A dying star with mysterious smoke rings could substantially expand stellar theories

A dying star called V Hya has blown out "smoke circles" in a pattern never seen before by astronomers.

The researchers, who outlined the new findings in a paper in The Astrophysical Journal, believe the new observations will provide new insight into the final moments of red giants before they become white dwarves or disintegrate into nebulae, before repeating the cycle that forms stars throughout the universe.

V Hya, located approximately 1,300 light-years from Earth is a red giant star that's in its final stage of life and will soon become a white dwarf. When a star gets to the final phase of its life cycle, it most often becomes a white dwarf, a type of star that has a mass similar to the Sun, but is more comparable in size to Earth.

Unlike most red giants observed throughout history, V Hya isn't releasing its energy in consistent waves. Instead, it has blown out several "smoke rings" according to a press release from the National Radio Astronomy Observatory. The rings were given the moniker DUDE, which stands for "Disk Undergoing Dynamical Expansion."

It's not the first time a white dwarf was observed displaying unusual behavior. Last year, astronomers from Durham University observed a white dwarf "blinking" for the first time. They believe something may be interfering with the white dwarf's food supply. 

The final moment of a red giant star

Astronomers seek out stars in the final violent phases of their lifespan to better understand the process that sees energy transferred out of a dying star as it collapses and becomes a white dwarf. By observing this rare event, they can better the phenomena that led to life flourishing on our planet.

"The end state of stellar evolution — when stars undergo the transition from being red giants to ending up as white dwarf stellar remnants — is a complex process that is not well understood," Mark Morris, co-author of the study, explained in a press release.

"The discovery that this process can involve the ejections of rings of gas, simultaneous with the production of high-speed, intermittent jets of material, brings a new and fascinating wrinkle to our exploration of how stars die.” 

Using the ALMA radio telescope, the team of researchers behind the new discovery observed six rings in total, which appear to have been produced approximately 2,100 years ago. They also observed large hourglass-like gas structures being thrown out of the star that are expanding at a speed of up to 537,000 mph. The astronomers will continue to observe V Hya to gain a better understanding of the unusual event.

Abstract

We have observed the mass-losing carbon star V Hya that is apparently transitioning from an AGB star to a bipolar planetary nebula, at an unprecedented angular resolution of ∼ 0. 004 − 0. 006 with the Atacama Large Millimeter/submillimeter Wave Array (ALMA). Our 13CO and 12CO (J=3–2 and J=2–1) images have led to the discovery of a remarkable set of six expanding rings within a flared, warped Disk structure Undergoing Dynamical Expansion (DUDE) that lies in the system’s equatorial plane. We also find, for the first time, several bipolar, high-velocity outflows, some of which have parabolic morphologies, implying wide opening angles, while one (found previously) is clumpy and highly collimated. The latter is likely associated with the high-velocity bullet-like ejections of ionized gas from V Hya; a possible molecular counterpart to the oldest of the 4 bullets can be seen in the 12CO images. We find a bright, unresolved central source of continuum emission (FWHM size .165 au); about 40% of this emission can be produced in a standard radio photosphere, while the remaining 60% is likely due to thermal emission from very large (mm-sized) grains, having mass & 10−5 M. We have used a radiative transfer model to fit the salient characteristics of the DUDE’s 13CO and 12CO emission out to a radius of 800 (3200 au) with a flared disk of mass 1.7 × 10−3 M, whose expansion velocity increases increases very rapidly with radius inside a central region of size ∼ 200 au, and then more slowly outside it, from 9.5 to 11.5 km s−1 . The DUDE’s underlying density decreases radially, interspersed with local increases that represent the observationally well-characterised innermost three rings.