Physicists discover first “black hole triple”

Depicted in this artist’s rendering is the central black hole, V404 Cygni (black dot), in the process of consuming a nearby star (orange body at left), while a second star (upper white flash) orbits at a much farther distance. Credits: Image: Jorge Lugo

System observed 8,000 light-years away may be the first direct evidence of “gentle” black hole formation.

Many black holes detected to date appear to be part of a pair. These binary systems comprise a black hole and a secondary object — such as a star, a much denser neutron star, or another black hole — that spiral around each other, drawn together by the black hole’s gravity to form a tight orbital pair.

Now a surprising discovery is expanding the picture of black holes, the objects they can host, and the way they form.

In a study appearing today in Nature, physicists at MIT and Caltech report that they have observed a “black hole triple” for the first time. The new system holds a central black hole in the act of consuming a small star that’s spiraling in very close to the black hole, every 6.5 days — a configuration similar to most binary systems. But surprisingly, a second star appears to also be circling the black hole, though at a much greater distance. The physicists estimate this far-off companion is orbiting the black hole every 70,000 years.

That the black hole seems to have a gravitational hold on an object so far away is raising questions about the origins of the black hole itself. Black holes are thought to form from the violent explosion of a dying star — a process known as a supernova, by which a star releases a huge amount of energy and light in a final burst before collapsing into an invisible black hole.

The team’s discovery, however, suggests that if the newly-observed black hole resulted from a typical supernova, the energy it would have released before it collapsed would have kicked away any loosely bound objects in its outskirts. The second, outer star, then, shouldn’t still be hanging around.

Instead, the team suspects the black hole formed through a more gentle process of “direct collapse,” in which a star simply caves in on itself, forming a black hole without a last dramatic flash. Such a gentle origin would hardly disturb any loosely bound, faraway objects.

Because the new triple system includes a very far-off star, this suggests the system’s black hole was born through a gentler, direct collapse. And while astronomers have observed more violent supernovae for centuries, the team says the new triple system could be the first evidence of a black hole that formed from this more gentle process.

“We think most black holes form from violent explosions of stars, but this discovery helps call that into question,” says study author Kevin Burdge, a Pappalardo Fellow in the MIT Department of Physics. “This system is super exciting for black hole evolution, and it also raises questions of whether there are more triples out there.”

The study’s co-authors at MIT are Erin Kara, Claude Canizares, Deepto Chakrabarty, Anna Frebel, Sarah Millholland, Saul Rappaport, Rob Simcoe, and Andrew Vanderburg, along with Kareem El-Badry at Caltech.

Tandem motion

The discovery of the black hole triple came about almost by chance. The physicists found it while looking through Aladin Lite, a repository of astronomical observations, aggregated from telescopes in space and all around the world. Astronomers can use the online tool to search for images of the same part of the sky, taken by different telescopes that are tuned to various wavelengths of energy and light.

The team had been looking within the Milky Way galaxy for signs of new black holes. Out of curiosity, Burdge reviewed an image of V404 Cygni — a black hole about 8,000 light years from Earth that was one of the very first objects ever to be confirmed as a black hole, in 1992. Since then, V404 Cygni has become one of the most well-studied black holes, and has been documented in over 1,300 scientific papers. However, none of those studies reported what Burdge and his colleagues observed.

As he looked at optical images of V404 Cygni, Burdge saw what appeared to be two blobs of light, surprisingly close to each other. The first blob was what others determined to be the black hole and an inner, closely orbiting star. The star is so close that it is shedding some of its material onto the black hole, and giving off the light that Burdge could see. The second blob of light, however, was something that scientists did not investigate closely, until now. That second light, Burdge determined, was most likely coming from a very far-off star.

“The fact that we can see two separate stars over this much distance actually means that the stars have to be really very far apart,” says Burdge, who calculated that the outer star is 3,500 astronomical units (AU) away from the black hole (1 AU is the distance between the Earth and sun). In other words, the outer star is 3,500 times father away from the black hole as the Earth is from the sun. This is also equal to 100 times the distance between Pluto and the sun.

The question that then came to mind was whether the outer star was linked to the black hole and its inner star. To answer this, the researchers looked to Gaia, a satellite that has precisely tracked the motions of all the stars in the galaxy since 2014. The team analyzed the motions of the inner and outer stars over the last 10 years of Gaia data and found that the stars moved exactly in tandem, compared to other neighboring stars. They calculated that the odds of this kind of tandem motion are about one in 10 million.

“It’s almost certainly not a coincidence or accident,” Burdge says. “We’re seeing two stars that are following each other because they’re attached by this weak string of gravity. So this has to be a triple system.”

Pulling strings

How, then, could the system have formed? If the black hole arose from a typical supernova, the violent explosion would have kicked away the outer star long ago.

“Imagine you’re pulling a kite, and instead of a strong string, you’re pulling with a spider web,” Burdge says. “If you tugged too hard, the web would break and you’d lose the kite. Gravity is like this barely bound string that’s really weak, and if you do anything dramatic to the inner binary, you’re going to lose the outer star.”

To really test this idea, however, Burdge carried out simulations to see how such a triple system could have evolved and retained the outer star.

At the start of each simulation, he introduced three stars (the third being the black hole, before it became a black hole). He then ran tens of thousands of simulations, each one with a slightly different scenario for how the third star could have become a black hole, and subsequently affected the motions of the other two stars. For instance, he simulated a supernova, varying the amount and direction of energy that it gave off. He also simulated scenarios of direct collapse, in which the third star simply caved in on itself to form a black hole, without giving off any energy.

“The vast majority of simulations show that the easiest way to make this triple work is through direct collapse,” Burdge says.

