An international research team has introduced a new look inside the “central engine” of the solar flare, accompanied by an eruption, finding a huge electric current “leaf”, offering the first measurements that characterize the magnetic field.
In a study published in Nature astronomy, an international team of researchers presents a new, detailed look at the “central engine” of a large solar flare, accompanied by a powerful eruption, first captured on September 10, 2017 by the Owens Valley Solar Massif (EOVSA) – a solar radio telescope object controlled New Jersey, Institute of Technology‘s (NJIT) Center for Solar Ground Research (CSTR).
The new data, based on EOVSA’s observations of the event at the microwave wavelength, offer the first measurements characterizing the magnetic fields and particles at the base of the explosion. The results revealed a huge “sheet” of electric current stretching more than 40,000 kilometers through the core of the flash, where opposite magnetic field lines approach each other, break and reconnect, generating intense energy that feeds the flash.
Notably, the team’s measurements also point to a magnetic bottle-shaped structure located at the top of the flash-shaped loop (known as an arcade flash) at an altitude of nearly 20,000 kilometers above the Sun’s surface. The structure, according to the team, is probably the primary place where high-energy flash electrons fall into the trap and accelerate almost to the speed of light.
Researchers say a new understanding of this study of the central engine that powers such powerful eruptions could help future weather forecasts in space for potentially catastrophic solar energy emissions – the most powerful solar system explosions that could severely disrupt technology on Earth. satellite operations, GPS navigation and communication systems, among many others.
“One of the main goals of this study is to better understand the fundamental physics of solar eruptions,” said Bin Chen, lead author and professor of physics at NJIT. “It has long been assumed that the sudden release of magnetic energy through the reconnection current sheet is the cause of these large eruptions, but its magnetic properties were not measured. With this study, we finally measured the magnetic field details engine of the main flares of the Sun “.
“The place where all the energy is stored and released in solar flares was still invisible. … To play on the term cosmology, this is a “problem of the sun’s dark energy,” and we previously had to indirectly conclude the existence of a magnetic flash recovery letter, “said Dale Gary, director of EOVSA at NJIT and co-author of the paper. “EOVSA images taken at many microwave frequencies have shown that we can capture radio radiation to illuminate this important region. Once we received this data and the analysis tools created by co-authors Gregory Fleischmann and Gel Nita, we were able to begin radiation analysis to enable these measurements. ”
Earlier this year in the journal Science, the team said it could finally provide quantitative measurements of the evolving force of the magnetic field immediately after the flash ignited.
Continuing his research, the team’s latest analysis combined numerical simulations performed at the Center for Astrophysics | Harvard and the Smithsonian (CfA) with EOVSA spectral observations and multi-wavelength data – covering radio waves to X-rays – collected from a solar flare of size X8.2. The outbreak is the second largest in the last 11-year solar cycle, which occurred during the rapid release of coronal mass (CME), which caused a large-scale impact in the upper solar corona.
Among the surprises of the study, the researchers found that the measured magnetic field profile along the current flash sheet has closely matched predictions from numerical team simulations based on the well-known theoretical model for explaining solar flare physics first proposed in the 1990s with analytical form.
“We were surprised that the measured magnetic field profile of the current sheet fits perfectly with the theoretical forecast made a decade ago,” Chen said.
“The strength of the Sun’s magnetic field plays a key role in acceleration plasma during the eruption. Our model was used to calculate the physics of magnetic forces during this eruption, which manifests itself as a strongly twisted “rope” of magnetic field lines or a rope of magnetic flux, “explained Katie Reeves, CfA astrophysicist and co-author of the study.” It is noteworthy that this complex process can be recorded by a simple analytical model, and that the predicted and measured magnetic fields correspond so well. “
Simulations performed by Chenhai Sheng in CfA were developed to numerically solve control equations to quantify the behavior of electrically conductive plasma throughout the magnetic field of the flash. Using advanced computing techniques known as “adaptive grid enhancement,” the team was able to solve a thin sheet of reconnection and capture its detailed physics on ultra-thin spatial scales below 100 kilometers.
“Our simulation results correspond both to the theoretical prediction of the magnetic field configuration during a solar eruption and to a set of observable features of this particular flash, including magnetic force and plasma inflow / outflow around the recovery sheet,” Shen said.
The measurement results and the corresponding team simulation results showed that the flash current has an electric field that produces 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 the three Earths, located next to each other.
The analysis also showed that a huge amount of magnetic energy is pumped into the current sheet at an estimated rate of 10-100 trillion (1022-1023) joules per second – that is, the amount of energy processed in the flash engine, per second, is equivalent to the total energy released. when about a hundred thousand of the most powerful hydrogen bombs (50-megaton class) explode simultaneously.
“Such a huge release of energy on the current sheet is impressive. The strong electric field created there can easily accelerate the electrons to relativistic energies, but the unexpected fact we found was that the electric field profile in the current region of the sheet did not match the spatial distribution of the relativistic electrons we measured, ”Chen said. “In other words, something else had to be played to speed up or redirect these electrons. Our data have shown that the special location at the bottom of the current sheet – the magnetic bottle – is crucial in the production or restriction of relativistic electrons.
“While there seems to be a place on the current sheet where energy is released to make the ball roll, most of the electron acceleration seems to take place in this other place, the magnetic bottle. “Such magnetic bottles are designed to limit and accelerate particles in some laboratory thermonuclear reactors.” Gary added. “Others have suggested such a structure in solar flares before, but we can really see it in numbers now.”
Approximately 99% of the relativistic flash electrons were observed to gather near the magnetic bottle for the entire duration of the radiation for five minutes.
Currently, Chen says the group will be able to use these new measurements as a comparative baseline for studying other solar flares, as well as to study the exact mechanism that accelerates particles, combining new observations, numerical simulations and advanced theories. Due to the breakthrough capabilities of EOVSA, NJIT was recently selected to work together NASACollaboration of the DRF DRIVE Research Center on Solar Flash Energy (SolFER).
“Our goal is to develop a full understanding of solar flares, starting with their initiation, until they finally spray high-energy particles into the solar wind, and finally into the Earth’s space environment,” said Jim Drake, a professor of physics at the University of Maryland. principal investigator SolFER, who did not participate in this study. These first observations already suggest that relativistic electrons can be trapped in a large magnetic bottle formed as the “magnetic field of the corona” reconnects “to release its energy. E EOVSA observations will continue to help us understand how the magnetic field moves these energy electrons. ”
“Further study of the role of the magnetic bottle in the acceleration and transport of particles will require better modeling for comparison with EOVSA observations,” Chen said. “We certainly have great prospects for studying these issues that relate to these key issues.”
Reference: “Measurement of magnetic field and relativistic electrons along the solar flare sheet” Bin Chen, Chengkai Shen, Dale E. Gary, Katharine K. Reeves, Gregory D. Fleischman, Siji Yu, Fan Go, Sam Krucker, June Lin, Gelu M Nita and Xiangyang Kong, July 27, 2020, Nature astronomy.
DOI: 10.1038 / s41550-020-1147-7