Archivi tag: supermassive black holes

The Evolving Blazar Paradigm

The international meeting “The Evolving Blazar Paradigm” is a follow up of our previous Krakow meetings focused on the physics of astrophysical jets in AGN and in the Galactic sources “Challenges of Relativistic Jets” (2006)” and “Understanding Relativistic Jets” (2011). Continua a leggere The Evolving Blazar Paradigm


IAU Symposium 313: “Extragalactic jets from every angle”

Jets appear in a wide range of astrophysical sources. In extragalactic systems, they signal accretion onto a supermassive black hole, providing unique testbeds in which to probe an array of fundamental physics processes. Over the past decade, major advances have been made in understanding jets due to the advent of an unprecedented number of space- and ground-based telescopes covering the entire electromagnetic spectrum, in parallel with commensurable progress in theory and simulations. Continua a leggere IAU Symposium 313: “Extragalactic jets from every angle”

99 years of Black Holes: from Astronomy to Quantum Gravity

This meeting shall bring together the Black Hole community (from Quantum to supermassive) as well as the Gravitational Wave Community. The main topics of the conference will cluster around Black Holes, Gravitational Waves and the Future of General Relativity and Quantum Physics.
Continua a leggere 99 years of Black Holes: from Astronomy to Quantum Gravity

Simulating the first realistic cosmic web

Un gruppo di ricercatori guidati da Mark Vogelsberger dell’Harvard-Smithsonian Center for Astrophysics, in collaborazione con l’Heidelberg Institute for Theoretical Studies in Germania, hanno realizzato la prima mappa virtuale, alquanto realistica, dell’Universo utilizzando una simulazione numerica denominata “Illustris“. Il modello ha permesso di ricreare uno spazio cubico di lato pari a 350 milioni di anni-luce in un intervallo di tempo di circa 13 miliardi di anni e con una  risoluzione senza precedenti.

Continua a leggere Simulating the first realistic cosmic web

G2’s ‘close’ encounter with the supermassive black hole Sgr A*

A simulation of the gas cloud G2’s encounter with the supermassive black hole Sgr A*. The blue lines mark the orbits of the so-called “S” stars that are in close orbits around the black hole. (Image by ESO/MPE/Marc Schartmann).
In queste ore, una nube “suicida” di gas si sta dirigendo verso il buco nero supermassiccio della nostra galassia. Si tratta di un evento raro che può accadere in qualsiasi momento durante questi giorni. Dunque, gli astronomi hanno oggi la possibilità di studiare questo fenomeno osservando un buco nero “in azione” mentre si alimenta di gas e polveri.

Northwestern University’s Daryl Haggard has been closely watching the little cloud, called G2, and the black hole, called Sgr A*, as part of a study that should eventually help solve one of the outstanding questions surrounding black holes. How exactly do they achieve such supermassive proportions? Her latest data has been discussed during “Advances in Astrophysics,” held at Gwinnett Room of the Savannah International Convention Center. The briefing is part of the American Physical Society (APS) April Meeting in Savannah, Ga.

The closest approach between the black hole and gas cloud is predicted to occur any day now.

Haggard has been using two world-class observatories, the Chandra X-ray Observatory and the Very Large Array, to gather data on this potentially spectacular encounter. “Our most recent Chandra observation does not show enhanced emission in the X-rays”, Haggard said. “From the X-ray perspective, the gas cloud is late to the party, but it remains to be seen whether G2 is fashionably late or a no show. This work is fascinating because it will teach us about the growth and feeding of supermassive black holes. We know they are big, and we know they are out there, in vast numbers, but we aren’t sure in detail how they get their mass. Do they grow rapidly when they are young, like our kids do, or do they grow in fits and starts, whenever fuel becomes available? In watching the encounter between Sgr A* and G2 we may catch a massive black hole in the act of snatching its next meal”, she said.

More at Northwestern University: Watching for a Black Hole to Gobble up a gas Cloud


Abstract: Hot News from the Milky Way's Central Black Hole

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?



Gas and stars in galaxies: A multi-wavelength 3D perspective

In 2008 ESO hosted the first conference on extragalactic 3D multi-wavelength astronomy. This very successful workshop attracted more than 150 astronomers with expertise ranging from the radio to the optical wavelengths. In the intervening five-year period, 3D spectroscopic techniques have greatly extended our understanding of the key subjects addressed in this workshop. The kinematics, mass assembly and evolution of galaxies has been explored in large samples in the optical and near-infrared by programs such as the SAURON/ATLAS3D and CALIFA surveys of nearby galaxies and the SINS and MASSIV surveys at z~1-2. 3D spectroscopy at these wavelengths has become a standard technique to such an extent that on 8-m telescopes survey style instruments have been developed. Meanwhile, for the next generation of extremely large telescopes IFU spectrographs are selected among the first instruments to be commissioned. At the longer end of the wavelength range, the JVLA has now come online and new radio facilities are producing commissioning results. Over the last few years millimeter interferometers have produced spectacular 3D maps of carbon monoxide and various other atomic and molecular lines of galaxies out to redshifts of z=6, as well as very detailed cubes of nearby galaxies. Against this background, it is an excellent moment to hold a second workshop in this series. The 2nd generation VLT instruments KMOS and MUSE are taking up science operations in 2013/14. ALMA is conducting Cycle 1 observations and is preparing for new observing modes and increased sensitivity and angular resolution in future Cycles. The timing is perfect to evaluate the scientific progress made since 2008 and to make the community aware of the expanding science capabilities of ESO’s 3D instrumentation suite.

Scientific topics covered at the conference will include:

  • Nearby Galaxy Dynamics
  • Starbursts and interacting galaxies
  • Supermassive black holes and AGN
  • High redshift galaxies
  • Cosmology and deep fields
By adapting a multi-wavelength approach to these scientific questions the stellar, hot and cold gas dynamics can be combined to provide an unprecedented opportunity to study many processes involved in galaxy formation such as infall, outflows, star-formation, mergers and AGN-related phenomena. Like in 2008, we envisage a highly interactive meeting with a focus on the presentation of scientific results based on current technology, but also an investigation into the exciting possibilities of future technologies. A secondary goal of this workshop is for the different communities to learn about the tools used to analyze and visualize 3-dimensional data, and to understand how they can be combined in optimal ways.

In support of this goal of the workshop, a concise description of the capabilities of these three new facilities is presented in this flyer.

Astrophysical Black Holes

Black holes are very fascinating and peculiar objects. According to General Relativity, uncharged black holes are completely specified by only two parameters, the mass M and the spin angular momentum J. In the last 40 years, we have discovered at least two classes of astrophysical black hole candidates: stellar-mass objects in X-ray binary systems and super-massive black hole candidates at the center of every normal galaxy. The mass of these objects can be inferred by robust dynamical measurements, by studying the orbital motion of gas or individual stars around them. The determination of the spin J is much more difficult and it is a hot topic of contemporary astrophysics. Then, there are still many open questions: What is the origin of the jets produced in the region around these objects? How could super-massive black holes become so heavy? Are these objects the Kerr black holes predicted by General Relativity? All our open questions may be addressed by studying the properties of the electromagnetic radiation emitted in the accretion process and, hopefully in a not distant future, by observing the gravitational waves emitted by these systems.

Read more: Fudan Winter School on Astrophysical Black Holes

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?