New Curtin University-led research has used a radio telescope that spans the Earth to snap images that measure the immense power of jets from black holes, confirming scientists’ theories of how black holes help shape the structure of the Universe.

The strong stellar wind from the supergiant star pushes the jets launched by the black hole away from the star. This causes the jet direction to vary as the black hole and the supergiant star move around their orbit. Credit: ICRAR/Curtin University

The direction of the radio jet changes as the black hole and the star move around their orbit (shown in red).

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Dancing' Jets reveal immense power of Black Holes
Video Vimeo (link)

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In a paper published in Nature Astronomy, researchers found the power of the jets in Cygnus X-1 – a system comprised of the first confirmed black hole and a supergiant star – was equivalent to the power output of 10,000 Suns.

To record the measurement, researchers used an array of linked up telescopes separated by large distances to observe the black hole jets being buffeted by the winds of the star as the black hole moved around its orbit – much like how strong winds on Earth can push around water in a fountain.

By knowing the power of the wind and measuring how much the jets were bent, the researchers could determine the instantaneous power of the jets for the first time.

In addition, they were able to determine the speed of the black hole’s jets – about half the speed of light, or 150,000 km per second – another measurement that has challenged scientists for decades.

The research was led from the Curtin Institute of Radio Astronomy (CIRA) and the Curtin node of the International Centre for Radio Astronomy Research (ICRAR), in collaboration with the University of Oxford.

Lead author Dr Steve Prabu, who worked at CIRA at the time of the research and who is now based at the University of Oxford, said researchers were able to make the measurement using a sequence of images of the “dancing jets” – a term he used to describe the jets’ movement pattern as they were repeatedly deflected indifferent directions by the supergiant star’s powerful winds as the star and black hole moved around their orbits.

Dr Prabu said the measurement allowed scientists to understand what fraction of the energy released around black holes could be deposited into the surrounding environment, thereby changing the environment.

“A key finding from this research is that about 10 per cent of the energy released as matter falls in towards the black hole is carried away by the jets,” Dr Prabu said.

“This is what scientists usually assume in large-scale simulated models of the Universe, but it has been hard to confirm by observation until now.”

Co-author Professor James Miller-Jones, from CIRA and the Curtin node of ICRAR, said previous methodscould only measure the average jet power over thousands or even millions of years, preventing accurate comparisons with the X-ray energy released instantaneously from the infalling matter.

“And because our theories suggest that the physics around black holes is very similar, we can now use this measurement to anchor our understanding of jets, whether they are from black holes 10 or 10 million times the mass of the Sun,” Professor Miller-Jones said.

“With radio telescope projects such as the Square Kilometre Array Observatory currently under construction in Western Australia and South Africa, we expect to detect jets from black holes in millions of distant galaxies, and the anchor point provided by this new measurement will help calibrate their overall power output.

“Black hole jets provide an important source of feedback to the surrounding environment and are critical to understanding the evolution of galaxies.”

Other collaborating institutions included the University of Barcelona, the University of Wisconsin-Madison, the University of Lethbridge and the Institute of Space Science.

Source: International Center for Radio Astronomy Research (ICRAR)/News

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A Hard Look at a Soft-State X-ray Binary

At the center of this image, in between the glowing star-forming region at center left and the bright star at center right, is a bluish star with an unseen companion. This binary system is designated Cygnus X-1. Credit: DSS

Astronomers recently tracked a famous X-ray binary system through a change in its accretion state. What does this transition tell us about how black holes accrete gas?

An artist’s impression of an X-ray binary, in which a compact object accretes material from a companion star and emits X-rays during intermittent outbursts. Credit: ESO/L. Calçada; CC BY 4.0

Accretion Questions

X-ray binaries contain a star and a compact object — either a black hole or a neutron star. As the compact object ensnares gas from its stellar companion, a number of X-ray-bright features can emerge: the gas collects in a super-hot accretion disk and in a tenuous structure called the corona, and transient outflowing jets can appear.

Astronomers have discovered hundreds of X-ray binaries in the Milky Way, but there are still many open questions about the accretion process: What’s the origin of the corona, and how is it structured? Does it sit high above the compact object, or does it hover just above the surface of the disk? What’s the connection between the disk, the corona, and the jets?

