Chinese-led team reveals secrets of giant star’s explosive death after boost from citizen scientists
- ‘The death of a massive star can be much more complex than previously thought,’ lead author says
- Non-professional astronomers may be more flexible to capture new objects of interest than professional experts, says biologist turned amateur stargazer
For the first time, a China-led team has revealed images of the immediate aftermath of a giant star’s explosive death, challenging the standard theory of stellar evolution.
Using professional and amateur telescopes based in China, the United States, Europe and Russia, the researchers were surprised to find that the star – some 85 million times the size of the sun in the Pinwheel galaxy – was surrounded by thick layers of dust as it ran out of fuel and blew up.
This “veil of death”, which was formed using materials expelled by the star during its final years of life, prevented the explosion’s shock wave from quickly breaking out into open space, they reported in the journal Nature on December 13.
“While the shock wave was expected to be very hot and short lived, our study showed that it was not the case within the first hours the star went supernova,” said the paper’s lead author Wang Xiaofeng from Tsinghua University in Beijing.
“It showed that the death of a massive star can be much more complex than previously thought.”
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Scientists have relatively well-matched theories and observations of how stars of small or medium mass live and die, according to Wang. However, the evolution mechanism of massive stars, which by definition have eight or more times the mass of the sun, remains unclear.
When a star of around 18 solar masses was first discovered by Japanese amateur astronomer Koichi Itagaki in May to have exploded, it immediately became a treasure trove of observation data for scientists thanks to its extreme brightness and proximity to Earth.
As one of the most beautiful galaxies in the night sky, the Pinwheel galaxy is constantly photographed by amateurs around the world. Wang collected pictures from both professional observatories and amateurs to reconstruct the entire explosion process.
His team contacted astronomy enthusiasts who had captured the galaxy before and after the supernova. Then the researchers retrieved information for each colour band, including red, green and blue bands, and did intensive calibration and comparison to obtain reliable multicolour photometry data.
To their surprise, the shock wave immediately after the explosion seemed to have a much lower temperature than expected.
“In the first couple of hours the shock wave appeared to be red, which corresponds to a few thousand degrees kelvin,” Wang said. Then it turned blue, or tens of thousands of degrees as predicted by the standard theory.
The shock wave was also observed to have lasted several hours – much longer than the predicted duration of about 30 minutes.
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Wang said these observations provided direct evidence that the giant star emitted a considerable amount of gas and dust to form dense surroundings, which ended up absorbing much of the shock wave’s energy.
Meanwhile, the dust layers were probably asymmetrical, leading to the wave’s prolonged travel from the core to open space, he added.
“Our work wouldn’t be possible without the help of amateur astronomers in and outside China,” he said. “I really hope such collaboration will happen more often, and even open up a new paradigm in astrophysics research in the future.”
Eliot Herman, an emeritus professor of plant biology at the University of Arizona in the US, was one of the amateur astronomers contacted by Wang’s team.
Herman said he happened to notice the alert about the supernova, and he stayed up much of the night to grab images using a remote network of telescopes in Utah as the supernova became brighter and brighter.
When he was asked to share the original data set with Wang’s group, Herman happily agreed. His data and that from other amateurs was merged, resulting in the analyses and conclusions outlined in the Nature paper.
Compared with professional observatories, which often operate based on schedules, amateurs have more flexibility, according to Herman.
“Amateurs can change their minds and jump on the alert of new objects of interest,” he said.
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Astronomy was a unique discipline in which amateurs played a significant role, Herman said. Historically, the science was done largely by amateurs and academics funded by rich people before it became government-funded.
Today, there is no other mainstream discipline like astronomy.
“I was at one time a programme manager at the National Science Foundation [in biology], and I never saw a grant or project with an amateur participating,” he said.
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Astronomy welcomes amateurs to help explain the wonders of the universe.
“This synergy is science at its best. I’m so thrilled to be included in this project and its publication,” Herman said.
