Sun’s coronal magnetic field measured
The Sun is our closest star and we have been studying it for a long time. Yet, it has many associated puzzles that are unexplained. A significant advance has been made by an international team of solar physicists led by those from Peking University, China, and National Center for Atmospheric Research of the U.S. The group has measured the global magnetic field of the sun’s corona, or outer atmosphere, for the very first time. This research has been published in the journal Science.
Hot corona puzzle
- There are two main puzzles about the Sun which this advancement will help address. First is the coronal heating problem. Though the core of the Sun is at a temperature of about 15 million degrees, its outer layer, the photosphere is a mere 5700 degrees hot.
- However, its corona or outer atmosphere, which stretches up to several million kilometres beyond its surface, is much, much hotter than the surface.
- It is at a temperature of one million degrees or more. What causes the atmosphere of the Sun (corona) to heat up again, though the surface (photosphere) is cooler than the interior.
- That is the question which has baffled solar physicists. Popular attempts to explain this puzzle invoke the magnetic field of the corona. Hence the present work will help understand and verify these theories better.
- The other set of questions concerns the mechanisms of eruptions of the Sun, such as solar flares and coronal mass ejections.
- These are driven by magnetic reconnections happening in the sun’s corona.
- The team used a technique known as coronal seismology or magnetoseismology to measure the coronal magnetic field which has been known for a few decades.
- This method requires the measurement of the properties of magnetohydrodynamic (MHD) waves and the density of the corona simultaneously.
- The team used the improved measurements of the Coronal Multi-channel Polarimeter (CoMP) and advanced data analysis to measure the coronal magnetic field.
- CoMP is an instrument operated by High Altitude Observatory, of the U.S. It is located at Mauna Loa Solar Observatory, near the summit of that volcano on the big island of Hawaii.