Space laboratory of plasma physics

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Apart from the commonly known states of matter: liquid, solid and gas, physicists distinguish one more, a fourth state called plasma. This kind of matter has an increasing number of applications in modern technology. It is used, among others, in television or computer screens and the rocket engines of the future. This is why research on plasma is one of the essential fields in modern physics.

Plasma is a mixture of free electrons and ions, i.e., atoms partly or completely devoid of electrons. It is often penetrated by a magnetic field. Outer space is the perfect laboratory for plasma research, due to the possibility of obtaining properties that are unattainable in laboratories on Earth, which provides various experimental conditions. In dark, dense clouds of gas, the temperature falls below –250°C, while in the remnants of supernova explosions it may reach even millions of degrees above zero. Also in this cosmic laboratory we can find both gas that is many billions of trillions times more diluted than air and matter that is so dense that an object the size of a die made from it would weigh millions of tons.

Radio astronomers from Kraków also use this space laboratory of plasma physics, focusing in particular on the gas that fills galaxies gas and dust. The properties of plasma are analyzed using its magnetism. Each magnetic field has a specific structure described by the shape of so-called magnetic lines that connect the magnetic poles. In Earthly conditions, we can discover the structure of these lines by means of a simple experiment. Simply put a glass panel on the magnet, strew some iron filings on the glass and tap on it lightly. The filings will arrange along the lines of the magnetic field.


The flow of cosmic plasma

Our team came upon the original idea to use the fact that the magnetic field can be deformed in a characteristic way, squeezed and stretched by the movements of plasma. On the other hand, a sufficiently strong magnetic field can control the flow of plasma, which is important for its technological applications. Radio waves generated in galactic magnetic fields inform us about the strength of the magnetic field and about the distortions of the magnetic lines themselves. Analyzing their properties with use of radio telescopes, we can in our own way ‘strew the iron filings' across the galaxy, revealing the structure of the magnetic lines," informs Professor Marek Urbanik from the Astronomical Observatory at the Jagiellonian University.

Scientists draw conclusions about the properties and movements of plasma in galaxies by studying the shape of magnetic lines. The analysis of the radiation of galaxies at radio frequencies is performed using the largest radio telescopes in the world: the one hundred-meter giant in Effelsberg (Germany) and large networks of radio telescopes in India and in the United States. The research is carried out in cooperation with the MaxPlanck Institut für Radioastronomie in Bonn, Ruhr Universität Bochum, Université de Strasbourg, Observatoire de Paris- Meudon and Columbia University.

In spiral galaxies, the "filings" from the experiment described above would show the presence of twisted magnetic lines that look like spirals. This is a result of the co-called dynamo process, controlled by the rotation of the galaxy. It amplifies and arranges the magnetic fields, giving the form to magnetic lines described above.

However, there is a whole class of irregularly shaped galaxies that rotate ten times slower than spiral galaxies. Even just a few years ago it was believed that the magnetic dynamo process cannot exist in such conditions and that such objects are devoid of magnetic fields. However, the research team at the Jagiellonian University, while observing one of the slowly rotating, irregular galaxies using a network of 27 antennas in the United States, made a surprising discovery: the metaphorical "filings" still show the existence of a spirally arranged magnetic field, which is strong enough to control interstellar plasma in this galaxy. "This led to the necessity of developing new theories of the evolution of galactic magnetism, and we are actively participating in this process," added Professor Urbanik.

Irregular galaxy NGC 4449. The image in visible light (so-called Hα line)
is shown in red. White lines: this is how iron filings would be arranged
if only we could strew them across the galaxy. Longer lines mean
more orderly magnetic fields.

Magnetic analysis of galaxies

The diagnostics of plasma movements based on magnetism proved to be a perfect tool for the analysis of gas flow in galaxies, which mutually perturb their structures through forces of gravity. Such objects are characterized by the presence of very strong effects of squeezing gas, which causes the "compression" of magnetic lines along the front of the wave squeezing the plasma. This phenomenon is visible in the form of narrow ridges of highly ordered "filings", allowing for the localization of gigantic, interstellar shock waves. Analogically, magnetic lines bent outwards from the galaxy indicate that streams of magnetized plasma are thrown out of this object. Such magnetic diagnostics have proven particularly useful in the research on galaxies grouped in clusters. The extensive program of research on magnetic fields in galaxies in the Virgo cluster, inspired by the scientists from the Faculty of Physics, Astronomy and Applied Computer Sciences at the Jagiellonian University and conducted in cooperation with the institutions listed above, enabled creation of a whole catalogue of various disturbances in gas movement in galaxies grouped in clusters. Phenomena found there include, among others, shock waves that are thousands of light years long, as well as intergalactic clouds and streams of magnetized gas drawn out from galaxies. These effects are almost unnoticeable in visible light, which makes the radio methods used by scientists from Kraków particularly useful diagnostic tools.

The existence of magnetized intergalactic plasma in clusters consisting of hundreds of galaxies was already proven more than ten years ago, although at that time little was known about the intergalactic magnetism in galaxy groups consisting of several objects. Meanwhile, scientists from Kraków, using a network of antennas in the United States, discovered ordered magnetic fields in a galaxy group called Stephan's Quintet. The magnetic fields there are so strong that they can control the physical processes in intergalactic plasma.

These examples do not exhaust all results of the works of scientists from the Kraków center. "Studying such exotic objects as galaxies, we managed to collect a wide database concerning various properties of magnetized plasma in conditions unattainable in laboratories on Earth. This is a valuable supplement to our knowledge about the physics of plasma, which is so important for the development of modern technologies," Professor Urbanik concluded.

Research team: Krzysztof Chyży, PhD; Robert Drzazga, MSc; Wojciech Jurusik, MSc; Professor Marek Urbanik; Marian Soida, PhD; Jacek Knapik, MSc; Błażej Nikiel-Wroczyński, MSc; Professor Katarzyna Otmianowska–Mazur; Natalia Nowak, MSc