Beta-decay experiment helps to pin down the fate of intermediate-mass stars

Stars have different evolutionary paths depending on their mass. Low-mass stars, such as the Sun, will eventually become white dwarfs. Massive stars, on the other hand, finish with a spectacular explosion known as a supernova, leaving either a neutron star or a black hole behind. The fate of both low- and high-mass stars is well understood but the situation for intermediate-mass stars has remained unclear. According to a recent study they are more likely to undergo a thermonuclear explosion and leave a special type of white dwarf as a remnant. This unexpected result was obtained via an international collaboration including researchers from the Ģֱ. The measurements were carried out using the IGISOL facility at the JYFL Accelerator Laboratory in Jyväskylä. The results were published in Physical Review Letters on 11th November, and highlighted as Editor’s Suggestion.
Stars have different evolutionary paths depending on their mass. Credit: Heiko Möller / TU Darmstadt
Published
7.1.2020

The fate of intermediate-mass stars, which weigh 7-11 times as much as the Sun, has remained unclear. This is surprising since intermediate-mass stars are prevalent in the Galaxy. As such, their fate can have a significant impact on the produced chemical elements, their abundances, and galactic chemical evolution. A few years ago it was noted that the final fate of intermediate-mass stars depends on a tiny detail, namely, how readily electrons are captured on the isotope neon-20 in the stellar core.

The fresh study focused on determining the crucial electron-capture rate on neon-20 and how it affects the fate of the star: whether it will undergo a thermonuclear explosion leaving a white dwarf behind or collapse to form a neutron star. The rate has now been determined for the first time through a beta-decay experiment on fluorine-20 and theoretical calculations.

“We discovered that the electron captures proceed far more easily and at a lower density than previously believed. For the star, this implies that it is more likely to be disrupted by a thermonuclear explosion than to collapse into a neutron star”, says Associate Professor Anu Kankainen from the Ģֱ. The experiment took place under conditions far more peaceful than those found in stars, namely at the Accelerator Laboratory of the Ģֱ.

Intermediate-mass stars could explain observed iron-60 in deep-sea sediments

Since thermonuclear explosions eject much more material than the gravitational collapse, the result may have implications also on galactic chemical evolution. The ejected material is rich in titanium-50, chromium-54, and iron-60. Therefore, the death of a nearby intermediate-mass star could explain the unusual titanium and chromium isotopic ratios found in some meteorites, or the origin of iron-60 found in deep-sea sediments.

The fate of intermediate-mass stars seems to be a thermonuclear explosion, producing a special type of supernova and an oxygen-neon-iron white dwarf. Detection or non-detection of such objects would provide important insights into the explosion mechanism in the future. Another thing to be clarified is the role played by convection in the explosion, namely, how the material moves around in the interior of the star.

But this is a job for the astrophysicists - now the nuclear physicists have contributed their part!

Link to article:

Link to the article in Physical Review C –publication:

Link to the article Physics –online magazine evaluating the results of the new research:

Link to the article in JYUnity online magazine presenting the research of Anu Kankainen's group:
 

For further information:
Associate Professor Anu Kankainen, anu.kankainen@jyu.fi, tel. +358 40 805 4880, Twitter: @anu_kankainen
Communications officer Tanja Heikkinen, tanja.s.heikkinen@jyu.fi, tel. + 358 50 581 8351

The Faculty of Mathematics and Science 
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