New observations from scientists at Sweden’s Chalmers University of Technology have cast doubt on the long-held idea that light from dying stars propels ‘seeds of life’ molecules like oxygen and carbon throughout the cosmos.
The new study, which found that the propulsive power of starlight and stardust emitted by red giant stars was insufficient to allow the seeds of life molecules to escape their host star’s gravitational pull, has resulted in a new astronomical mystery for scientists to solve.
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“We thought we had a good idea of how the process worked,” explained Chalmers astronomer Theo Khouri, the joint leader of the study detailing the newly discovered mystery. “It turns out we were wrong. For us as scientists, that’s the most exciting result.”
Seeds of Life Findings Create All New Stardust Mystery
Although researchers have yet to find irrefutable evidence of life beyond Earth, most agree that the seeds of life molecules needed for Earth’s biological life to exist and thrive were born in the heart of stars. For the last several decades, most scientists have been relatively confident that these molecules and other critical life-supporting elements have been propelled by stellar winds aboard grains of dust into the depths of the cosmos, where they could seed the formation of new planets, and, potentially, life.
Described as the “cooler cousins” of the Sun, red giants lose massive amounts of material through the phenomenon of stellar winds. Although likely critical for the theoretical spread of life throughout the cosmos, the team said the exact mechanism that drives these winds “has remained uncertain.”
To better understand the process, the Chalmers scientists focused on a red giant star, R Doradus, only 180 light-years away in the constellation Dorado. Although the cosmically close dying star once had a relatively similar mass to the Sun, R Doradus now loses about one-third of Earth’s mass every decade.
The research team said this process is characteristic of asymptotic giant branch (AGB) stars, which “lose their outer layers to interstellar space,” via stellar winds made of gas and dust. When our sun reaches the end of its life, billions of years from now, it is expected to turn into this category of dying stars.
“R Doradus is a favourite target of ours – it’s bright, nearby, and typical of the most common type of red giant,” Khouri explained.
World’s ‘Best’ Telescopes Shed Light on Stellar Winds
The first step in the process involved measuring starlight reflected by tiny grains of stardust surrounding R Doradus. Due to the minute amount of light that the team was hoping to detect, they were granted access to the Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) instrument mounted on the European Space Agency’s (ESA) Very Large Telescope VLT) in Chile.
“Using the world’s best telescopes, we can now make detailed observations of the closest giant stars,” Khouri said.
After successfully analyzing polarized light at different wavelengths, the team made several discoveries. For example, SPHERE detected light signatures consistent with dust grains surrounding the star. The Chalmers team said the data also revealed the size and composition of the grains were “consistent with common forms of stardust,” including silicates and alumina.
Next, the researchers combined the real-life telescope data with computer simulations designed to model the interaction between stardust and starlight. Study co-author Thiébaut Schirmer said these comparisons represented the first stringent tests intended to confirm whether grains of dust that include seeds of life molecules “can feel a strong enough push from the star’s light.”
Results Show Light is Not Enough, but Opens “Exciting Alternatives” to Explore
After comparing the data, the team said the push from starlight was “not enough” to push the stardust grains into interstellar space. That’s because most of the grains surrounding R Doradus were only about one ten-thousandth of a millimeter across. The research team said this made the grains “too small for starlight alone” to propel them into interstellar space.
“Dust is definitely present, and it is illuminated by the star,” Schirmer explained. “But it simply doesn’t provide enough force to explain what we see.”
While the new findings seem to contradict the traditional explanation, the team said their research points to “more complex processes” behind the phenomenon. Study co-author and Chalmers professor Wouter Vlemmings agreed, noting that even though the simplest explanation appears incorrect, their findings have uncovered “exciting alternatives to explore” moving forward.
One possible explanation for the dispersal of such molecules involves images of enormous convective bubbles rising and falling over R Doradus’ surface, previously captured by the same team. Vlemmings suggested that it’s possible these stellar pulsations could enhance the push of starlight enough to drive the seeds of life into interstellar space. The scientist also suggested that something unexpected, such as dramatic episodes of stardust formation, might combine with the other phenomena, which “could all help explain how these winds are launched” into the cosmos.
The study “An empirical view of the extended atmosphere and inner envelope of the asymptotic giant branch star R Doradus” was published in Astronomy and Astrophysics.
