Astronomers have used radio observations from the Atacama Large Millimeter/submillimeter Array (ALMA) to catch a dying star in the middle of a dramatic transformation, and the data show a ring that records its final outburst. The new research was posted to the arXiv preprint server on Sept. 18. The paper has been accepted for publication in The Astrophysical Journal.
Before the end
Most stars in the sun’s mass range end their lives as planetary nebulae—appearing as colorful remnants in deep-space photos—rather than explosive supernovae. As simple as that sounds, there is a puzzle: They start as slow, rounded shells of gas thrown off by red giant stars, yet most planetary nebulae and their predecessors are nonspherical—sometimes bipolar, multipolar or elliptical.
The leading explanation is that fast, collimated jets, probably launched through interaction with a binary companion, sculpt the slow wind from the inside out during the short preplanetary phase and reshape its structure.
To test and improve simulations of this process, astronomers need high-resolution measurements of the masses and motions of the outflows and central regions for a representative sample of objects.
This study, led by Raghvendra Sahai of the Jet Propulsion Laboratory, is part of a survey called PANORAMA (Pre-planetAry Nebulae high-angular-resOlution suRvey with AlMA) that aims to supply them.
IRAS 06530 is a carbon-rich, bipolar preplanetary nebula, on its way to becoming a glowing planetary nebula. It has already been imaged by Hubble, which makes it a good target.
Three-component structure
The team observed it with ALMA to capture both fine detail and large-scale emissions.
They tracked carbon monoxide and other molecules to learn how dense, warm and massive each region is. From the gas speeds, they worked out how old each structure was and how fast the star was shedding material. They also measured the star’s brightness to estimate its original mass and found it to be around 1.6 to 3.4 times the sun’s mass.
The high-resolution images revealed a large circular ring with a radius of about 16,950 times the Earth–sun distance. The team says it is the first evidence of the star’s last brief flare-up near the end of its life. Its mass-loss rate decreased for about 2,000 years right after the flare-up, then picked up again before the star moved into its next phase.
At the center, there are two components. One is a two-lobed nebula with a dense, doughnut-shaped torus, formed within the last 700 years or so. The torus has unusual carbon, oxygen and nitrogen ratios that standard models can’t explain, possibly pointing to explosive nuclear burning.
The fainter component between the torus and the ring consists of curved arcs that hold most of the mass, far more than the ring or the central nebula. They look like the spiral patterns seen around some bloated red giant stars with binary companions. Their shape hints at a hidden companion star at roughly 155 to 340 times Earth’s distance from the sun.
A puzzling end
If the central region was created by fast, collimated jets from interaction with a binary companion, sculpting the wind from the inside out—the proposed primary mechanism for the creation of nonspherical preplanetary nebulae—astronomers should detect signs of fast outflows in their spectra.
Typically, preplanetary nebulae show fast-moving material with speeds above 50 km/s (31 miles per second). But that is not the case for IRAS 06530.
The team found no sign of fast jets with gas speeds greater than 16.5 km/s (10.3 miles per second) and no compact dusty disk at the star’s position.
“So it is rather surprising that we find no evidence for such high velocities in IRAS 06530’s spectra,” the team writes in the paper. They suggest a short-lived disk may once have launched brief jets before dissipating.
The researchers also note that the large separation makes strong interaction between the two stars “somewhat unlikely,” unless the orbit is elongated enough for the companion to come very close to the primary.
The researchers estimate that gas accreting onto a companion could still supply enough energy to power the outflow, even at a separation of about 75 times the Earth–sun distance, and that the same companion could be responsible for the arcs if its orbit is elongated.
Together, the ring, arcs and central nebula make IRAS 06530 a complex system with a layered history and some puzzles yet to be solved.
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Publication details
Raghvendra Sahai et al., The Last Gasps of a Dying Star: ALMA Observations of the Pre-Planetary Nebula IRAS 06530-0213, arXiv (2026). DOI: 10.48550/arxiv.2609.22489
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ALMA catches a dying star mid-transformation, with a ring from its last outburst (2026, October 12)
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