• Scientists observe mysterious death of a

    From ScienceDaily@1:317/3 to All on Mon Mar 28 22:30:40 2022
    Scientists observe mysterious death of a star emitting six rings

    Date:
    March 28, 2022
    Source:
    University of California - Los Angeles
    Summary:
    Astrophysicists studying in unprecedented detail a red giant
    star named V Hydrae have witnessed the star's mysterious
    death throes. Researchers discovered that the carbon-rich
    star has expelled six slowly expanding molecular rings and two
    hourglass-shaped structures ejecting matter out into space at
    high speeds.



    FULL STORY ========================================================================== Astrophysicists studying in unprecedented detail a red giant star named
    V Hydrae -- abbreviated as V Hya -- have witnessed the star's mysterious
    death throes.


    ========================================================================== Researchers from 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, signaling that the star is undergoing rapid evolution 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 series of expanding rings has been
    seen around a star that is in its death throes -- a series of expanding
    'smoke rings' that we have calculated are being blown every few hundred
    years," said Mark Morris, a UCLA professor of physics and astronomy and
    a co-author of the study.

    The results of the study, which was conducted using the Atacama Large Millimeter/submillimeter Array, known as ALMA, and data from the Hubble
    Space Telescope, are published March 28 in theAstrophysical Journal.

    More than 90% of stars with a mass equal to or greater than the sun's mass evolve into what scientists call asymptotic giant branch stars, or AGB
    stars, of which V Hya is an example. The star is located approximately
    1,300 light- years from Earth in the constellation Hydra.

    Among these millions of stars, V Hya has been of particular interest to astronomers due to its unique behaviors and features, including extremely
    large eruptions of plasma that occur approximately every eight years
    and the presence of a nearly invisible companion star that contributes
    to V Hya's explosive behavior.



    ==========================================================================
    "We have caught this dying star in the process of shedding its atmosphere
    - - ultimately most of its mass -- which is something that most late-stage
    red giant stars do," Morris said. "But much to our surprise, we have
    found that the matter in this case is being expelled as a series of
    rings." Morris said the team also observed high-speed blasts of gas, perpendicular to those rings, that were expelled into two opposite
    directions. He added that the mechanism that produces the rings is
    unknown and will require further investigation.

    "We suspect that it might be related to the presence of orbiting companion stars, but it is difficult to explain that given the few-hundred-year
    interval between ring ejections," Morris said. "This star is providing
    a new and fascinating wrinkle to our understanding of how stars end
    their lives." Raghvendra Sahai, an astronomer at JPL and the study's
    lead author, said the research indicates that previous assumptions about
    star deaths may be wrong.

    "Our study dramatically reveals that the traditional model of how AGB
    stars die -- through the mass ejection of fuel via a slow, relatively
    steady, spherical wind over 100,000 years or more -- is at best,
    incomplete, or at worst, incorrect," he said.



    ==========================================================================
    The six rings that have expanded outward from V Hya over the course of
    roughly 2,100 years have formed a warped, disk-like structure, creating
    a dust-rich region around the star, the researchers report. The team
    dubbed the structure the DUDE, for Disk Undergoing Dynamical Expansion.

    "V Hya is in the brief but critical transition phase that dying stars
    go through at the end of their lives," Sahai said. "It's the phase
    when they lose most of their mass. It's likely that this phase does
    not last very long, so it is difficult to catch them in the act. We
    got lucky with V Hya, and were able to image all of the different
    activities going on in and around this star to better understand how
    dying stars lose mass at the end of their lives." V Hya's final act
    also has produced an hourglass-shaped structure centered on the star
    and oriented perpendicularly to the disk. The two lobes of the hourglass
    have been shaped by a directed, fast wind that is blowing in two opposite directions at speeds up to 500,000 miles per hour.

    Due to the large quantities of dust surrounding the star, studying V
    Hya required a unique instrument with the power to clearly see cold
    matter that is impossible to detect with optical telescopes. ALMA's
    receivers are exceptionally sensitive to very short radio wavelengths
    of approximately 1 millimeter, which revealed the star's multiple rings
    and outflows of molecular gas in stark clarity.

    The researchers used additional infrared, optical and ultraviolet data
    to produce a remarkable picture of a spectacular show in our galaxy,
    much of which was unexpected, Morris said.

    "Each time we observe V Hya, it becomes more and more like a circus,
    with each new evolutionary stage characterized by an even bigger variety
    of impressive feats," Sahai said. "V Hydrae has impressed us with its
    multiple rings and acts, and because our own sun may one day experience
    a similar fate, it has us at rapt attention." The research was funded
    in part by the National Science Foundation and NASA.


    ========================================================================== Story Source: Materials provided by
    University_of_California_-_Los_Angeles. Note: Content may be edited for
    style and length.


    ========================================================================== Related Multimedia:
    * Renderings_of_the_star_V_Hydrae ========================================================================== Journal Reference:
    1. R. Sahai, P-S. Huang, S. Scibelli, M. R. Morris, K. Hinkle,
    C-F. Lee. The
    Rapidly Evolving AGB Star, V Hya: ALMA finds a Multi-Ring Circus
    with High-Velocity Outflows. arXiv.org (Accepted for ApJ), 2022;
    DOI: https:// doi.org/10.48550/arXiv.2202.09335 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/03/220328153937.htm

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