Stellar light is the term used to describe the electromagnetic radiation emitted by stars, primarily due to the nuclear fusion of hydrogen atoms occurring within their cores.
- Unlike traditional sources of light on Earth, stars ignite with a far more powerful process – nuclear fusion.
- Deep within their incredibly dense and hot cores, immense pressure and temperatures fuel nuclear fusion.
- This process forces hydrogen atoms to merge into heavier elements, primarily helium, releasing tremendous energy.
- A fraction of this energy escapes the star as the radiant light we call sunlight and starlight.
Nuclear Fusion Process
- Fuel and Fusion: Nuclear fusion (thermonuclear fusion) primarily occurs in a star’s core, consuming hydrogen and generating energy and light.
- Immense Conditions: The immense pressure and temperature within the core are crucial for hydrogen atoms to overcome their natural repulsion and fuse.
- Energy Release: This fusion process releases vast amounts of energy, including the light we see from stars. Fusion reactions release millions of times more energy than traditional chemical reactions, like burning fossil fuels.
- Temperature and Colour: Hotter stars, fusing at a faster rate, emit more energy and appear blue or white. Cooler stars with slower fusion emit less and appear red or orange.
- Lifespan and Evolution: Massive stars burn hotter and brighter, but as their hydrogen reserves deplete and their fusion processes change, they produce a dimmer glow.
From Core to Surface
- The light generated in the core of stars doesn’t immediately escape.
- It interacts with surrounding layers of hot gas (plasma) within the star.
- These layers absorb and re-emit light at different wavelengths, ultimately shaping the final spectrum we detect.
- Finally, the light escaping a star’s surface embarks on its interstellar journey, eventually reaching Earth, our telescopes and eyes.
- Sunlight originates from the Sun’s core and reaches Earth in about 8 minutes after travelling through its outer layers.
Sunlight and stellar light
- Light emitted by the Sun and stars is not just a single colour but a spectrum of colours.
- The electromagnetic spectrum extends far beyond the visible light we perceive.
- The Sun and stars emit radiation across the whole electromagnetic spectrum, although a limited range of wavelengths make it through the Earth’s atmosphere.
- Sun and stellar light on Earth include wavelengths stretching into the ultraviolet and infrared.