In addition to giving clues to the black hole’s origins, the outer star has also revealed the system’s age. The physicists observed that the outer star happens to be in the process of becoming a red giant — a phase that occurs at the end of a star’s life. Based on this stellar transition, the team determined that the outer star is about 4 billion years old. Given that neighboring stars are born around the same time, the team concludes that the black hole triple is also 4 billion years old.

“We’ve never been able to do this before for an old black hole,” Burdge says. “Now we know V404 Cygni is part of a triple, it could have formed from direct collapse, and it formed about 4 billion years ago, thanks to this discovery.”

This work was supported, in part, by the National Science Foundation.

Jennifer Chu | MIT News

Source: Massachusetts Institute of Technology

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'Listen' to the Light Echoes From a Black Hole Quick Look: 'Listen' to the Light Echoes From a Black Hole

V404 Cygni

Credit X-ray: Chandra: NASA/CXC/U.Wisc-Madison/S. Heinz et al.; Swift: NASA/Swift/Univ. of Leicester/A. Beardmore; Optical: DSS; Sonification: NASA/CXC/SAO/K.Arcand, SYSTEM Sounds (M. Russo, A. Santaguida)

JPEG (365.2 kb) - Large JPEG (7.9 MB) - Tiff (106.4 MB) - More Images

A Quick Look at V404 Cygni - More Animations

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One of the surprising features of black holes is that although light (such as radio, visible, and X-rays) cannot escape from them, surrounding material can produce intense bursts of electromagnetic radiation. As they travel outward, these blasts of light can bounce off clouds of gas and dust in space, similar to how light beams from a car’s headlight will scatter off fog.

A new sonification turns these “light echoes” from the black hole called V404 Cygni into sound. Located about 7,800 light-years from Earth, V404 Cygni is a system that contains a black hole, with a mass between five and 10 times the Sun’s, that is pulling material from a companion star in orbit around it. The material is funneled into a disk that encircles the stellar-mass black hole.

This material periodically generates bursts of radiation, including X-rays. As the X-rays travel outward they encounter clouds of gas and dust in between V404 Cygni and Earth and are scattered at various angles. NASA’s Chandra X-ray Observatory and Neil Gehrels Swift Observatory have imaged the X-ray light echoes around V404 Cygni. Because astronomers know exactly how fast light travels and have determined an accurate distance to this system, they can calculate when these eruptions occurred. This data, plus other information, helps astronomers learn more about the dust clouds, including their composition and distances.

Illustration showing how the rings seen by Chandra were produced
Credit: Univ. of Wisconsin-Madison/S.Heinz

The sonification of V404 Cygni translates the X-ray data from both Chandra and Swift into sound. During the sonification, the cursor moves outward from the center of the image in a circle. As it passes through the light echoes detected in X-rays (seen as concentric rings in blue by Chandra and red by Swift in the image), there are tick-like sounds and changes in volume to denote the detection of X-rays and the variations in brightness. To differentiate between the data from the two telescopes, Chandra data is represented by higher-frequency tones while the Swift data is lower. In addition to the X-rays, the image includes optical data from the Digitized Sky Survey that shows background stars. Each star in optical light triggers a musical note. The volume and pitch of the note are determined by the brightness of the star.

V404 Cygnus Sonification (Wavelengths) (104 mb)

More sonifications of astronomical data, as well as additional information on the process, can be found at the "A Universe of Sound" website:https://chandra.si.edu/sound/

These sonifications were led by the Chandra X-ray Center (CXC) and included as part of NASA's Universe of Learning (UoL) program. The collaboration was driven by visualization scientist Kimberly Arcand (CXC), astrophysicist Matt Russo, and musician Andrew Santaguida (both of the SYSTEM Sounds project). NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science from Cambridge Massachusetts and flight operations from Burlington, Massachusetts. NASA's Universe of Learning materials are based upon work supported by NASA under cooperative agreement award number NNX16AC65A to the Space Telescope Science Institute, working in partnership with Caltech/IPAC, Center for Astrophysics | Harvard & Smithsonian, and the Jet Propulsion Laboratory.

Quick Look: 'Listen' to the Light Echoes From a Black Hole

Source: NASA’s Chandra X-ray Observatory

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Fast Facts for V404 Cygni:

About the Sound:

• This is an inside-out scan of the light echo rings formed by dust scattering and the background stars.
• Dust scattering rings
• The sound is generated by a series of tick-like sounds. The volume and density of ticks is controlled by the ring brightness.
• Listening to the pattern of rings in this way traces the density of dust clouds that the light has scattered off of on its way towards Earth.
• The sound generated by the Swift X-ray data is represented as lower frequencies.
• The Chandra X-ray data represents higher frequency light and its corresponding sound is limited to higher frequencies.
• Background stars (DSS Optical data)
• Each visible light star triggers a musical note. The volume and pitch of the note are determined by the brightness of the star. Brighter stars are louder and higher pitched.

Scale: Image is about 35 arcmin (80 light-years) across.
Category: Black Holes
Coordinates (J2000): RA 20h 24m 03s | Dec +33° 52´ 02"
Constellation: Cygnus
Observation Date: 2 observations: July 13th and 29th, 2015
Observation Time: 18 hours 51 minutes
Obs. ID: 17701, 17704
Instrument: ACIS
References: Heinz, S., et al., ApJ, 2016, 825, 15; arXiv:1605.01648
Color Code: X-ray: Chandra: blue & teal, Swift: red, green, blue; Optical: red, green blue
Distance Estimate: About 7,800 light-years

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Huge Rings Around a Black Hole

V404 Cygni
Image Credit X-ray: NASA/CXC/U.Wisc-Madison/S. Heinz et al.; Optical/IR: Pan-STARR

This image features a spectacular set of rings around a black hole, captured using NASA's Chandra X-ray Observatory and Neil Gehrels Swift Observatory. The X-ray images of the giant rings reveal information about dust located in our galaxy, using a similar principle to the X-rays performed in doctor's offices and airports.

