May 27, 2022

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Cosmic mystery: Astronomers capture dying star spewing rings of smoke

Cosmic mystery: Astronomers capture dying star spewing rings of smoke
Zoom / A display of the star V Hydrae or V Hya for short. In the throes of its death, the star unleashed a series of expanding rings that scientists calculated form every few hundred years, according to astronomer Mark Morris of the University of California.

Alma (ESO / NAOJ / NRAO) / S. Dagnello (NRAO / AUI / NSF)

Astronomers have discovered a red giant star going through its final death throes in unprecedented detail, revealing an unusual feature. The star known as V Hydri (or V Hya for short), take out six distinct episodes of material, according to Preliminary version Accepted for publication in The Astrophysical Journal. The exact mechanism of these mysterious “smoke rings” is not yet fully understood. However, the observation could shake up existing models for this late stage of stellar evolution and shed more light on the The fate of our sun.

“V Hydrae is caught in the process of shedding its atmosphere – eventually most of its mass – which is something most late-stage red giants do,” Co-author Mark Morris said:, an astronomer at the University of California. However, “this is the first and only time that a series of expanding rings has been seen around a star going through its death throes – a series of expanding ‘smoke rings’ that we thought get blown out every few hundred years.”

red giants It is one of the final stages of star evolution. Once the star’s core stops converting hydrogen into helium via nuclear fusion, gravity begins to compress the star, raising its internal temperature. This process ignites a shell of hydrogen burning around an inert core. Eventually, pressure and heating in the core caused the star to expand dramatically, reaching diameters between 62 million and 620 million miles (100 million to 1 billion km). Surface temperatures are relatively cool by stellar standards: 4000 to 5800 degrees Fahrenheit (2200 to 3200 degrees Celsius). So these stars take on an orange-red appearance, hence the nickname red giant.

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V Hydrae is a carbon-rich star located 1,300 light-years away in the constellation Hydra.
Zoom / V Hydrae is a carbon-rich star located 1,300 light-years away in the constellation Hydra.

IAU, Sky & Telescope

Eventually, the helium in the red giant’s core will be spent, and the core will shrink again. Then become a star asymptotic giant branch (AGB) star (last red giant stage). The inner structure of the AGB star consists of a central core of carbon and oxygen, a shell in which fusion turns helium into carbon, and another shell where hydrogen turns into helium. These stars typically produce dramatic pulsations of increasing brightness every 100 to 1,000 days. In addition, intense surface winds cause the formation of a gaseous cloud known as the periplasm around the star.

These intense stellar winds will eventually dislodge the atmosphere and stellar atmosphere, and the star will become a white dwarf within a planetary nebula. The faster the rate at which an AGB star loses mass, the closer it is to that final transition. Our Sun will eventually become a red giant in about 5 billion years, eventually evolving into the AGB before finally evolving into a planetary nebula with a white dwarf star at its center.

This is the process as astronomers have understood it for years. However, V Hya’s unusual characteristics make them rethink things. Located 1,300 light-years away in the constellation Hydra, V Hya is a carbon-rich star, meaning that its atmosphere contains more carbon than oxygen. It has a high rate of mass loss, so astronomers believe it is likely in the process of shedding its atmosphere to become a planetary nebula.

An introduction showing the carbon-rich star V Hya in its final chapter.
Zoom / An introduction showing the carbon-rich star V Hya in its final chapter.

Alma (ESO / NAOJ / NRAO) / S. Dagnello (NRAO / AUI / NSF)

This AGB star is also interesting because every eight years or so, a large plasma eruption occurs, and a sharp dip in brightness occurs about every 17 years. These events indicate the presence of a companion star that is barely visible. (The decrease in brightness may be caused by a cloud associated with this second star passing in front of V Hya.)

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This latest study combines data from the Hubble Space Telescope with observations using the Atacama Large Millimeter/ Sub-millimeter Array (ALMA), which includes infrared, optical, and ultraviolet data to capture the death throes of V Hya across multiple wavelengths. The star is far away and shrouded in thick dust, but ALMA’s high-resolution capabilities have revealed its rings and outflows in great detail.

The timing was also a coincidence. “V Hya is going through a short but crucial transition that dying stars go through at the end of their lives,” Co-author Raghvendra Sahai . said:, an astronomer at NASA’s Jet Propulsion Laboratory. “It’s the phase where they lose most of their mass. This phase probably doesn’t last very long, so it’s hard to catch it in the act. We were lucky with V Hya, and were able to photograph all the different activities going on in and around this star to better understand how the stars are lost. moribund for the mass at the end of its life.”

Sahai and colleagues found that the star sheds its atmosphere by blowing out a series of smoke rings, which have extended outward over the course of 2,100 years or so to form a dust-disk-like region around V Hya. the team dubbed This structure is DUDE (disk undergoes dynamic expansion).

Their observations also revealed high-speed explosions of gas expelled from the star in opposite directions, perpendicular to the smoke rings, forming two hourglass-shaped structures. These structures expand at speeds of more than half a million miles per hour (240 km/s). “The discovery that this process can involve firing rings of gas, in conjunction with the production of intermittent, high-speed jets of material, brings a fascinating new wrinkle to our understanding of how stars end their lives,” Morris said.

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All this indicates that the star is undergoing a particularly rapid evolution, which goes against the current model. “Our study dramatically reveals that the traditional model for how AGB stars die—by expelling mass fuels through relatively slow and steady globular winds over 100,000 years or more—is incomplete at best, or at worst incorrect,” Sahi said. “It is very likely that a companion stellar or quasi-star plays an important role in their death. In the case of V Hya, the combination of a nearby and hypothetical distant companion star is responsible, at least to some extent, for the presence of its six rings, and the high-speed outbursts that cause the miraculous death of the star. .”