Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Iron in the sun: a greenhouse gas for X-ray radiation

Novel X-ray spectroscopic method provides valuable data on highly charged iron ions for astrophysics

Scientists from the Heidelberg Max Planck Institute for Nuclear Physics (MPIK) in cooperation with DESY (Hamburg) at the synchrotron PETRA III have investigated for the first time X-ray absorption of highly charged iron ions.

Illustration of the inner structure of the Sun: The energy released by nuclear fusion of hydrogen to helium in the Sun’s core is transported outwards via radiation. In the outer shell energy transfer is dominated by convection.

Graphics (modified by MPIK): Kelvinsong, Wikimedia Commons

Transportable trap for highly charged ions (EBIT) in operation at the X-ray laser LCLS (Stanford Linear Accelerator Center, Menlo Park, California, USA).

Photo: J. R. Crespo López-Urrutia, MPIK

A transportable ion trap developed at MPIK was used for generation and storage of the ions. The high-precision measurements provide important new insight into the role of highly charged ions in astrophysical plasmas, e. g. for radiation transport inside stars. [Physical Review Letters, September 5, 2013]

Highly charged ions - that is, atoms which have been stripped off most of their electrons - play an important role in astrophysics. Within the large accumulations of visible (luminous) matter in the universe, the highly charged state is the natural one. This is the case in stellar atmospheres as well as in the interior of stars, where temperatures of several million degrees Celsius rule. Highly charged ions also abound around exotic objects such as neutron stars or black holes. Before matter plunges into their cores, it delivers gravitational energy, heating up and emitting extremely intense X-rays, which can be observed.

X-rays also determine the energy transport inside the Sun. At its core temperature of 15 million degrees, a natural fusion power plant runs with a total capacity of about 4•10^26 watts. The power density of 200 watts per cubic meter is, however, modest, and corresponds to about that of a compost heap. In contrast to such, the Sun is very large. If the solar core would freely radiate X-rays at those temperatures, a power exceeding the fusion energy yield by 11 orders of magnitude would be lost. The sun works because the radiation transport to the outside is inhibited, thus maintaining the high core temperature. Convection, the heat transport by turbulent upstream flows of hot matter, only takes place further outward, starting at about 70% of the solar radius. This good insulation reduces hydrogen consumption and extends the duration of fusion in our central star to the billions of years that are needed for the formation of a stable planetary system, and ultimately for the development of life.

A measure of the inhibition of radiation transport is the ‘opacity’ of the solar matter, a term describing how efficiently radiation is absorbed by it. Although the Sun consists mainly of hydrogen and helium, these elements only play a secondary role for the opacity. Their share of it diminishes from about 50% in the outer core to below 20% in the radiation zone. Crucial there are the tiny impurities (about 1.6% by mass) of heavier elements, dubbed by astronomers ‘metals’. Besides oxygen, iron, with its mass fraction of only 0.14%, plays for X-rays the role of a greenhouse gas, and contributes about a quarter of the total opacity. To illustrate it: the total amount of iron in the sun would reach for a solid wall of about 100 km thickness at the edge of the radiation zone, at 500,000 km radius. As a dilute impurity in the solar plasma, iron takes a substantial role in the X-ray shielding.

In order to better understand the role of these stellar ‘trace gases’ and obtain reliable data for comparison with astronomical observations, physicists in the team of José R. Crespo López-Urrutia from the Heidelberg Max Planck Institute for Nuclear Physics (MPIK) have prepared, in cooperation with colleagues from DESY (Hamburg) and eight other institutions worldwide, highly charged iron ions in eight different charge states and studied them systematically. PhD student Jan Rudolph and his colleagues installed a mobile electron beam ion trap (EBIT) for the production and storage of highly charged ions at the PETRA III storage ring. This facility provides one of the world's most powerful X-ray beams, which was focused onto the trapped ions and tuned in its energy. In this way, the absorption of the X-ray radiation by the iron ions could be measured for the first time, and with high precision. This new laboratory astrophysical data show a good agreement with the latest theoretical calculations. In addition to the characteristic energies of the absorption lines found in the spectra, their natural line width (for the first time measured in this experiment) is also very important, because it determines the maximum radiant power which a single iron ion can handle. It amounts almost one watt per ion for the observed X-ray transitions. Even within the solar core, iron ions are not yet saturated with respect to radiation transport, because they can absorb and emit X-ray photons a million times faster than normal atoms can do with the much less energetic visible photons. This combination of high rates and high photon energy crucially determines the dominance of iron in the solar radiation balance.

The new data provide valuable insights for the opacity calculations that can be used as the basis of stellar models. In addition, they also help in the diagnostics of astrophysical plasmas, such as those surrounding active galactic nuclei, or in binary systems containing compact objects - such as neutron stars or black holes - accreting matter from the partner star. The iron X-ray lines studied here are usually the last spectroscopic witnesses of such processes.

Original publication:
X-Ray Resonant Photoexcitation: Linewidths and Energies of Kα Transitions in Highly Charged Fe Ions

J. K. Rudolph et al., Physical Review Letters 111, 103002 (2013) DOI: 10.1103/PhysRevLett.111.103002

Dr. Bernold Feuerstein | Max-Planck-Institut
Further information:

More articles from Physics and Astronomy:

nachricht New thruster design increases efficiency for future spaceflight
16.08.2017 | American Institute of Physics

nachricht Tracking a solar eruption through the solar system
16.08.2017 | American Geophysical Union

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: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

Im Focus: Scientists improve forecast of increasing hazard on Ecuadorian volcano

Researchers from the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science, the Italian Space Agency (ASI), and the Instituto Geofisico--Escuela Politecnica Nacional (IGEPN) of Ecuador, showed an increasing volcanic danger on Cotopaxi in Ecuador using a powerful technique known as Interferometric Synthetic Aperture Radar (InSAR).

The Andes region in which Cotopaxi volcano is located is known to contain some of the world's most serious volcanic hazard. A mid- to large-size eruption has...

All Focus news of the innovation-report >>>



Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

Latest News

New thruster design increases efficiency for future spaceflight

16.08.2017 | Physics and Astronomy

Transporting spin: A graphene and boron nitride heterostructure creates large spin signals

16.08.2017 | Materials Sciences

A new method for the 3-D printing of living tissues

16.08.2017 | Interdisciplinary Research

More VideoLinks >>>