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 Study offers new theoretical approach to describing non-equilibrium phase transitions
27.04.2017 | DOE/Argonne National Laboratory

nachricht SwRI-led team discovers lull in Mars' giant impact history
26.04.2017 | Southwest Research Institute

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: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Fighting drug resistant tuberculosis – InfectoGnostics meets MYCO-NET² partners in Peru

28.04.2017 | Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

 
Latest News

Wireless power can drive tiny electronic devices in the GI tract

28.04.2017 | Medical Engineering

Ice cave in Transylvania yields window into region's past

28.04.2017 | Earth Sciences

Nose2Brain – Better Therapy for Multiple Sclerosis

28.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>