Brazilians Achieve Important Results on Astrophysical Plasma

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It follows one article published day (02/13) in the english website of the Agência FAPESP highlighting that Brazilian researchers achieve important results in study on astrophysical plasmas.

Duda Falcão

Brazilian Researchers Achieve Important
Results in Study on Astrophysical Plasmas

José Tadeu Arantes
February 13, 2013

Studies were carried out in a
Thematic Project at the USP
Institute of Astronomy, Geophysics
and Atmospheric Sciences (Nasa)
Agência FAPESP – Most of the visible matter in the universe is composed of ionized or partially ionized gas permeated by magnetic fields. This gas makes up more than 90% of the visible material identified in intergalactic and interstellar space.

Some of the most important cosmic phenomena are associated with this gas: from the large-scale structure of the universe to the formation of galaxies, stars and planets to the “signatures” that compact objects (such as supernovas, neutron stars, black holes and active galaxy nuclei, among others) produce in their vast surroundings, such as ultra-high-energy particles, accretion disks, gravitational waves and gamma ray eruptions.

These and other phenomena were studied in the recently concluded Thematic Project titled “Investigation of High-Energy and Plasma Astrophysics Phenomena: Theory, Observation and Numerical Simulations.” The Thematic Project was coordinated by Professor Elisabete Maria de Gouveia Dal Pino of the Universidade de São Paulo Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG-USP).

“It was a broad study that brought together the High-Energy Astrophysics Group, coordinated by myself at IAG, and the group from the Mackenzie Presbyterian University Radioastronomy and Astrophysics Center, led by Adriana Benetti Marques Valio, along with researchers from other institutions,” said de Gouveia Dal Pino.

Theoretical and computational tools were used, with a focus on exploiting the magneto-hydrodynamics of fluids to study phenomena that seem varied but are intrinsically similar, such as solar spots, wind produced by stars and jets emitted by active galactic nuclei.

“We paid special attention to the basic processes of plasma physics, such as the formation of magnetic fields, magnetic reconnection (the rearrangement of magnetic topology due to the interaction of two or more flows of magnetic fields, where magnetic energy is converted into kinetic energy, thermal energy and particle acceleration), magneto-hydrodynamic instabilities, stochastic turbulence and acceleration. These are fundamental to explaining a number of phenomena related to astrophysical sources and the medium in which they are found,” detailed de Gouveia Dal Pino.

The coordinator highlighted six of the Thematic Project’s numerous developments that made possible the completion of many masters and doctoral theses, as well as publication of a number of articles in high-profile international journals. The first of these is an article on the acceleration of cosmic rays in regions of magnetic reconnection.

“The confinement of particles between the topographical lines in magnetic fields with opposite polarities, such as those formed by a central black hole and the accretion disk that revolves around it in active galaxy nuclei, make them ricochet many times, accumulating energy until they acquire relativistic velocities (approaching the speed of light) and manage to escape the magnetic reconnection zone in the form of cosmic rays,” explained the researcher.

This mechanism for the formation of cosmic rays, theoretically proposed by de Gouveia Dal Pino and Alexander Lazarian of the University of Wisconsin (in the United States), was corroborated by computer simulation models created by IAG post-doctoral candidate Grzegorz Kowal. The mechanism is effective at many scales of the universe, from stellar rings to active galactic nuclei and the gaseous intergalactic medium.

Another highlight of the research project was an investigation of the formation of clouds and generation of new stars in the interstellar and intergalactic medium due to the shock waves produced by supernova explosions, in a collaborative study carried out with Claudio Melioli (also an IAG post-doctoral candidate) and others.

Computer simulations of the central region of the Perseus galaxy cluster (the brightest cluster in the sky under x-ray detection) suggested that the turbulence mostly produced by supernova explosions on the surface of the central galaxy causes a number of effects in the intergalactic medium, such as a near-isotropic distribution (uniform in all directions) of gaseous filaments extending over 100 megaparsecs (approximately 1021 kilometers).

“Diego Falceta-Gonçalves (from the USP School of Arts, Sciences and Humanities), de Gouveia Dal Pino and others have shown that the combination of these turbulent winds with the more parallel (compact) jets emitted by the central active galactic nucleus can explain the nearly isotropic warming (to temperatures from 107 to 108 K) of the gas that permeates the nucleus of the cluster,” said de Gouveia Dal Pino.

The third highlight involves intragalactic stellar formation. “Numerical simulations run by de Gouveia Dal Pino’s IAG doctoral students Reinaldo Santos de Lima and Marcia R. Moreira Leão have shown that turbulence in the interstellar medium caused by phenomena such as supernova explosions and jets from stars contribute to the removal of magnetic fields. As we know, they resist the gravitational contraction of protostellar clouds, and their partial removal contributes to the formation of stars,” explained de Gouveia Dal Pino.

The model proposed by the group’s researchers and staff is based on the diffusion of magnetic fields through turbulent magnetic reconnection. When turbulence is present, magnetic reconnection becomes faster and therefore more effective.

Solar Dynamo

Exoplanetary research is another important contribution of the Thematic Project coordinated by de Gouveia Dal Pino. She and her collaborators participated in the discovery of new substellar and exoplanetary systems through use of the NICI (Near-Infrared Coronagraphic Imager) Planet-Finding Campaign at the Gemini Observatory.

The Gemini Observatory consists of two identical telescopes with mirrors 8.1 meters in diameter that operate in both the visual and infrared ranges. These are located in two of the best locations on Earth for observing the universe: Cerro Pachón, at 2720 meters above sea level in the Chilean Andes, and Mauna Kea in Hawaii, at 4220 meters above sea level.

“Aside from these, the work on exoplanetary transit, which provides information on the activity of their host stars, was conducted by Adriana Benetti Marques Valio, professor at Mackenzie and the main researcher for the Thematic,” said de Gouveia Dal Pino.

The fifth highlight of the project was related to research on the solar dynamo, a mechanism generated inside the Sun by ionized gas in motion. “Theoretical and numerical studies allowed us to map out the cycles of solar spots, which are areas of increased magnetic field concentration that present two maximums and two minimums within a complete 22-year cycle. Based on the model, we built diagrams showing this type of activity,” said de Gouveia Dal Pino.

An article on the subject by Stanford University (U.S.) post-doctoral student Gustavo Guerrero and de Gouveia Dal Pino was featured in the Astronomy & Astrophysics journal in 2008. In addition, Guerrero’s doctoral thesis was awarded an Honorable Mention by the Brazilian Federal Agency for the Support and Evaluation of Graduate Education (CAPES).

Another important contribution of the FAPESP-funded Thematic Project was a group of studies on the origin and evolution of magnetic fields in the intercluster (ICM) and intergalactic (IGM) mediums.

“We ran simulations of turbulent amplifications of seed magnetic fields in approximately acollisional magnetohydrodynamic scenarios. Due to the extremely low density of these mediums and to the presence of the magnetic field, the pressure and temperature variables became anisotropic, showing distinct values in the directions parallel and perpendicular to the field. This anisotropism produces kinetic instabilities,” explained de Gouveia Dal Pino.

The simulations, which were studied by, among others, Reinaldo Santos de Lima (whose doctoral studies at IAG are funded by FAPESP, under de Gouveia Dal Pino’s supervision) showed that these instabilities limit the increase of anisotropism, which causes the magnetic field seeding to increase to rates similar to those of standard magnetohydrodynamic models.

Source: English WebSite of the Agência FAPESP


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