What happens when Sun-like stars reach the end of their lives? The recently observed Egg Nebula is here to show us.
This structure, located about one thousand light-years away in the constellation Cygnus, has been immortalized by the Hubble Space Telescope with remarkable precision. We can see a central star, similar to an egg yolk, surrounded by clouds of dust and gas that form concentric arcs. Two beams of light traverse these layers, creating a dynamic and energetic image.
New image of the Egg Nebula by the Hubble Space Telescope.
Credit: NASA, ESA, Bruce Balick (University of Washington)
The Egg Nebula represents one of the first stages in the process of forming a planetary nebula. Unlike many other nebulae that shine on their own, the light here comes directly from the dying star, filtering through the gaps in its dusty envelope. This phase, called a pre-planetary nebula, is relatively short on an astronomical scale, lasting only a few thousand years.
Furthermore, the symmetrical patterns observed around the star indicate that these structures do not result from a violent explosion. For scientists, they could be the result of a series of events still poorly understood, related to the carbon-enriched core of the dying star. Thus, these observations allow the study of the star's matter ejection in near real-time.
By combining different Hubble images, researchers have been able to reconstruct the layered structure of the nebula with an unprecedented level of detail. This data helps understand how dying stars shape their environment, preparing the material that can serve in the birth of future stars and planets.
The next stages in this star's evolution will see its core become hotter, ionizing the surrounding gas and causing the nebula to glow with its own light. This transition will mark the passage into a full-fledged planetary nebula, contributing to the cycle of matter in the galaxy.
How do stars evolve at the end of their lives?
This journey depends mainly on the initial mass of the star. For solar-type stars, the end of life begins when they have consumed the hydrogen in their core. The helium-rich core then contracts and the temperature increases, leading to the expansion of the outer layers into a red giant.
During this phase, nuclear reactions produce heavier elements like carbon and oxygen. The star becomes unstable, periodically ejecting significant amounts of matter into space. These ejections form envelopes of gas and dust that can be observed as pre-planetary nebulae, like the Egg Nebula.
Once the outer layers are dissipated, the hot and dense core of the star is exposed. Its ultraviolet radiation ionizes the surrounding gases, making the nebula glow and marking the planetary nebula stage. The residual core gradually cools to become a white dwarf, a compact and hot object that will take billions of years to cool down.
This sequence of events is important for the recycling of matter in the Universe. The elements synthesized in stars are redistributed, contributing to the formation of new stellar and planetary generations.