Weighing a Red Giant's Mass Loss express
A red giant is like a balloon slowly letting out gas. The star swells, its outer layers weaken, and stellar wind carries mass into space. But exactly how much does a star lose? This is a crucial question: the answer determines what kind of remnant it will leave behind — a white dwarf, a neutron star, or a black hole.
Astronomers have found a way to measure mass loss without watching a star for centuries. In a star's interior, carbon and nitrogen are mixed during burning, and their surface ratio depends on the mass with which the star was born. Mass loss does not change this ratio: it's like a fingerprint. By comparing the masses of stars with the same 'fingerprint' but at different life stages, scientists calculated the net mass loss.
This means old models of stellar evolution need calibration. The authors propose a new tuning of the formula, depending on mass and metallicity. Also, the sample contained 207 stars (3.33%) that deviate from the overall trend — possibly survivors of mass transfer from a companion star. Such cases are important for studying the history of our Galaxy.
The discovery reminds us: a balloon that looks the same can lose gas differently depending on what it's made of and how tight it is. Red giants are no exception, and now we have a way to measure their 'leak' more accurately.
Original abstract
as written by the authors arXiv:2601.10800
The surface [C/N] of red giants is correlated with birth mass, but not directly impacted by mass loss. Exploiting this, we compare asteroseismic masses of red giants with the same [C/N] and but different evolutionary states. We find bulk differences between stars at the beginning of the red giant branch and in the subsequent evolutionary phase, the red clump, providing a direct constraint on the strength of net RGB mass loss in field stars. We find that net mass loss decreases with metallicity and mass, matching recent studies for field giants, but contradicting expectations from the widely used Reimers' mass loss formula. We propose a mass- and metallicity-dependent Reimers' $$\eta$$ calibration that reproduces the empirical trends that we see. In addition, we identify 207 stars (3.33% of our sample) that are clear outliers from their population in these birth mass bins, which we believe are likely candidates for mass transfer events. These stars do not show any obvious discrepancies in abundances or binary properties from their counterparts. This population should be accounted for in Galactic archaeological studies. Further follow-up is required to quantify their occurrence rate and origin.
Red giants can lose up to half their mass, but the exact amount depends on the star's composition and initial mass, and now this can be measured without waiting for the end of its life.
In Stanislaw Lem's novel 'Solaris', the ocean-planet behaves like a living organism, changing its mass and shape — almost like a red giant shedding material into space.