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Home / Science / Take a look at an unprecedented “central engine” that generates huge amounts of sunlight

Take a look at an unprecedented “central engine” that generates huge amounts of sunlight

A flash of sunshine in extreme UV rays

Large solar flare monitoring in 2017 September 10 In extreme ultraviolet light (gray background – NASA Solar Dynamics Observatory) and in the microwave (red to blue indicates increasing frequency observed by the solar collector of the extended Owens Valley). The light orange curves are selected by the magnetic field line from a harmonized theoretical solar flare model. The burst is caused by ruptured magnetic flux ropes (illustrated by a beam of color curves). Microwave sources are monitored throughout the central region, which has a large-scale reconnection current sheet, the “central motor” of the flame, and are used to measure its physical properties. Credit: CSTR / NJIT, B. Chen, S. Yu; NASA Solar Dynamics Observatory

An international research team has provided a new picture of the “central motor” of the solar flare, the accompanying eruption, and has revealed a huge “sheet” of electric current, providing the first measurements describing the magnetic field.

In a study published Natural astronomy, an international team of researchers gave a new, comprehensive look at the “central engine” of the large solar flare, accompanied by a powerful eruption first recorded in 2017. September 10 In the Owens Valley Solar Range (EOVSA) – on solar radio. telescopic unit controlled New Jersey Institute of Technology‘(NJIT) Solar and Earth Research Center (CSTR).

The new findings, based on EOVSA observations of the event at microwave wavelengths, provide the first measurements describing the magnetic fields and particles at the center of the explosion. The results revealed a giant “sheet” of electric current stretching more than 40,000 kilometers through the core flame region, where opposing magnetic field lines approach each other, break and reconnect, creating an intense energy that emits a flash.

Notably, the team’s measurements also show a magnetic bottle-like structure at the top of a flame-loop-shaped base (known as a flame arcade), nearly 20,000 kilometers above the Sun’s surface. The team suggests a structure, most likely, a major location where very strong energy electrons are trapped and accelerated almost to the speed of light.

Researchers say new research insights into the central engine that drives such powerful eruptions could help predict future weather forecasts for potentially catastrophic solar energy – the most powerful solar system explosions that could severely disrupt Earth-based technologies such as satellite, GPS navigation and communication systems, among others.

“One of the main goals of this study is to better understand the basic physics of solar flares,” said Bin Chen, principal author of the paper and professor of physics at NJIT. “It has long been thought that the sudden release of magnetic energy through the junction current sheet causes these large eruptions, but its magnetic properties have not been measured. In this study, we first measured the magnetic field data of the current sheet, providing a new understanding of the main solar rocket engine. “

“The place where all the energy is stored and released in the sun has been invisible until now. … To play from the cosmological term this is the “dark energy problem” of the Sun. In the past, we had to implicitly conclude that there is a flame magnetic bonding sheet, ”said Dale Gary, NJIT EOVSA director and co-author. paper. “EOVSA images generated at many microwave frequencies have shown that we can capture radio waves to illuminate this important region. Once we had the data and analysis tools developed by co-authors Gregory Fleishman and Gelu Nita, we were able to begin analyzing radiation to make these measurements. “

Earlier this year, the team reported in Science that they could finally quantify the strength of the changing magnetic field immediately after the flame ignited.

Continuing the study, the latest team analysis combined digital simulations performed at the Astrophysics Center | Harvard and Smithsonian (CfA) with EOVSA spectral imaging observations and multi – wavelength data covering radio waves up to X – rays collected from a solar flare of size X8.2. The burst is the second largest of the previous 11-year solar cycle, resulting from rapid coronal mass displacement (CME), which caused a large-scale blow to the upper solar corona.

Among the surprises of the study, the researchers found that the measured magnetic field profile along the flame current sheet feature closely matched the predictions of the team’s numerical simulations based on a known theoretical model for explaining solar physics physics, first proposed in the 1990s with an analytical form.

“It surprised us that the measured magnetic field profile of the current sheet fit nicely with a theoretical prediction made decades ago,” Chen said.