One way to potentially answer these questions is to track an X-ray binary as it undergoes a state transition, shifting from producing more low-energy X-rays (“soft state”) to more high-energy X-rays (“hard state”). State transitions are thought to occur when a binary changes how it’s accreting gas, so observing a binary across state transitions can reveal whether the binary’s geometry changes in different accretion modes. Luckily, one of the best-studied X-ray binaries in our galaxy recently gave researchers a chance to study a state transition with a powerful observatory.

Side view of the favored coronal geometry; a wedge-shaped corona (blue) lies parallel to the accretion disk (yellow). The arrows show the direction of the black hole’s spin. Credit: AAS Nova/Kerry Hensley

From Hard to Soft

Cygnus X-1 is an X-ray binary containing a 41-solar-mass supergiant star and a 21-solar-mass black hole. Over decades of monitoring, scientists have witnessed Cygnus X-1 repeatedly transition between soft and hard states. Phase switches happen randomly, and a phase can last weeks or years.

Since the launch of the new Imaging X-ray Polarimetry Explorer (IXPE) spacecraft in 2021, Cygnus X-1 has held steady in a hard state. When researchers examined Cygnus X-1’s hard-state behavior with IXPE, they found that the X-ray emission was unexpectedly strongly polarized. In other words, the orientation of the X-rays as they traveled through space was more orderly than expected. Based on these observations, a “lamppost” model — in which the corona is situated above the black hole’s poles — is now disfavored. Instead, researchers favor a model in which the corona lies parallel to the accretion disk.

Left: Polarization degree and polarization angle for the hard (blue) and soft (red) states. Right: Polarization degree and angle as a function of energy for the soft state. Click to enlarge. Credit: Steiner et al. 2024

Soft-State Insights

In April 2023, Cygnus X-1 transitioned out of its long-lived hard state, giving researchers their first opportunity to study the system’s soft-state behavior with IXPE. James Steiner (Center for Astrophysics ∣ Harvard & Smithsonian) and collaborators analyzed five epochs of IXPE data spread over two months. They found that while Cygnus X-1’s X-ray emission in the soft state is less polarized — 2% polarization compared to 4% in the hard state — the two states were otherwise similar; the polarization angle is parallel to the outflowing jet, and the degree of polarization increases with the temperature of the gas.

Using a fully relativistic spectral model, Steiner’s team found that the corona likely lies parallel to the accretion disk, just as in the hard state. While there are many similarities between the hard and soft states of this system, the team suggested that the majority of the polarized light in each state comes from a different source.

In the hard state, X-ray photons become polarized when they scatter off the corona. In the soft state, a substantial fraction of the X-ray photons from the accretion disk are bent back toward the disk by the black hole’s immense gravity, and they become polarized when they are reflected off the surface of the disk. In other words, X-rays from the accretion disk undergo gravitational lensing — showing that the same process that bends the light from distant galaxies is at work in a system billions of times less massive!

Citation

“An IXPE-led X-Ray Spectropolarimetric Campaign on the Soft State of Cygnus X-1: X-Ray Polarimetric Evidence for Strong Gravitational Lensing,” James F. Steiner et al 2024 ApJL 969 L30. doi:10.3847/2041-8213/ad58e4

By Kerry Hensley

Source: American Astronomical Society/AAS-Nova

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First black hole ever detected is more massive than we thought

An artist’s impression of the Cygnus X-1 system. This system contains the most massive stellar-mass black hole ever detected without the use of gravitational waves, weighing in at 21 times the mass of the Sun. Credit: International Centre for Radio Astronomy Research. Credit: International Centre for Radio Astronomy Research. Hi-res image

New observations of the first black hole ever detected have led astronomers to question what they know aboeut the Universe’s most mysterious objects.

Published today in the journal Science, the research shows the system known as Cygnus X-1 contains the most massive stellar-mass black hole ever detected without the use of gravitational waves.

Cygnus X-1 is one of the closest black holes to Earth. It was discovered in 1964 when a pair of Geiger counters were carried on board a sub-orbital rocket launched from New Mexico.

The object was the focus of a famous scientific wager between physicists Stephen Hawking and Kip Thorne, with Hawking betting in 1974 that it was not a black hole. Hawking conceded the bet in 1990.

In this latest work, an international team of astronomers used the Very Long Baseline Array—a continent-sized radio telescope made up of 10 dishes spread across the United States—together with a clever technique to measure distances in space.

