A star is a massive, luminous sphere of plasma held together by its own gravity. Stars are formed from clouds of gas and dust called nebulae. The most common type of star, like our Sun, undergoes a specific life cycle known as the main sequence.
Formation: Stars form when regions within a nebula become gravitationally unstable, causing the gas and dust to collapse. As the collapsing material gathers, it forms a dense core known as a protostar.
Protostar: The protostar continues to accrete mass from its surrounding material. Through gravitational contraction, the protostar heats up, and when its temperature and pressure reach a critical point, nuclear fusion ignites in its core.
Main Sequence: A star enters the main sequence phase when it achieves a stable balance between gravity's inward pull and the outward pressure from the energy generated through nuclear fusion. During this phase, the star fuses hydrogen into helium in its core, releasing vast amounts of energy and emitting light.
Stellar Evolution: The duration of a star's life and its subsequent evolution depend on its mass. High-mass stars burn through their fuel relatively quickly, leading to more dramatic evolutionary paths, such as expanding into red giants, undergoing supernova explosions, and potentially leaving behind remnants like neutron stars or black holes. Low-mass stars, like our Sun, undergo a more gradual evolution, eventually swelling into red giants and shedding their outer layers to form planetary nebulae and leaving behind a dense core called a white dwarf.
Stars move in space due to two primary factors:
Galactic Rotation: Stars, along with the entire Milky Way galaxy, are in a state of rotation. The gravitational forces within the galaxy cause stars to orbit around the center of the galaxy. This motion contributes to the overall movement of stars within the galaxy.
Proper Motion: Stars also have their own individual motions within the galaxy. This motion, known as proper motion, is a result of their velocities and trajectories. Proper motion can be influenced by interactions with other stars, galactic structures, and gravitational forces.
From our perspective on Earth, it may appear that all the stars are moving in one direction. This phenomenon is largely due to the combined effects of the Earth's rotation and the motion of stars within the galaxy. However, it's important to note that stars have diverse trajectories and velocities within the galaxy, and their individual movements are not necessarily uniform or in a single direction when observed on larger scales.