NEWS | September 16, 2020

The Lives, Times, and Deaths of Stars

Who among us doesn’t covertly read tabloid headlines when we pass them by? But if you’re really looking for a dramatic story, you might want to redirect your attention from Hollywood’s stars to the real thing. From birth to death, these burning spheres of gas experience some of the most extreme conditions our cosmos has to offer.

This visualization provides a three-dimensional perspective on Hubble's image of the nebula Gum 29 with the star cluster Westerlund 2 at its core. The flight traverses the foreground stars and approaches the lower left rim of the nebula Gum 29. Passing through the wispy darker clouds on the near side, the journey reveals bright gas illuminated by the intense radiation of the newly formed stars of cluster Westerlund 2. Within the nebula, several pillars of dark, dense gas are being shaped by the energetic light and strong stellar winds from the brilliant cluster of thousands of stars.
A visualization flying into the nebula Gum 29 and the star cluster Westerlund 2 at its core. Credit: NASA, ESA, G. Bacon, L. Frattare, Z. Levay, and F. Summers (Viz3D Team, STScI), and J. Anderson (STScI)

All stars are born in clouds of dust and gas like the Pillars of Creation in the Eagle Nebula pictured below. In these stellar nurseries, clumps of gas form, pulling in more and more mass as time passes. As they grow, these clumps start to spin and heat up. Once they get heavy and hot enough (like, 27 million degrees Fahrenheit or 15 million degrees Celsius), nuclear fusion starts in their cores. This process occurs when protons, the nuclei of hydrogen atoms, squish together to form helium nuclei. This releases a lot of energy, which heats the star and pushes against the force of its gravity. A star is born.

 On a background awash in blue and orange cloudy light stands a darker cloud with three pillars rising from it. The edges of the dark regions glow with white and light-blue light.
These tendrils of cosmic dust and gas sit at the heart of M16, or the Eagle Nebula. The aptly named Pillars of Creation, featured in these stunning Hubble images, are part of an active star-forming region within the nebula and hide newborn stars in their wispy columns. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

From then on, stars’ life cycles depend on how much mass they have. Scientists typically divide them into two broad categories: low-mass and high-mass stars. (Technically, there’s an intermediate-mass category, but we’ll stick with these two to keep it straightforward!)

Low-mass stars

In this GIF, a mottled yellow Sun rotates against a black background. The surface shows activity like flares.
The Solar Dynamics Observatory captured this ultraviolet view of our Sun from its orbit around Earth. Credit: NASA's Scientific Visualization Studio/SDO

A low-mass star has a mass eight times the Sun’s or less and can burn steadily for billions of years. As it reaches the end of its life, its core runs out of hydrogen to convert into helium. Because the energy produced by fusion is the only force fighting gravity’s tendency to pull matter together, the core starts to collapse. But squeezing the core also increases its temperature and pressure, so much so that its helium starts to fuse into carbon, which also releases energy. The core rebounds a little, but the star’s atmosphere expands a lot, eventually turning into a red giant star and destroying any nearby planets. (Don’t worry, though, this is several billion years away for our Sun!)

A red, glowing star starts out small and starts to grow, eventually taking up the entire frame. As the star grows, a small planet first skims the surface of the star on the left, creating a fiery skid mark. But then the star overtakes the planet, engulfing it completely in a small orange blip.
In this visualization a red giant star swallows a planet. Credit: NASA/JPL-Caltech/D. Berry

Red giants become unstable and begin pulsating, periodically inflating and ejecting some of their atmospheres. Eventually, all of the star’s outer layers blow away, creating an expanding cloud of dust and gas misleadingly called a planetary nebula. (There are no planets involved.)

This planetary nebula, known as NGC 2818, takes up the entire frame. It is surrounded by an orange oval of wispy clouds shaped almost like lips. Inside the oval is a bright blue cloud pierced by a few small spikes of the orange clouds.
The planetary nebula designated NGC 2818, lies in the southern constellation of Pyxis. The colors in the image, captured by the Hubble Space Telescope, represent a range of emissions coming from the clouds of the nebula: red represents nitrogen, green represents hydrogen, and blue represents oxygen. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

All that’s left of the star is its core, now called a white dwarf, a roughly Earth-sized stellar cinder that gradually cools over billions of years. If you could scoop up a teaspoon of its material, it would weigh more than a pickup truck.

