Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Cosmic turbulences result in star and black hole formation

HZDR physicists offer new concept for the development of turbulences within 'dead zones'

Just how stars and black holes in the Universe are able to form from rotating matter is one of the big questions of astrophysics. What we do know is that magnetic fields figure prominently into the picture.

This image shows an artist's rendering of a protoplanetary disc.

Credit: Pat Rawlings / NASA

However, our current understanding is that they only work if matter is electrically well conductive -- but in rotating discs this isn't always the case. Now, a new publication by Helmholtz-Zentrum Dresden-Rossendorf physicists in the scientific journal Physical Review Letters shows how magnetic fields can also cause turbulences within "dead zones," thus making an important contribution to our current understanding of just how compact objects form in the cosmos.

When Johannes Kepler first proposed his laws of planetary motion in the early days of the 17th century, he could not have foreseen the central role cosmic magnetic fields would play in planetary system formation. Today, we know that in the absence of magnetic fields, mass would not be able to concentrate in compact bodies like stars and black holes. One prominent example is our solar system, which formed 4.6 billion years ago through the collapse of a gigantic cloud of gas, whose gravitational pull concentrated particles in its center, culminating in the formation of a large disc.

"These accretion discs are extremely stable from a hydrodynamic perspective as according to Kepler's laws of planetary motion angular momentum increases from the center towards the periphery," explains HZDR's own Dr. Frank Stefani. "In order to explain the growth rates of stars and black holes, there has to exist a mechanism, which acts to destabilize the rotating disc and which at the same time ensures mass is transported towards the center and angular momentum towards the periphery."

As early as 1959, Evgenij Velikhov conjectured that magnetic fields are capable of prompting turbulences within stable rotating flows. Although it wasn't until 1991 that astrophysicists Steven Balbus and John Hawley fully grasped the fundamental significance of this magneto rotational instability (MRI) in cosmic structure formation. Balbus and Hawley will be this year's recipients of the one million Dollar Shaw Prize for astronomy, which will be given in September 2013. However, în order to ensure the MRI actually works, the discs have to exhibit a minimum degree of electrical conductivity.

In areas of low conductivity like the "dead zones" of protoplanetary discs or the far-off regions of accretion discs that surround supermassive black holes, the MRI's effect is numerically difficult to comprehend and is thus a matter of dispute. HZDR scientists, who to date have been mostly concerned with an experimental study of the MRI, have now offered a new theoretical explanation for this phenomenon.

Rivalry between physicists and astrophysicists

If you try and simulate the MRI in a liquid metal experiment with an exclusively vertically oriented magnetic field this field has to be rather strong. At the same time, since the rotational speed has to be very high, these types of experiments are extremely involved and thus far success has eluded them. Back in 2005, for the first time ever, Dr. Stefani and his colleagues at the HZDR and the Leibniz Institute for Astrophysics Potsdam managed to successfully simulate the cosmic process in the lab. By adding a circular magnetic field to a vertical one, they were able to observe the MRI at substantially smaller magnetic fields and rotational speeds. According to Steven Balbus and Hantao Ji per the current August edition of the magazine Physics Today, one of the blemishes of this "helical MRI" is the fact that it only acts to destabilize rotational profiles that are relatively precipitous towards the periphery, which for now does not include rotation profiles obeying Kepler's law.

Magnetic fields and rotating flows reinforce each other

The HZDR scientists are now countering this weighty astrophysics argument with their latest insights. The calculations by Dr. Oleg Kirillov and Dr. Frank Stefani have shown that the helical MRI very much applies to the Keplerian rotation profile if only the circular magnetic field is produced not entirely from the outside but at least partly from within the accretion disc. "This is in fact a much more realistic scenario. In the extreme case that there does not exist a vertical field, we're looking at a problem of what came first – the chicken or the egg. A circular magnetic field acts to destabilize the disc and the resulting turbulence generates components of vertical magnetic fields. They in turn reproduce the circular magnetic field because of the special form of the disc's rotational movement." Regardless of whether with or without a vertical magnetic field, current calculations show that the MRI is possible even in areas of low conductivity like the "dead zones" -- something astrophysicists had not previously thought possible.

The HZDR scientists were driven by their long-standing experience with cosmic magnetic field experiments in the lab, from a model of Earth's dynamo to magneto-rotational instability all the way to Tayler instability. The latter is being debated by astrophysicists with reference to cosmic jets and the formation of neutron stars, among others, but also has to be considered in the construction of large liquid metal batteries, for example. At this time, the scientists are planning a large-scale experiment using liquid sodium, which they are hoping to realize over the next few years as part of the DRESDYN Project. "Once we get this experiment, which for the first time ever will combine the MRI with Tayler instability, up and running, we will much improve our understanding of the interaction between various magnetic cosmic phenomena," says a happy Stefani. Regardless of who is the one to push the envelope in this amicable competition -- the experimental physicists or the theoretical astrophysicists -- the angular momentum transport in astrophysics and in the lab will continue to be a hotly contested topic.

Christine Bohnet | EurekAlert!
Further information:

More articles from Physics and Astronomy:

nachricht Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1
21.03.2018 | Fraunhofer-Institut für Hochfrequenzphysik und Radartechnik FHR

nachricht Taming chaos: Calculating probability in complex systems
21.03.2018 | American Institute of Physics

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: Researchers Discover New Anti-Cancer Protein

An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.

The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

Im Focus: Tiny implants for cells are functional in vivo

For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.

In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

Latest News

Modular safety concept increases flexibility in plant conversion

22.03.2018 | Trade Fair News

New interactive map shows climate change everywhere in world

22.03.2018 | Earth Sciences

New technologies and computing power to help strengthen population data

22.03.2018 | Earth Sciences

Science & Research
Overview of more VideoLinks >>>