The Science of Existence (16) Stars

Stars

You must have chaos within you to give birth to a dancing star. ~ German philosopher Friedrich Nietzsche

A stellar mass forms when gravity squeezes a dense portion of a molecular cloud into a ball of plasma, consuming and releasing heat.

When temperatures approach 107 K, atomic collisions become so energetic that they spark nuclear fusion. Hydrogen molecules lock into an irreversible embrace, becoming helium while releasing prodigious energy in an exothermic reaction. A galaxy gains a shiner.

When a star is born, it can have a mass 0.1 to 100 times that of the Sun. This property controls a star’s influence on its environment, its lifetime and even its ability to host habitable planets. ~ English science writer Nate Bastian

As a clump of gas tries to collapse under gravity, it hots up. The heat creates radiation pressure that opposes gravity. Unless a star can shed some of this heat, collapse stalls.

Silently, one by one, in the infinite meadows of heaven, blossomed the lovely stars, the forget-me-nots of the angels.
~ American poet Henry Wadsworth Longfellow

The first stars were hydrogen gas ablaze, rather terrible at shedding heat. These protostars accumulated hydrogen fuel, but the high pressure prevented them from forming a dense core. This left them unable to collapse into fusion reaction, which would drive much of the surrounding gas back out into space.

Instead, early stars gorged on gas until they had built a massive, diffuse core. The first stars could have been a million times as massive as the Sun.

The above scenario is one of many that may have transpired. Feedback loops that act on hydrogen gas as it collapses could have fragmented collapsing clouds, creating stars just a few tens that of solar masses.

While gigantic stars would have lived fast and died young, smaller stars churned through their nuclear fuel more slowly. Regardless of size, the earliest stars ended their existence in fiery supernovae before collapsing into black holes. Supernova explosions seeded the interstellar medium with an initial inventory of heavier elements, including oxygen, carbon, and silicon, while leaving behind diminished, dense neutron stars.

Hundreds of millions of supernovas have come and gone in this greedy cycle of gorge and regurgitate, with the residue as starter material for further cosmic construction. Star dust is the material medium of a maturing universe.

The tug of gravity and nudge of coherence gamed the cosmos into galaxies. A homogenous beginning begat a heterogeneous universe from the earliest blips in being. Galaxies evolved in a vast variety of formations.

Likewise, stars shine with a wide range of expanse, from 10% that of the Sun to at least 100 times more massive. A star’s size depends upon how much fodder is found in the vicinity.

Star formation is an accretion ballet based upon fluid dynamics. The planetary ecosystem that evolves nearby has much to do with the feeding of a growing star, and how cosmic building material is distributed.

◊ ◊ ◊

A faint star in the constellation Leo (The Lion) has been shining for over 13 billion years. Based upon its scarcity of source material, the star’s longevity defies comprehension.

A widely accepted theory predicts that stars like this, with low mass and extremely low quantities of metals, shouldn’t exist because the clouds of material from which they formed could never have condensed. ~ French cosmologist Elisabetta Caffau

The way in which stars form depends on their gestation habitat. Star origination is but an episode in galactic evolution which resembles an organic process in its interrelated growth and decay over an astronomical time frame. The local dynamics of star-making depend upon the galactic ecosystem.

Stars do not typically form in isolation. They are instead born in batches, cradled together within a cloud of dusty gas. These clouds are surrounded by a fog of hydrogen that interacts with the clouds. Depending upon galactic dynamics, hydrogen fog may decrease cloud pressure, suppressing star formation instead of fanning its flames.

Star systems come in myriad forms. There can be single stars, binary stars, triple stars, even quintuple star systems. ~ American astronomer Lewis Roberts

Planets can form within all the different types of star systems, in a vast diversity of sizes and orbits. Multiple star systems produce an abundance of massive planets.

Star formation peaked when the universe was a few billion years old. It has declined steeply ever since, as the supply of molecular hydrogen gas that fuels new stars has dwindled.

70% of the original gas is locked up in white dwarfs, neutron stars, and planets. 66% of the rest is spread thin in the intergalactic medium. Only a small portion is shed by stars at various stages of their lives, or recycled wholesale by supernovae.

The Milky Way suddenly stopped birthing stars after it formed its thick, saucer-like disc ~9 billion years ago. The galaxy resumed forming stars after this sudden die-off, but at a much slower rate.

Star formation boils down to a battle between gravity and other things, like turbulence. ~ American astronomer Katherine Alatalo

The Milky Way’s bulging disc and bar-like concentration of stars at its center stir galactic gas, injecting energy that keeps gas from coalescing, thus arresting star formation. The mass of stars in the Milky Way’s central bulge is ~20 billion times the mass of the Sun.

Half the stars in the Milky Way have a companion, traveling as a binary system. Infant triplets are not unusual.

Partnered stars are often torn apart by a collision on the galactic dance floor sometime during their lives, often in their infancy. By this, the population of binaries is diminished before the stars spread out into the wider galaxy.