The black hole is part of a binary system called V404 Cygni, located about 7,800 light years away from Earth. The black hole is actively pulling material away from a companion star — with about half the mass of the Sun — into a disk around the invisible object. This material glows in X-rays, so astronomers refer to these systems as "X-ray binaries."

Editor: Yvette Smith

Source: NASA/Black Holes

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Huge Rings Around a Black Hole

V404 Cygni

Image credit: X-ray: NASA/CXC/U.Wisc-Madison/S. Heinz et al.; 

Optical/IR: Pan-STARRS

A spectacular set of rings around a black hole has been captured using NASA's Chandra X-ray Observatory and Neil Gehrels Swift Observatory. The X-ray images of the giant rings have revealed new information about dust located in our Galaxy, using a similar principle to the X-rays performed in doctor's offices and airports.

The black hole is part of a binary system called V404 Cygni, located about 7,800 light-years away from Earth. The black hole is actively pulling material away from a companion star — with about half the mass of the Sun — into a disk around the invisible object. This material glows in X-rays, so astronomers refer to these systems as "X-ray binaries."

On June 5 2015, Swift discovered a burst of X-rays from V404 Cygni. The burst created the high-energy rings from a phenomenon known as light echoes. Instead of sound waves bouncing off a canyon wall, the light echoes around V404 Cygni were produced when a burst of X-rays from the black hole system bounced off of dust clouds between V404 Cygni and Earth. Cosmic dust is not like household dust but is more like smoke, and consists of tiny, solid particles.

In a new composite image, X-rays from Chandra (light blue) have been combined with optical data from the Pan-STARRS telescope on Hawaii that show the stars in the field of view. The image contains eight separate concentric rings. Each ring is created by X-rays from V404 Cygni flares observed in 2015 that reflect off different dust clouds. (An artist's illustration explains how the rings seen by Chandra and Swift were produced. To simplify the graphic, the illustration shows only four rings instead of eight.)

The team analyzed 50 Swift observations made in 2015 between June 30 and August 25. Chandra observed the system on July 11 and 25. It was such a bright event that the operators of Chandra purposely placed V404 Cygni in between the detectors so that another bright burst would not damage the instrument.

The rings tell astronomers not only about the black hole's behavior, but also about the landscape between V404 Cygni and Earth. For example, the diameter of the rings in X-rays reveals the distances to the intervening dust clouds the light ricocheted off. If the cloud is closer to Earth, the ring appears to be larger and vice versa. The light echoes appear as narrow rings rather than wide rings or haloes because the X-ray burst lasted only a relatively short period of time.

The researchers also used the rings to probe the properties of the dust clouds themselves. The authors compared the X-ray spectra — that is, the brightness of X-rays over a range of wavelengths — to computer models of dust with different compositions. Different compositions of dust will result in different amounts of the lower energy X-rays being absorbed and prevented from being detected with Chandra. This is a similar principle to how different parts of our body or our luggage absorb different amounts of X-rays, giving information about their structure and composition.

The team determined that the dust most likely contains mixtures of graphite and silicate grains. In addition, by analyzing the inner rings with Chandra, they found that the densities of the dust clouds changes are not uniform in all directions. Previous studies have assumed that they did not.

This result is related to a similar finding of the X-ray binary Circinus X-1, which contains a neutron star rather than a black hole, published in a paper in the June 20, 2015, issue of The Astrophysical Journal, titled, "Lord of the Rings: A Kinematic Distance to Circinus X-1 from a Giant X-Ray Light Echo" (preprint). This study was also led by Sebastian Heinz.

The V404 Cygni results were led by the same astronomer, Sebastian Heinz of the University of Wisconsin in Madison. This paper was published in the July 1, 2016 issue of The Astrophysical Journal (preprint). The co-authors of the study are Lia Corrales (University of Michigan); Randall Smith (Center for Astrophysics | Harvard & Smithsonian); Niel Brandt (The Pennsylvania State University); Peter Jonker (Netherlands Institute for Space Research); Richard Plotkin (University of Nevada, Reno) and Joey Neilson (Villanova University). NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.

Read more from NASA's Chandra X-ray Observatory.

For more Chandra images, multimedia and related materials, visit: http://www.nasa.gov/chandra

Editor: Lee Mohon

Source: NASA/Chandra X-ray

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Microquasars: The “Elusive” Gamma-Ray Emitters

Artistic view of a microquasar
Credit: NASA/ CXC/M.Weiss

Microquasars are Galactic binary systems composed of a star and a compact object (a black hole or a neutron star) that eats up matter from its companion, usually via an accretion disk, giving rise to relativistic jets, i.e. beams of particles moving almost at the speed of light. These jets, which can be either intermittent or persistent structures depending on the specific state of the system, emanate from the vicinity of the compact object and can expand light years away from the binary system. 

The word “microquasar” was used for the first time in 1992 to describe the Galactic binary system 1E1740.7–2942, characterized by radio-emitting double-sided jets [1]. The jets resembled the relativistic collimated outflows launched by quasars (active galaxies with supermassive black holes at the centre that devour its surrounding material), although, in the latter case, the powerful jets reach distances of up to millions of light years. Thus, we can say that microquasars, as their name suggests, are the little siblings of the quasars, sharing multiple similarities. One of the advantages of studying microquasars is that, given their smaller size, processes inside the system and jets happen on a shorter timescale, allowing scientists to analyze rapid variabilities in their emission.

Microquasars’ outflows are efficient sites of extreme particle acceleration and are responsible for transient and persistent non-thermal radiation, spanning from radio to gamma-ray energies. Nevertheless, the emission at GeV and TeV energies from microquasars has only been sporadically observed up to this point, making these systems a class of non-thermal emitters that is actually “elusive” in the gamma-ray energy range. With its improved sensitivity compared to the current gamma-ray instruments, CTA will be fundamental to the study of these systems and the physical processes inside the jets. In particular, two microquasars, SS 433 and Cygnus X-1, have been drawing attention over the past few years.