“If we can view the same object from different locations, we can calculate its distance away from us by measuring how far the object appears to move relative to the background,” said lead researcher, Professor James Miller-Jones from Curtin University and the International Centre for Radio Astronomy Research (ICRAR).

“If you hold your finger out in front of your eyes and view it with one eye at a time, you’ll notice your finger appears to jump from one spot to another. It’s exactly the same principle.”

Astronomers observed the Cygnus X-1 system from different angles using the orbit of the Earth around the Sun to measure the perceived movement of the system against the background stars. This allowed them to refine the distance to the system and therefore the mass of the black hole. Credit: International Centre for Radio Astronomy Research. Hi-res image

“Over six days we observed a full orbit of the black hole and used observations taken of the same system with the same telescope array in 2011,” Professor Miller-Jones said. “This method and our new measurements show the system is further away than previously thought, with a black hole that’s significantly more massive.”

Co-author Professor Ilya Mandel from Monash University and the ARC Centre of Excellence in Gravitational Wave Discovery (OzGrav) said the black hole is so massive it’s actually challenging how astronomers thought they formed.

An artist’s impression of the Cygnus X-1 system. A stellar-mass black hole orbits with a companion star located 7,200 light years from Earth. Credit: International Centre for Radio Astronomy Research. Hi-res image

“Stars lose mass to their surrounding environment through stellar winds that blow away from their surface. But to make a black hole this heavy, we need to dial down the amount of mass that bright stars lose during their lifetimes” he said.

“The black hole in the Cygnus X-1 system began life as a star approximately 60 times the mass of the Sun and collapsed tens of thousands of years ago,” he said. “Incredibly, it’s orbiting its companion star—a supergiant—every five and a half days at just one-fifth of the distance between the Earth and the Sun.

“These new observations tell us the black hole is more than 20 times the mass of our Sun—a 50 per cent increase on previous estimates.”

Recent observations show the black hole in the Cygnus X-1 system is 21 times the mass of the Sun—a 50 per cent increase on previous estimates. To form such a massive black hole, astronomers had to revise their estimates of how much mass stars lose via stellar winds. Credit: International Centre for Radio Astronomy Research. Hi-res image

Xueshan Zhao is a co-author on the paper and a PhD candidate studying at the National Astronomical Observatories—part of the Chinese Academy of Sciences (NAOC) in Beijing.

“Using the updated measurements for the black hole’s mass and its distance away from Earth, I was able to confirm that Cygnus X-1 is spinning incredibly quickly—very close to the speed of light and faster than any other black hole found to date,” she said.

“I’m at the beginning of my research career, so being a part of an international team and helping to refine the properties of the first black hole ever discovered has been a great opportunity.”

CYGNUS X-1: the most massive black hole near to Earth from ICRAR on Vimeo.

 

More Information:

The International Centre for Radio Astronomy Research (ICRAR) is a joint venture between Curtin University and The University of Western Australia with support and funding from the State Government of Western Australia.

Original Publication:

‘Cygnus X-1 contains a 21-solar mass black hole – implications for massive star winds’, published in Science on February 18^th, 2021.

Companion Papers:

‘Reestimating the Spin Parameter of the Black Hole in Cygnus X-1’, published in The Astrophysical Journal on February 18th, 2021.

‘Wind mass-loss rates of stripped stars inferred from Cygnus X-1’, published in The Astrophysical Journal on February 18th, 2021.

Contacts:

Professor James Miller-Jones (ICRAR / Curtin University)

Ph: +61 488 484 825                        E: James.Miller-Jones@icrar.org

Professor Ilya Mandel (OzGrav / Monash University)

Ph: +61 8 466 710 590                     E: Ilya.Mandel@monash.edu

Pete Wheeler — Media Contact, ICRAR

Ph: +61 423 982 018                        E: Pete.Wheeler@icrar.org

Lauren Sydoruk (Media Contact, Curtin University)

Ph: +61 401 103 373                       E: Lauren.Sydoruk@curtin.edu.au

  

Source: International Centre for Radio Astronomy Research   ICRAR/News

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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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In The Heart Of Cygnus, NASA's Fermi Reveals A Cosmic-ray Cocoon

Tour the Cygnus X star factory. This video opens with wide optical and infrared images of the constellation Cygnus, then zooms into the Cygnus X region using radio, infrared and gamma-ray images. Fermi LAT shows that gamma rays fill cavities in the star-forming clouds. The emission occurs when fast-moving cosmic rays strike hot gas and starlight. Credit: NASA/Goddard Space Flight Center. Download this video and related content from NASA Goddard's Scientific Visualization Studio.

