Cinque miliardi di anni fa, si ebbe un brillamento in una regione dello spazio in prossimità del buco nero che risiede nel nucleo del quasar 3C 279. Lo scorso 14 Giugno, l’impulso della radiazione di alta energia, o flare, prodotto da questo evento è arrivato finalmente a Terra mettendo in moto i rivelatori a bordo del telescopio spaziale per raggi gamma Fermi e di altri satelliti. Gli astronomi di vari osservatori sparsi sul globo hanno subito puntato gli strumenti verso la sorgente per osservare questo brillamento da record, sia pur di breve durata, in grande dettaglio. Continua a leggere 3C 279, che fantastico flare!
In questi giorni, i cosmologi sono riuniti a Palazzo Costabili, nella città di Ferrara, per discutere gli ultimi risultati ottenuti dal satellite Planck sulla temperatura e la polarizzazione della radiazione cosmica di fondo (post). Il risultato principale è una nuova mappa a tutto cielo che mostra lo stato fisico dell’Universo infante appena 380 mila anni dopo il Big Bang e i cui dati saranno pubblicati sulla rivista Astronomy & Astrophysics non prima del 22 Dicembre 2014.
Grazie ad una serie di osservazioni realizzate mediante tre potenti telescopi ottici terrestri, e cioè il Very Large Telescope in Cile, i telescopi del Keck Observatory e il telescopio Subaru che sono situati nelle Hawaii, un gruppo di astronomi guidati dai ricercatori della Swinburne University of Technology hanno analizzato la luce di un singolo quasar ottenendo dati preziosi al fine di verificare il valore della costante di struttura fine. Continua a leggere Misurare l’intensità dell’elettromagnetismo analizzando la luce dei quasar
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”.
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.
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 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.
Un gruppo di astrofisici di del Dartmouth College hanno studiato le modalità con cui i quasar, e i buchi neri che in essi risiedono, influenzano le galassie ospiti. I ricercatori hanno documentato l’immensa radiazione emessa dai quasar che si estende per migliaia di anni-luce nello spazio, fino ai bordi più esterni della galassia.
“For the first time, we are able to see the actual extent to which these quasars and their black holes can affect their galaxies, and we see that it is limited only by the amount of gas in the galaxy” says Kevin Hainline. “The radiation excites gas all the way to the margins of the galaxy and stops only when it runs out of gas“. The illumination of gas can have a profound effect, since gas that is lit up and heated by the quasar is less able to collapse under its own gravity and form new stars. Thus, the tiny central black hole and its quasar can slow down star formation in the entire galaxy and influence how the galaxy grows and changes over time. “This is exciting because we know from a number of different independent arguments that these quasars have a profound effect on the galaxies in which they live“, Ryan Hickox says.
“There is a lot of controversy about how they actually influence the galaxy, but now we have one aspect of the interaction that can extend on the scale of the entire galaxy. Nobody had seen this before“.
The radiation released by a quasar covers the entire electromagnetic spectrum, from radio waves and microwaves at the low-frequency end through infrared, ultraviolet, and X-rays, to high-frequency gamma rays. A central black hole, also called an active galactic nucleus, may grow by swallowing material from the surrounding interstellar gas, releasing energy in the process. This leads to the creation of a quasar, emitting radiation that illuminates the gas present throughout the galaxy. “If you take this powerful, bright radiation source in the center of the galaxy and blast the gas with its radiation, it will get excited in just the same way the neon gets excited in neon lamps, producing light“, says Hickox. “The gas will produce very specific frequencies of light that only a quasar can produce. This light functioned as a tracer that we were able to use to follow the gas excited by the black hole out to large distances“.
Quasars are small compared to a galaxy, like a grain of sand on a beach, but the power of their radiation can extend to the galactic boundaries and beyond.
Hickox, Hainline, and their co-authors based their conclusions on observations made with the Southern African Large Telescope (SALT), the largest optical telescope in the southern hemisphere. Dartmouth is a partner in SALT, giving faculty and students access to the instrument. The observations were performed using spectroscopy, where light is broken down into its component wavelengths. “For this particular kind of experiment, it is among the best telescopes in the world“, says Hickox. They also used data from NASA’s Wide-field Infrared Survey Explorer (WISE), a space telescope that imaged the whole sky in the infrared. The scientists used observations in infrared light because they give a particularly reliable measure of the total energy output by the quasar.
