The origin of the jet from the close vicinity of the central black hole of an active galaxy
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the transformation of gravity into radiation.
Active black holes produce radiation via accretion of matter forming an accretion disk surrounding the central machine. A clear signpost of actively accreting massive black holes in the central cores of galaxies are enormous jets reaching out from the galaxies centers to scales of megaparsec and thus far beyond the optically visible galaxy.
M87, the central galaxy of the Virgo cluster, is at a distance of only 17 Mpc (corresponding to 50 million light years). It is the second closest active galactic nucleus (AGN), harboring an active black hole of six billion (6 x 10^9) solar masses in its centre. M87 was the first galaxy where a jet could be identified. It was found in optical observations at the Lick observatory almost 100 years ago (“a curious straight ray … apparently connected with the nucleus by a thin line of matter”, Heber Curtis, 1918).
The jet of M87 is one of the most thoroughly studied. It shows up across the electromagnetic spectrum from radio to X-ray wavelengths. M87 was also the first radio galaxy detected at highest gamma-ray energies in the TeV range.
Despite the wealth of observational material, the connection between the accreting black hole and the radiating jet is not known so far. The research team addressed this question by investigating interferometric radio observations of M87 with the VLBA network connecting radio telescopes across the United States from Hawaii to the Virgin Islands. The observations at 15 GHz (or 2 cm wavelength) provide an angular resolution of 0.6 mas (milli-arcseconds). At a distance of 17 Mpc this corresponds to 0.05 pc or 84 Schwarzschild radii only.
More than a hundred jets of active black holes have been studied thoroughly, but only M87 allows to explore the immediate vicinity of the central black hole.
The radio data were obtained within the MOJAVE (Monitoring of Jets in Active galactic nuclei with VLBA Experiments) project. “We re-analyzed these data providing us with an insight into the complex processes connecting the jet and the accretion disk of M87”, says Silke Britzen from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, the first author of the paper. “To our knowledge, this is the first time that processes related to the launching and loading of the jet can be investigated”. Fast turbulent processes involving magnetic reconnection phenomena, similar to those observed on much smaller scales on the surface of the Sun, provide the best explanation for the observed results (see Fig. 1).
“There are good reasons to think that the surface of the accretion disk behaves similar to the surface of the Sun - bubbling hot gas with ongoing magnetic activity such as reconnection and flares”, adds Christian Fendt from the Max Planck Institute for Astronomy (MPIA) in Heidelberg, co-author in the team and an expert for jet-launching phenomena.
While close to the disk surface the small-scale magnetic structures dominate the mass loading of the jet, over long distances only the global helical magnetic field structure survives and governs the jet motion.
In the future, observations at higher frequencies and thus better resolution in the framework of the Event Horizon Telescope (EHT) project will allow to approach supermassive black holes even further. “There are only two targets which give us a chance to image the event horizon showing up as a shadow in the radio observations”, concludes Andreas Eckart from Cologne University. “The central black holes of M87 and our galaxy, the Milky Way, are very different in activity and mass, but also in distance. In both objects, however, the black hole subtends a similar angle on the sky and thus they cover similar portions of the image by a dark shadow.” Vladimir Karas (Astronomical Institute of the Czech Academy of Sciences) emphasizes that the new observational evidence for M87 can be seen as basis for follow-up work, both observational and theoretical. The immediate vicinity of the black hole is surrounded by a very interesting region called ergosphere, which however stays below the resolution limit of current telescopes.
The observations within the EHT project providing the highest angular resolution in astronomy just took place in the first two weeks of April 2017. The results from these observations could help to further refine the model presented in the paper and, more generally, our understanding of the connection between jets and supermassive black holes.
The research team comprises Silke Britzen, Christian Fendt, Andreas Eckart, and Vladimir Karas.
The Schwarzschild radius is defined as the radius of a sphere such that, if all its mass was compressed within that radius, the escape velocity from the surface of the sphere would equal the speed of light. The radius is named after Karl Schwarzschild who, in 1916, obtained the first exact solution to Einstein’s field equations for a non-rotating, spherically symmetric object.
