Tagged: AGN-Active Galatic Nuclei” Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 1:56 pm on March 15, 2019 Permalink | Reply
    Tags: "Bright X-Ray Galactic Nuclei", AGN-Active Galatic Nuclei”, , , , , ,   

    From Harvard-Smithsonian Center for Astrophysics: “Bright X-Ray Galactic Nuclei” 

    Harvard Smithsonian Center for Astrophysics

    From Harvard-Smithsonian Center for Astrophysics

    A Chandra X-Ray Observatory image of a field of galaxies in the costellation Bootes. A new study of 703 galaxies with supermassive black holes in this field finds that although infrared from dust and X-ray emission from the nucleus tend to be correlated, the infrared emitted by the supermassive black holes is not well correlated with the dust, suggesting the role of our viewing angle of a torus around the black hole nuclei. X-ray: NASA/CXC/CfA/R.Hickox et al.; Moon: NASA/JPL

    All massive galaxies are believed to host supermassive black holes (SMBH) at their centers that grow by accreting mass from their environment. The current picture also imagines that the black holes grow in size as their host galaxy evolves, perhaps because galaxy evolution includes accretion triggered, for example, by galaxy mergers. This general picture has been substantiated by two lines of data.

    The peak epoch of black hole accretion can be measured by observations of nuclear activity, and coincides with the peak epoch of star formation in the universe about ten billion years after the big bang. Star formation is associated with disruptions that stir up the gas and induce accretion. Moreover, the local universe shows a tight correlation between SMBH mass, host galaxy bulge mass, and the spread of stellar velocities. These methods (but with weaker confirmation) can similarly estimate the sizes of SMBH in galaxies in the earlier universe, and find that SMBH growth and galaxy growth are co-evolutionary processes. Indeed, it seems the processes may regulate each other over time to produce the galaxy and SMBH sizes we observe today.

    Both central black hole growth and star formation are fed by the abundance of molecular gas and dust that can be traced by the infrared emitted by the dust.

    Dust grains, heated by the radiation from young stars and AGN accretion, emit strongly in the infrared. Since AGN activity also produces X-rays, the expectation is that AGN should track strong dust emission and that X-ray and infrared emission should be correlated.

    CfA astronomer Mojegan Azadi was a member of a team that examined 703 galaxies with active SMBH nuclei using both X-ray data from Chandra and infrared from Spitzer and Herschel, the largest sample to date making this comparison. Although the team did find a trend consistent with the infrared correlating with AGN X-ray activity over a wide range of cases, they did not find one when compared with the AGN’s infrared (not- X-ray) contributions.

    Since the AGN infrared comes largely from a dusty emitting torus around the SMBH, the difference could point to the role of the angle with which we view the torus. These results help to refine the current models of AGN activity, but the authors note that more sensitive, deeper observations should be able to sort out more clearly the physical processes associated with the AGN.

    Science paper:
    Infrared Contributions of X-Ray Selected Active Galactic Nuclei in Dusty Star-forming Galaxies
    Arianna Brown, Hooshang Nayyeri, Asantha Cooray, Jingzhe Ma, Ryan C. Hickox, and Mojegan Azadi
    The Astrophysical Journal

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

  • richardmitnick 1:45 pm on June 25, 2018 Permalink | Reply
    Tags: AGN-Active Galatic Nuclei”, , , , , Galaxy OJ 287, , , , , Super-mass-rich black hole   

    From MPG: “Close-up of a galaxy nucleus” 

    MPG bloc

    From Max Planck Gesellschaft

    June 25, 2018

    Dr. Norbert Junkes
    Press and public relations
    Max Planck Institute for Radio Astronomy, Bonn
    +49 2 28525-399

    Dr. Silke Britzen
    Max Planck Institute for Radio Astronomy, Bonn
    +49 228 525-280 sbritzen

    Dr. Christian Fendt
    Max Planck Institute for Astronomy, Heidelberg
    +49 6221 528-387

    Max Planck Institute for Radio Astronomy Bonn Germany

    Max Planck Institute for Astronomy campus Heidelberg, Baden-Württemberg, Germany

    In the centre of the galaxy OJ 287, there is one active, super-mass-rich black hole. An international research team led by Silke Britzen of the Max Planck Institute for Radio Astronomy has now discovered that the active nucleus of this galaxy generates a jet that staggers like a spinning top on a time jet on a timescale of about 22 years. With this movement called ‘precession’, the fluctuation of the radiation of OJ 287 can be explained. The discovery thus provides the key to understanding the variability in active galaxy nuclei.

