics at Penn State. “Just as you can use the Doppler shift for sound to tell if an airplane is moving away from you or toward you, we used the Doppler shift for light to tell whether the gas in these quasars is moving away from Earth or toward these distant black holes, which have a mass from millions to billions of times that of the Sun“. Matter around these black holes forms a quasar disc that is bigger than Earth’s orbit around the Sun and hotter than the surface of the Sun. These quasars generate enough light to be seen across the observable Universe. The international research team, led by Patrick Hall of York University in Toronto, discovered the unusual quasars with data from a large sky survey, the Sloan Digital Sky Survey (SDSS-III). “Matter falling into black holes may not sound surprising“, said Hall, “but what we found is, in fact, quite mysterious and was not predicted by current theories“. Such gas is found in only about 1 out of 10,000 quasars, and only 17 cases now are known. “The gas in the disc must eventually fall into the black hole to power the quasar, but what is often seen instead is gas blown away from the black hole by the heat and light of the quasar, heading toward us at velocities up to 20 per cent of the speed of light“, Hall said. “If the gas is falling into the black hole, then we don’t understand why it’s so rare to see infalling gas. There’s nothing else unusual about these quasars. If gas can be seen falling into them, why not in other quasars?” Hall noted there is one other possible explanation for these objects. “It could be that the gas moving away from us is not falling into the black hole but is orbiting around it, just above the disc of hot gas and is very gradually being pushed away from the black hole“, he said. “A wind like that will show gas moving both toward us and away from us. To make an analogy, imagine an ant on a spinning merry-go-round, crawling from the center to the edge. You will see the ant moving toward you about half the time and away from you about half the time. The same idea could apply to the gas in these quasars. In either case, the gas in these quasars is moving in an unusual fashion“. Models of quasars and their winds will have to be revised to account for these objects. To help understand what revision is needed, the research team is observing these quasars further using Canadian and American access to the Gemini-North telescope in Hawaii.

PSU : Researchers discover new type of black hole quasar


arXiv: Broad Absorption Line Quasars with Redshifted Troughs: High-Velocity Infall or Rotationally Dominated Outflows?

Black Holes at all scales

The COST action “Black Holes in a Violent Universe” (MP-0905) organizes a Summer School on “Black Holes at all scales”, in Ioannina, Greece, betweenSeptember 16 and 18, 2013. The Summer School “Black Holes at all scales” aims at postgraduate students and young postdoctoral fellows. The program includes reviews on various aspects of Black Hole-related science, such as: demographics and formation theories of galactic black hole binaries in our and nearby galaxies, our “own” supermassive black hole on the Galactic center, formation and cosmic evolution of supermassive black holes, phenomenology of active galactic nuclei and a review of their “unification” theories, theory of jet formation and energy extraction in black hole systems, as well as the scaling of accretion and jet physics from mini-quasars to quasars.

Fifty Years of Quasars: A Symposium in Honor of Maarten Schmidt

Fifty years ago, the discovery of quasars transformed astronomy. Studies of quasars and other active galactic nuclei still are a major, vibrant, and developing part of astronomy, astrophysics, and cosmology. This year we celebrate the 50th anniversary of this discovery, and honor Maarten Schmidt, whose insight into the nature of quasar spectra was a decisive milestone in the rise of this new field of research, in addition to his continued contributions ever since.

The meeting will consist of invited talks only, covering various aspects of the history and the current state of quasar research. Contributed papers are accepted as posters.  Please register early, since the attendance is limited by the size of the venue.

Galaxy Evolution Over Five Decades

The last few years have seen a transformation in our understanding of the formation and evolution of galaxies. These advances have been driven by observations that cover a broad range in wavelength. In the years ahead, new facilities like the JWST, CCAT, the LMT, ALMA, the JVLA, LOFAR and the SKA will shed further light on how galaxies form by providing huge increases in sensitivity over five decades in wavelength: from the near-infrared to long radio-wavelengths. This conference will bring together researchers from around the world to discuss the current state of the field and future directions that should be taken as these new telescopes come into operation. The meeting is in honour of Professor Malcolm Longair, who has made invaluable contributions to our knowledge of galaxy evolution and to the Astrophysics Group at the Cavendish Laboratory.

Scientific areas to be covered:

  • AGN and Galaxy Evolution
  • Gas in Galaxies
  • The High-redshift Universe and the First Galaxies
  • Galaxy Assembly and Cosmic Star-formation History
  • Galaxy Clusters and the Role of Environment