Gamma-ray emission detected by Fermi LAT fills bubbles of hot gas created by the most massive stars in Cygnus X. The turbulence and shock waves produced by these stars make it more difficult for high-energy cosmic rays to traverse the region. When the particles strike gas nuclei or photons of starlight, gamma rays result. Credit: NASA/DOE/Fermi LAT Collaboration/I. A. Grenier and L. Tibaldo . Larger image

Cygnus X hosts many young stellar groupings, including the OB2 and OB9 associations and the cluster NGC 6910. The combined outflows and ultraviolet radiation from the region's numerous massive stars have heated and pushed gas away from the clusters, producing cavities of hot, lower-density gas. In this 8-micron infrared image, ridges of denser gas mark the boundaries of the cavities. Bright spots within these ridges show where stars are forming today. Credit: NASA/IPAC/MSX . Larger Image - Labeled image

The constellation Cygnus, now visible in the western sky as twilight deepens after sunset, hosts one of our galaxy's richest-known stellar construction zones. Astronomers viewing the region at visible wavelengths see only hints of this spectacular activity thanks to a veil of nearby dust clouds forming the Great Rift, a dark lane that splits the Milky Way, a faint band of light marking our galaxy's central plane.

Located in the vicinity of the second-magnitude star Gamma Cygni, the star-forming region was named Cygnus X when it was discovered as a diffuse radio source by surveys in the 1950s. Now, a study using data from NASA's Fermi Gamma-ray Space Telescope finds that the tumult of star birth and death in Cygnus X has managed to corral fast-moving particles called cosmic rays.

Cosmic rays are subatomic particles -- mainly protons -- that move through space at nearly the speed of light. In their journey across the galaxy, the particles are deflected by magnetic fields, which scramble their paths and make it impossible to backtrack the particles to their sources.

Yet when cosmic rays collide with interstellar gas, they produce gamma rays -- the most energetic and penetrating form of light -- that travel to us straight from the source. By tracing gamma-ray signals throughout the galaxy, Fermi's Large Area Telescope (LAT) is helping astronomers understand the sources of cosmic rays and how they're accelerated to such high speeds. In fact, this is one of the mission's key goals.

The galaxy's best candidate sites for cosmic-ray acceleration are the rapidly expanding shells of ionized gas and magnetic field associated with supernova explosions. For stars, mass is destiny, and the most massive ones -- known as types O and B -- live fast and die young.

They're also relatively rare because such extreme stars, with masses more than 40 times that of our sun and surface temperatures eight times hotter, exert tremendous influence on their surroundings. With intense ultraviolet radiation and powerful outflows known as stellar winds, the most massive stars rapidly disperse their natal gas clouds, naturally limiting the number of massive stars in any given region.

Which brings us back to Cygnus X. Located about 4,500 light-years away, this star factory is believed to contain enough raw material to make two million stars like our sun. Within it are many young star clusters and several sprawling groups of related O- and B-type stars, called OB associations. One, called Cygnus OB2, contains 65 O stars -- the most massive, luminous and hottest type -- and nearly 500 B stars.

Astronomers estimate that the association's total stellar mass is 30,000 times that of our sun, making Cygnus OB2 the largest object of its type within 6,500 light-years. And with ages of less than 5 million years, few of its most massive stars have lived long enough to exhaust their fuel and explode as supernovae.

Intense light and outflows from the monster stars in Cygnus OB2 and from several other nearby associations and star clusters have excavated vast amounts of gas from their vicinities. The stars reside within cavities filled with hot, thin gas surrounded by ridges of cool, dense gas where stars are now forming. It's within the hollowed-out zones that Fermi's LAT detects intense gamma-ray emission, according to a paper describing the findings that was published in the Nov. 25 edition of the journal Science.

"We are seeing young cosmic rays, with energies comparable to those produced by the most powerful particle accelerators on Earth. They have just started their galactic voyage, zig-zagging away from their accelerator and producing gamma rays when striking gas or starlight in the cavities," said co-author Luigi Tibaldo, a physicist at Padova University and the Italian National Institute of Nuclear Physics.

