Encountering the "flame" of the starry sky: exploring the mystery of the sun

Produced by: Science Popularization China

Author: Yun Chaoang, Shen Jinhua (Xinjiang Astronomical Observatory, Chinese Academy of Sciences)

Producer: China Science Expo

Editor's note: In order to unveil the mystery of scientific work, the China Science Popularization Frontier Science Project launched a series of articles called "Me and My Research", inviting scientists to write articles themselves, share their scientific research experiences, and create a scientific world. Let us follow the explorers at the forefront of science and technology and embark on a journey full of passion, challenges, and surprises.

In May 2024, a TV series about Altay topped the online ratings chart. The beauty of Altay in the series is natural. Under the camera, the mountains, jungles, sky and wilderness are all unique. As one of the "postcards" of Xinjiang's beautiful scenery, the starry sky of Altay is also unique, and the "Aurora" feast that is staged one after another is beautiful.

This is the aurora photographed in Fuyun County, Altay Prefecture, Xinjiang

(Photo source: Xinhua News Agency, Dai Jianfeng)

Photographed by Dai Jianfeng in Altay, Xinjiang

(Photo source: Xinhua News Agency)

Beautiful starry sky "flame" - Aurora

The aurora is a natural phenomenon that can be seen with the naked eye on the ground, caused by the interaction between solar wind plasma and the Earth's magnetosphere.

The appearance of aurora is related to solar flares. Flares are active phenomena in which local areas of the solar atmosphere suddenly brighten. The sun itself is a huge "magnetic ball". Flares often appear in active areas with complex magnetic field structures. In flare active areas, as magnetic energy continues to accumulate in the active areas, magnetic lines of force will be "distorted". These twisted magnetic lines of force are like tightened rubber bands. Once the twisted magnetic lines of force are cut off due to reconnection, a large amount of energy will be released in a short time. At this time, the plasma in the coronal atmosphere will be rapidly heated and accelerated, accompanied by enhanced electromagnetic radiation and particle emission in various bands. This strong explosion phenomenon is called a flare.

During a solar flare, a large amount of corona plasma is often ejected into the space between the Sun and Earth, which is called a "coronal mass ejection". The Sun continuously ejects matter from its surface into the surrounding space. During the peak of the solar activity cycle, 2-3 coronal mass ejections (CMEs) may occur every day. These plasma materials travel at speeds of several hundred to thousands of kilometers per second. The plasma facing the Earth will cause disturbances in the size and direction of the Earth's magnetic field, thus generating "geomagnetic storms" and other extreme space weather events. The aurora is a visual manifestation of geomagnetic storms.

During a magnetic storm, the number of particles injected into the polar regions after the interaction between plasma and the magnetosphere will increase significantly, and the latitudinal range of injection into the Earth's magnetic field will also expand, allowing places such as Xinjiang, which are located in the middle and high latitudes of the Earth, to see the auroras.

Solar flares

(Photo source: veer photo gallery)

Xinjiang Astronomical Observatory of the Chinese Academy of Sciences is the only comprehensive observatory in Northwest China. As the aurora has received widespread social attention, members of the solar group of Xinjiang Astronomical Observatory have recently upheld the responsibility of scientists and are very willing to share relevant popular science knowledge with the public. In fact, solar activity has a cycle of about 11 years. The most active period of solar activity is called the "maximum period", and the least active period is called the "minimum period". During the maximum period, the number of sunspots increases and the frequency of flares also increases. On the contrary, during the minimum period, the number of sunspots and the frequency of flares will decrease.

2013-2014 was the peak period of solar activity. It is expected that solar activity will reach its 25th peak period in 2024-2025. 2024 is in the rising stage of the peak period. Solar flares are very frequent. The following figure shows dozens of extreme flare events in May 2024, which triggered geomagnetic storms and formed colorful auroras in Xinjiang and Beijing. The energy levels of flare eruptions are divided into five levels from small to large: A, B, C, M, and X, and the levels increase in sequence.

The lifespan of most solar flares is only between a few minutes and tens of minutes, and is accompanied by a large amount of energy release in a short period of time. For example, the energy released instantly by a level XX1 flare is equivalent to the total energy received by the same receiving area on Earth over more than 1,000 years.

Observation results of solar flare energy during part of May this year

(Image source: Space Environment Forecast)

Know yourself and your enemy to prevent trouble

Geomagnetic storms can cause communication problems, power outages, and satellite failures around the world. The most famous of these is the Carrington Event. On the morning of September 1, 1859, British astronomy enthusiast Carrington was observing sunspots when he discovered that two extremely bright white lights suddenly appeared in a large group of sunspots on the north side of the sun, and a pair of bright crescent-shaped objects were forming near a large group of sunspots. It was later confirmed that the phenomenon Carrington saw was the process of a solar flare, and this event was called the Carrington Event.

