Astronomers get a glimpse of what will happen when our sun dies

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Astronomers observed 57 different “sides” of a distant exploding star, using different molecules to capture a varying picture of stellar death and its impact on its environment. The research could give us a more complete prediction of what will happen to the Sun in about 5 billion years when it begins its own death throes and transforms into a red giant star, devouring its inner planets, including Earth.

The observations were made using the Large Millimeter/submillimeter Array at Atacama (ALMA), a collection of 66 radio antennas located in northern Chile, brought together to constitute the largest astronomical project in existence.

The dying star being investigated by ALMA, with help from the Very large telescope (VLT), is W Hydrae, a red giant or AGB star, located 320 light years from Earth. ALMA observed this red giant in an entirely new way by observing the emissions and absorption of light by 57 different molecules, called spectral lines, each revealing a different layer of W Hydrae’s turbulent and violent atmosphere.

“With ALMA, we can now see the atmosphere of a dying star with a similar level of clarity to what we do for the sun, but through dozens of different molecular views,” team leader Keiichi Ohnaka, of Andres Bello University (Chile), said in a statement. statement. “Each molecule reveals a different face of W Hydrae, revealing a surprisingly dynamic and complex environment.

“The combination of ALMA and VLT/SPHERE data allows us to link gas movements, molecular chemistry and dust formation in almost real time, which has been difficult until now.”

Different molecules tell a different story about dying stars

It was ALMA’s exceptional sensitivity, capable of capturing the equivalent of taking a photo of a grain of rice from a distance of 10 kilometers, that allowed the team to see the changing structures within the red giant and its atmosphere. These included “tufts, arcs and plumes,” all of which varied depending on the molecule studied. The different molecules offer unique views of W Hydrae because the spectral lines observed by ALMA, the optical “fingerprints” of different chemicals, form under different conditions.

Seen in these different spectral lines, the red giant was swollen until it reached several times its original size. In fact, if it were placed where the Sun is in the solar system, its outer layers would engulf planets up to the orbit of Mars. These expanded regions appear as clouds sculpted by shocks, pulsations and heat transfer from the central star.

ALMA observations showed a variation in the movement of gas around W Hydrae, with gas closer to the red giant’s core moving outward at speeds of about 22,400 miles per hour (36,000 km/h), while gas in the upper layers falls inward at a speed of about 29,000 miles per hour (46,000 km/h). This creates an ever-changing layered flow model, which matches the 3D modeling of how convective cells and pulsation-driven shocks shape the atmosphere of red giants.

One of the most remarkable elements of the team’s findings was the revelation of the observed molecules and newborn dust, which emerged when ALMA’s findings were compared to data collected by the VLT’s SPHERE instrument. The fact that the two sets of observations were made just nine days apart allowed the team to link gas chemistry to dust formation in real time. The team found that molecules such as silicon monoxide, water vapor and aluminum monoxide appear exactly where clumped dust clouds were observed in the VLT data. This indicates that these chemicals are directly involved in the formation of dust grains.

They also found that other molecules, such as sulfur monoxide, sulfur dioxide, titanium oxide, and possibly titanium dioxide, overlap with dust in some regions around W Hydrae and therefore may contribute to dust formation through shock-driven chemistry. On the other hand, molecules like hydrogen cyanide form near the star but do not appear to participate directly in dust formation.

As dying stars like W Hydrae shed their outer layers, they enrich their cosmic environment, or interstellar medium, with molecules that become the building blocks of new stars and planets. This research and observations of a red giant’s formation and dust outflows could help better understand how AGB stars lose mass, one of the oldest unsolved problems in stellar astrophysics.

“The mass loss of AGB stars is one of the biggest unsolved challenges in stellar astrophysics,” said team member Ka Tat Wong from Uppsala University. “With ALMA, we can now directly observe the regions where this flow begins, where shocks, chemistry and dust formation interact. W Hydrae gives us a rare opportunity to test and refine our models with real, spatially resolved data.”

W Hydrae can also act as a scientific crystal ball, providing insight into the fate of the sun and how our star will enrich our cosmic backyard with the elements needed to create new stars, planets and even life itself.

The team’s research was published Dec. 2 in the journal Astronomy and astrophysics.