The event horizon, in general relativity, is a boundary in spacetime beyond which events cannot affect an outside observer. The Schwarzschild radius is the radius of the event horizon surrounding a non-rotating black hole. Sgr A*’s Schwarzschild radius is 10 micro arcseconds. For M87, because of ist larger distance from Earth the event horizon appears to be smaller, between 4-7 micro arcseconds on the sky. However, the visible event horizon, affected by lensing in its own gravitational potential, is predicted to be larger. The shadow diameter is expected to be about 1 to 5 times the Schwarzschild radius.
The VLBA observations discussed here allow us to investigate the jet of M87 from about 30 Schwarzschild radii distance from the black hole to 3500 Schwarzschild radii. The VLBA (Very Long Baseline Array) of radio telescopes includes 10 radio telescopes of 25 m diameter each in the United States – from Hawaii to Virgin Islands.
A supermassive black hole in the nucleus of the galaxy M87 (the
biggest galaxy in the Virgo Cluster, 55 million light years from us).
The jet shoots out of the hot plasma region surrounding the black hole
(top left) and we can see it streaming down across the galaxy, over a
distance of 6,000 light-years. The white/purple light of the jet in this
stunning image is produced by the stream of electrons spiralling around
magnetic field lines at a speed of approximately 98% of the speed of
- Our universe is almost certainly going to die a heat death in which energy in the universe shall be spread so thinly that everything will freeze, the stars will burn out and not shall be left but eternal darkness.
- We might live in a multiverse. If in fact, we do: basic statistics shows that we may in fact be more likely than not be a computer program, living in a sort of simulated universe. Yes, there’s actual scientific research being done to figure out if we’re a hologram and others trying to make progress into multiverse theory.
Imagine the existential horror if we turned out to be the artificial intelligence of someone else’s universe!
- There are almost certainly a multitude of “rogue black holes”, secretly drifting through the Milky Way. If one were to drift into the solar system it could spell our end… that’s obvious though I’m sure.
- As many of you are aware, Earth’s been sending out signals for around a century now. The fact that these signals get exponentially weaker doesn’t mean they stop existing:
Who’s to say such signals can’t be detected by some advanced-and-none-too-benevolent extraterrestrial civilization?
After all, we astronomers regularly tout our exponential advancements in the search for extraterrestrial life. Maybe next time you see that light moving against a backdrop of stars it… never mind. It couldn’t possibly be…
- Certain galaxies, like M87, emit jets of matter at near the speed of light. The high amounts of energy speeding out of these galaxies could, in some cases, end life in any solar system it were to point at:
I hope all the stars above you still seem pleasant!
I’m not necessarily advocating in favor of any of these events and don’t necessarily think any of them are likely but for each item above, there are astrophysicists who do…
Virgo Cluster Galaxies : Well over a thousand galaxies are known members of the Virgo Cluster, the closest large cluster of galaxies to our own local group. In fact, the galaxy cluster is difficult to appreciate all at once because it covers such a large area on the sky. This careful wide-field mosaic of telescopic images clearly records the central region of the Virgo Cluster through faint foreground dust clouds lingering above the plane of our own Milky Way galaxy. The cluster’s dominant giant elliptical galaxy M87, is just below and to the left of the frame center. To the right of M87 is a string of galaxies known as Markarian’s Chain. A closer examination of the image will reveal many Virgo cluster member galaxies as small fuzzy patches. Sliding your cursor over the image will label the larger galaxies using NGC catalog designations. Galaxies are also shown with Messier catalog numbers, including M84, M86, and prominent colorful spirals M88, M90, and M91. On average, Virgo Cluster galaxies are measured to be about 48 million light-years away. The Virgo Cluster distance has been used to give an important determination of the Hubble Constant and the scale of the Universe. via NASA
Record massive black holes discovered lurking in monster galaxies
An artist’s concept of stars moving in the central regions of a giant elliptical galaxy that harbors a supermassive black hole.
University of California, Berkeley, astronomers have discovered the largest black holes to date ‑- two monsters with masses equivalent to 10 billion suns that are threatening to consume anything, even light, within a region five times the size of our solar system.
