Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

X-ray 'echoes' map a supermassive black hole's environs

01.06.2012
An international team of astronomers using data from the European Space Agency's (ESA) XMM-Newton satellite has identified a long-sought X-ray "echo" that promises a new way to probe supersized black holes in distant galaxies.

Most big galaxies host a big central black hole containing millions of times the sun's mass. When matter streams toward one of these supermassive black holes, the galaxy's center lights up, emitting billions of times more energy than the sun. For years, astronomers have been monitoring such "active galactic nuclei" (AGN) to better understand what happens on the brink of a monster black hole.


This illustration compares the environment around NGC 4151's supermassive black hole with the orbits of the planets in our solar system; the planets themselves are not shown to scale. Echoes of X-ray flares detected in XMM-Newton data demonstrate that the X-ray source (blue sphere, center) is located above the black hole's accretion disk. The time lag between flares in the source and their reflection in the accretion disk places the X-ray source about four times Earth's distance from the sun.

Credit: Credit: NASA's Goddard Space Flight Center

"Our analysis allows us to probe black holes through a different window. It confirms some long-held ideas about AGN and gives us a sense of what we can expect when a new generation of space-based X-ray telescopes eventually becomes available," said Abderahmen Zoghbi, a postdoctoral research associate at the University of Maryland at College Park (UMCP) and the study's lead author.

One of the most important tools for astronomers studying AGN is an X-ray feature known as the broad iron line, now regarded as the signature of a rotating black hole. Excited iron atoms produce characteristic X-rays with energies around 6,000 to 7,000 electron volts -- several thousand times the energy in visible light – and this emission is known as the iron K line.

Matter falling toward a black hole collects into a rotating accretion disk, where it becomes compressed and heated before eventually spilling over the black hole's event horizon, the point beyond which nothing can escape and astronomers cannot observe. A mysterious and intense X-ray source near the black hole shines onto the disk's surface layers, causing iron atoms to radiate K-line emission. The inner part of the disk is orbiting the black hole so rapidly that the effects of Einstein's relativity come into play -- most notably, how time slows down close to the black hole. These relativistic effects skew or broaden the signal in a distinctive way.

Astronomers predicted that when the X-ray source near the black hole flared, the broad iron K line would brighten after a delay corresponding to how long the X-rays took to reach and illuminate the accretion disk. Astronomers call the process relativistic reverberation. With each flare from the X-ray source, a light echo sweeps across the disk and the iron line brightens accordingly.

Unfortunately, neither ESA's XMM-Newton satellite nor NASA's Chandra X-ray Observatory possess telescopes powerful enough to spot reverberations from individual flares.

he team reasoned that detecting the combined echoes from multiple flares might be possible if a sufficiently large amount of data from the right object could be analyzed. The object turned out to be the galaxy NGC 4151, which is located about 45 million light-years away in the constellation Canes Venatici. As one of the brightest AGN in X-rays, NGC 4151 has been observed extensively by XMM-Newton. Astronomers think that the galaxy's active nucleus is powered by a black hole weighing 50 million solar masses, which suggested the presence of a large accretion disk capable of producing especially long-lived and easily detectable echoes.

Since 2000, XMM-Newton has observed the galaxy with an accumulated exposure of about four days. By analyzing this data, the researchers uncovered numerous X-ray echoes, demonstrating for the first time the reality of relativistic reverberation. The findings appear in the May 8 issue of Monthly Notices of the Royal Astronomical Society.

The team found that echoes lagged behind the AGN flares by a little more than 30 minutes. Moving at the speed of light, the X-rays associated with the echo must have traveled an additional 400 million miles -- equivalent to about four times Earth's average distance from the sun -- than those that came to us directly from the flare.

"This tells us that the mysterious X-ray source in AGN hovers at some height above the accretion disk," said co-author Chris Reynolds, a professor of astronomy at UMCP and Zoghbi's adviser. Jets of accelerated particles often are associated with AGN, and this finding meshes with recent suggestions that the X-ray source may be located near the bases of these jets.

"The data show that the earliest echo comes from the most broadened iron line emission. This originates from closest to the black hole and fits well with expectations," said co-author Andy Fabian, an astrophysicist at the University of Cambridge in England.

Amazingly, the extreme environment at the heart of NGC 4151 is built on a scale comparable to our own solar system. If we replaced the sun with the black hole, the event horizon would extend less than halfway to Earth if the black hole spins rapidly; slower spin would result in a larger horizon. The X-ray source would hover above the black hole and its accretion disk at a distance similar to that between the sun and the middle of the asteroid belt.

"Teasing out the echo of X-ray light in NGC 4151 is a remarkable achievement. This work propels the science of AGN into a fundamental new area of mapping the neighborhoods of supermassive black holes," said Kimberly Weaver, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md., who was not involved in the study. NASA Goddard hosts the XMM-Newton Guest Observer Facility, which supports U.S. astronomers who request observing time on the satellite.

The detection of X-ray echoes in AGN provides a new way of studying black holes and their accretion disks. Astronomers envision the next generation of X-ray telescopes with collecting areas large enough to detect the echo of a single AGN flare in many different objects, thereby providing astronomers with a new tool for testing relativity and probing the immediate surroundings of massive black holes.

Francis Reddy | EurekAlert!
Further information:
http://www.nasa.gov

More articles from Physics and Astronomy:

nachricht Significantly more productivity in USP lasers
06.12.2016 | Fraunhofer-Institut für Lasertechnik ILT

nachricht Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

NTU scientists build new ultrasound device using 3-D printing technology

07.12.2016 | Health and Medicine

The balancing act: An enzyme that links endocytosis to membrane recycling

07.12.2016 | Life Sciences

How to turn white fat brown

07.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>