    Zoom into the heart of a galaxy: artist’s impression of the central region of the active galaxy OJ 287 with a preceding jet. The precession could either be caused by a binary black hole (Inset A) or by a mis-aligned accretion disk (Inset B).
    © Axel Quetz / MPIA Heidelberg

    It took a long time to decipher the Egyptian hieroglyphs, the inscriptions of the pyramids. It finally succeeded with the help of the so-called Rosetta Stone found in 1799. This stele was inscribed with three versions of the same text – one in Ancient Egyptian using hieroglyphic script, one in Demotic script, and the bottom one in Ancient Greek. Realizing that it is the same text, the enigmatic hieroglyphs could be deciphered and translated with the help of the ancient Greek language. This discovery opened up a whole new window to understand the ancient Egyptian culture. A research team now has deciphered the jet of a galaxy which has been named the Rosetta Stone of blazars. Blazars are active galactic nuclei where a central supermassive black hole is being fed.

    The well-known galaxy OJ 287 at a distance of about 3.5 billion light years harbors at least one supermassive black hole weighing Millions to Billions of solar masses. The supermassive black hole is active and produces a jet – a plasma stream which originates in the central nuclear region of galaxies in the vicinity of the central black hole. This jet is observable at radio wavelengths. The galaxy is also a well-known target to optical astronomers. The brightness fluctuations of this galaxy in the optical regime are legendary and have been observed since the late 19th century, providing one of the longest light-curves in astronomy.

    However, despite decades of radio observations of many jet sources and many sophisticated studies, jets remained enigmatic. Traditionally, the origin of the jet brightness variations observed at radio wavelengths was attributed to the jet feeding mechanism by the central black hole system. On the other hand, the observed moving features in the jets – called knots – were attributed to shocks traveling in the jet. Researchers looked for a connection between both phenomena but this could not be done consistently so far.

    The research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn used a clever observational technique to monitor the jet of OJ 287 close to its launching site near the central black hole in precious detail. The technique of radio interferometry involves radio telescopes around the globe in order to construct a virtual monster telescope of earth size diameter that is able to zoom into the very centers of galaxies and to observe jets close to the central black hole with unprecedented resolution.

    By considering a large data set spanning a long period of time, the team has now found strong indication that both phenomena have the same origin: both types of observations can be explained by the motion of the jet only. The jet itself is precessing. Michal Zajacek, also from the MPIfR, who has done the modeling of the precession model: “The brightness variations result from the jet precession that induces a variation of the Doppler boosting when the viewing angle of the jet changes. It was really surprising when we found that not only does the jet precess, it also seems to follow a smaller nutation-like motion. The combined precession-nutation motion leads to the radio variability and can also explain some of the light flares.“

    “We realized that it is the same physical process that explains both the jet wandering in the sky and the brightness variations of the galaxy – that is the change of motion of the jet. It’s all geometry and deterministic. No magic involved, so far”, adds Silke Britzen. “This offers a unique opportunity to understand the jets and their potential origin in the immediate vicinity of the black hole. This jet really serves as Rosetta stone for us and will allow to understand jets and their active black holes much more fundamentally.”Britzen and her team are convinced that the precession-scenario can also explain the 130 years of optical flaring of this source but, as always, more data and more work is required for a final confirmation.

