The highest angular resolution image in Astronomy reveals the insides of a galactic nucleus

Credit: MPIfR/A. Lobanov

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The space mission RadioAstron (Russian Space Agency) has observed, along with fifteen other radio telescopes spread across the globe, the environment of the black hole at the core of the active galaxy BL Lacertae

Since 1974, observations with very long baseline interferometry (VLBI) have combined the signals from a cosmic object received at different radio telescopes spread around the globe to synthetize an antenna with the equivalent size of the largest separation between them. This has provided unprecedented sharpness of the images, with over 1000 times better resolution than the Hubble Space Telescope can achieve in visible light. Now, an international collaboration has broken all records by combining fifteen radio telescopes on Earth and the radio dish of the RadioAstron mission (Russian Space Agency), in orbit around Earth. The work, lead by the Instituto de Astrofísica de Andalucía (IAA-CSIC), provides new insights into the nature of active galaxies, where an extremely massive black hole swallows surrounding matter while simultaneously shooting out a pair of jets of high-energy particles and magnetic fields at nearly light speed.

Observations of microwave light are essential for exploring these jets, since high-energy electrons moving in magnetic fields are very proficient at producing microwaves. But most active galaxies with bright jets are billions of light years away from Earth, so their jets are tiny on the sky. High resolution is essential for viewing the jets in action to reveal phenomena like shock waves and turbulence that control how much light is produced at any given time. “Combining for the first time ground-based radio telescopes with the space radio telescope of the RadioAstron mission, operating at its maximum resolution, has allowed our team to imitate an antenna with a size of eight times the Earth’s diameter, corresponding to about twenty microarcseconds”, said José L. Gómez, the team leader at the Instituto de Astrofísica de Andalucía (IAA-CSIC).

Seen from Earth, twenty microarcseconds corresponds to the size of a two euro coin on the Moon; this high resolution probes with unprecedented detail the central regions of BL Lacertae, an active galactic nucleus located nine hundred million light-years from Earth, powered by a supermassive black hole two hundred million times more massive than our Sun.

Artist concept showing how long base interferometry works. 

Credit:  MPIfR/A. Lobanov.

Extreme Sources

Active galactic nuclei (AGN) are the most energetic objects in the Universe, harboring a giant black hole at the center. Accretion of material toward the black hole leads to the formation of an accretion disk that tightly orbits the black hole, plus a pair of jets of particles shooting out of the nucleus in opposite directions at speeds nearly equal to that of light. “It is thought that jets originate from material drawn toward the black hole, but how the jets are collimated and accelerated is still largely unknown,” said Gómez. “We know, however, that the magnetic field should play an important role”.

Current models suggest that, due to the rotation of the black hole and accretion disk, the magnetic field lines are “twisted” into a spiral structure. Such a coiled field confines the jet to a narrow beam and accelerates its motion. This model is confirmed by the BL Lacertae observations, which reveal the existence of a large-scale spiral magnetic field in one of the jets.

Artist concept of an active galactic nuclei 

Credit: Wolfgang Steffen, UNAM.

The exceptional resolution obtained with RadioAstron also reveals an unusually intensity of light at the upstream end of BL Lacertae’s jet not observed before in other AGN. This is making astronomers wonder whether their established ideas on how the jets produce microwave light is correct.

“Our current understanding of how the emission is generated in AGN establishes a clear limit on the intensity of microwaves that their cores can produce over long time spans. The extreme intensity observed in BL Lacertae exceeds that limit, requiring either velocities in the jet even closer to the speed of light than thought before or a revision of our theoretical models”, concludes Jose L. Gómez (IAA-CSIC).

Reference:

J. L. Gómez et al. "Probing the innermost regions of AGN jets and their magnetic fields with Radioastron. I. Imaging BL Lacertae at 21 microarcsecond resolution". The Astrophysical Journal, 817, 96 (2016). DOI: 10.3847/0004-637X/817/2/96

http://iopscience.iop.org/article/10.3847/0004-637X/817/2/96


More información:

RadioAstron: http://www.asc.rssi.ru/radioastron/index.html

Contact:

Instituto de Astrofísica de Andalucía (IAA-CSIC)
Unidad de Divulgación y Comunicación
Silbia López de Lacalle - sll@iaa.es - 958230532
http://www.iaa.es
http://www-divulgacion.iaa.es

Source: Instituto de Astrofísica de Andalucía - CSIC

Distant Black Hole Wave Twists Like Giant Whip

 

This cartoon shows how magnetic waves, called Alfven S-waves, propagate outward from the base of black hole jets. 

Image credit: Caltech.  › Full image and caption

This artist's concept illustrates a supermassive black hole with millions to billions times the mass of our sun. 

Image credit: NASA/JPL-Caltech.  › Full image and caption

Fast-moving magnetic waves emanating from a distant supermassive black hole undulate like a whip whose handle is being shaken by a giant hand, according to a new study using data from the National Radio Astronomy Observatory's Very Long Baseline Array. Scientists used this instrument to explore the galaxy/black hole system known as BL Lacertae (BL Lac) in high resolution.

"The waves are excited by a shaking motion of the jet at its base," said David Meier, a now-retired astrophysicist from NASA's Jet Propulsion Laboratory and the California Institute of Technology, both in Pasadena.

The team's findings, detailed in the April 10 issue of The Astrophysical Journal, mark the first time so-called Alfven (pronounced Alf-vain) waves have been identified in a black hole system.

Alfven waves are generated when magnetic field lines, such as those coming from the sun or a disk around a black hole, interact with charged particles, or ions, and become twisted or coiled into a helical shape. In the case of BL Lac, the ions are in the form of particle jets that are flung from opposite sides of the black hole at near light speed.

"Imagine running a water hose through a slinky that has been stretched taut," said first author Marshall Cohen, an astronomer at Caltech. "A sideways disturbance at one end of the slinky will create a wave that travels to the other end, and if the slinky sways to and fro, the hose running through its center has no choice but to move with it."

A similar thing is happening in BL Lac, Cohen said. The Alfven waves are analogous to the propagating sideways motions of the slinky, and as the waves propagate along the magnetic field lines, they can cause the field lines -- and the particle jets encompassed by the field lines -- to move as well.

It's common for black hole particle jets to bend -- and some even swing back and forth. But those movements typically take place on timescales of thousands or millions of years. "What we see is happening on a timescale of weeks," Cohen said. "We're taking pictures once a month, and the position of the waves is different each month."

"By analyzing these waves, we are able to determine the internal properties of the jet, and this will help us ultimately understand how jets are produced by black holes," said Meier.

Interestingly, from the vantage of astronomers on Earth, the Alfven waves emanating from BL Lac appear to be traveling about five times faster than the speed of light, but it's only an optical illusion. 

The illusion is difficult to visualize but has to do with the fact that the waves are traveling slightly off our line of sight at nearly the speed of light. At these high speeds, time slows down, which can throw off the perception of how fast the waves are actually moving.

Other Caltech authors on the paper include Talvikki Hovatta, a former Caltech postdoctoral scholar. Scientists from the University of Cologne and the Max Planck Institute for Radioastronomy in Germany; the Isaac Newton Institute of Chile; Aalto University in Finland; the Astro Space Center of Lebedev Physical Institute, the Pulkovo Observatory, and the Crimean Astrophysical Observatory in Russia; Purdue University in Indiana and Denison University in Granville, Ohio.

Caltech manages JPL for NASA

Media Contact

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, California
818-354-4673
whitney.clavin@jpl.nasa.gov

Source: JPL-Caltech