The behaviour of physical fundamental constants is an effective way to probe fundamental physics and cosmological models. The fine-structure constant α and the proton-to-electron mass ratio µ can be studied with a range of physical observables across the Universe, including spectra of the more distant quasars, Cosmic Microwave Background and Primordial Nucleosynthesis. A connection between the variation of fundamental parameters and the nature of dark energy could be tested. We will bring together the most active researchers in this area to discuss the latest developments. The conference proceedings will be possibly published in the Memorie della Società Astronomica Italiana.
Le galassie primordiali avevano un aspetto alquanto differente rispetto a quelle che popolano l’Universo oggi. Grazie ad una serie di osservazioni condotte con il Very Large Telescope (VLT) e il telescopio spaziale Hubble (HST), alcuni ricercatori hanno studiato una galassia molto antica, con una accuratezza senza precedenti, e da cui è stato possibile determinare alcuni parametri astrofisici che la caratterizzano, come la massa, la dimensione, il contenuto chimico e il tasso di formazione stellare.
“Galaxies are deeply fascinating objects. The seeds of galaxies are quantum fluctuations in the very early Universe and thus, understanding of galaxies links the largest scales in the Universe with the smallest. It is only within galaxies that gas can become cold and dense enough to form stars and galaxies are therefore the cradles of starsbirths”, explains Johan Fynbo, professor at the Dark Cosmology Centre at the Niels Bohr Institute at the University of Copenhagen. Early in the Universe, galaxies were formed from large clouds of gas and dark matter. Gas is the Universe’s raw material for the formation of stars. Inside galaxies the gas can cool down from the many thousands of degrees it has outside galaxies. When gas is cooled it becomes very dense. Finally, the gas is so compact that it collapses into a ball of gas where the gravitational compresion heats up the matter, creating a glowing ball of gas, a star is born. In the red-hot interior of massive stars, hydrogen and helium melt together and form the first heavier elements like carbon, nitrogen, oxygen, which go on to form magnesium, silicon and iron. When the entire core has been converted into iron, no more energy can be extracted and the star dies as a supernova explosion. Every time a massive star burns out and dies, it hence flings clouds of gas and newly formed elements out into space, where they form gas clouds that get denser and denser and eventually collapse to form new stars. The early stars contained only a thousandth of the elements found in the Sun today. In this way, each generation of stars becomes richer and richer in heavy elements. In today’s galaxies, we have a lot of stars and less gas. In the early galaxies, there was a lot of gas and fewer stars. “We want to understand this cosmic evolutionary history better by studying very early galaxies. We want to measure how large they are, what they weigh and how quickly stars and heavy elements are formed”, explains Johan Fynbo.
The research team has studied a galaxy located approximately 11 billion years back in time in great detail.
Behind the galaxy is a quasar, which is an active black hole that is brighter than a galaxy. Using the light from the quasar, they found the galaxy using the giant telescopes, VLT in Chile. The large amount of gas in the young galaxy simply absorbed a massive amount of the light from the quasar lying behind it. Here they could ‘see’, via absorption, the outer parts of the galaxy. Furthermore, active star formation causes some of the gas to light up, so it could be observed directly. With the Hubble Space Telescope they could also see the recently formed stars in the galaxy and they could calculate how many stars there were in relation to the total mass, which is comprised of both stars and gas. They could now see that the relative proportion of heavier elements is the same in the centre of the galaxy as in the outer parts and it shows that the stars that are formed earlier in the centre of the galaxy enrich the stars in the outer parts with heavier elements. “By combining the observations from both methods – absorption and emission – we have discovered that the stars have an oxygen content equivalent to approx. 1/3 of the Sun’s oxygen content. This means that earlier generations of stars in the galaxy had already built up elements that made it possible to form planets like Earth 11 billion years ago”, conclude Johan Fynbo.
University of Copenaghen: New knowledge about early galaxies