This GIF starts with a size comparison between a possible giant planet and the white dwarf that it orbits. The planet is shown as a striped, pink orb and it is nearly seven times larger than the bright white dwarf star. The animation then pulls out to show the relative size of the orbit of the white dwarf and its planet.
A possible giant planet may have survived its tiny star’s chaotic history. Jupiter-size WD 1856 b is nearly seven times larger than the white dwarf it orbits every day and a half. Astronomers discovered it using data from NASA’s Transiting Exoplanet Survey Satellite and now-retired Spitzer Space Telescope. Credit: NASA's Goddard Space Flight Center

High-mass stars

A high-mass star has a mass eight times the Sun’s or more and may only live for millions of years. (Rigel, a blue supergiant in the constellation Orion, pictured below, is 18 times the Sun’s mass.)

AG Carinae
AG Carinae, imaged here by the Hubble Space Telescope, is a giant star on the verge of collapse. Credit: NASA, ESA, STScI

The star’s iron core collapses until forces between the nuclei push the brakes, and then it rebounds back to its original size. This change creates a shock wave that travels through the star’s outer layers. The result is a huge explosion called a supernova.

This visualization opens on a star field with a bright star at the center of the image. The star then explodes, filling the frame with white light for a moment. As that bright light fades, we see there is a bubble of yellow and red material expanding away from the site of the exploded star.
When a star that is eight times larger than the sun ends its life, it does not go gentle into that good night. Shifting pressure in its core causes it to collapse and trigger a supernova, the largest explosion in the universe. The initial flash of light, which can outshine the star’s host galaxy, may last only seconds. But the resulting debris that is flung into space can be studied for millennia. Credit: Courtesy of ESA/Hubble/L. Calçada

What’s left behind depends on the star’s initial mass. Remember, a high-mass star is anything with a mass more than eight times the Sun’s — which is a huge range! A star on the lower end of this spectrum leaves behind a city-size, superdense neutron star. (Some of these weird objects can spin faster than blender blades and have powerful magnetic fields. A teaspoon of their material would weigh as much as a mountain.)

This simulation shows the possible arcs of magnetic field lines from a pulsar. At the center is a gray orb representing the pulsar. Close to the pulsar are various-sized ovals of orange that pierce the pulsar, looking like a tangled knot, though the lines do not actually cross each other. There are larger blue arcs that come off the screen, representing even more magnetic field lines.
Simulation of a possible quadrupole magnetic field configuration for a pulsar with hot spots in the only the southern hemisphere. Credit: NASA's Goddard Space Flight Center

At even higher masses, the star’s core turns into a black hole, one of the most bizarre cosmic objects out there. Black holes have such strong gravity that light can’t escape them. If you tried to get a teaspoon of material to weigh, you wouldn’t get it back once it crossed the event horizon — unless it could travel faster than the speed of light, and we don’t know of anything that can! (We’re a long way from visiting a black hole, but if you ever find yourself near one, there are some important safety considerations you should keep in mind.)

In this data visualization, material swirls around a black hole, but our line of sight skews our view of the disk. The center of the image is a black hole, with a thin ring of orange around it, then a small gap, and then a striped disk of material. The disk in front of the black hole appears as we would expect, with the disk arcing in front of the black hole like a flat pancake. However, the far side of the disk is visible above and below the black hole, instead of being blocked by the black hole. This is due to the black hole’s gravity, which redirects the light up and over the black hole on its path to us.
This visualization of a black hole illustrates how its gravity distorts our view, warping its surroundings as if seen in a carnival mirror. Credit: NASA’s Goddard Space Flight Center/Jeremy Schnittman

The explosion also leaves behind a cloud of debris called a supernova remnant. These and planetary nebulae from low-mass stars are the sources of many of the elements we find on Earth. Their dust and gas will one day become a part of other stars, starting the whole process over again.

That’s a very brief summary of the lives, times, and deaths of stars. (Remember, there’s that whole intermediate-mass category we glossed over!) ​

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