 Prolonged observations of SS 433 with the High Altitude Water Cherenkov (HAWC) observatory were able to resolve two lobes at energies of ~20 TeV related the terminal parts of its jets, where the relativistic outflows interact with the surrounding environment [2]. According to the authors, to produce such a TeV signal, the system needs to accelerate particles up to PeV energies along the jets and, therefore, SS 433 might be a so-called Galactic PeVatron. Furthermore, a recent study with the Fermi-LAT has reported sub-TeV persistent emission from a site lying in the proximity of the eastern lobe [3]. Still some mysteries remain: What is the maximum energy to which the particles are accelerated in the jets? Does gamma-ray emission occur near or inside the binary system? What are the exact acceleration sites and mechanisms? CTA’s excellent angular resolution will play a key role in answering these questions.

 In the Cygnus region, three microquasars have been observed above 50 MeV: Cygnus X-1, Cygnus X-3 and V404 Cygni (see e.g. [4,5]). The case of Cygnus X-1 is intriguing. At GeV energies, short-time transient emission [6] and persistent emission coming from the jets [7] have been detected, while at TeV energies, only a hint during a short hard X-ray flare has been reported by MAGIC [8]. Therefore, even though theoretically predicted, a clear TeV component has not yet been detected. According to recent simulations, the CTA-North array, located in La Palma (Spain), would detect a short transient event, similar to the hint reported by MAGIC, in just a few minutes, and would be able to characterize the TeV persistent emission from the jet with a set of prolonged observations (see Figure 1).

Figure 1: CTA-North (100 GeV – 1 TeV) simulations for Cygnus X-1. Panel a.: After 30 minutes observation of a transient event, similar to the hint reported by MAGIC, CTA would clearly detect a TeV signal. Panel b.: 5h (grey triangles) and 50h observation (black points), assuming that the spectrum follows the Fermi-LAT 4FGL power-law; CTA would detect persistent emission after a few hours. Panel c.: 50h observation, assuming that the spectrum is consistent with the theoretical jet leptonic model of [9]; CTA would need more than 50 hours to detect a persistent TeV signal. The MAGIC upper limits (violet squares) in panels b and c are referred to ~83 hours of observation [10].

With CTA, we expect to unveil the timing of a possible TeV flare in a multi-wavelength context, the maximum limit of acceleration along the jets, the nature of the emission mechanisms (leptonic/hadronic) responsible for the very high-energy gamma-ray radiation and more.  Particularly, CTA’s unprecedented sensitivity between 20 GeV to 300 TeV will allow us to delve into these sources like never before: at the lowest energies, we will be able to comprehend the physics mechanisms between the GeV and TeV gamma-ray component (e.g., in Cygnus X-1) and, at the highest energies, we will be able to open a new window at the high end of the electromagnetic spectrum to study the jet-medium interaction (e.g., in SS 433). Thanks to CTA’s improved angular resolution, lower energy threshold and fast telescope repositioning to respond to external triggers for transient events, a better understanding of the physics of extreme particle acceleration in microquasars will finally be well within our grasp.

Written by: Giovanni Piano

References:

[1] Mirabel, I. F. et al., Nature 358, 215 (1992)
[2] Abeysekara, A. U. et al. (HAWC Collaboration), Nature 562, 82 (2018)
[3] Li, Jian et al., https://doi.org/10.1038/s41550-020-1164-6, Nat Astron (2020)
[4] Tavani, M. et al., Nature 462, 620 (2009)
[5] Piano, G. et al., ApJ 839, id. 84 (2017)
[6] Sabatini, S. et al., ApJL 712, L10 (2010)
[7] Zanin, R. et al., A&A 596, id. A55 (2016)
[8] Albert, J. et al., ApJ 665, L51 (2007)
[9] Zdziarski, A. A. et al., MNRAS 471, 3657 (2017)
[10] Ahnen, M. L. et al., MNRAS 472, 3474 (2017)

Source: Cherenkov Telescope Array/News

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Scientists get to the bottom of a spitting black hole

Black hole spitting out ‘bullets’ of plasma
Copyright: ICRAR - Hi-res Image

Data from ESA’s Integral high-energy observatory have helped shed light on the workings of a mysterious black hole found spitting out ‘bullets’ of plasma while rotating through space.

The black hole is part of a binary system known as V404 Cygni and is sucking in material from a companion star. It is located in our Milky Way, some 8000 light-years away from Earth, and was first identified in 1989, when it caused a huge outburst of high-energy radiation and material.

After 26 years of dormancy, it woke up again in 2015, becoming for a short period of time the brightest object in the sky observable in high-energy X-rays.

Astronomers from all over the world pointed their ground and space-based telescopes towards the celestial object, and discovered that the black hole was behaving somewhat strangely.

A new study, based on data collected during the 2015 outburst, has now revealed the inner workings of this cosmic monster. The results are reported today in the journal Nature.

Black hole and companion star
Copyright: ICRAR - Hi-res Image

“During the outburst we observed details of the jet emissions when material is ejected at a very high speed from the vicinity of the black hole,” says Simone Migliari, an astrophysicist at ESA who is a co-author on the paper.

“We can see the jets shooting out in different directions on a timescale of less than an hour, which means that the inner regions of the system are rotating quite fast.”

Usually astronomers see the jets shooting straight out from the poles of black holes, perpendicular to the surrounding disc of material that is accreted from the companion star.

Previously, there had only been one black hole observed with a rotating jet. It was, however, rotating much slower, completing one cycle in about six months.

