PHoto courtesy of Aaron M. Geller, in collaboration with Northwestern University professor Raffaella Margutti and graduate student Wynn Jacobson-Galán
“We are made of star stuff,” the famous astronomer Carl Sagan had once said in an early 1980s television series about the cosmos, encapsulating the mind-boggling reality that our bodies are literally made of elements forged in the cores of stars. Scientists can, in a study now, not only confirm the truth in Sagan’s words but have also finally observed how stars explode to give the material out in the universe.
As it happens, half of all the calcium in the universe—including the very calcium that makes our teeth and bones—was created by dying stars. These stars explode in supernovae and scatter this mineral across the universe in massive quantities. While explosions and mergers of stars are known to also create elements like gold and platinum, the creation of calcium has been a mystery. These stellar explosions—called "calcium-rich supernovae”—have turned out to be incredibly rare events that scientists have struggled observing. So, the nature of these supernovae and their mechanism for creating calcium has remained mysterious for decades.
Until now. The study, published in The Astrophysical Journal on August 5, sees scientists finally examining a calcium-rich supernova with X-ray imaging.
In April 2019, an amateur astronomer observed a bright burst while stargazing. And the next day, he saw a bright orange dot in the frame that wasn’t there before. He shared this observation with the local astronomical community, and the news of a possible supernova spread like a wildfire. A global team of almost 70 scientists was formed to observe the star in action.
It turns out that the scientists had observed a calcium-rich supernova just 10 hours after the explosion. And this observation provided an unprecedented glimpse into the star’s life and ultimate explosion.
While all calcium comes from stars, calcium-rich supernovae are the richest: typical stars create small amounts of calcium slowly through burning helium throughout their lives but calcium-rich supernovae produce massive amounts of calcium within seconds.
The new findings revealed that a calcium-rich supernova is a compact star that sheds an outer layer of gas during the final stages of its life. When the star explodes, its matter collides with the loose material in that outer shell, emitting bright X-rays. The overall explosion causes intensely hot temperatures and high pressure, driving a chemical reaction that produces the calcium that we know.
"These events are so few in number that we have never known what produced calcium-rich supernovae," said Wynn Jacobson-Galan, a first-year Northwestern graduate student who led the study in a statement. "By observing what this star did in its final month before it reached its critical, tumultuous end, we peered into a place previously unexplored, opening new avenues of study within transient science." In the world of transients, the scientists said, they have to discover things very fast before they fade.
Their findings suggest that the stars responsible for these explosions must be undergoing some sort of instability. The researchers are working on a follow-up study that includes how the supernova is evolving after the explosion.
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