Stars live for billions of years and then take millions of years to die. But what happens when a star dies? Many stars use up their nuclear fuel, collapse, and then explode as a supernova. How’s that for going out with a bang?
Let’s delve deeper into star deaths to explore what’s happening at the end of the lifecycle of a star.
Table of Contents
Starting at the Beginning: How a Star Is Born
Stars form as clumps of cosmic dust and gas gather inside stellar nurseries. The clusters gain mass, spin, and heat over a few hundred thousand years. Nuclear fusion occurs once the clump’s core heats to millions of degrees.
Next, the fusion releases star-heating energy, creating enough pressure to push against gravity’s forces. Thus, a star is born.
Does a Star’s Size Dictate Its Lifespan and Death?
At the other end of the spectrum, what happens when a star dies depends on its mass. In general, smaller stars die slowly. They die over millions of years, forming planetary nebulae and white dwarfs in the dying process.
More giant stars, however, die more dramatically. Their death sometimes involves massive explosions, supernovas, and black holes.
Why Do Stars Die?
A Star dies when it has consumed all of its fuel. If there’s no fuel, no nuclear fusion occurs. No energy equals no star.
Red Giant Stars And White Dwarfs
When stars about the size of our Sun die, it’s a less dramatic affair than massive supernova explosions. This process occurs in stars with less than eight times the Sun’s mass.
First, stars live by fusing the hydrogen fuel in their cores into helium. However, when these average-sized stars exhaust their hydrogen fuel supply, gravity takes over, and they start to collapse. Interestingly, the collapse causes the core to heat back up, thus creating red giants.
Such stars like the Sun turn into red giants, burning helium and creating carbon. Eventually, they exhaust the helium supply, but they’re no longer hot enough to consume the remaining carbon.
Red giants succumb to gravity once again. Their cores contract and then release vast amounts of energy. However, the star loses mass and sheds its outer layer since it isn’t very stable.
As a result, the dying star’s outer layer often forms a vast planetary nebula millions of kilometers across. These nebulae are so massive they could gobble up Mercury and Venus.
Becoming a White Dwarf
Planetary nebulae are often the markers for a red giant’s transition to a white dwarf. That’s because as the red giant’s burning core loses its outer layer, it becomes an intensely hot white dwarf.
White dwarfs have temperatures exceeding 100,000 Kelvin. In addition, their size is about half that of the Sun, but they are 200,000 times denser than the Earth.
Stars die slowly, becoming red giants. In the red giant dying process, they form planetary nebulae, while their hot centers become white dwarfs. Then finally, the white dwarf cools and dies over the next millions to billions of years.
In the images below, note the optical image of globular cluster M4 on the left. Then the Hubble Space Telescope image on the right shows a closer view of the circled white dwarfs.
Neutron Stars and Supernovas
Neutron stars are incredibly dense stellar remnants. With a denser mass than the Sun’s, neutron stars are small spheres about the width of New York’s Manhatten Island’s length.
These types of stars form when massive, dense stars (8 to 20 times the Sun’s mass) exhaust their hydrogen supply and die. Then, like smaller, lower-density stars, neutron stars begin fusing helium into carbon.
However, after exhausting the helium supply, the core releases energy by converting the remaining carbon to Neon (Ne). From there, the star converts Neon into oxygen, oxygen into silicon, and silicon into iron. This process can take millions of years.
On the other hand, once the silicon fuses into iron, the star’s fuel supply then only lasts a few days. Since there’s no more remaining energy, the core collapses into itself. Then it bounces back to its original size and creates a shock wave that bursts through the star’s outer layers.
That massive explosion is a supernova, and the remaining collapsed core becomes an incredibly dense neutron star surrounded by an expanding cloud of scorching gas. Alternatively, a black hole occurs if there’s enough remaining mass.
Neutron stars are too faint to observe with binoculars or even backyard telescopes. Although the Hubble Space Telescope has captured a few in visible light, x-ray, and radio emissions offer the best viewing options.
Supernova Remnant Examples
Neutron stars start their life with a bang! That giant explosion, or supernova, provides one of the universe’s most impressive displays.
The Lupus Constellation is home to a supernova remnant SN 1006. When it first appeared on May 1, 1006, it was brighter than Venus, even having daytime visibility. SN 1006 remained visible for about two and a half years before dimming.
Do Stars Become Black Holes When They Die?
When smaller stars run out of fuel, they become neutron stars. When giant stars (with a weight greater than eight times that of the Sun) run out of power, gravity collapses their cores to form black holes.
Black holes eat up surrounding gasses and sometimes even nearby stars. However, their gravity is so strong that nothing can escape it. Not even light.
Black Hole Facts
While astronomers still have many questions about black holes, they know some interesting facts.
- The closest black hole: (1A 06200-00) is 3,000 light-years away from Earth
- The furthest black hole: (J0313-1806) is 13 billion light-years away in the QSO Galaxy
- The biggest black hole: Ton 618 = 66 billion times the Sun’s mass
- The smallest black hole: XTE J1650 = 3.8 times the Sun’s mass
NASA’s illustration below shows a supermassive black hole at the center of a blazar galaxy. It depicts a bright accretion disk surrounded by a dark gas and dust ring. Finally, the center light shows a bright stream of particles erupting from the black hole.
Image Credit: NASA’s Goddard Space Flight Center/Conceptual Image Lab
How Old Are the Oldest Stars?
Red dwarfs are the tiniest stars at just a fraction of the Sun’s mass and size. Some low-mass red dwarfs, containing only about one-third of the Sun’s mass, may live up to 14 trillion years since they burn their nuclear fuel very slowly. That’s significantly older than our universe’s current age.
Most stars die slowly over millions of years. Stars, like the Sun, become red giants that gradually morph into white dwarfs. Stars with eight times greater mass than the Sun swell into red supergiants. They consume all available elemental fuel sources as they complete their lifecycles. Eventually, these supergiants blow themselves up into supernovas.
The supernova lights up the skies. After the supernova fades, only small, dense objects remain. These are neutron stars or vast black holes. Finally, the star’s exploded elements drift through space, eventually becoming the cosmic stardust that creates new stars and planets.