The energy of the gamma-ray emission, which is measured up to 100 billion electron volts by the LAT and even higher by ground-based gamma-ray detectors, indicates the extreme nature of the accelerated particles. (For comparison, the energy of visible light is between 2 and 3 electron volts.) The environment holds onto its cosmic rays despite their high energies by entangling them in turbulent magnetic fields created by the combined outflows of the region's numerous high-mass stars.

"These shockwaves stir the gas and twist and tangle the magnetic field in a cosmic-scale jacuzzi so the young cosmic rays, freshly ejected from their accelerators, remain trapped in this turmoil until they can leak into quieter interstellar regions, where they can stream more freely," said co-author Isabelle Grenier, an astrophysicist at Paris Diderot University and the Atomic Energy Commission in Saclay, France.

The well known Gamma Cygni supernova remnant – so named for its proximity to the star -- also lies within this region; astronomers estimate its age at about 7,000 years. The Fermi team considers it possible that the supernova remnant spawned the cosmic rays trapped in the Cygnus X "cocoon," but they also suggest an alternative scenario where the particles became accelerated through repeated interaction with shockwaves produced inside the cocoon by powerful stellar winds.

"Whether the particles further gain or lose energy inside this cocoon needs to be investigated, but its existence shows that cosmic-ray history is much more eventful than a random walk away from their sources," Tibaldo added.

Fermi is providing a never-before-seen glimpse of the early life of cosmic rays, long before they diffuse into the galaxy at large. Astronomers know of a dozen stellar clusters at least as young and rich as Cygnus OB2, including the Arches and Quintuplet clusters near the galaxy's center. Energetic gamma rays are detected in the vicinity of several of them, so perhaps they also corral cosmic rays in their own high-energy cocoons.

NASA's Fermi is an astrophysics and particle physics partnership managed by NASA's Goddard Space Flight Center in Greenbelt, Md., and developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

Related Links:

Nursery of Giants Captured in New Spitzer Image
http://www.nasa.gov/vision/universe/starsgalaxies/spitzer-041304.html

NASA's Fermi Telescope Detects Gamma-Rays From 'Star Factories' in Other Galaxies
http://www.nasa.gov/mission_pages/GLAST/news/star_factories.html

What is Cygnus X?
http://www.cfa.harvard.edu/cygnusX/whatis.html


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

Cygnus X-1: NASA's Chandra Adds to Black Hole Birth Announcement

Credit: Optical: DSS; Illustration: NASA/CXC/M.Weiss

JPEG (693.8 kb) - Tiff (31 MB) - PS ( bytes) - Image with Scalebar

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On the left, an optical image from the Digitized Sky Survey shows Cygnus X-1, outlined in a red box. Cygnus X-1 is located near large active regions of star formation in the Milky Way, as seen in this image that spans some 700 light years across. An artist's illustration on the right depicts what astronomers think is happening within the Cygnus X-1 system. Cygnus X-1 is a so-called stellar-mass black hole, a class of black holes that comes from the collapse of a massive star. The black hole pulls material from a massive, blue companion star toward it. This material forms a disk (shown in red and orange) that rotates around the black hole before falling into it or being redirected away from the black hole in the form of powerful jets.

A trio of papers with data from radio, optical and X-ray telescopes, including NASA's Chandra X-ray Observatory, has revealed new details about the birth of this famous black hole that took place millions of years ago. Using X-ray data from Chandra, the Rossi X-ray Timing Explorer, and the Advanced Satellite for Cosmology and Astrophysics, scientists were able to determine the spin of Cygnus X-1 with unprecedented accuracy, showing that the black hole is spinning at very close to its maximum rate. Its event horizon -- the point of no return for material falling towards a black hole -- is spinning around more than 800 times a second.

Chandra X-ray Image of Cygnus X-1

Over three decades ago, Stephen Hawking placed -- and eventually lost - a bet against the existence of a black hole in Cygnus X-1. Today, astronomers are confident the Cygnus X-1 system contains a black hole. In fact, a team of scientists has combined data from radio, optical, and X-ray telescopes including Chandra to determine the black hole's spin, mass, and distance more precisely than ever before. With these key pieces of information, the history of the black hole has been reconstructed. This new information gives astronomers strong clues about how the black hole was born, how much it weighed, and how fast it was spinning. This is important because scientists still would like to know much more about the birth of black holes. (Credit: NASA/CXC)

Using optical observations of the companion star and its motion around its unseen companion, the team also made the most precise determination ever for the mass of Cygnus X-1, of 14.8 times the mass of the Sun. It was likely to have been almost this massive at birth, because of lack of time for it to grow appreciably.

