colloquium Gregory Sloan: Carbon stars and dust in the Universe

Intermediate-mass stars become carbon-rich in the final phases of their
lives as stars.  As they die, carbon stars produce significant
quantities of carbon-rich dust, and they dominate the dust production in nearby
metal-poor galaxies like the Magellanic Clouds.  Infrared spectroscopy
of carbon stars in these galaxies and our own reveals that (1) the
initial metallicity of a carbon star has little influence on how much
dust it will produce, and (2) the transition to strong pulsations in the
atmospheres of these stars leads to high rates of mass loss and dust
production, which will end the life of the star and eject most of its
mass back into its host galaxy.  Stellar modeling shows that at lower
metallicity, stars evolve more quickly, and higher-mass stars can
become carbon stars.  Carbon-rich dust has now been detected in
galaxies with redshifts up to 7, or only 800 million years after the
Big Bang.  While carbon stars can evolve in this time, higher-mass
objects such as core-collapse supernovae or Wolf-Rayet stars are often
invoked as the likely source of that dust.  Nonetheless, the available
evidence points to carbon stars as the most likely culprit.