The astronomers could observe the V404 Cygni jets in radio waves using telescopes like those of the Very Long Baseline Array in the US.

Meanwhile, high-energy X-ray data from Integral and other space observatories helped them decode what was happening at the same time inside the inner region of the 10 million kilometre-wide accretion disc. This was important since it is the mechanics of the disc that causes the jet’s strange behaviour.

“What’s different in V404 Cygni is that we think the disc of material and the black hole are misaligned,” says Associate Professor James Miller-Jones, from the International Centre for Radio Astronomy Research (ICRAR) at Curtin University, Australia, who is the lead author of the new paper.

“This appears to be causing the inner part of the disc to wobble like a spinning top that is slowing down, and fire jets out in different directions as it changes orientation.”

Tilted accretion disc
Copyright: ICRAR - Hi-res Image

During the outburst, a large amount of the surrounding material was falling into the black hole at once, temporarily increasing the accretion rate of disc material towards the black hole and resulting in a sudden surge of energy. This was seen by Integral as an abrupt increase of the X-ray emission.

Integral’s observations were used to estimate the energy and geometry of the accretion onto the black hole, which in turn were crucial to understand the link between the incoming and outflowing material to create a complete picture of the situation. “With Integral, we were able to keep looking at V404 Cygni continuously for four weeks, while other high-energy satellites could only take shorter snapshots,” says Erik Kuulkers, Integral Project Scientist at ESA.

ESA’s Integral observatory is able to detect gamma-ray bursts, the most energetic phenomena in the Universe.

Integral high-energy observatory 

Copyright: ESA/Medialab -  Hi-res image

“The X-ray data support a model where the inner part of the accretion disc is tilted with respect to the rest of the system, most likely due to the spin of the black hole being inclined with respect to the orbit of the companion star,” explains Simone.

Scientists have been studying what caused this strange misalignment. One possibility is that the black hole spin axis may have been tilted by the ‘kick’ received during the supernova explosion that created it.

“The results would fit in a scenario, also studied in recent computer simulations, where the accretion flow in the vicinity of the black hole and the jets can rotate together,” says Erik.

“We should expect similar dynamics in any strongly-accreting black hole whose spin is misaligned with the inflowing gas, and we will have to take into account varying jet inclination angles when interpreting observations of black holes across the Universe.”  

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Notes for editors

“A rapidly-changing jet orientation in the stellar-mass black hole V404 Cygni” by J. C. A. Miller-Jones et al is published in Nature.

Integral, the International Gamma-ray Astrophysics Laboratory, was launched on 17 October 2002. It is an ESA project with instruments and a science data centre funded by ESA Member States (especially the Principal Investigator countries: Denmark, France, Germany, Italy, Spain and Switzerland), and with the participation of Russia and the USA. The mission is dedicated to spectroscopy and imaging of celestial gamma-ray sources in the energy range 15 keV to 10 MeV with concurrent source monitoring in X-ray (3–35 keV) and optical (V-band, 550 nm) wavelengths.

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For further information, please contact:

Simone Migliari
Aurora Technology for ESA
European Space Agency
Email: smigliari@sciops.esa.int

Erik Kuulkers
Integral Project Scientist
European Space Agency
Email: ekuulker@sciops.esa.int

James Miller-Jones
Associate Professor
International Centre for Radio Astronomy Research (ICRAR)
Curtin University, Australia
Email: james.miller-jones@icrar.org

Pete Wheeler
Outreach, Education and Communications Manager
International Centre for Radio Astronomy Research (ICRAR)
Email: pete.wheeler@icrar.org

Markus Bauer








ESA Science Programme Communication Officer
Tel: +31 71 565 6799









Mob: +31 61 594 3 954









Email: markus.bauer@esa.int

Source: ESA/Space Science

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NuSTAR Probes Black Hole Jet Mystery

This artist's concept shows a black hole with an accretion disk -- a flat structure of material orbiting the black hole - and a jet of hot gas, called plasma. Credit: NASA/JPL-Caltech.  › Larger view

Black holes are famous for being ravenous eaters, but they do not eat everything that falls toward them. A small portion of material gets shot back out in powerful jets of hot gas, called plasma, that can wreak havoc on their surroundings. Along the way, this plasma somehow gets energized enough to strongly radiate light, forming two bright columns along the black hole's axis of rotation. Scientists have long debated where and how this happens in the jet.

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.

Scientists looked at two systems in the Milky Way called "X-ray binaries," each consisting of a black hole feeding off of a normal star. They studied these systems at different points during periods of outburst -- which is when the accretion disk -- a flat structure of material orbiting the black hole -- brightens because of material falling in.

One system, called V404 Cygni, had reached nearly peak brightness when scientists observed it in June 2015. At that time, it experienced the brightest outburst from an X-ray binary seen in the 21st century. The other, called GX 339-4,was less than 1 percent of its maximum expected brightness when it was observed. The star and black hole of GX 339-4 are much closer together than in the V404 Cygni system.

Despite their differences, the systems showed similar time delays - about one-tenth of a second -- between when NuSTAR first detected X-ray light and ULTRACAM detected flares in visible light slightly later. That delay is less than the blink of an eye, but significant for the physics of black hole jets.

"One possibility is that the physics of the jet is not determined by the size of the disc, but instead by the speed, temperature and other properties of particles at the jet's base," said Poshak Gandhi, lead author of the study and astronomer at the University of Southampton, United Kingdom.

The best theory scientists have to explain these results is that the X-ray light originates from material very close to the black hole. Strong magnetic fields propel some of this material to high speeds along the jet. This results in particles colliding near light-speed, energizing the plasma until it begins to emit the stream of optical radiation caught by ULTRACAM.

Where in the jet does this occur? The measured delay between optical and X-ray light explains this. By multiplying this amount of time by the speed of the particles, which is nearly the speed of light, scientists determine the maximum distance traveled.

