The Physics Of The Universe

how a star is born?

A star is born within a vast, cold cloud of gas and dust in space called a nebula. The process of star formation begins when gravitational forces within the nebula cause the cloud to contract and collapse under its own weight.

Here are the main steps in the birth of a star:

1. Gravitational collapse: As the nebula collapses, the gas and dust particles within it start to clump together, forming a dense core. This process is driven by gravity and may be triggered by external factors, such as shockwaves from a nearby supernova explosion or the collision of two massive molecular clouds.

2. Formation of a protostar: As the core of the collapsing nebula continues to compress, it heats up and forms a protostar. A protostar is an early stage in stellar evolution where the core hasn't yet ignited nuclear fusion. During this phase, the protostar is primarily heated by gravitational energy, and it emits infrared radiation.

3. Accretion and rotation: Surrounding the protostar is a rotating disk of gas and dust called the accretion disk. The protostar continues to grow as it accumulates more material from the accretion disk. The conservation of angular momentum causes the disk and protostar to rotate faster as they contract.

4. Nuclear fusion ignition: When the core of the protostar reaches a temperature of around 15 million Kelvin (27 million degrees Fahrenheit), nuclear fusion begins. During this process, hydrogen atoms combine to form helium, releasing a tremendous amount of energy in the form of light and heat. This marks the birth of a true star, also known as a main-sequence star.

5. Stellar equilibrium: The newly formed star reaches a stable state when the outward pressure created by the energy from nuclear fusion balances the inward pull of gravity. At this point, the star enters the main sequence phase of its life, where it will continue to burn hydrogen in its core for millions to billions of years, depending on its mass.

The size, temperature, and brightness of a star depend on its mass. The more massive a star, the hotter and brighter it will be. The least massive stars are small, cool, and dim red dwarfs, while the most massive ones are large, hot, and extremely bright blue giants.

One of the most recent notable star formation observations was made by the Atacama Large Millimeter/submillimeter Array (ALMA) in 2020. ALMA observed a high-mass protostar called G353.273+0.641, located about 12,000 light-years away from Earth, in the constellation Scorpius.

The observation was significant because it provided valuable insights into the complex process of high-mass star formation, which has been difficult to study in detail due to their rarity and the rapid pace at which they evolve. The researchers found that the protostar was accumulating mass through a rotating, fragmented accretion disk, challenging previous models of high-mass star formation that suggested direct, spherical infall of material onto the protostar.

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