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Scientists offer an unprecedented look at the “central engine” that drives a solar flare

Scientists offer an unprecedented look at the

Observations of a large solar flare on September 10, 2017 in extreme ultraviolet environments (gray background, NASA Solar Dynamics Observatory) and a microwave (red to blue indicates increasing frequencies observed through the extended Owens Valley solar system). Light orange curves are selected magnetic field lines from a comparable theoretical model of solar flare. The flares are driven by the eruption of a twisted magnetic flux rope (illustrated by a bundle of colored curves). Microwave sources are observed in the central area, where there is an extensive reconnection sheet – the “central motor” of the flare, which is used to measure its physical properties. Credit: CSTR / NJIT, B. Chen, S. Yu; NASA Solar Dynamics Observatory

In a study published in Astronomy of nature, an international team of scientists unveiled a new, detailed look at the “central engine” of a large solar flare accompanied by a strong eruption, first captured September 10, 2017 Owens Valley Solar Array (EOVSA) – a solar radio telescope device operated at the New Jersey Institute of Technology (NJIT) for Solar Terrestrial Research (CSTR).

New findings based on observations of the EOVSA event at microwave wavelengths offer the first measurements characterizing the magnetic fields and particles in the nucleus of the explosion. The results revealed a huge “leaf” with an electric current that stretches more than 40,000 kilometers through the burning area of ​​the core, where the opposite lines of the magnetic field approach each other, break and re-create, creating intense energy that drives the flares.

In particular, the team’s measurements also suggest a magnetic bottle-like structure located at the top of the loop-shaped base (known as the flare arcade) at a height of nearly 20,000 kilometers above the Sun’s surface. The structure proposed by the team is probably the primary place where the high-energy electrons of the flare are captured and accelerated to almost the speed of light.

Scientists say a new study view of the central engine that powers such powerful eruptions may help predict space weather in the future for potentially catastrophic energy leaks from solar flares – the most powerful solar system explosions capable of seriously disrupting technologies on Earth such as satellite operations, GPS navigation and communication systems, among others.

“One of the main goals of this research is to better understand the basic physics of solar flares,” said Bin Chen, lead author and professor of physics at NJIT. “It has long been suggested that these large eruptions are responsible for the sudden release of magnetic energy through the reconnection sheet, but its magnetic properties have not yet been measured. With this study, we finally measured the details of the magnetic field of the first leaf for the first time, which gives us a new understanding of the central motor of the Sun’s main flares. “

“The place where all the energy is stored and released into the sun has been invisible so far. … If you want to play about cosmology, it is a “problem of the dark energy of the Sun” and before that we had to indirectly draw an indirect conclusion. that there is a Flare Magnetic Interconnection Sheet, ”said Dale Gary, Director of EOVSA at NJIT and co-author of the paper. “EOVSA images taken on many microwave frequencies have shown that we can capture radio emissions to illuminate this important region. Once we had these data and analytical tools created by co-authors Gregory Fleishman and Gel Nita, we could begin to analyze the radiation to enable these measurements. ‘ “

Earlier this year in the magazine scienceThe team said it could finally provide quantitative measurements of the evolving strength of the magnetic field directly after the ignition of the flame.

As part of further research, the team’s latest analysis combined numerical simulations performed at the Center for Astrophysics | Harvard and Smithsonian (CfA) with EOVSA spectral observations and multi-wavelength data – exceeding radio waves to X-rays – collected from a X8.2 solar flare. Glare is the second largest occurrence in the last 11 years of the solar cycle, which has occurred during rapid coronal mass ejection (CME), which has caused a large shock in the upper solar corona.

Among the surprises of the study, the researchers found that the measured magnetic field profile along the current flare sheet has closely related predictions from team numerical simulations based on a well-known theoretical model to explain solar flare physics first designed in the 1990s with an analytical form.

“We were surprised that the measured profile of the magnetic field of the current sheet beautifully matched the theoretical prediction made decades ago,” Chen said.