This expanse of about 19,000 miles (30,000 kilometers) represents the inner acceleration zone in the jet, where plasma feels the strongest acceleration and "turns on" by emitting light. That's just under three times the diameter of Earth, but tiny in cosmic terms, especially considering the black hole in V404 Cygni weighs as much as 3 million Earths put together.

"Astronomers hope to refine models for jet powering mechanisms using the results of this study," said Daniel Stern, study co-author and astronomer based at NASA's Jet Propulsion Laboratory, Pasadena, California.

Making these measurements wasn't easy. X-ray telescopes in space and optical telescopes on the ground have to look at the X-ray binaries at exactly the same time during outbursts for scientists to calculate the tiny delay between the telescopes' detections. Such coordination requires complex planning between the observatory teams. In fact, coordination between NuSTAR and ULTRACAM was only possible for about an hour during the 2015 outburst, but that was enough to calculate the groundbreaking results about the acceleration zone.

The results also appear to connect with scientists' understanding of supermassive black holes, much bigger than the ones in this study. In one supermassive system called BL Lacertae, weighing 200 million times the mass of our Sun, scientists have inferred time delays millions of times greater than what this study found. That means the size of the acceleration area of the jets is likely related to the mass of the black hole.

"We are excited because it looks as though we have found a characteristic yardstick related to the inner workings of jets, not only in stellar-mass black holes like V404 Cygni, but also in monster supermassive ones," Gandhi said.

The next steps are to confirm this measured delay in observations of other X-ray binaries, and to develop a theory that can tie together jets in black holes of all sizes.

"Global ground and space telescopes working together were key to this discovery. But this is only a peek, and much remains to be learned. The future is really bright for understanding the extreme physics of black holes," said Fiona Harrison, principal investigator of NuSTAR and professor of astronomy at Caltech in Pasadena.

NuSTAR is a Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corp., Dulles, Virginia. NuSTAR's mission operations center is at UC Berkeley, and the official data archive is at NASA's High Energy Astrophysics Science Archive Research Center. ASI provides the mission's ground station and a mirror archive. Caltech manages JPL for NASA.

For more information on NuSTAR, visit: https://www.nasa.gov/nustar - http://www.nustar.caltech.edu/

News Media Contact

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
Elizabeth.landau@jpl.nasa.gov

Source: JPL-Caltech/News

Fast and Furious Black Hole Observed with the William Herschel Telescope

The inset shows a still image showing one of the frames, only 1/40th of a second in exposure time, with a red flash, as observed by the ULTRACAM fast imager on the WHT in the early morning hours of June 26, 2015. Click on the image above to see a movie of fast red flashes from V404 Cygni. A ~6 second segment of the ULTRACAM movie is repeated continuously. The flashes are incredibly short and last less than one second, with some of them being even faster than 1/40th of a second. The flashes are equivalent to a luminosity of about 1000 times the Sun's power. The background image shows a region of the sky in the Cygnus constellation, with the Cygnus Loop supernova remnant on the bottom left [ animated GIF | PNG ]. 

In a paper published in the journal Monthly Notices of the Royal Astronomical Society, astronomers report catching V404 Cygni black hole while it was shimmering and emitting red flashes, some of which were shorter than a timespan of only 1/40th of a second. 

In June 2015, V404 Cygni abruptly started emitting a huge amount of power, becoming one of the brightest objects in the Milky Way Galaxy as seen in X-rays. Telescopes worldwide, including the William Herschel and Isaac Newton Telescopes, followed its ascent in brightness for about two weeks, leading up to June 26, after which the black hole gradually faded away. 

Imagine an object 9 times larger in mass than the Sun, which is radiating 1000 times more energy than our Sun gives off every second. This is the power that was seen to be emitted. As if this weren’t extreme enough, on June 26, the black hole appeared to be agitated and flickering red at high speed. 

The astronomers speculate that while the black hole was being force-fed with material that it had stripped off a neighbouring star, it reacted furiously by blasting away some of the material in the form of a fast-moving ‘jet’. Lead author of the study Dr Poshak Gandhi, Associate Professor and STFC Ernest Rutherford Fellow in the University of Southampton’s Astronomy Group, said: "The duration of these flashing episodes could be related to the switching on and off of a steady jet, seen for the first time in detail.” 

Gandhi also comments: “The very high speed tells us that the region where this red light is being emitted must be very compact. Piecing together clues about the colour, speed, and the power of these flashes, we conclude that this light is being emitted from the base of the black hole jet. The origin of these jets is still unknown, although strong magnetic fields are suspected to play a role." 

Due to the unpredictable nature and rarity of these bright black hole ‘outbursts’, astronomers have very little time to react. For example, V404 Cygni last erupted back in 1989. V404 Cygni was exceptionally bright in June 2015 and provided an excellent opportunity for such work. In fact, this was one of the brightest black hole outbursts in recent years. But most outbursts are far dimmer, making them difficult to study. 

At a distance of 7800 light years from Earth, the black hole is too far away to image its jet in fine detail. But the speedy red flashes were important clues telling the astronomers that such a jet had formed. These observations are state-of-the-art, and could only be carried out with the fast ULTRACAM imager, which happened to be mounted on the WHT in June 2015 for about one week, just in time to catch the flurry of activity. 

Liam Hardy, PhD student at the University of Sheffield, and an ex-ING student support astronomer, said: "It was difficult to catch these signals from V404 Cygni in the small gaps in our scheduled observing, but when we finally spotted the fast flaring activity on our last night, it was tremendously exciting. We knew immediately that these observations would be of great interest to the community." 

The nature of V404 Cygni system was unveiled in 1992, when observations made using the telescopes of the Isaac Newton Group provided the strongest observational evidence for the existence of a stellar-size black hole in our Galaxy. 

