Evolved stars

Large surveys of emission from the carbon monoxide (CO) molecule and other molecules show that evolved stars are losing mass in the form of stellar winds at relatively low outflow speeds. The current observations suggest that, roughly speaking, the winds are isotropic (equal in all directions) and that the mass loss rates and outflow velocities are constant with time. Observations of very large numbers of stars will be required, perhaps of thousands, in order to achieve a model that will allow to draw conclusions of the evolution in question, through physical and chemical parameters.

Winds from cool evolved stars are probably the dominant source of refractory dust grains in the interstellar medium. They are the star-stuff from which we and our planet were formed. The grains manifest themselves through thermal emission extending from the far infrared through millimeter -wavelengths.  ALMA is able to analyze the chemical composition of these stars and of the ejected material.

This composite shows the region around the massive star-forming region SDC 335.579-0.292 seen using NASA’s Spitzer Space Telescope and ALMA. The Spitzer view is at infrared wavelengths (3.6, 4.5 and 8.0 microns) and the ALMA view is at wavelengths around three millimeters. The yellow blob at the center of the ALMA images is a stellar womb with over 500 times the mass than the Sun — the largest ever seen in the Milky Way. The embryonic star within is hungrily feeding on the material that is racing inwards. It is expected to give birth to a very brilliant star with up to 100 times the mass of the Sun.

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