Today's featured denizen of the galactic bestiary: the kilonova.
This is believed to be the signature of a rare but important sort of stellar cataclysm: two neutron stars merging. They merge because their orbital energy is eroded (at an accelerating rate) and radiated as extremely intense gravity waves. In August 2017 two gravity-wave observatories recorded the characteristic "chirp" of two such massive objects spiraling into each other.
This gave astronomers a shot at seeing the very transient optical signature of the event: a short hard gamma-ray burst followed by a day to a week of optical flare. When the stars meet
, a fair amount of neutron-degenerate matter escapes and diffuses to form a neutron gas. Neutrons (that are not gravitationally bound) have a half-life of about 10 minutes, so there is a sharp pulse of light as that energy is released.
When they meet, enough energy is released to power a thousand classical novae (so 10 to the power of 43 joules) at the upper range of their energy production (thermonuclear runaway explosions on the surface of a white dwarf that generate a weeks-long optica lflare). A classical supernova generates 10 to 100 times as much energy.
Kilonovae are the principal source of "r-process" elements. such as gold and platinum. The usual element-forming processes (stellar winds off red supergiants and especially supernovae) don't have a mechanism to form r-process nuclei. So bling came from a very special bang.
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