Star Basics: The Celestial Globes That Illuminate Our Night Sky

Stars, the radiant beacons that punctuate our darkened heavens, are estimated to number up to one septillion. That’s a staggering figure, equivalent to a 1 followed by 24 zeros. Our very own Milky Way is home to over 100 billion stars, with the Sun being the most familiar among them.

The Starry Origins

Stars are born within immense clouds of gas and dust called molecular clouds. These cosmic wonders can reach sizes as vast as hundreds of light-years and weigh from a thousand to a million times that of our Sun. The cold temperatures in these clouds cause the gas to clump together, forming high-density pockets. As more matter collides or accumulates, some of these dense areas become even stronger under the force of gravity, eventually leading to their collapse. This collapse generates heat through friction, resulting in the formation of a protostar - a star’s embryonic phase. These stellar clusters and molecular clouds teeming with them are often referred to as ‘stellar nurseries.’

The Starry Life

In its infancy, a protostar relies on heat from its initial collapse for energy. However, after millions of years, the immense pressures and temperatures in the star’s core cause hydrogen atoms to fuse together, forming helium in a process known as nuclear fusion. This process releases energy, preventing further collapsing under gravity and illuminating the star we see from afar. Such stars that are stably undergoing nuclear fusion of hydrogen into helium are known as main sequence stars.

The main sequence stage is the longest phase in a star’s life. The luminosity, size, and temperature of a star will gradually change over millions or billions of years during this period. Our Sun is currently approximately midway through its main sequence lifespan. A star’s mass dictates how quickly it burns through its fuel, with lower-mass stars shining for longer, dimmer, and cooler than very massive stars.

The Starry End

As a star exhausts its supply of hydrogen, the core begins to collapse, causing the star to swell. The details of the late stages of a star’s life depend greatly on its mass. A low-mass star will become a subgiant or giant, converting helium into carbon in its core before shedding its outer layers, forming a planetary nebula, and leaving behind a white dwarf.

On the other hand, high-mass stars follow a more dramatic path, converting heavier elements like carbon, oxygen, and magnesium into future fuel sources for the core. Eventually, the star will run out of fuel in a matter of mere millions of years. The core’s subsequent collapse results in a cataclysmic explosion known as a supernova, leaving behind either a neutron star or a black hole.

Star Tales from NASA

• Hubble Seeks Clusters in ‘Lost Galaxy’
• NASA’s TESS Spacecraft Triples Size of Pleiades Star Cluster
• NASA’s Roman Could Bring New Waves of Information on Galaxy’s Stars
• Webb First to Show 4 Dust Shells ‘Spiraling’ Apep, Limits Long Orbit
• Hubble Studies Star Ages in Colorful Galaxy

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