The origins of a torus in a galactic nucleus

Mar 13, 2012
An artist's conception of a quasar, with a Chandra X-ray Observatory image of the quasar GB1508+5714 inset. The data reveal a jet of high-energy particles that extends more than 100,000 light years from the supermassive black hole powering the quasar. A new study shows for the first time that a torus of gas and dust will naturally form around the nuclear black hole as material falls in toward the nucleus. Credit: NASA/Chandra

(PhysOrg.com) -- Quasars are among the most energetic objects in the universe, with some of them as luminous as ten thousand Milky Way galaxies. Quasars are thought to have massive black holes at their cores, and astronomers also think that the regions around the black holes actively accrete matter, a process that releases vast amounts of energy and often ejects a powerful, narrow jet of material. Because they are so bright, quasars can be seen even when they are very far away, and this combination of being both highly energetic and located at cosmological distances makes them appealing to astronomers trying to figure out the nature of galactic center black holes (our own Milky Way has one) and the conditions in the early universe that prompt these monsters to form.

Quasars, and other galaxies with less dramatic but still active nuclei, come in a variety of subgroups. Some, for example, contain hot gas moving at huge velocities, while others do not; some are seen with strong dust absorption features, but others are not. One problem in unraveling the mystery of is that many (perhaps most) quasar nuclei seem to be surrounded by a of obscuring dust that makes them difficult to study. In fact, the of these objects proposes that the various subgroups result from viewing the active nuclei at different angles with respect to its dusty torus. If the nucleus happens to be seen face-on, and if there is a jet present, the gas velocities are large and the dust is not apparent; if seen edge-on through the torus, the observed velocities are much smaller and the dust absorption features are dominant. But so far no one knows for sure how quasars form, how they develop in time, or how (or what) generate their stupendous energies.

The situation may be about to change. The violent activity around a black hole is very difficult to analyze with just pen and paper, and so for years researchers have tried to use to identify what happens. But these simulations have faced a major challenge: tracing the detailed flow of material from galaxy-wide scales of hundreds of thousands of light-years down into the central tenth of a light-year around the black hole. It has just been too hard to keep track of everything at such a fine scale across such a large one.

CfA astronomers Chris Hayward and Lars Hernquist, together with ex-CfA member Phil Hopkins and a fourth colleague, have figured out a way to deal with the computational dilemma. They use a clever scheme of multi-scale "zoom-ins" which allows them to track and model, in a physically consistent way, selected parcels of gas as they move inward towards the torus. Their simulations lead them to reach two very significant conclusions. First, they show that a dusty torus is likely to be produced around the black hole - in the past it had been postulated in order to explain the various morphologies but had never been demonstrated, even in a simulation. Secondly, the scientists show that the torus is not just a passive screen: it plays an active role in feeding gas and dust into the accretion disk around the black hole itself.

Explore further: First potentially habitable Earth-sized planet confirmed: It may have liquid water

Related Stories

Quasar Dust in the Early Universe

Mar 26, 2010

(PhysOrg.com) -- Quasars are galaxies whose very bright cores are thought to contain massive black holes around which disks are actively accreting matter.

Galaxy encounter fires up quasar

Jun 24, 2010

(PhysOrg.com) -- Using two of the world’s largest telescopes, an international team of astronomers have found evidence of a collision between galaxies driving intense activity in a highly luminous quasar. ...

Chandra finds evidence for quasar ignition

Mar 23, 2006

New data from NASA's Chandra X-ray Observatory may provide clues to how quasars "turn on." Since the discovery of quasars over 40 years ago, astronomers have been trying to understand the conditions surrounding ...

The power of spin

Jan 28, 2011

(PhysOrg.com) -- Supermasssive black holes - objects with masses of millions or billions of suns - are found at the nuclei of dramatic galaxies like quasars where they are responsible for some of the most ...

Astronomers observe fast growing primitive black holes

Mar 17, 2010

(PhysOrg.com) -- Astronomers have come across what appear to be two of the earliest and most primitive supermassive black holes known. The discovery, based largely on observations from NASA's Spitzer Space ...

Recommended for you

A sharp eye on Southern binary stars

11 hours ago

Unlike our sun, with its retinue of orbiting planets, many stars in the sky orbit around a second star. These binary stars, with orbital periods ranging from days to centuries, have long been the primary ...

Hubble image: A cross-section of the universe

11 hours ago

An image of a galaxy cluster taken by the NASA/ESA Hubble Space Telescope gives a remarkable cross-section of the Universe, showing objects at different distances and stages in cosmic history. They range ...

Cosmologists weigh cosmic filaments and voids

15 hours ago

(Phys.org) —Cosmologists have established that much of the stuff of the universe is made of dark matter, a mysterious, invisible substance that can't be directly detected but which exerts a gravitational ...

User comments : 0

More news stories

Cosmologists weigh cosmic filaments and voids

(Phys.org) —Cosmologists have established that much of the stuff of the universe is made of dark matter, a mysterious, invisible substance that can't be directly detected but which exerts a gravitational ...

Hubble image: A cross-section of the universe

An image of a galaxy cluster taken by the NASA/ESA Hubble Space Telescope gives a remarkable cross-section of the Universe, showing objects at different distances and stages in cosmic history. They range ...

Hackathon team's GoogolPlex gives Siri extra powers

(Phys.org) —Four freshmen at the University of Pennsylvania have taken Apple's personal assistant Siri to behave as a graduate-level executive assistant which, when asked, is capable of adjusting the temperature ...

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

Deadly human pathogen Cryptococcus fully sequenced

Within each strand of DNA lies the blueprint for building an organism, along with the keys to its evolution and survival. These genetic instructions can give valuable insight into why pathogens like Cryptococcus ne ...