Seventeen and a half hours after the flare erupted, the pointer of the magnetometer jumped out of the scale due to the extremely strong magnetic field. At almost the same time, operators of telegraph machines in telegraph offices around the world reported that their machines were sparking and even the wires were melted. That night, the colorful aurora borealis in the sky spread southward to Cuba, Hawaii and other places.

Northern Lights

(Photo source: veer photo gallery)

The Carrington Event was a super-strong solar activity explosion. Similar super-strong events have occurred many times in history, such as the solar storm in March 1989, which caused the entire power distribution network in Quebec, Canada to fail, and the super-strong solar storm on October 30, 2003, which caused two satellites to malfunction and caused communication and power grid outages around the world.

Based on this, scientists believe that the study of solar activity bursts is, on the one hand, a core issue in basic research in solar physics and a natural laboratory for studying other stars and plasma physics, providing help for future exploration of coronal heating issues; on the other hand, it can predict solar activity and provide effective early warning for catastrophic space weather.

Conceptual image of the sun's surface and solar flares

(Photo source: veer photo gallery)

We have something to say about solar research

Since the 1980s, the Xinjiang Astronomical Observatory of the Chinese Academy of Sciences has built equipment such as solar chromosphere, photospheric binocular telescopes and solar radio telescopes at the Nanshan Observatory, mainly conducting research on the physical mechanisms of solar flare eruptions and providing forecasts of solar activities.

Nanshan Observatory View

(Image source: Xinjiang Astronomical Observatory, Chinese Academy of Sciences)

After years of development, the Xinjiang Astronomical Observatory Solar Physics Research Group was officially established in 2018. After its establishment, the group focused on the work of the Xinjiang Astronomical Observatory's scientific research center, aiming to seize the commanding heights of science and technology, and achieved a series of research results:

First, the dynamic evolution of flare rings and coronal magnetic loops was studied during the release of magnetic energy in solar activity outbreaks (Shen ApJ, 2014), and the process of magnetic flux rope formation in the early stage of flares was revealed for the first time (Shen, ApJ, 2017). It was reported for the first time that the injection of magnetic flux rope currents in the early stage of flares drove the eruption of flares (Shen, RAA, 2022, 2023). Using high-resolution observations, the dipole field separation motion and the formation of arched dark stripes in the process of rice-grain emergence in emergent active regions were reported, revealing the origin of small-scale magnetic flux emergence (Shen, ApJ, 2022). In the study of coronal heating, the coronal heating caused by magnetoacoustic oscillations of the solar photospheric area was directly observed (Hashim, RAA, 2021, ApJ 2024).

Second, in the study of solar radio bursts and radiation mechanisms, possible radiation models of radio type V and motion type IV bursts were proposed (Tang, ApJ, 2016, 2020), and research on the fine structure of solar radio was conducted (Tang, RAA, 2021, Wan A&A, 2021).

Third, in terms of shock wave particle acceleration, the double shock wave chasing effect was simulated and studied, and the "head-on" collision between the CME shock wave and the Earth's bow shock was simulated. It was found that the energy spectrum of the merged particles showed a "broken" feature (Wang, ApJ, 2017), and it was found that the particle injection rate was positively correlated with the acceleration efficiency (Wang, ApJ, 2019).

Evidence for the formation of magnetic flux ropes

(Image source: provided by the author Shen et al, ApJ, 2017)

Evidence for non-thermal electron acceleration in flare precursors

(Image source: Shen et al, RAA, 2022)

As a key development direction of the "14th Five-Year Plan", Xinjiang Astronomical Observatory's solar physics "Solar Activity Outbursts and Space Weather Research" has conducted a series of research work by revealing the dynamic evolution of solar activity outbursts of different scales, flare magnetic energy accumulation and release, and coronal heating. Our research results can solve the core problems of basic research in solar physics on the one hand, and accurately predict the outburst of solar activity on the other hand, and provide reliable early warning information for disastrous space weather.

Evidence for coronal heating channels

(Image source: Haxim et al. ApJ, 2024 provided by the author)

Although it is higher than a flying wild goose, it still cannot reach the blue sky. The solar physics research group of Xinjiang Astronomical Observatory is in its golden age. In the near future, it will strive to build a radio telescope with ultra-high time and spectral resolution in the low-frequency band, or carry out necessary upgrades and modifications to the existing observation equipment to meet the needs of higher-level solar observations; second, strive to implement more small solar telescopes to support the rapid development of solar physics field research in my country; third, use large-aperture telescopes at home and abroad to study the physical mechanisms of solar eruption activities of different scales, and provide timely warnings for space weather forecasts.

The road ahead will need to be verified by time. Members of the solar physics team of the Xinjiang Astronomical Observatory will seize the present, plan for the future, and use their unregretful youth to pave the scientific road leading to a better tomorrow.