Travel the universe with Dr. Ethan Siegel as he answers the biggest questions of all
Mass determines a star’s fate… except when it doesn’t.
Supernova events are common, visually spectacular astronomical cataclysms.
In 1987, a supernova just ~168,000 light-years away was observed in the Large Magellanic Cloud. Dubbed SN1987a, we observed neutrinos and light from it, and have observed the remnant continue to expand and evolve over the subsequent years and decades. (ESA/HUBBLE, NASA)
A massive star’s death throes shine brighter than 10 billion Suns combined.
Artist’s illustration (left) of the interior of a massive star in the final stages, pre-supernova, of silicon-burning in a shell surrounding the core. Other layers fuse other elements, a number of which dead-end in magnesium: the 7th most abundant element in the Universe. (NASA/CXC/M.WEISS; X-RAY: NASA/CXC/GSFC/U.HWANG & J.LAMING)
Radiation from fusion reactions typically prevents stars from collapsing gravitationally.
Various reactions occur inside the Sun at a variety of temperatures/densities. By measuring the neutrino flux at a variety of energies, we can reconstruct not only which reactions are occurring where in the Sun’s interior, but we can infer the size and temperature of the Sun’s core. (KELVIN MA/KELVIN13 OF WIKIMEDIA COMMONS (L); JOHN BAHCALL/NEUTRINO ASTROPHYSICS (R))
With exhausted fuel sources, stellar cores implode, rebound, and trigger explosive conflagrations: type II supernovae.
An animation sequence of the 17th century supernova in the constellation of Cassiopeia. This explosion, despite occurring in the Milky Way and about 60–70 years after 1604, could not be seen with the naked eye due to the intervening dust. Surrounding material plus continued emission of EM radiation both play a role in the remnant’s continued illumination. A supernova is the typical fate for a star greater than about 10 solar masses, although there are some exceptions. (NASA, ESA, AND THE HUBBLE HERITAGE STSCI/AURA)-ESA/HUBBLE COLLABORATION. ACKNOWLEDGEMENT: ROBERT A. FESEN (DARTMOUTH COLLEGE, USA) AND JAMES LONG (ESA/HUBBLE))
But sometimes, despite sufficient masses, stars never explode. Here’s why.
A massive star that would otherwise go supernova can have its fate altered by a binary companion. If the companion can steal enough mass, particularly during the low-density supergiant phase of the massive star, an otherwise inevitable supernova can be avoided. (NASA/ESA HUBBLE SPACE TELESCOPE COLLABORATION)
1.) Mass thievery. The outer, lighter-element layers are required for massive supernovae.
When a star destined for a supernova has a dense binary companion, that companion can steal enough mass to prevent that supernova from occurring. This mass siphoning by the denser star can lead to the eventual creation of white dwarfs dominated by heavier elements than the typical carbon-and-oxygen. (NASA/ESA, A. FEILD (STSCI))
When a star or stellar corpse passes too close to a black hole, the tidal forces from this concentrated mass are capable of completely destroying the object by tearing it apart. Although a small fraction of the matter will be devoured by the black hole, most of it will simply accelerate and be ejected back into space. (ILLUSTRATION: NASA/CXC/M.WEISS; X-RAY (TOP): NASA/CXC/MPE/S.KOMOSSA ET AL. (L); OPTICAL: ESO/MPE/S.KOMOSSA (R))
2.) Stellar destruction. Nearby, large masses can rip stars apart entirely.
This artist’s impression depicts a Sun-like star being torn apart by tidal disruption as it nears a black hole. Objects that have previously fallen in will still be visible, although their light will appear faint and red (easily shifted so far into the red they are invisible to human eyes) in proportion to the amount of time that’s passed since they, from the infalling matter’s perspective, crossed the event horizon. (ESO, ESA/HUBBLE, M. KORNMESSER)
We normally expect massive stars to burn through their fuel and die in a supernova. The Wolf-Rayet star WR 124 and its surrounding nebula, M1–67, both arise from the same source: a very massive star. However, for stars born with about 17–30 solar masses, supernovae are not the inevitable fate; instead, they may collapse to a black hole directly, with no intervening supernova. (ESA/HUBBLE & NASA; ACKNOWLEDGEMENT: JUDY SCHMIDT (GECKZILLA.COM))
The visible/near-IR photos from Hubble show a massive star, about 25 times the mass of the Sun, that has winked out of existence, with no supernova or other explanation. Direct collapse is the only reasonable candidate explanation. (NASA/ESA/C. KOCHANEK (OSU))
Stars born with 17-to-30 solar masses may all suffer this ignominious fate.
In 2010, a suspected supernova was seen in galaxy NGC 3184. Follow-up observations indicated that this wasn’t a supernova after all, but rather a rare supernova impostor, similar to what occurred in Eta Carinae in our own galaxy back in the 19th century. (KEVIN HEIDER @ LIGHTBUCKETS)
The ‘supernova impostor’ of the 19th century precipitated a gigantic eruption, spewing many Suns’ worth of material into the interstellar medium from Eta Carinae. High mass stars like this within metal-rich galaxies, like our own, eject large fractions of mass in a way that stars within smaller, lower-metallicity galaxies do not. Eta Carinae might be over 100 times the mass of our Sun and is found in the Carina Nebula, but it is not among the most massive stars in the Universe, nor is it alone. (NATHAN SMITH (UNIVERSITY OF CALIFORNIA, BERKELEY), AND NASA)
At the centers of some red supergiants, neutron stars or white dwarfs may exist. These ‘stars-within-a-star’ get there via mergers, and can dramatically alter the fate of these red supergiants, preventing supernova explosions and ending their lives in under a million years. (BERND FREYTAG WITH SUSANNE HÖFNER & SOFIE LILJEGREN)
When a neutron star and a massive star merge, the neutron star can sink to the center. If the massive star evolves to the red supergiant phase, either before or after the merger, the result will be a Thorne-Zytkow object; it’s estimated that there may be hundreds of these in the Milky Way at any point in time. (WALT FEIMER, NASA/GODDARD SPACE FLIGHT CENTER)
Normally, stars like our Sun will die by blowing off their outer layers in a planetary nebula, while the central core contracts down to form a white dwarf. Numerous, uncommon massive star fates will also lead to white dwarfs. If two white dwarfs later merge or collide, they can create type Ia supernovae events. (NORDIC OPTICAL TELESCOPE AND ROMANO CORRADI / WIKIMEDIA COMMONS / CC BY-SA 3.0)
However, supernova “failures” that end in white dwarfs create second chances.
When two white dwarfs come into contact with one another, they can exchange mass, interact, or merge, with the potential of leading to a type Ia supernova if the right conditions are met. In the case of a merger triggering a type Ia supernova, the entirety of both stellar remnants should be destroyed by the process. (DAVID A. AGUILAR (HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS))
Two different ways to make a Type Ia supernova: the accretion scenario (L) and the merger scenario (R). The merger scenario is responsible for the majority of many of the heavy elements in the Universe, including iron, which is the 9th most abundant element and the heaviest one to crack the top 10. (NASA / CXC / M. WEISS)
The distance/redshift relation, including the most distant objects of all, seen from their type Ia supernovae. The data strongly favors an accelerating Universe. Note how these lines are all different from one another, as they correspond to Universes made of different ingredients. (NED WRIGHT, BASED ON THE LATEST DATA FROM BETOULE ET AL.)
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.
