Our study of the universe started with stargazing.


Looking up at the stars connects you to a legacy of wonder and science stretching back thousands of years, in civilizations all around the world. While the night sky definitely inspires awe, early astronomy was also practical—farming according to the solstices and equinoxes yielded better crops, and more food fueled the growth of human society and innovation. 

ancient star gazing Image source: Pexels.com. (CC0 license)
Pages from the 1690 star atlas Firmamentum Sobiescianum sive Uranographia, by Johannes and Elisabetha Hevelius. Johannes is credited with identifying seven new constellations still recognized today. He preferred to observe the stars without the aid of a telescope, and did so with remarkable accuracy. Courtesy of the United States Naval Observatory and the Office of Public Outreach at STScI.

A Cosmic Recycling System

Star Lifecycle infographic
Diagram showing the lifecycles of Sun-like and massive stars. CREDIT: NASA and the Night Sky Network. GET THE FULL IMAGE IN RESOURCE GALLERY >

Today we know that stars are the essential sources of raw material in the universe, recycling and distributing the elemental building blocks of everything we observe: new stars, nebulas of gas and dust, planets, and even humans. All life on Earth contains the element carbon, and all carbon was originally formed in the core of a star.

Stars populate the universe with elements through their “lifecycle”—an ongoing process of formation, burning fuel, and dispersal of material when all the fuel is used up. Different stars take different paths, however, depending on how much matter they contain—their mass. A star’s mass depends on how much hydrogen gas is brought together by gravity during its formation. We measure the mass of stars by how they compare to the “parent star” of our system, the Sun. Stars are considered high-mass when they are five times or more massive than the Sun. 

When high-mass stars have no more fuel to generate outward energy, their iron cores begin to collapse until the pressure overcomes the inward push of gravity and they explode in a spectacular supernova, dispersing elements into space to recombine as future stars, planets, asteroids, or even eventually life like us.

After supernova, massive stars can go one of two ways. If the remnant of the explosion is about 1.4 to 3 times the mass of our sun, it will collapse into a very small, very dense core of neutrons called a neutron star. If the remnant is more than three times as massive as the Sun, gravity overwhelms the neutrons and the star collapses completely into a black hole—so-called because the matter within is so compressed and the pull of gravity is so intense that even light is drawn in and not reflected, so that area is “black” or unobservable.

 

Surely it is a great thing to increase the numerous host of fixed stars previously visible to the unaided vision, adding countless more which have never before been seen.

 

Galileo Galilei

Pillars of Creation
Hubble's Wide View of 'Mystic Mountain (HH 901),' pillars in the Carina Nebula, in visible and infrared light. CREDIT: NASA, ESA, and M. Livio and the Hubble 20th Anniversary Team (STScI).

In the Dark

Despite over a thousand years of astronomy, looking up at a starry sky is still awe-inspiring, and some elements of the star lifecycle are still shrouded in mystery—stars and the planets that orbit them form together inside dense clouds of dust and gas that visible light cannot penetrate. This why a high-resolution infrared space telescope like Webb is essential to illuminate this area of astronomy. Infrared light travels through dense gas clouds, and so by detecting it, Webb will shed light on the previously unseen processes of planetary system formation. By observing the formation process of stars and worlds very different from our own, we will begin to grasp the unique—or not—nature of our home in the universe.

Astronomers also hope Webb will reveal more about the puzzling brown dwarf, a strange type of cosmic object that is not easily classified as a planet or a star, but has characteristics of both. As they are not massive enough to generate their own light like a star, brown dwarfs are hot but dim, making them another ideal subject for study with Webb’s infrared instruments. Observing star and planet formation stages may help explain how and why some masses of matter become small stars, others gas giant planets, and some become brown dwarfs.

A final unanswered question about the star lifecycle takes astronomers back to the beginning. As we understand it, every cycle has to have a start, so how did the first generations of stars form, if not from the cloud of a previous supernova? How much did the universe’s first stars deviate from the lifecycles we are familiar with today? What role did black holes play in the evolution of early individual stars into great galaxies like our own Milky Way? Webb’s instruments will allow astronomers to observe this unexplored realm at the beginning of time and space, the light from which is so old that it only visible with infrared instruments. In this way, Webb will help to fill in blanks in the earliest chapters of our history, improving our understanding of how the universe functions through the lifecycles of stars, and how we got to where we are today.

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