Blazing Hair of the Sun

An international team of solar physicists, including academics from Northumbria University in Newcastle, recently measured the global magnetic field of the solar corona, the outermost layer of the Sun’s atmosphere for the first time.

The sun is a magnetized star, with its magnetic field playing a critical role in shaping the solar atmosphere. This magnetic field affects and governs the behaviour of the Sun in many aspects, causing an 11-year solar cycle, magnificent solar flares, and the heating of the plasma gas in the solar corona to millions of degrees.

The solar corona or the sun’s very thin upper atmosphere is an ever-changing forest of bubbling plasma. However, it is quite a difficult task to map the forces of magnetic fields that largely control this environment. Magnetic fields are relatively weak, and the total brightness of the Sun outshines its corona.

In an article published in the August 7 issue of Science, researchers report that the magnetic field strength in the solar corona mostly changes between 1 and 4 gauss, which is several times the strength of the Earth’s magnetic field on the planet’s surface.

Theorists had shown decades ago that the velocities of coronal waves could be used to understand the magnetic field strength. Such waves would also help carry heat from the Sun’s surface to the solar corona. But no one had ever measured them across the entire corona.

Observations made in the study, by using a special instrument called a coronagraph to block the sun’s bright disk, allowed solar physicists to measure the velocity and intensity of fluctuations in the coronal plasma. And thus, the technique allowed mapping the coronal magnetic field on a large scale for the first time.

In principle, this technique can be used to routinely obtain maps of global coronal magnetic fields and to complete the missing parts of the measurements of the Sun’s magnetism. Along with magnetic field measurements simultaneously taken from the Sun’s surface, these synoptic coronal magnetograms will provide critical information to enhance the understanding of how the magnetic field connects the different layers of the Sun’s atmosphere, as well as the physical mechanisms responsible for solar flares and the solar cycle.

Preparing global maps of the coronal magnetic field strength will pave the way for getting better predictions of space weather events that may adversely affect our planet of intense digital life.

The researchers are now working on an improved version of the coronagraph for the Coronal Solar Magnetism Observatory (COSMO), which will use the same technique over and over to predict the Sun’s behaviour.