The response of relativistic outflowing gas to the inner accretion disk of a black hole
Nature 543, 7643 (2017). doi:10.1038/nature21385
Authors: Michael L. Parker, Ciro Pinto, Andrew C. Fabian, Anne Lohfink, Douglas J. K. Buisson, William N. Alston, Erin Kara, Edward M. Cackett, Chia-Ying Chiang, Thomas Dauser, Barbara De Marco, Luigi C. Gallo, Javier Garcia, Fiona A. Harrison, Ashley L. King, Matthew J. Middleton, Jon M. Miller, Giovanni Miniutti, Christopher S. Reynolds, Phil Uttley, Ranjan Vasudevan, Dominic J. Walton, Daniel R. Wilkins & Abderahmen Zoghbi
The brightness of an active galactic nucleus is set by the gas falling onto it from the galaxy, and the gas infall rate is regulated by the brightness of the active galactic nucleus; this feedback loop is the process by which supermassive black holes in the centres of galaxies may moderate the growth of their hosts. Gas outflows (in the form of disk winds) release huge quantities of energy into the interstellar medium, potentially clearing the surrounding gas. The most extreme (in terms of speed and energy) of these—the ultrafast outflows—are the subset of X-ray-detected outflows with velocities higher than 10,000 kilometres per second, believed to originate in relativistic (that is, near the speed of light) disk winds a few hundred gravitational radii from the black hole. The absorption features produced by these outflows are variable, but no clear link has been found between the behaviour of the X-ray continuum and the velocity or optical depth of the outflows, owing to the long timescales of quasar variability. Here we report the observation of multiple absorption lines from an extreme ultrafast gas flow in the X-ray spectrum of the active galactic nucleus IRAS 13224−3809, at 0.236 ± 0.006 times the speed of light (71,000 kilometres per second), where the absorption is strongly anti-correlated with the emission of X-rays from the inner regions of the accretion disk. If the gas flow is identified as a genuine outflow then it is in the fastest five per cent of such winds, and its variability is hundreds of times faster than in other variable winds, allowing us to observe in hours what would take months in a quasar. We find X-ray spectral signatures of the wind simultaneously in both low- and high-energy detectors, suggesting a single ionized outflow, linking the low- and high-energy absorption lines. That this disk wind is responding to the emission from the inner accretion disk demonstrates a connection between accretion processes occurring on very different scales: the X-ray emission from within a few gravitational radii of the black hole ionizing the disk wind hundreds of gravitational radii further away as the X-ray flux rises.
Astrophysics: Supernova clues from neutrinos
Nature 543, 7643 (2017). doi:10.1038/543008b
Neutrinos detected by Earth-based observatories could one day help to reveal the sequence of events that occur in supernovae.When a white-dwarf star becomes too massive to support itself, the internal pressure is thought to trigger a runaway thermonuclear reaction followed by an explosion —
Outflowing gas is a common features of the supermassive black holes that reside at the centre of large galaxies. Often millions of times more massive than the Sun, these black holes feed off the surrounding gas that swirls around them. Space telescopes observe this as a bright light from the innermost part of the disc around the black hole.
Occasionally the black holes consume too much gas and release an ultra-fast wind. These winds are an important characteristic to study because they could have a strong influence on regulating the growth of the host galaxy by clearing the surrounding gas away and therefore suppressing the birth of stars.
Using ESA’s XMM-Newton and NASA’s NuStar telescopes, scientists have now made the most detailed observation yet of such an outflow. The winds recorded from the black hole reach 71,000 km/s – a quarter of the speed of light – putting it in the top 5% of fastest known black hole winds.
XMM-Newton focused on the black hole for 17 consecutive days, revealing the extremely variable nature of the winds.
“We often only have one observation of a particular object, then several months or even years later we observe it again and see if there’s been a change,” says Dr Michael Parker of the Institute of Astronomy at the University of Cambridge, UK, lead author on a paper published in Nature this week which describes the discovery.
“Thanks to this long observation campaign, we observed changes in the winds on a timescale of less than an hour for the first time.”
The changes were seen in the increasing temperature of the winds, a signature of their response to greater X-ray emission from the disc right next to the black hole.
Furthermore, the observations also revealed changes to the chemical fingerprints of the outflowing gas: as the X-ray emission increased, it stripped electrons in the wind from their atoms, erasing the wind signatures seen in the data.
“The chemical fingerprints of the wind changed with the strength of the X-rays in less than an hour, hundreds of times faster than ever seen before,” says co-author Professor Andrew Fabian, also from the Institute of Astronomy, and principal investigator on the project.
“It allows us to link the X-ray emission arising from the material falling into the black hole, to the variability of the outflowing wind farther away.”
Dr Parker adds: “Black hole winds are one of the mechanisms for feedback, where the energy coming out from the black hole regulates the growth of the host galaxy. Understanding these winds is crucial to understanding how galaxies, including our own, grow.”
Michael Parker et al: "The response of relativistic outflowing gas to the inner accretion disk of a black hole" Nature 2 March 2017
Adapted from a press release by the European Space Agency
Astronomers have made the most detailed observation yet of an ultra-fast wind emanating from a Black Hole at a quarter of the speed of light. Using the European Space Agency (ESA)’s XMM-Newton and NASA’s NuSTAR telescopes, the scientists observed the phenomenon in an active galaxy known as IRAS 13224-3809.Understanding these winds is crucial to understanding how galaxies, including our own, growDr Michael ParkerEuropean Space Agency (ESA)Artist's impression of the winds emanating from the supermassive black hole
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