The researchers also announced that they have made the most accurate distance estimate yet of Cygnus X-1 using the National Radio Observatory's Very Long Baseline Array (VLBA). The new distance is about 6,070 light years from Earth. This accurate distance was a crucial ingredient for making the precise mass and spin determinations.

Fast Facts for Cygnus X-1:

Scale: Wide field optical image is 4x5 degrees (560x700 light years)
Category: Black Holes
Coordinates (J2000): RA 19h 58m 21.70s | Dec +35° 12' 05.80"
Constellation: Cygnus
Color Code: Intensity Map
Distance Estimate : About 8,000 light years

Integral Spots Matter a Millisecond from Doom

An artist's impression of the Cygnus X-1 black hole system. Gas from a nearby supergiant star spirals down into the black hole but a small fraction is diverted by magnetic fields into jets that shoot back into space. Credits: ESA

ESA’s Integral gamma-ray observatory has spotted extremely hot matter just a millisecond before it plunges into the oblivion of a black hole. But is it really doomed? These unique observations suggest that some of the matter may be making a great escape.

No one would want to be so close to a black hole. Just a few hundred kilometres away from its deadly surface, space is a maelstrom of particles and radiation. Vast storms of particles are falling to their doom at close to the speed of light, raising the temperature to millions of degrees.

Ordinarily, it takes just a millisecond for the particles to cross this final distance but hope may be at hand for a small fraction of them.

Thanks to the new Integral observations, astronomers now know that this chaotic region is threaded by magnetic fields.

This is the first time that magnetic fields have been identified so close to a black hole. Most importantly, Integral shows they are highly structured magnetic fields that are forming an escape tunnel for some of the doomed particles.

The Imager on Board the Integral Satellite (IBIS) was first activated and put through its paces in November 2002. It captured this image during that test phase and shows not only Cygnus X-1 (centre) but also Cygnus X-3 (upper left). High-energy sources are shown with an 'X' followed by a number according to their strength. Cygnus X-3 is the third brightest high-energy emitter in the constellation of Cygnus, the Swan. Instead of a black hole, Cygnus X-3 is thought to be a neutron star (a tiny dead stellar core) pulling its companion star to pieces. Taken on 16 November 2002, the new IBIS observations support this theory. Cygnus X-1 is about 10 000 light years from Earth and one of the brightest high-energy emitters in the sky. It was discovered in 1966 and is thought to be a black hole, ripping its companion star to pieces. The companion star, HDE 226868, is a blue supergiant with a surface temperature of around 31 000 K. It orbits the black hole once every 5.6 days. Credits: ESA. Original image by the Integral IBIS team. Image processing by ESA/ECF.

Philippe Laurent, CEA Saclay, France, and colleagues made the discovery by studying the nearby black hole, Cygnus X-1, which is ripping a companion star to pieces and feeding on its gas.

Their evidence points to the magnetic field being strong enough to tear away particles from the black hole’s gravitational clutches and funnel them outwards, creating jets of matter that shoot into space. The particles in these jets are being drawn into spiral trajectories as they climb the magnetic field to freedom and this is affecting a property of their gamma-ray light known as polarisation.

A gamma ray, like ordinary light, is a kind of wave and the orientation of the wave is known as its polarisation. When a fast particle spirals in a magnetic field it produces a kind of light, known as synchrotron emission, which displays a characteristic pattern of polarisation. It is this polarisation that the team have found in the gamma rays. It was a difficult observation to make.

“We had to use almost every observation Integral has ever made of Cygnus X-1 to make this detection,” says Laurent.

This is an artist’s impression of ESA’s orbiting gamma-ray observatory, Integral.

Credits: ESA

Amassed over seven years, these repeated observations of the black hole now total over five million seconds of observing time, the equivalent of taking a single image with an exposure time of more than two months. Laurent’s team added them all together to create just such an exposure.

“We still do not know exactly how the infalling matter is turned into the jets. There is a big debate among theoreticians; these observations will help them decide,” says Laurent.

