The researchers then traced the evolution of the white dwarfs back in time, deriving their initial masses with the help of an important relationship in astrophysics, the initial-final mass relation (IFMR), which, despite its ubiquity, still has its quirks. The initialfinal mass relation connects the mass of a white dwarf with the mass of its progenitor in the main sequence, says Ramirez-Ruiz. By understanding this relationship, we are able to put stringent constraints on the carbon-containing mass that was ejected during the evolution of the star.

Generally speaking, the more massive a progenitor star, the more massive its remnant. But the team discovered an apparent kink in that relationship. Stars starting with about 1.8 to 1.9 times the mass of the Sun seem to be leaving behind larger-than-expected corpses.

The break in the IFMR was noticed independently by both Cummings and the studys lead author, Paola Marigo, a theoretical astrophysicist at the University of Padova in Italy. Importantly, Cummings found the kink through observations, while Marigo uncovered it in her theoretical modeling.

According to the researchers, the fact that stars with just under two solar masses seem to produce plus-sized white dwarfs suggests these stars were still forging carbon in the final stages of their lives. This carbon was then passed into the interstellar medium by stellar winds, which is a far more gentle process than being violently propelled by supernova shock waves. This revelation places a constraint on the evolution of low-mass stars, as well as how they chemically enrich their surroundings.

This new low-mass star theory of chemical enrichment doesnt so much compete with previous ideas as it does bolster them. Its not that low-mass stars are solely responsible for enriching their host galaxies with carbon, but they do work with their bulkier counterparts to get it done.

There is ample evidence that both exploding massive stars and low-mass stars contribute to the production and distribution of carbon in the universe, says Ramirez-Ruiz. This is evident by looking at the fossil stellar record in the Milky Way. Ramirez-Ruiz goes on to suggest that massive stars could contribute more to carbon-enrichment early on, while low-mass stars might inject more carbon into galaxies at later times. After all, smaller stars live much longer than larger stars.

With all of the complex processing that can occur in astronomy, the production of elements is never an only A or only B type of process, Cummings stresses. Both processes are likely major contributors, and our work does not rule out the contribution of more massive stars and their supernovae.

However, one thing is for sure, there is still much to learn about low-mass stars and their evolution, as well as the role they play in the chemical enrichment of their host galaxies. Cummings says astronomers need to intensely study stars ranging from about one to two times the mass of the Sun, as well as the white dwarf remnants they leave behind.

Whilst I do hope to be involved at some level in future work of this nature, the researcher says, I am just as excited about the prospect of this current study inspiring a younger astronomer to take the lead.

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Small stars are vital to dispersing the building blocks of life - Astronomy Magazine