“The force of the sun’s magnetic field plays an acceleration plasma during the eruption. Our model was used to calculate the physics of magnetic forces during this eruption, which manifests itself as a highly twisted magnetic field line rope or magnetic flux rope, ”explained Kathy Reeves, CfA astrophysicist and co-author of the study. . “Surprisingly, this complex process can be captured by a straight-line analytical model and that the predicted and measured magnetic fields match so well.”

The simulation performed by Chengcai Shen by CfA was developed to numerically solve the governing equations to quantify the behavior of electrically conductive plasma over the entire flash magnetic field. Using a state-of-the-art computational method known as “adaptive network enhancement,” the team was able to solve a thin interconnection current sheet and capture its detailed physics on super perfect spatial scales up to 100 kilometers.

“Our simulation results are consistent with theoretical predictions about the configuration of the magnetic field during solar radiation and reproduce a set of observable properties from this particular flash, including magnetic strength and plasma flow / leakage around the reconnected current sheet,” Shen noted.

Shock measurements

The team’s measurements and harmonized simulation results showed that the current flash sheet contains an electric field that generates a shocking 4,000 volts per meter. Such a strong electric field is in a region of 40,000 kilometers longer than three Earths arranged side by side.

The analysis also showed that a large amount of magnetic energy is pumped into the current sheet at an estimated speed of 10 to 100 billion trillion (1022 to 1023) joules per second, that is, the amount of energy processed in the flame engine per second is equal to the total energy. released by the explosion of about one hundred thousand most powerful hydrogen bombs (class of 50 megatons) at a time.

“It simply came to our notice then. The strong electric field there can easily accelerate the electrons to relativistic energies, but the unexpected fact we found was that the electric field profile in the current sheet does not match our measured spatial distribution of relativistic electrons, ”said Chen. In other words, something more had to be played to accelerate or direct these electrons. Our data showed that a special place at the bottom of the current sheet – a magnetic bottle – is an essential condition for the production or binding of relativistic electrons. “

Although the current sheet appears to be the place where the energy is released to roll the ball, most of the electron acceleration occurs in this other place, the magnetic bottle. … Similar magnetic bottles are being developed to trap and accelerate particles in some laboratory fusion reactors. Gary added. “Others have suggested such a sunlight structure in the past, but now we can really see it in numbers.”

Approximately 99% of the relativistic electrons in the flash were observed to accumulate at the magnetic vial over the entire five-minute radiation.

So far, Chen says the group will be able to apply these new measurements as a comparative starting point for studying other solar flare events, as well as exploring a precise mechanism that accelerates particles by combining new observations, digital models, and advanced theories. Due to the potential for a breakthrough in EOVSA, NJIT was recently selected to participate in the joint venture NASA/ NSF DRIVE Science Center Collaboration on Solar Energy Release (SolFER).

“Our goal is to develop a thorough understanding of the sun’s rays from their inception until they finally spray highly energy particles into the solar wind and eventually into the Earth’s cosmic environment,” said Jim Drake, a professor of physics at the university. Maryland and principal SolFER researcher who did not participate in this study. These first observations already suggest that relativistic electrons may be trapped in a large magnetic bottle made when the crown’s magnetic fields “reconnect” to release their energy. … EOVSA observations will continue to help us figure out how the magnetic field drives these energy electrons. “

“Further investigation into the role of the magnetic bottle in particle acceleration and transport will require more sophisticated modeling to compare with EOVSA’s observations,” said Chen. “There are, of course, great prospects for studying these key issues.”

Reference: “Measurement of Magnetic Field and Relativistic Electrons Along the Solar Heat Current Sheet,” by Bin Chen, Chengcai Shen, Dale E. Gary, Katharine K. Reeves, Gregory D. Fleishman, Sijie Yu, Fan Guo, Säm Krucker, Jun Lin. , Gelu M. Nita and Xiangliang Kong, 2020 July 27 Natural astronomy.
DOI: 10.1038 / s41550-020-1147-7

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