Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

How to feed a black hole

05.12.2006
A special magnetic effect, the so-called magnetorotational instability (MRI), plays a key role in the formation of stars and planetary systems. It is also what feeds the black holes in the center of galaxies. For the first time, this effect has been observed in a laboratory experiment at the Forschungszentrum Dresden-Rossendorf (FZD). These results have recently been published in “Physical Review Letters”.

Everybody remembers the picture of the hungry black hole swallowing all matter in its vicinity. Not even light has a chance to escape. However, closer inspection reveals that feeding a black hole is far from trivial. Typically, the matter around black holes has organized itself into so-called accretion disks.

And just as the Earth is not falling into the sun, the black hole cannot just scarf up the matter encircling it. Before being swallowed by the black hole, the gas in the disk has to be slowed down in order to weaken the centrifugal forces, which keep the gas rotating. But how does one put the brakes on matter in an accretion disk? Since this problem not only applies to black holes, but also to normal stars, it is of fundamental importance for the formation of cosmic structures.

Balbus and Hawley proposed the solution to this problem in 1991. They showed mathematically that stable rotating flows can be destabilized by external magnetic fields. This effect, now known as magnetorotational instability (MRI), enables sufficient angular momentum transport in accretion disks, which is essential for the mass concentration in stars and black holes.

Laboratory simulation of star formation

For approximately five years, teams throughout the world have tried to create this instability in a laboratory. Two recent papers in the journal “NATURE” (November 16, 2006) underlined the urgent need for an experimental demonstration of MRI by showing evidence that hydrodynamics alone is not capable of producing turbulence in accretion disks. At the Forschungszentrum Dresden-Rossendorf the experiment PROMISE (Potsdam Rossendorf Magnetic InStability Experiment) was set-up and carried out as a joint project between scientists from Dresden and from the Astrophysikalisches Institut Potsdam (AIP). The experimental set-up contains unusual details, such as the use of a simple wastewater tube carrying the coil that produces the vertical magnetic field. Within this tube, there are two co-axial copper cylinders with a two to one ratio in radius. As long as the rotation rate of the outer cylinder is larger than a quarter of the rate of the inner cylinder, the liquid metal flow between them is stable. The flow field is measured with ultrasonic velocity sensors. The interesting point is that this initially stable flow is destabilized by an externally applied spiral magnetic field. For the first time, this experiment allowed the observation of a magnetorotational instability in a laboratory.

The figure shows the measured axial flow as a function of the vertical position and time for three different currents in the coils. In each case, the azimuthal magnetic field is produced by an axial current of 6000 Ampères. In good agreement with numerical simulations, an upward traveling wave is observed only for certain levels of current in the coils. Moreover, the measured frequency of the traveling wave agrees well with the numerical prediction.

The results were published recently in “Physical Review Letters” and “Astrophysical Journal Letters”.

Christine Bohnet | alfa
Further information:
http://www.fzd.de
http://www.aip.de

More articles from Physics and Astronomy:

nachricht Breakthrough with a chain of gold atoms
17.02.2017 | Universität Konstanz

nachricht New functional principle to generate the „third harmonic“
16.02.2017 | Laser Zentrum Hannover e.V.

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: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Switched-on DNA

20.02.2017 | Materials Sciences

Second cause of hidden hearing loss identified

20.02.2017 | Health and Medicine

Prospect for more effective treatment of nerve pain

20.02.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>