More Information

• P. Gandhi et al., 2016, "Furiously Fast and Red: Sub-second Optical Flaring in V404 Cyg during the 2015 Outburst Peak", accepted for publication in MNRAS, 10.1093/mnras/stw571. Paper.
• "Astronomers see black hole raging red", movie and image.
• "Astronomers see black hole raging red", Southampton University press release, 16th March 2016.
• "Astronomers see black hole raging red", RAS press release, 16th Mar 2016.
• ULTRACAM web site.

  
Contact:  

Javier Méndez  (Public Relations Officer)

Source: Isaac Newton Group of Telescopes

NASA's Swift Reveals a Black Hole Bull's-eye

Rings of X-ray light centered on V404 Cygni, a binary system containing an erupting black hole (dot at center), were imaged by the X-ray Telescope aboard NASA's Swift satellite from June 30 to July 4. A narrow gap splits the middle ring in two. Color indicates the energy of the X-rays, with red representing the lowest (800 to 1,500 electron volts, eV), green for medium (1,500 to 2,500 eV), and the most energetic (2,500 to 5,000 eV) shown in blue. For comparison, visible light has energies ranging from about 2 to 3 eV. The dark lines running diagonally through the image are artifacts of the imaging system. Credits: Andrew Beardmore (Univ. of Leicester) and NASA/Swift. Download frames from NASA Goddard's Scientific Visualization Studio

The Swift X-ray image of V404 Cygni covers a patch of the sky equal to about half the apparent diameter of the full moon. This image shows the rings as they appeared on June 30. Credits: NASA's Scientific Visualization Studio (left), Andrew Beardmore (Univ. of Leicester); NASA/Swift (right)

What looks like a shooting target is actually an image of nested rings of X-ray light centered on an erupting black hole. On June 15, NASA's Swift satellite detected the start of a new outburst from V404 Cygni, where a black hole and a sun-like star orbit each other. Since then, astronomers around the world have been monitoring the ongoing light show.

On June 30, a team led by Andrew Beardmore at the University of Leicester, U.K., imaged the system using the X-ray Telescope aboard Swift, revealing a series concentric rings extending about one-third the apparent size of a full moon. A movie made by combining additional observations acquired on July 2 and 4 shows the expansion and gradual fading of the rings.

Astronomers say the rings result from an "echo" of X-ray light. The black hole's flares emit X-rays in all directions. Dust layers reflect some of these X-rays back to us, but the light travels a longer distance and reaches us slightly later than light traveling a more direct path. The time delay creates the light echo, forming rings that expand with time.   

Detailed analysis of the expanding rings shows that they all originate from a large flare that occurred on June 26 at 1:40 p.m. EDT. There are multiple rings because there are multiple reflecting dust layers between 4,000 and 7,000 light-years away from us. Regular monitoring of the rings and how they change as the eruption continues will allow astronomers to better understand their nature.

"The flexible planning of Swift observations has given us the best dust-scattered X-ray ring images ever seen," Beardmore said. "With these observations we can make a detailed study of the normally invisible interstellar dust in the direction of this black hole."

V404 Cygni is located about 8,000 light-years away. Every couple of decades the black hole fires up in an outburst of high-energy light. Its previous eruption ended in 1989.

The investigating team includes scientists from the Universities of Leicester, Southampton, and Oxford in the U.K., the University of Alberta in Canada, and the European Space Agency in Spain.

Swift was launched in November 2004 and is managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland. Goddard operates the spacecraft in collaboration with Penn State University in University Park, Pennsylvania, the Los Alamos National Laboratory in New Mexico and Orbital Sciences Corp. in Dulles, Virginia. International collaborators are located in the United Kingdom and Italy. The mission includes contributions from Germany and Japan.

Related Links

• NASA Missions Monitor a Waking Black Hole
• INTEGRAL light curve of V404 Cygni
• NASA’s Chandra Captures X-Ray Echoes Pinpointing Distant Neutron Star

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Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

 Source:NASA/Swift

Monster black hole wakes up after 26 years

Black hole with stellar companion

Copyright: ESA/ATG medialab

Integral image before and after the outburst

Copyright: ESA/Integral/IBIS/ISDC

Integral light curve 
Copyright: ESA/Integral/IBIS/ISDC

Over the past week, ESA's Integral satellite has been observing an exceptional outburst of high-energy light produced by a black hole that is devouring material from its stellar companion.

X-rays and gamma rays point to some of the most extreme phenomena in the Universe, such as stellar explosions, powerful outbursts and black holes feasting on their surroundings.

In contrast to the peaceful view of the night sky we see with our eyes, the high-energy sky is a dynamic light show, from flickering sources that change their brightness dramatically in a few minutes to others that vary on timescales spanning years or even decades.

On 15 June 2015, a long-time acquaintance of X-ray and gamma ray astronomers made its comeback to the cosmic stage: V404 Cygni, a system comprising a black hole and a star orbiting one another. It is located in our Milky Way galaxy, almost 8000 light-years away in the constellation Cygnus, the Swan. In this type of binary system, material flows from the star towards the black hole and gathers in a disc, where it is heated up, shining brightly at optical, ultraviolet and X-ray wavelengths before spiralling into the black hole.

First signs of renewed activity in V404 Cygni were spotted by the Burst Alert Telescope on NASA's Swift satellite, detecting a sudden burst of gamma rays, and then triggering observations with its X-ray telescope. Soon after, MAXI (Monitor of All-sky X-ray Image), part of the Japanese Experiment Module on the International Space Station, observed an X-ray flare from the same patch of the sky.

These first detections triggered a massive campaign of observations from ground-based telescopes and from space-based observatories, to monitor V404 Cygni at many different wavelengths across the electromagnetic spectrum. As part of this worldwide effort, ESA's Integral gamma-ray observatory started monitoring the out-bursting black hole on 17 June.

