This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: 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. 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. 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.
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