Astrophysicists monitoring a red giant star designated V Hydrae – abbreviated as V Hya – in unprecedented detail have watched the star’s strange death throes.
UCLA and NASA’s Jet Propulsion Laboratory discovered that the carbon-rich star has expelled six slowly expanding molecular rings and an hourglass-shaped structure ejecting matter out into space at high speeds, indicating that the star is rapidly evolving as it ends its life in a blaze of glory before shutting down its energy production.
“This is the first and only time that a sequence of expanding rings has been spotted around a dying star — a series of expanding’smoke rings’ that we have estimated are being blown every few hundred years,” said Mark Morris, a UCLA professor of physics and astronomy and one of the study’s co-authors.
The study’s findings, which were obtained using the Atacama Large Millimeter/submillimeter Array (ALMA) and Hubble Space Telescope data, were published on March 28 in the Astrophysical Journal.
More than 90% of stars with masses equal to or larger than the mass of the sun develop into asymptotic giant branch stars, or AGB stars, of which V Hya is an example. The star is around 1,300 light-years away from Earth in the constellation Hydra.
Among these millions of stars, V Hya has piqued astronomers’ curiosity because to its unusual behaviors and traits, such as exceptionally huge plasma eruptions that occur every eight years and the existence of an almost undetectable partner star that contributes to V Hya’s explosive activity.
“We captured this dying star in the midst of losing its atmosphere — eventually most of its mass — which is something that most late-stage red giant stars do,” Morris said. “However, much to our astonishment, we discovered that the substance in this instance is being evacuated in the form of a series of rings.”
Morris said that the crew also witnessed high-speed jets of gas ejected perpendicular to those rings and ejected in two different directions. He went on to say that the process that creates the rings is unclear and that further research is needed.
“We think it may be tied to the existence of orbiting partner stars,” Morris said. “However, given the few hundred-year delay between ring ejections, this is difficult to explain.” “This star adds a new and exciting twist to our knowledge of how stars die.”
According to Raghvendra Sahai, the study’s principal author and an astronomer at JPL, the findings suggest that earlier beliefs regarding star deaths may be incorrect.
“Our research demonstrates that the classic idea of how AGB stars die — by the mass ejection of fuel through a slow, generally constant, spherical wind spanning 100,000 years or more — is, at best, incomplete, and, at worst, inaccurate,” he added.
According to the researchers, the six rings that have extended outward from V Hya over the period of around 2,100 years have produced a distorted, disk-like shape, generating a dust-rich zone surrounding the star. The structure was named the DUDE by the researchers, which stands for Disk Undergoing Dynamical Expansion.
“V Hya is in the short but essential transition period that dying stars experience near the conclusion of their lifetimes,” Sahai said. “It is the stage at which they shed the majority of their bulk. This period is likely to be brief, making it difficult to capture them in the act. We were fortunate with V Hya, since we were able to photograph all of the diverse events occurring in and around this star, allowing us to get a better understanding of how dying stars lose mass towards the conclusion of their lifetimes.”
V Hya’s last act similarly resulted in an hourglass-shaped structure centered on the star and perpendicular to the disk. A directed, rapid wind flowing in two opposing directions at rates of up to 500,000 kilometers per hour sculpted the hourglass’s two lobes.
Because of the vast amount of dust around the star, researching V Hya needed a one-of-a-kind device capable of clearly seeing cold materials that optical telescopes cannot detect. ALMA’s sensors are extraordinarily sensitive to very short radio wavelengths of around 1 millimeter, which showed the star’s numerous rings and molecular gas outflows in stunning detail.
Morris said that the researchers combined additional infrared, optical, and ultraviolet data to create a fantastic image of a dazzling display in our galaxy, most of which was unexpected.
“With each observation of V Hya, it grows more and more like a circus, with each new developmental stage defined by an ever greater diversity of astonishing performances,” Sahai said. “V Hydrae has amazed us with its many rings and actions, and since our own sun may one day suffer a same fate, we are paying close watch.”
The National Science Foundation and NASA contributed to the study.