“The behaviour of this source is extraordinary at the moment, with repeated bright flashes of light on time scales shorter than an hour, something rarely seen in other black hole systems,” comments Erik Kuulkers, Integral project scientist at ESA.

“In these moments, it becomes the brightest object in the X-ray sky – up to fifty times brighter than the Crab Nebula, normally one of the brightest sources in the high-energy sky.”

The V404 Cygni black hole system has not been this bright and active since 1989, when it was observed with the Japanese X-ray satellite Ginga and high-energy instruments on board the Mir space station.

“The community couldn't be more thrilled: many of us weren't yet professional astronomers back then, and the instruments and facilities available at the time can’t compare with the fleet of space telescopes and the vast network of ground-based observatories we can use today. It is definitely a 'once in a professional lifetime' opportunity,” adds Kuulkers.

The 1989 outburst of V404 Cygni was crucial in the study of black holes. Until then, astronomers knew only a handful of objects that they thought could be black holes, and V404 Cygni was one of the most convincing candidates.

A couple of years after the 1989 outburst, once the source had returned to a quieter state, the astronomers were able to see its companion star, which had been outshone by the extreme activity. The star is about half as massive as the Sun, and by studying the relative motion of the two objects in the binary system, it was determined that the companion must be a black hole, about twelve times more massive than the Sun.

At the time, the astronomers also looked back at archival data from optical telescopes over the twentieth century, finding two previous outbursts, one in 1938 and another one in 1956.

These peaks of activity, which occur every two to three decades, are likely caused by material slowly piling up in the disc surrounding the black hole, until eventually reaching a tipping point that dramatically changes the black hole's feeding routine for a short period.

“Now that this extreme object has woken up again, we are all eager to learn more about the engine that powers the outburst we are observing,” says Carlo Ferrigno from the Integral Science Data Centre at the University of Geneva, Switzerland.

“As coordinators of Integral operations, Enrico Bozzo and I received a text message at 01:30 am on 18 June from our burst alert system, which is designed to detect gamma-ray bursts in the Integral data. In this case, it turned out to be 'only' an exceptional flare since Integral was observing this incredible black hole: definitely a good reason to be woken up in the middle of the night!”

Since the first outburst detection on 15 June by the Swift satellite, V404 Cygni has remained very active, keeping astronomers extremely busy. Over the past week, several teams around the world published over twenty Astronomical Telegrams and other official communications, sharing the progress of the observations at different wavelengths.

This exciting outburst has also been discussed by astronomers attending the European Week of Astronomy and Space Science conference this week in Tenerife, sharing information on observations that have been made in the past few days.

Integral too has been observing this object continuously since 17 June, except for some short periods when it was not possible for operational reasons. The X-ray data show huge variability, with intense flares lasting only a couple of minutes, as well as longer outbursts over time scales of a few hours. Integral also recorded a huge emission of gamma rays from this frenzied black hole.

Because different components of a black-hole binary system emit radiation at different wavelengths across the spectrum, astronomers are combining high-energy observations with those made at optical and radio wavelengths in order to get a complete view of what is happening in this unique object. “We have been observing V404 Cygni with the Gran Telescopio Canarias, which has the largest mirror currently available for optical astronomy,” explains Teo Muñoz-Darias from the Instituto de Astrofísica de Canarias in Tenerife, Spain.

Using this 10.4-m telescope located on La Palma, the astronomers can quickly obtain high quality spectra, thus probing what happens around the black hole on short time scales.

“There are many features in our spectra, showing signs of massive outflows of material in the black hole's environment. We are looking forward to testing our current understanding of black holes and their feeding habits with these rich data,” adds Muñoz-Darias.

Radio astronomers all over the world are also joining in this extraordinary observing campaign. The first detection at these long wavelengths was made shortly after the first Swift alert on 15 June with the Arcminute Microkelvin Imager from the Mullard Radio Astronomy Observatory near Cambridge, in the UK, thanks to the robotic mode of this telescope.

Like the data at other wavelengths, these radio observations also exhibit a continuous series of extremely bright flares. Astronomers will exploit them to investigate the mechanisms that give rise to powerful jets of particles, moving away at velocities close to the speed of light, from the black hole's accretion disc.

There are only a handful of black-hole binary systems for which data have been collected simultaneously at many wavelengths, and the current outburst of V404 Cygni offers the rare chance to gather more observations of this kind. Back in space, Integral has a full-time job watching the events unfold.

“We have been devoting all of Integral's time to observe this exciting source for the past week, and we will keep doing so at least until early July,” comments Peter Kretschmar, ESA Integral mission manager.

“The observations will soon be made available publicly, so that astronomers across the world can exploit them to learn more about this unique object. It will also be possible to use Integral data to try and detect polarisation of the X-ray and gamma ray emission, which could reveal more details about the geometry of the black hole accretion process. This is definitely material for the astrophysics textbooks for the coming years.”

Note for Editors 

The International Gamma-ray Astrophysics Laboratory Integral was launched on 17 October 2002. It is an ESA project with the instruments and a science data centre funded by ESA Member States (especially the Principal Investigator countries: Denmark, France, Germany, Italy, Spain and Switzerland), and with the participation of Russia and the USA. The mission is dedicated to spectroscopy (E/∆E = 500) and imaging (angular resolution: 12 arcmin FWHM) of celestial gamma-ray sources in the energy range 15 keV to 10 MeV with concurrent source monitoring in the X-ray (3–35 keV) and optical (V-band, 550 nm) wavelengths. 

For further information, please contact:

Markus Bauer















ESA Science and Robotic Exploration Communication Officer
















Tel: +31 71 565 6799
















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Email: markus.bauer@esa.int

Source: ESA