Given enough time, every star will eventually die.
Artist’s illustration (left) of the interior of a massive star in the final stages of silicon combustion before supernova. (When silicon burns, iron, nickel and cobalt are formed in the core.) A Chandra image (right) of Cassiopeia. Today’s supernova remnant shows elements such as iron (blue), sulfur (green) and magnesium (red). Ejected stellar material can glow for tens of thousands of years due to heat in the infrared region, and supernovae ejecta can be asymmetrical and contain separate elements, as shown here. In the right environment, this asymmetric material can be incorporated unevenly into future generations of stars.
Stars always form when gaseous matter accumulates, fragments and collapses.
Here, evaporating gas globules are seen at the edge of a star-forming region in the Orion Nebula, with newborn stars, Herbig-Haro objects and many fainter light sources including protostars, brown dwarfs and even planetary-mass objects found inside. As the gas continues to evaporate, more and more of these lower-mass objects are likely to emerge.
The initiation of hydrogen fusion in their cores officially triggers the birth of a star.
This ALMA observation of a massive protostar cluster, G351.77-0.54, has achieved a spatial resolution of ~120 AU, which corresponds to 0.06 arcseconds in the distance of these protostars. The gaseous material breaks up into at least four separate cores, a hint (now with more evidence) that core fragmentation, and not anything to do with a disk, plays an important role in how many stars form in these massive star-forming regions . When nuclear fusion reactions begin in these protostar cores, they officially become full-fledged stars.
The outward pressure from nuclear reactions keeps the star from gravitational collapse.
This detail shows the different regions of the Sun’s surface and interior, including the core, which is the only place where nuclear fusion occurs. As time passes and hydrogen is consumed, the helium-containing region in the core expands and the maximum temperature increases, increasing the Sun’s energy output. The balance between the inward pull of gravity and the outward radiation pressure determines the size and stability of a star.
If not enough pressure is generated, the star collapses directly into a black hole.
Hubble’s visible/near-infrared photos show a massive star, about 25 times the mass of the Sun, disappearing from existence without a supernova or other explanation. Direct collapse is the only reasonable possible explanation and, along with supernovae or neutron star mergers, is a known way of forming a black hole for the first time.
The most massive stars burn their fuel quickly, fusing heavier elements.
The anatomy of a very massive star throughout its life, culminating in a Type II supernova (core collapse) when the core runs out of nuclear fuel. The final phase of fusion is typically the combustion of silicon, producing iron and iron-like elements in the core for only a short time before a supernova occurs. The most massive core collapse supernovae typically result in the formation of black holes, while the less massive supernovae only produce neutron stars.
Eventually they become supernovas, leaving behind a black hole or the remnant of a neutron star.
In the inner regions of a star experiencing a core collapse supernova, a neutron star begins to form in the core while the outer layers slam into it and undergo their own runaway fusion reactions. Neutrons, neutrinos, radiation and extraordinary amounts of energy are produced, with neutrinos and antineutrinos carrying away most of the core collapse supernova’s energy. Whether the remnant becomes a neutron star or a black hole ultimately depends on how much mass remains in the core during this process.
Less massive stars like the Sun cannot fuse elements other than helium.
As the Sun evolves into a true red giant, expanding to more than 100 times its current size as its interior contracts and heats up to fuse helium, the Earth itself may be swallowed or devoured, but will definitely become like never before roasted. The Sun’s outer layers will swell, but the precise details of their evolution and how these changes will affect the orbits of the planets are still subject to great uncertainty. Mercury and Venus will definitely be swallowed by the Sun, but Earth will be very close to the edge between survival and being swallowed up.
Their fate is to die in a planetary nebula, leaving white dwarfs behind.
When our sun runs out of fuel, it becomes a red giant, followed by a planetary nebula with a white dwarf at the center. The Cat’s Eye Nebula is a visually spectacular example of this possible fate, with the intricate, layered, asymmetric shape of this particular nebula suggesting a binary companion. At the center, a young white dwarf is heating up as it contracts, reaching temperatures tens of thousands of Kelvin hotter than the surface of the red giant that gave birth to it. The outer gas envelopes consist largely of hydrogen, which is returned to the interstellar medium at the end of a Sun-like star’s life.
The lowest-mass stars, on the other hand, only fuse hydrogen in their cores.
The simplest and lowest energy version of the proton-proton chain, producing helium-4 from initial hydrogen fuel. Note that only fusion of deuterium and a proton creates helium from hydrogen; All other reactions either produce hydrogen or create helium from other helium isotopes. This set of reactions occurs inside all young, hydrogen-rich stars, regardless of mass.
They live the longest and become white dwarfs made of pure helium: with no counterpart to the planetary nebula.
Energy generated in a star’s core must pass through large amounts of ionized material before reaching the photosphere, where it is radiated. Inside the Sun there is a large non-convective radiation zone surrounding the core, but for lower mass stars the entire star can be convective on timescales of tens or hundreds of billion years, allowing red dwarf stars to merge 100% of it hydrogen in them. Red dwarfs cannot fuse elements heavier than hydrogen. So when all their hydrogen is fused, they simply contract into a helium white dwarf.
As stars and brown dwarfs merge, they achieve larger masses, which changes their fate.
When an orbiting body enters the photosphere of a massive star, the star will swell in size and become significantly brighter, but it will also stop spewing dusty material; that was just part of the pre-merger phase of the astronomical system in question. Stars often grow into more massive, shorter-lived stars through mergers.
Encounters with black holes destroy stars through tidal disruption and tear them apart through gravity.
This illustration of a tidal disruption shows the fate of a massive, large astronomical body that has the misfortune of getting too close to a black hole. It is stretched and compressed in one dimension, causing it to shred, accelerating its matter, and alternately devouring and expelling the debris that emerges from it. Black holes with accretion disks are often highly asymmetrical in their properties, but are far more luminous than inactive black holes that lack them.
Black holes ultimately decay into radiation through the Hawking process.
A black hole’s event horizon is a spherical or spherical region from which nothing, not even light, can escape. But outside the event horizon, the black hole is expected to emit radiation. Hawking’s 1974 paper was the first to prove this and was arguably his greatest scientific achievement. Solar-mass black holes decay after 10^67 years, with more massive black holes surviving longer.
White dwarf mergers produce and annihilate Type Ia supernovae.
The two main ways to create a Type Ia supernova: the accretion scenario (left) and the merger scenario (right). Most white dwarfs that become supernova lie below the Chandrasekhar mass limit, which strongly favors the merger scenario for most Type Ia supernovae.
Meanwhile, lonely white dwarfs and neutron stars simply fade to black: cold, non-luminous, but lasting forever.
A detailed size/color comparison of a white dwarf (left), the Earth reflecting light from our sun (center), and a black dwarf (right). When white dwarfs finally emit their last energy, they all eventually become black dwarfs. However, the degeneracy pressure between the electrons within the white/black dwarf will always be large enough to prevent further collapse as long as it does not accumulate too much mass. A similar process, albeit over longer periods of time, should occur in neutron stars.
Only low-mass, isolated star corpses will last forever.
After the sun dies, its remaining core will contract and become a white dwarf. Over the course of 100 trillion years it will disappear and eventually become a black dwarf. Any surviving planets in its orbit must survive gravitational encounters in order to remain where gravitational radiation will eventually cause them to be devoured by the black dwarf. Black dwarfs are believed to be the last remaining stellar remnants of all.
Mostly Mute Monday tells an astronomical story in pictures, pictures and no more than 200 words.