- Astronomers studied 130 years of data on planetary nebula IC 418 and found its central star is heating up faster than any star seen before.
- The star’s temperature has increased by 3,000 degrees Celsius (5,400 F) over 130 years. But that rate of increase is still less than current models predict.
- These findings suggest scientists may need to revise how they think stars like our sun evolve and die.
Do we need a rethink on how planetary nebulae evolve?
A planetary nebula is the cast-off outer layer of a dying star, appearing as glowing shells of gas and dust around a hot stellar core. IC 418 is one of the first planetary nebulae ever studied, and it has a long record of observations. Astronomers said on August 20, 2025, that they’ve analyzed data on IC 418 going all the way back to 1893. They discovered its stellar core is heating up much faster than any star ever observed. However, that rate of change in temperature is still slower than what recent stellar evolution models predict. It suggests astronomers need to reexamine their understanding of how stars like our sun will someday die.
Quentin Parker, at the University of Hong Kong, is a co-author of the paper. He said:
We believe this research is important because it offers unique, direct evidence of how planetary nebulae central stars evolve. It will prompt us to rethink some of our existing models of stellar life cycles. It’s been a strong joint effort — collecting, verifying, and carefully analyzing more than a century’s worth of astronomical data and then melding that with stellar evolutionary models.
The paper’s lead author, Albert Zijlstra at The University of Manchester, added:
We often ignore scientific data obtained long in the past. In this case, these data revealed the fastest evolution of a typical star that has been seen directly. The past shows that the skies are not as unchanging as we may think.
The researchers published their findings in the peer-reviewed Astrophysical Journal Letters on August 20, 2025.
A rapidly changing phase in stellar evolution
Stars between 0.8 to 8 times the mass of our sun will someday become planetary nebulae. For much of their existence, these stars shine steadily, converting hydrogen to helium in the core. Astronomers call this phase the main sequence.
But when that hydrogen fuel is exhausted, the star expands to become a red giant star. Then, helium in the core fuses to become carbon and oxygen. Subsequently, that inert core is surrounded by a thin layer of helium fusing to carbon and oxygen, and another outer layer of hydrogen fusing to helium.
Eventually, strong stellar winds eject the star’s outer layer, forming shells of glowing gas and dust energized by the hot central core. This phase, the planetary nebula, is brief by stellar evolution timescales; it’s just a few tens of thousands of years. In comparison, our sun spends 10 billion years on the main sequence.
Studying planetary nebula IC 418
IC 418 is a young planetary nebula. At its center is a white dwarf star, a very hot, dense core of carbon and oxygen. The gases that make up the planetary nebula are excited – or ionized – by radiation emitted by the white dwarf.
As the white dwarf contracts, it heats up. The amount of that heating can be determined using spectroscopic observations of the planetary nebula. Astronomers do this by breaking up the nebula’s light into its component colors – called a spectrum – using instruments attached to telescopes. In particular, the astronomers looked at specific spectral signatures from hydrogen and oxygen.
Over the past 130 years, the methods for measuring these spectral signatures have changed dramatically. In 1893, Victorian astronomers obtained some measurements, the first visual observation used in this study. Since then, astronomers have captured data on photographic plates, using different types of electronic cameras and, most recently, using CCD detectors.
The researchers collected the data from these different sources and carefully calibrated them to see how IC 418’s hydrogen and oxygen signatures changed over 130 years.
How planetary nebula IC 418 changed over 130 years
The astronomers found significant changes in the spectral signature emitted by oxygen in IC 418. It increased by about 2.5 times since Victorian astronomers first observed it. Researchers said this was driven by the rising temperature of the white dwarf; it has risen in temperature by 3,000 C (5,400 F) since 1893.
Moreover, based on how fast the white dwarf was heating up, they were also able to learn something about the star before it became a white dwarf and planetary nebula. It was about 1.25 to 1.55 times the mass of our sun. But the remaining white dwarf is just 0.6 times the sun’s mass.
So this is the biggest increase in temperature ever observed for a single star. But modern stellar evolution models predict an even faster increase. Therefore, these observations challenge current models of how stars like our sun age and die.
Bottom line: Astronomers looked at 130 years’ worth of data on planetary nebula IC 418. They found its central star heating up faster than any star ever observed. But that increase is still slower than predicted.
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