Jets around black holes have been seen before by radio telescopes but such observations cannot see the black hole in sufficient detail to know exactly how close to the black hole the jets originate. That makes these new observations invaluable.

"This discovery of polarized emission from a black hole jet is a unique result demonstrating that Integral, which is covering the high-energy band in ESA's wide spectrum of scientific missions, continues to produce key results more than eight years after its launch," says Christoph Winkler, ESA Integral Project Scientist.

Contact for further information

Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Email: markus.bauer@esa.int
Tel: +31 71 565 6799
Mob: +31 61 594 3 954

Philippe Laurent
Integral/IBIS Instrument Scientist
IRFU / Service d'Astrophysique, CEA Saclay
Laboratoire APC
Email: philippe.laurent@cea.fr
Tel: +33 1 69 08 80 66 / +33 1 57 27 60 72

Christoph Winkler
ESA Integral Project Scientist
Email: cwinkler@rssd.esa.int
Tel: +31 71 565 3591

Notes for editors

Polarized Gamma-ray Emission from the Galactic Black Hole Cygnus X-1 by P. Laurent et al. is published online by Science today and will appear in a future issue of the printed journal.

Cygnus X-1: Still a "Star" After All Those Years

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• Originally discovered in 1964, Cygnus X-1 has been observed intensely since

• In the 1970s, X-ray and optical observations led to the conclusion that Cygnus X-1 contained a black hole, the first one identified

• Because it is only 6,000 light years from Earth, Cygnus X-1 is a very bright and therefore a good target for astronomers to study

Since its discovery 45 years ago, Cygnus X-1 has been one of the most intensively studied cosmic X-ray sources. About a decade after its discovery, Cygnus X-1 secured a place in the history of astronomy when a combination of X-ray and optical observations led to the conclusion that it was a black hole, the first such identification.

The Cygnus X-1 system consists of a black hole with a mass about 10 times that of the Sun in a close orbit with a blue supergiant star with a mass of about 20 Suns. Gas flowing away from the supergiant in a fast stellar wind is focused by the black hole, and some of this gas forms a disk that spirals into the black hole. The gravitational energy release by this infalling gas powers the X-ray emission from Cygnus X-1.

Although more than a thousand scientific articles have been published on Cygnus X-1, its status as a bright and nearby black hole continues to attract the interest of scientists seeking to understand the nature of black holes and how they affect their environment. Observations with Chandra and ESA's XMM-Newton are especially valuable for studying the property of the stellar wind that fuels Cygnus X-1, and determining its rate of spin. This latter research has revealed that Cygnus X-1 is spinning very slowly. This puzzling result could indicate that Cygnus X-1 may have formed in an unusual type of supernova that somehow prevented the newly formed black hole from acquiring as much spin as other stellar black holes.

Fast Facts for Cygnus X-1:

Scale: Image is about 4.7 arcmin across
Category: Black Holes
Coordinates: (J2000) RA 19h 58m 21.70s | Dec +35° 12' 05.80
Constellation: Cygnus
Observation Date: 01/30/2001 - 04/19/2003
Observation Time: 16 hours
Obs. ID: 2742-2743, 3814
Color Code: Intensity
Instrument: ACIS
References: M. Hanke et al. 2009 , Astrophys. J. 690, 330 J. Miller, 2007 Ann.Rev.Astron.Astrophys.45:441-479
Distance Estimate: About 8,000 light years

Possible Jet Blown Shells Near Microquasar Cygnus X-1

Credit & Copyright: Steve Cullen (lightbuckets.com)
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Explanation: What happens to matter that falls toward an energetic black hole? In the case of Cygnus X-1, perhaps little of that matter actually makes it in. Infalling gas may first collide not only with itself but with an accretion disk of swirling material surrounding the black hole.

The result may be a microquasar that glows across the electromagnetic spectrum and produces powerful jets that expel much of the infalling matter back into the cosmos at near light speed before it can even approach the black hole's event horizon. Confirmation that black hole jets may create expanding shells has come recently from the discovery of shells surrounding Cygnus X-1.

Pictured above on the upper right is one such shell quite possibly created by the jet of microquasar and black hole candidate Cygnus X-1. Rolling your cursor over the image will bring up an annotated version. The physical processes that create the black hole jets is a topic that continues to be researched.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
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Source: Astronomy Picture of the Day