Two telescopes — one on the ground and one in space — watched a black hole’s jet turn on, enabling astronomers to probe its origin.

Black hole accretion disk + jet
This artist's concept shows a black hole with hot gas spiraling into it via an accretion disk. Magnetic field lines fling a minute amount of this material into an ultrafast jet that shoots out into space.
NASA / JPL-Caltech

Maybe when you were little, you devised a secret code, such as replacing A with 1, B with 2, and so on. Astronomers use a similar principle to decode the intense environments around gas-guzzling black holes, using different wavelengths to probe what they cannot see directly (at least, not yet).

Radio waves, for example, arise from the powerful jets that the black hole sends shooting outward into space, while X-rays originate in superhot plasma, called the corona, closer to the black hole. As for visible light — well, those photons could come from just about anywhere, and that’s what makes the code hard to break.

Now, astronomers have taken a major step in solving the code, using visible light and X-rays to paint a picture of V404 Cygni, a black hole-star binary system, even though it remains a blur in even the best current telescopes. The results appear in Nature Astronomy (full text available here).

Poshak Gandhi (University of Southampton, UK) and colleagues employed NASA’s NUSTAR X-ray satellite and ULTRACAM, a super-fast (28 frames per second) camera attached to the William Herschel Telescope in La Palma, Spain, to track emissions from V404 Cygni. The black hole, nine times the mass of the Sun, pulls away gas from its K-class stellar companion as they whip around each other every 6½ days. The result is a violently variable system that flares frequently across the electromagnetic spectrum. In June 2015 the whole system underwent an outburst, the brightest seen in the 21st century.

Astronomers have monitored visible-light variability from black hole systems before, but it’s difficult to track where the photons are coming from — they could arise in the gaseous disk that feeds the black hole, the stellar companion that feeds the disk, or the jets that the black hole-disk system powers.

But the use of X-ray data breaks that ambiguity. Precisely timing changes is critical: the ULTRACAM uses GPS to time-stamp images with an accuracy of about a thousandth of a second (1 millisecond), which was calibrated using observations of the Crab pulsar. NUSTAR gives time measurements of similar accuracy using an onboard crystal oscillator, which is adjusted during contact with ground stations.

On June 25, 2015, the team began observing the system with coordinated observations using both instruments. Low-energy X-rays dominated the source’s spectrum, and the radio emissions indicated no jet was present. After half an hour, NUSTAR had to stop observing for a brief period as Earth passed between it and V404 Cygni. When the space telescope resumed its observations, it was clear something dramatic had happened: high-energy X-rays now dominated, and radio emissions indicated that the plasma jet had turned on.

By exactly timing incoming X-rays and visible photons, Gandhi and colleagues discovered that visible-light flashes were trailing X-ray flares by just 0.1 second. So the visible-emitting region couldn’t lie far from the X-ray corona — the photons had to come from the jet.

This data paints a clear picture of what’s happening in V404 Cygni: Gas stolen from the companion star mostly feeds the black hole, but strong magnetic fields fling some of it away into a superheated, X-ray-emitting corona. This region may serve as the base of the black hole’s jet. The gas then accelerates, flowing 19,000 miles downstream along the jet, where it radiates visible light.

Jet launch and acceleration
These three stills from an animation show the launch and acceleration of a blob of plasma down the jet (first frame), its travel downstream (second frame), and its passage through a standing shock, where it brightens again. The full animation may be download in .mov format here.
Cosmovision / W. Steffen

Gandhi had previously studied another stellar-mass black hole, GX 339-4, which displays a similar 0.1-second delay between X-ray and visible-light flares.

The region that lies between the corona and the visible-light between the the X-rays and the visible light is critical to understanding jets — this is the unseen region where plasma accelerates by as-yet unknown means. "Astronomers hope to refine models for jet-powering mechanisms using the results of this study," said study coauthor Daniel Stern (NASA JPL).

The results mesh nicely with previous studies of the supermassive black holes BL Lacertae and PKS 1510-089, says Alan Marscher (Boston University). Even though these black holes are millions of times more massive than V404 Cygni, the distance between their X-ray-emitting and visible-emitting regions is the same if you take the differing masses into account.

But that doesn’t hold true for all objects — the supermassive black hole at the center of the galaxy M87, for example, appears to defy the rule. The devil, it appears, still lies in the details of our understanding of black holes and their jets.


Image of xinhangshen


November 10, 2017 at 5:01 pm

As I have pointed out before that Einstein's relativity has been disproved both theoretically and experimentally, light and electromagnetic waves are waves of aether - a compressible viscous fluid filling up the entire visible part of the universe. With the existence of aether, it is easy to understand the phenomenon: the jets from high density massive celestial objects (not mathematical singularities) are pushed out by the pressure of aether which are displaced by heavier dusts attracted to the celestial objects. We can also understand many other phenomena: stars in galaxies are bound by the extra gravitation from the mass of aether (not mysterious "dark matter"), galaxies moving away from each other acceleratingly are pushed by the pressure of aether (not ridiculous "dark energy"); light bending around massive celestial objects is caused by the higher density and/or velocity of aether around the objects, the rotation of the surface of the sun much slower than its core is caused by the friction of aether around the sun; the phenomenon of moving electrons emitting light is the result of the velocities of the electrons relative to aether just like a boat generating waves when it moves relative to the water, double slit interference is the result of the interference of aether waves (not waves of "probability") generated by the particles which exerts non-uniform forces on the particles to form stripes of landing spots, etc. Because of the missing of the effects of aether, quantum mechanics is also a wrong theory.

You must be logged in to post a comment.

Image of Kim-Boriskin


November 11, 2017 at 9:20 pm

You should get in touch with Robert Oldershaw. He fully supports relativity (both general and special), but keeps telling us that the standard models of astronomy, especially dark matter, and particle physics are all wrong, and he has the real answers. Between the two of you you should be able to get all of physics on all scales completely straightened out.

You must be logged in to post a comment.

Image of

November 10, 2017 at 6:35 pm

ULTRACAM is on the William Herschel Telescope. See

"Astronomers have new clues to this mystery. Using NASA's NuSTAR space telescope and a fast camera called ULTRACAM on the William Herschel Observatory in La Palma, Spain, scientists have been able to measure the distance that particles in jets travel before they "turn on" and become bright sources of light. This distance is called the "acceleration zone." The study is published in the journal Nature Astronomy."

You must be logged in to post a comment.

Image of philip-gardner


November 11, 2017 at 4:04 am

A "superfast" camera is not 28 frames/minute? /sec?? or higher?? PG

You must be logged in to post a comment.

Image of Monica Young

Monica Young

November 13, 2017 at 1:10 pm

Apologies for the mis-type! That should say 28 frames per second, and I've changed the text accordingly.

You must be logged in to post a comment.

Image of Monica Young

Monica Young

November 13, 2017 at 1:12 pm

You're right, of course - while the Very Large Telescope has its own ULTRACAM, the ULTRACAM observations used for this research were carried out on the William Herschel Telescope. I've corrected the text.

You must be logged in to post a comment.

Image of PeteDeGraff


November 12, 2017 at 10:01 pm

Monica, how in the world do you put up with these monkeys?
Aether? Quantum Mechanics is wrong too?
Measuring light or x-rays from something nearly 8,000ly distant can be done faster than 28 times per minute?
Carry on, love. You're doing a Great job!

You must be logged in to post a comment.

You must be logged in to post a comment.