Astronomers Reveal 57 “Faces” of a Dying Star Using ALMA

What does a dying star look like? The answer depends on the molecules you observe. This is what a UNAB research team led by Keiichi Ohnaka discovered through new observations using the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile.

By analyzing signals from 57 different molecules, the team captured 57 unique views of W Hydrae, a red giant located about 320 light-years from Earth.

The star’s appearance shifts dramatically depending on the molecule being observed, revealing different atmospheric layers in a dynamic, turbulent, and chemically rich environment. As Professor Ohnaka explains:

“With ALMA, we can now observe the atmosphere of a dying star with a level of detail comparable to what we achieve for the Sun, but through dozens of distinct molecular lenses. Each one reveals a different facet of W Hydrae, offering insight into a remarkably complex and dynamic stellar environment.”

A Living Atmosphere: Clumps, Plumes, and Colliding Flows

ALMA’s exceptional resolution—comparable to photographing a grain of rice from 10 kilometers away—revealed that W Hydrae’s atmosphere extends well beyond the star’s surface. Gas clouds and structures form as a result of stellar pulsations and shockwaves. If placed at the center of our solar system, W Hydrae would engulf Mercury, Venus, Earth, and Mars.

The team also detected simultaneous gas flows. In some regions, material is expelled from the star at speeds reaching 36,000 kilometers per hour, while in others, gas falls back toward the surface at nearly 47,000 kilometers per hour. This constant motion results in a highly dynamic and ever-changing pattern.

Such behavior is typical of stars in the Asymptotic Giant Branch (AGB) phase—an advanced stage of stellar evolution marked by pulsations and massive loss of material. W Hydrae serves as a natural laboratory for studying how stars shed their outer layers, enriching the interstellar medium with elements and compounds that later give rise to new stars, planets, and ultimately, the building blocks of life.

From Gas to Dust in Nine Days

One of the most striking findings is the direct link between gas movement and dust formation. The researchers compared ALMA data with images captured by the SPHERE instrument on the Very Large Telescope (VLT), taken just nine days apart.

“By combining data from ALMA and VLT/SPHERE, we can connect gas dynamics, molecular chemistry, and dust formation in near real time—something that was extremely difficult to achieve until now,” noted Professor Ohnaka.

Molecules such as silicon monoxide (SiO), water vapor (H₂O), and aluminum monoxide (AlO) appeared in the same regions where VLT detected dust clouds, suggesting they play a direct role in transforming gas into solid particles.

Other molecules—including sulfur monoxide (SO), sulfur dioxide (SO₂), titanium oxide (TiO), and possibly titanium dioxide (TiO₂)—were also found in overlapping areas and may contribute through shock-induced chemical reactions.

A Glimpse Into Our Sun’s Future

Coauthor Ka Tat Wong, of Uppsala University in Sweden, emphasized the broader significance of the study:

“Mass loss in dying stars is one of the biggest unsolved challenges in stellar astrophysics. ALMA allows us to observe the regions where this process begins—where shocks, chemistry, and dust formation all interact. W Hydrae provides a unique opportunity to test and refine our models using real, spatially resolved data.”

This detailed glimpse into W Hydrae’s complex atmosphere offers rare insight into the processes that will one day shape the final chapters of our own Sun.

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