SUPER-EDDINGTON ACCRETION IN ACTIVE GALACTIC NUCLEI

Supermassive black holes at the cores of galaxies blast radiation and ultra-fast winds outward, as illustrated in this artist's conception. Credit: NASA/JPL-Caltech

Broad emission lines are a hallmark feature of type 1 active galactic nuclei (AGNs) and quasars. Many basic properties of the broad-line region (BLR), such as its basic geometry, dynamics, and physical connection to the accretion disk around the supermassive black hole (BH), remain illdefined. AGN spectra exhibit both tremendous diversity as well as discernable patterns of systematic regularity.

In a recent paper (Du, Wang et al. 2016) published on ApJL, the authors study correlations among three dimensionless AGN parameters: accretion rate (or Eddington ratio), shape of the broad Hβ line, and flux ratio of optical Fe II to Hβ. A strong correlation among them is found, denoted as the fundamental plane of AGN BLRs. The BLR fundamental plane allows to conveniently explore the accretion status of the AGN central engine using single-epoch spectra, opening up many interesting avenues for exploring AGNs, including their cosmological evolution. The authors apply the plane to a sample of z < 0.8 quasars to demonstrate the prevalence of super-Eddington accreting AGNs are quite common at low redshifts.

(The Eddington limit, is the maximum luminosity a body - such as a star - can achieve when there is balance between the force of radiation acting outward and the gravitational force acting inward. The state of balance is called hydrostatic equilibrium. When a star exceeds the Eddington limit, it will initiate a very intense radiation-driven stellar wind from its outer layers).

▪ Du, Wang et al., 2016 ApJL - The Fundamental Plane of the Broad-line Region in Active Galactic Nuclei (arXiv)

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Image: The sequence illustrates the macronova model for the formation of a short-duration gamma-ray burst. 1. A pair of neutron stars in a binary system spiral together. 2. In the final milliseconds, as the two objects merge, they kick out highly radioactive material. This material heats up and expands, emitting a burst of light called a macronova. 3. The fading fireball blocks visible light but radiates in infrared light. 4. A remnant disk of debris surrounds the merged object, which may have collapsed to form a black hole Credit: NASA, ESA, and A. Feild (STScI) A macronova (also called a 'kilonova' or an 'r-process supernova' ) occurs when two neutron stars or a neutron star and a black hole merge. It is a near-infrared/optical transient powered by the radioactive decay of heavy elements synthesized in the ejecta (~10 -4 -10 -1 M sun with velocities ~ 0.1-0.3c) of a compact binary merger. Strong electromagnetic radiation is emitted due to the decay of h

Antares overlooking an Auxiliary Telescope

Credit: ESO/B. Tafreshi Brilliant blue stars litter the southern sky and the galactic bulge of our home galaxy, the Milky Way, hangs serenely above the horizon in this spectacular shot of ESO’s Paranal Observatory. This image was taken atop Cerro Paranal in Chile, home to ESO’s Very Large Telescope (VLT). In the foreground, the open dome of one of the four 1.8-metre Auxiliary Telescopes can be seen. The four Auxiliary Telescopes can be utilised together, to form the Very Large Telescope Interferometer (VLTI). The plane of the Milky Way is dotted with bright regions of hot gas. The very bright star towards the upper left corner of the frame is Antares — the brightest star in Scorpius and the fifteenth brightest star in the night sky. Text Credit: ESO Resources Antares overlooking an Auxiliary Telescope Next Post Small Asteroid or Comet 'Visits' from Beyond the Solar System

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