These black holes are at the centers of two galaxies more than 300 million light years from Earth, and may be the dark remnants of some of the very bright galaxies, called quasars, that populated the early universe.
“In the early universe, there were lots of quasars or active galactic nuclei, and some were expected to be powered by black holes as big as 10 billion solar masses or more,” said Chung-Pei Ma, UC Berkeley professor of astronomy. “These two new supermassive black holes are similar in mass to young quasars, and may be the missing link between quasars and the supermassive black holes we see today.”
Black holes are dense concentrations of matter that produce such strong gravitational fields that even light cannot escape. While exploding stars, called supernovas, can leave behind black holes the mass of a single star like the sun, supermassive black holes have presumably grown from the merger of other black holes or by capturing huge numbers of stars and massive amounts of gas.
“These black holes may shed light on how black holes and their surrounding galaxies have nurtured each other since the early universe,” said UC Berkeley graduate student Nicholas McConnell, first author of a paper on the discovery published in the Dec. 8, 2011 issue of the British journal Nature by McConnell, Ma and their colleagues.
To date, approximately 63 supermassive black holes have been found sitting in the cores of nearby galaxies. The largest for more than three decades was a 6.3 billion solar mass black hole in the center of the nearby galaxy M87.
One of the newly discovered black holes is 9.7 billion solar masses and located in the elliptical galaxy NGC 3842, the brightest galaxy in the Leo cluster of galaxies, 320 million light years away in the direction of the constellation Leo. The second is as large or larger and sits in the elliptical galaxy NGC 4889, the brightest galaxy in the Coma cluster about 336 million light years from Earth in the direction of the constellation Coma Berenices.
According to McConnell, these black holes have an event horizon – the “abandon all hope” edge from which not even light can escape – that is 200 times the orbit of Earth, or five times the orbit of Pluto. Beyond the event horizon, each black hole has a gravitational influence that would extend over a sphere 4,000 light years across.
“For comparison, these black holes are 2,500 times as massive as the black hole at the center of the Milky Way Galaxy, whose event horizon is one fifth the orbit of Mercury,” McConnell said.
These 10 billion solar mass black holes have remained hidden until now, presumably because they are living in quiet retirement, Ma said. During their active quasar days some 10 billion years ago, they cleared out the neighborhood by swallowing vast quantities of gas and dust. The surviving gas became stars that have since orbited peacefully. According to Ma, these monster black holes, and their equally monster galaxies that likely contain a trillion stars, settled into obscurity at the center of galaxy clusters.
NGC 3842 (upper left) is the brightest galaxy in a rich cluster of galaxies. The black hole at its center (shown in middle as artist’s concept) is surrounded by stars distorted by its immense gravitational field. The black hole, which is seven times larger than Pluto’s orbit, would dwarf our solar system (inset).
Astronomers believe that many, if not all, galaxies have a massive black hole at the center, with the larger galaxies harboring larger black holes. The largest black holes are found in elliptical galaxies, which are thought to result from the merger of two spiral galaxies. Ma found, however, that mergers of elliptical galaxies themselves could produce the largest elliptical galaxies as well as supermassive black holes approaching 10 billion solar masses. These black holes can grow even larger by consuming gas left over from a merger.
Using telescopes at the Gemini and Keck observatories in Hawaii and at McDonald Observatory in Texas, McConnell and Ma obtained detailed spectra of the diffuse starlight at the centers of several massive elliptical galaxies, each the brightest galaxy in its cluster. So far, they’ve analyzed the orbital velocities of stars in two galaxies and calculated the central masses to be in the quasar range. Having such huge masses contained within a volume only a few hundred light years across led the astronomers to conclude that the masses were massive black holes.
“If all that mass were in stars, then we would see their light”, Ma said.
Modeling these massive galaxies required use of state-of-the-art supercomputers at the Texas Advanced Computing Center.
“For an astronomer, finding these insatiable black holes is like finally encountering people nine feet tall, whose great height had only been inferred from fossilized bones. How did they grow so large?” Ma said. “This rare find will help us understand whether these black holes had very tall parents or ate a lot of spinach.”