    A pressing question remains about the origin of the jet precession. Precession is a physical process well-known from spinning tops or the Earth itself. The rotational axis of our planet is not stable but orbiting in space with a period of 26,000 years due to the tidal influence of the Sun and the moon. For the jet precession in OJ 287 the team has indicated two possible scenarios. “We either have a system of two supermassive black holes with the disk-ejecting jet forced to wobble by tidal effects of the secondary black hole or a single black hole that is tidaly interacting with a misaligned accretion disk,” concludes Christian Fendt from the Max Planck Institute for Astronomy (MPIA) in Heidelberg.Either way, the jet of the active galaxy OJ 287 is one of the best understood jets so far and will certainly be used to decipher other extragalactic jets as well. It might even help to further unravel the enigmatic activity of supermassive black holes.

    Science papers:
    OJ287: Deciphering the “Rosetta stone of blazars”, MNRAS
    Jet precession in binary black holes Nature

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    MPG campus

    The Max Planck Society for the Advancement of Science (German: Max-Planck-Gesellschaft zur Förderung der Wissenschaften e. V.; abbreviated MPG) is a formally independent non-governmental and non-profit association of German research institutes founded in 1911 as the Kaiser Wilhelm Society and renamed the Max Planck Society in 1948 in honor of its former president, theoretical physicist Max Planck. The society is funded by the federal and state governments of Germany as well as other sources.

    According to its primary goal, the Max Planck Society supports fundamental research in the natural, life and social sciences, the arts and humanities in its 83 (as of January 2014)[2] Max Planck Institutes. The society has a total staff of approximately 17,000 permanent employees, including 5,470 scientists, plus around 4,600 non-tenured scientists and guests. Society budget for 2015 was about €1.7 billion.

    The Max Planck Institutes focus on excellence in research. The Max Planck Society has a world-leading reputation as a science and technology research organization, with 33 Nobel Prizes awarded to their scientists, and is generally regarded as the foremost basic research organization in Europe and the world. In 2013, the Nature Publishing Index placed the Max Planck institutes fifth worldwide in terms of research published in Nature journals (after Harvard, MIT, Stanford and the US NIH). In terms of total research volume (unweighted by citations or impact), the Max Planck Society is only outranked by the Chinese Academy of Sciences, the Russian Academy of Sciences and Harvard University. The Thomson Reuters-Science Watch website placed the Max Planck Society as the second leading research organization worldwide following Harvard University, in terms of the impact of the produced research over science fields.

  • richardmitnick 5:16 am on November 2, 2017 Permalink | Reply
    Tags: AGN-Active Galatic Nuclei”, , , , , New Method for Researching Activity Around Quasars and Black Holes,   

    From Universe Today: “New Method for Researching Activity Around Quasars and Black Holes” 


    Universe Today

    1 Nov , 2017
    Matt Williams

    An artist’s impression of the accretion disc around the supermassive black hole that powers an active galaxy. Credit: NASA/Dana Berry, SkyWorks Digital

    Ever since the discovery of Sagittarius A* at the center of our galaxy, astronomers have come to understand that most massive galaxies have a Supermassive Black Hole (SMBH) at their core.

    SGR A* NASA’s Chandra X-Ray Observatory

    These are evidenced by the powerful electromagnetic emissions produced at the nuclei of these galaxies – which are known as “Active Galatic Nuclei” (AGN) – that are believed to be caused by gas and dust accreting onto the SMBH.

    For decades, astronomers have been studying the light coming from AGNs to determine how large and massive their black holes are. This has been difficult, since this light is subject to the Doppler effect, which causes its spectral lines to broaden. But thanks to a new model developed by researchers from China and the US, astronomers may be able to study these Broad Line Regions (BLRs) and make more accurate estimates about the mass of black holes.

    The study, Tidally disrupted dusty clumps as the origin of broad emission lines in active galactic nuclei, recently appeared in the scientific journal Nature Astronomy. The study was led by Jian-Min Wang, a researcher from the Institute of High Energy Physics (IHEP) at the Chinese Academy of Sciences, with assistance from the University of Wyoming and the University of Nanjing.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

Compose new post
Next post/Next comment
Previous post/Previous comment
Show/Hide comments
Go to top
Go to login
Show/Hide help
shift + esc
%d bloggers like this: