Astronomy & Astrophysics 101: Stellar Wind

This Hubble Space Telescope image of the Veil Nebula reveals the fine details of the nebula’s delicate threads and filaments of ionized gas. Credit: ESA/Hubble & NASA, Z. Levay

What Is Stellar Wind?

Stellar winds are fast-flowing streams of particles that are emitted from a star.

Even though stars may appear to be stable and static, they are in fact extremely hot, active, and dynamic. Particles, including protons, electrons, and atoms, can be emitted from a star, resulting from either the outward pressure of internal fusion reactions or the star’s magnetic field. Stellar winds in low- to intermediate-mass stars, such as the Sun, tend to be driven by the stellar magnetic fields.

Particles in the outermost layers of a star acquire sufficient energy from magnetic field interactions to escape its gravity. This process generates stellar winds that only cause stars to lose a very small percentage of their mass during the stable period of their lifetime (prior to their evolution into red giants). In contrast, some more massive stars cast off their own mass in very powerful stellar winds, which are driven directly by outward pressure from the stars’ own radiation. This type of stellar wind can cause a star to lose up to half of its own mass during the course of its lifetime.

Stellar winds are fast-flowing streams of particles that are emitted from a star. Credit: ESA/Hubble, NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team

Hubble’s imagery has captured the effects and presence of stellar wind, as seen in the Veil Nebula (pictured at the top of the page). Astronomers suspect that the Veil Nebula’s source star had a strong stellar wind before it exploded. This wind blew a large cavity into the surrounding interstellar gas. As the shock wave from the supernova expanded outwards, it encountered the walls of this cavity — and formed the nebula’s distinctive structures. Bright filaments are produced as the shock wave interacts with a relatively dense cavity wall, while fainter structures are generated by regions nearly devoid of material.

The Veil Nebula’s colorful appearance is due to variations in the temperature and density of the gas present. By applying new processing techniques to Hubble’s data in 2021, the fine details of the Veil nebula’s delicate threads and filaments of ionized gas have brought out new details, particularly enhanced details of emissions from doubly ionized oxygen, ionized hydrogen, and ionized nitrogen (compared to its previous images in 2015 and 2007).