“The strength of the Sun’s magnetic field plays a key role in accelerating the plasma during an eruption. Our model was used to calculate the physics of magnetic forces during this eruption, which manifests itself as a highly twisted “rope” of magnetic field lines, or a rope with magnetic flux, “explained Kathy Reeves, astrophysicist at CfA and co-author of the study. “It’s remarkable that this complicated process can be captured using a direct analytical model, and that the predicted and measured magnetic fields match so well.”

Simulations performed by Chengcai Shen in CfA were developed to numerically solve control equations to quantify the behavior of electrically conductive plasma in the entire magnetic field of a flare. Using modern computational techniques known as “adaptive mesh enhancement”, the team was able to solve a thin layer of reconnection and capture its detailed physics at fine spatial scales up to 100 kilometers.

“Our simulation results are consistent with a theoretical prediction of the magnetic field configuration during a solar flare and reproduce a number of observable features from that particular flare, including magnetic force and plasma inflow / outflow around the regenerating current layer,” Shen noted.

Shocking measurements

The results of team measurement and compliance simulation revealed that the current flare leaf has an electric field that generates a shocking 4,000 volts per meter. Such a strong electric field is present in an area of ​​40,000 kilometers, greater than the length of three Earths placed side by side.

The analysis also showed that a huge amount of magnetic energy is pumped into the current sheet at an estimated rate of 10-100 billion trillion (10)22-1023) joules per second – this means that the amount of energy processed in the flare engine in each second is equivalent to the total energy released by the explosion of about hundreds of thousands of the strongest hydrogen bombs (50-megatat class)) at the same time.

“Such a huge release of energy in the current layer is blowing into the mind. The strong electric field that is created there can easily accelerate the electrons to relativistic energies, but the unexpected fact that we found was that the profile of the electric field in the current area of ​​the leaf did not match. with the spatial distribution of the relativistic electrons that we measured, “said Chen. “In other words, there must be something else at play to accelerate or redirect these electrons. What our data show was the peculiar location at the bottom of the current sheet – the magnetic bottle – that seems to be crucial in producing or limiting relativistic electrons. . “

“While the current blade appears to be the place where energy is released to spin the ball, most of the electron acceleration seems to occur at this other place, the magnetic bottle. … Similar magnetic flasks are being developed to reduce and accelerate particles in some laboratory fusion reactors. Gary added. “Others have already suggested such a structure of solar flares, but now we can really see them in numbers.”

Approximately 99% of the relativistic electrons of the flare were observed to collect on the magnetic bottle during the five-minute emission.

Chen says the group will now be able to apply these new measurements as a benchmark to study other solar flare events, as well as explore the exact mechanism that accelerates particles by combining new observations, numerical simulations, and advanced theories. Due to EOVSA’s groundbreaking capabilities, NJIT was recently selected to participate in the NASA / NSF DRIVE Science Center for the Release of Solar Energy (SolFER).

“Our goal is to gain a full understanding of solar flares, from their onset to the final spray of high-energy particles into the solar wind and finally into the Earth’s cosmic environment,” said Jim Drake, a professor of physics at the university. Maryland and Principal Investigator SolFER, who did not participate in this study. “These first observations already suggest that relativistic electrons could be trapped in a large magnetic bottle created as the magnetic fields of a corona ‘reconnection’ to release their energy. EOVSA’s observations will continue to help us decipher how it drives the magnetic field. these energy electrons. ‘ “

“Further investigation of the role of the magnetic bottle in particle acceleration and transport will require more advanced modeling compared to EOVSA observations,” Chen said. “We certainly have great prospects for studying these basic questions.”

Measuring the structure of a huge solar flare

More information:
Bin Chen et al., Measurement of magnetic field and relativistic electrons along a solar flare flow sheet, Astronomy of nature (2020). DOI: 10,1038 / s41550-020-1147-7

Provided by the New Jersey Institute of Technology

Citations: Scientists offer an unprecedented look at the “central engine” driving the solar flare (2020, July 27) obtained on July 29, 2020 from https://phys.org/news/2020-07-unprecedented-central-powering-solar-flare. html

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