Scientists studying V Hydrae (V Hya) have witnessed the mysterious death of the star in unprecedented detail. Using the Atacama Large Millimeter / submillimeter Array (ALMA) Array and data from the Hubble Space Telescope (HST), the team discovered six slowly expanding rings and two hourglass structures caused by high-velocity matter ejection into space. The results of the study are published in The Astrophysical Journal. V Hya is a carbon-rich asymptotic branch (AGB) star located about 1,300 light-years from Earth in the constellation Hydra. More than 90 percent of stars with mass equal to or greater than the Sun evolve into AGB stars as the fuel needed to power nuclear processes is removed. Among these millions of stars, V Hya is of particular interest to scientists because of its unique behaviors and characteristics so far, including extreme-scale plasma explosions that occur about every 8.5 years and the presence of an almost invisible companion star that contributes to The explosive behavior of V Hya. The carbon-rich star V Hydrae is in his final act and so far, his death has proved majestic and violent. Scientists studying the star have discovered six ring outbursts (shown here in composite material) and other structures created by the explosive mass of matter ejected into space. Credit: ALMA (ESO / NAOJ / NRAO) / S. Dagnello (NRAO / AUI / NSF) “Our study dramatically confirms that the traditional model of how AGB stars die – through massive fuel launches through a slow, relatively steady, spherical wind for over 100,000 years or more – is at best incomplete or “Worse, wrong,” he said. Raghvendra Sahai, an astronomer at NASA’s Jet Propulsion Laboratory and the lead researcher in the study. “It is very possible that a close astral or sub-astral partner plays an important role in their deaths, and understanding the physics of binary interactions is as important in astrophysics as one of its greatest challenges. In the case of V Hya, the combination of a near and a hypothetical distant star companion is responsible, at least to some extent, for the presence of its six rings and the high-velocity outflows that cause the star to die miraculously. UCLA astronomer Mark Morris, co-author of the study, added: “V Hydra has been caught in the process of eliminating its atmosphere – eventually most of its mass – something most red giant stars do in the final stages. To our great surprise, we found that the issue, in this case, is eliminated as a series of ring outputs. This is the first and only time anyone has seen gas fired from an AGB star flow in the form of a series of expanding “smoke rings”. Scientists studying the dying carbon-rich star V Hya have discovered six slowly expanding rings that form as the star expels its matter. Appearing here in composite material, these ring outputs and the diffuse arc structure of the sixth ring are moderately visible at the 12CO carbon isotope emission line and become clearly defined on the faces of the 13CO carbon isotopes. These rings are part of an unknown story about the death of stars and help scientists unravel what happens in the “final act”. Credit: ALMA (ESO / NAOJ / NRAO) / S. Dagnello (NRAO / AUI / NSF) The six rings have been extending outward from V Hya for about 2,100 years, adding matter and leading to the development of a high-density inflated and distorted disk-like structure around the star. The group has named this structure DUDE, or Disk that undergoes dynamic expansion. “The final state of stellar evolution – when stars undergo the transition from red giants to ending up as stellar remnants of white dwarfs – is a complex process that is not well understood,” Morris said. “The discovery that this process can involve the release of gas rings, along with the production of high-velocity, intermittent jets of material, brings a new and exciting wrinkle to the exploration of how stars die.” Sahai added, “V Hya is in the short but critical transition phase that does not last long, and it is difficult to find stars in this phase, or rather ‘catch them in the leech’.” “We were lucky enough to be able to visualize all the different mass loss phenomena in V Hya to better understand how dying stars lose mass at the end of their lives.” V Hydrae is a carbon-rich star located 1,300 light-years away in the constellation Hydra. It is the subject of recent observations revealing the violent deaths of stars, which include, in the case of V Hya, explosive plasma launches into space that shape the structural environment around the star. Credit: IAU and Sky & Telescope In addition to a complete set of expanding rings and a twisted disc, the V Hya final act includes two hourglass structures – and an additional jet-like structure – which expand at high speeds of over half a million miles per hour (240 km / s). . Large hourglass structures have previously been observed in planetary nebulae, including MyCn 18 – also known as the Hourglass Nebula – a young emission nebula about 8,000 light-years from Earth in the southern constellation of Musca and the most famous Nebula an emission nebula located about 7,000 light-years from Earth in the southern constellation Centaurus. Sahai said, “We first observed the presence of very rapid outflows in 1981. Then, in 2022, we found a jet-like flow consisting of solid plasma bubbles ejecting at high speeds from V Hya. And now, our discovery of wide-angle outputs in V Hya connects the dots, revealing how all of these structures can be created during the evolutionary phase in which this extremely bright red giant star is now. “ Due to both the distance and the density of the dust surrounding the star, V Hya’s study required a unique instrument with the power to see clearly matter that is too far away and also difficult or impossible to detect with most optical telescopes. The team used ALMA Band 6 (1.23 mm) and Band 7 (.85 mm) receivers, which revealed the star’s multiple rings and outputs with absolute purity. “The processes that take place in the final stages of low-mass stars, and especially during the AGB phase, have long fascinated astronomers and were difficult to understand,” said Joe Pesce, NSO astronomer and NSO program manager. ALMA. “ALMA’s capabilities and analysis finally allow us to witness these events in the extraordinary detail that is necessary to give some answers and enhance our understanding of an event that happens to most of the stars in the Universe.” Sahai added that the inclusion of infrared, optical and ultraviolet data in the study created a complete multi-wavelength picture of what could be one of the largest shows in the galaxy, at least for astronomers. “Every time we observe V Hya with new observation skills, it becomes more and more like a circus, characterized by an even greater variety of impressive achievements. “V Hydrae has impressed us with its multiple rings and actions, and because our Sun may one day experience a similar fate, it caught our attention.” Research

“The fast-growing AGB star, V Hya: ALMA finds a high-velocity multi-ring circus”, Sahai et al, (2022) The Astrophysical Journalpreprint: arXiv: 2202.09335

Resources

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