Scientists discover unusual spectacle in star death

A group of scientists witnessed an unprecedented event where the star V Hydrae (V Hya) showed six slowly expanding rings and two hourglass-shaped structures generated by the expulsion of matter at high speed.

Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile and the Hubble Space Telescope (HST), it was possible to analyze the data supplied from the last moments of this star in its final phase.

It should be noted that this study was published in The Astrophysical Journal. Raghvendra Sahai, an astronomer at NASA's Jet Propulsion Laboratory and principal investigator for this project, commented that:

“Our study clearly confirms that the traditional model of how RAG stars die out – by a mass ejection effect that takes the form of a relatively stable, spherical jet over 100,000 years – is at best incomplete and, at worst, incorrect.

It should be noted that V Hya is a star in the asymptotic giant branch (AGS) stage, which has to do with a period of stellar evolution through which all low to intermediate mass stars (0.6-10 solar masses) at the end of their lives. Furthermore, V Hya is carbon-rich and located in the constellation Hydra 1,300 light-years from Earth.

“It is very likely that a nearby stellar or substellar companion is significantly involved in its extinction, and understanding binary interactions is of the utmost importance for astrophysics, as well as being one of its main challenges. In the case of V Hya, the combination of a nearby star and a hypothetical distant star would be responsible, at least to some extent, for the presence of the six rings and the fast jets that are causing the star's unusual extinction." Sahai added.

It is necessary to limit that more than 90% of the stars equal in size or greater than the Sun, by depriving themselves of the necessary fuel to sustain nuclear processes, end up becoming RAG.

There are millions of stars like this, but V Hya has attracted the attention of many scientists due to its peculiarity, especially due to its large plasma eruptions that occur every 8.5 years, as well as the presence of a neighboring star that is hardly visible. and it is believed that this encourages the explosive behavior of V Hya.

For his part, Mark Morris, an astronomer at the University of California at Los Angeles and co-author of this research, stated that:

“V Hydrae is caught in a process of shedding its own atmosphere and ultimately its mass, something most red giant stars do. But to our surprise, we discover that, in this case, the matter is being expelled in the form of a series of rings. This is the first and only time that gas ejected from a RAG star has been observed to flow like expanding smoke rings."

The team of scientists in charge of this investigation named the structure formed by the rings as DUDE, which stands for Disk Undergoing Dynamical Expansion. These six rings are approximately 2,100 years moving away from V Hya, at the same time they are expanding and adding mass.

In the same way, it feeds the growth of the DUDE structure, which is found around the star, has a high density and, moreover, is shaped like a stretched and twisted disk. In addition to this, V Hya contains two structures with the shape of an hourglass and another with the shape of a jet, these expand at 240 kilometers per second.

These forms have already been seen before in the planetary nebulae of MyCn 18 (Hourglass Nebula), found in the Musca constellation 8,000 light-years from Earth, and in the Crab Nebula, located in the Centaurus constellation 7,000 light-years from Earth. light years from Earth.

“The final stage of stellar evolution, when stars make the transition from red giant to white dwarf stellar remnant, is a complex process that we do not fully understand. Discovering that this process can involve the ejection of rings of gas and at the same time the expulsion of intermittent jets of material at high speed represents a new and fascinating edge in our investigation of how stars die,”adds Mark Morris.

For his part, Raghvendra Sahai, explaining the process in which the star under investigation is undergoing, stated that:

“V Hya is in a critical but short transition stage, and it is very difficult to find stars at this stage, or rather, in flagrant. We were lucky, and we were able to image all of V Hya's mass loss phenomena, allowing us to better understand how dying stars lose mass at the end of their lives."

It should be noted that the team of scientists had to use ALMA's Band 6 (1.23 mm) and Band 7 (0.85 mm) receivers, since only then could the different rings and jets of the star be seen with incredible definition.. The reason for all this is that due to the density of the dust that surrounds the star, it is impossible to try it with optical telescopes.

“We first observed the presence of very fast jets in 1981. Then, in 2022, we discovered eruptions consisting of compact plasma spots ejected by V Hya at high speed. And now our finding of wide-angle flares in V Hya completes the puzzle by revealing how these structures can be created during the evolutionary stage this extraluminous giant red star is in," Raghvendra Sahai explained.

Similarly, Joe Pesce, astronomer and NSF Program Officer of NRAO/ALMA, adding to the topic of star stages and praising ALMA technology, stated that:

“The processes that occur in the final stages of low-mass stars, and during the RAG stage in particular, have long fascinated astronomers and have been difficult to understand. ALMA's capacity and resolution are finally allowing us to witness these events in incredible detail, which is needed to get some answers and improve our understanding of a stage that most stars in the Universe go through."

In the same vein, Sahai also explains that using infrared, optical and ultraviolet data in the study provided a complete multi-wavelength picture of what could be one of the biggest Milky Way shows for astronomers..

“Each time we watch it with new viewing capabilities, V Hya turns out to be more and more like a circus, with an ever-widening and impressive variety of shows. V Hydrae has impressed us with its many rings and acts, and since our Sun could one day suffer the same fate, it has captured all our attention”, he concluded.