beecee Posted June 14, 2018 Share Posted June 14, 2018 https://phys.org/news/2018-06-black-hole-clouds-puzzling-features.html One black hole or two? Dust clouds can explain puzzling features of active galactic nuclei: Researchers at the University of California, Santa Cruz (UCSC), believe clouds of dust, rather than twin black holes, can explain the features found in active galactic nuclei (AGNs). The team publish their results today (14 June) in a paper in Monthly Notices of the Royal Astronomical Society. Many large galaxies have an AGN, a small bright central region powered by matter spiralling into a supermassive black hole. When these black holes are vigorously swallowing matter, they are surrounded by hot, rapidly-moving gas known as the "broad-line region" (so-called because the spectral lines from this region are broadened by the rapid motion of the gas). The emission from this gas is one of the best sources of information about the mass of the central black hole and how it is growing. The nature of this gas is however poorly understood; in particular there is less emission than expected from gas moving at certain velocities. The breakdown of simple models has led some astrophysicists to think that many AGNs might have not one but two black holes in them. Read more at: https://phys.org/news/2018-06-black-hole-clouds-puzzling-features.html#jCp LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL the paper: https://academic.oup.com/mnras/article/478/2/1660/4961154 Partial dust obscuration in active galactic nuclei as a cause of broad-line profile and lag variability, and apparent accretion disc inhomogeneities Abstract The profiles of the broad emission lines of active galactic nuclei (AGNs) and the time delays in their response to changes in the ionizing continuum (lags) give information about the structure and kinematics of the inner regions of AGNs. Line profiles are also our main way of estimating the masses of the supermassive black holes (SMBHs). However, the profiles often show ill-understood, asymmetric structure and velocity-dependent lags vary with time. Here, we show that partial obscuration of the broad-line region (BLR) by outflowing, compact, dusty clumps produces asymmetries and velocity-dependent lags similar to those observed. Our model explains previously inexplicable changes in the ratios of the hydrogen lines with time and velocity, the lack of correlation of changes in line profiles with variability of the central engine, the velocity dependence of lags, and the change of lags with time. We propose that changes on time-scales longer than the light-crossing time do not come from dynamical changes in the BLR, but are a natural result of the effect of outflowing dusty clumps driven by radiation pressure acting on the dust. The motion of these clumps offers an explanation of long-term changes in polarization. The effects of the dust complicate the study of the structure and kinematics of the BLR and the search for sub-parsec SMBH binaries. Partial obscuration of the accretion disc can also provide the local fluctuations in luminosity that can explain sizes deduced from microlensing. Link to comment Share on other sites More sharing options...
T. McGrath Posted June 15, 2018 Share Posted June 15, 2018 Since they are talking about hot ionized gas, shouldn't they be calling it plasma? I suppose I should be happy they are referring to it as an "active galactic nuclei" and not a "quasar" or "blazar" from the 1960s, before we knew what they were. Which many still do. I was very surprised by the outflow being measured at only a few thousands of kilometers per second. That close to the event horizon I was expecting much faster relativistic speeds. I was expecting closer to supernovae speeds (10,000 km/s), or even faster since the plasma is only a few light-days away from the event horizon. They made some really nice observations. Thanks for sharing. Link to comment Share on other sites More sharing options...
beecee Posted June 15, 2018 Author Share Posted June 15, 2018 (edited) 1 hour ago, T. McGrath said: Since they are talking about hot ionized gas, shouldn't they be calling it plasma? I suppose I should be happy they are referring to it as an "active galactic nuclei" and not a "quasar" or "blazar" from the 1960s, before we knew what they were. Which many still do. I was very surprised by the outflow being measured at only a few thousands of kilometers per second. That close to the event horizon I was expecting much faster relativistic speeds. I was expecting closer to supernovae speeds (10,000 km/s), or even faster since the plasma is only a few light-days away from the event horizon. They made some really nice observations. Thanks for sharing. No probs...Your comment re AGN and Quazars/Blazars are differentiated by the fact that from Earth, Quazars/Blazars are orientated in such a way that we are receiving the immense radio signals from polar jets that are aligned pointing towards the Earth, from an obvious "point like" object from our perspective.. The term Quazar actually arose before AGN, and the first was discovered by Jocylin Bell and named 3c273. From memory she was an "post graduate" ? yet it was her senior Professor Hewish that received the Nobel for that momentous discovery. Hmmm, Imagine the outcry if that had of occurred today! Edited June 15, 2018 by beecee Link to comment Share on other sites More sharing options...
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