ASU astronomer contributes to study revealing clues about century-old stellar cold case
The Deep Sky Collective image of the nebula surrounding GK Persei. Image courtesy of Deep Sky Collective
More than a century after a spectacular stellar explosion lit up the night sky above the constellation Perseus, NASA’s newest space telescope, SPHEREx, has uncovered something no one expected: The ancient nova GK Persei is surrounded by a previously unknown envelope of molecular hydrogen, the most abundant molecule in the universe, stretching roughly 8-by-5 light-years across.
The study, led by Professor D. P. K. Banerjee of the Physical Research Laboratory in Ahmedabad, India, in collaboration with an international team including Arizona State University Regents Professor Sumner Starrfield of the School of Earth and Space Exploration, also includes researchers from the United States, the United Kingdom and Estonia. The findings published in The Astrophysical Journal Letters represent an important new chapter in the history of one of astronomy’s most iconic objects, offering new clues about the evolution of classical novae.
“The eruption occurred 125 years ago, yet it continues to reveal new phenomena that surprise us,” Starrfield said. “We are trying to understand how the nova outburst is interacting with the nebula and the H2 molecular envelope."
A stellar explosion that keeps surprising astronomers
Nova Persei 1901, known to astronomers as GK Persei, was the first bright classical nova of the 20th century. In these events, a dense white dwarf star pulls gas from a companion star until a surface explosion makes the system about a million times brighter for a short time, before it dims again.
GK Persei’s 1901 eruption was dramatic. Within months, astronomers observed ghostly light echoes racing outward at apparent speeds faster than light: an optical illusion caused by the explosion’s flash illuminating surrounding clouds of gas and dust. The shell of debris from the explosion is still visible today and spans about 1 light-year.
Around this small remnant is a much bigger structure: a bipolar, two-lobed nebula about 8 light-years wide. Its origin has puzzled astronomers for years. Some thought it was an old planetary nebula from an earlier stage of the star’s life, while others were not convinced.
"GK Persei keeps holding major surprises," Banerjee said. "The eruption occurred 125 years ago, yet it continues to reveal new phenomena that challenge our understanding. In this study, we have tried to explain the nova outburst, the nebula and the H2 molecular envelope in a unified way."
SPHEREx: A new kind of cosmic detective
NASA’s SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) is designed to survey the entire sky in infrared light with unprecedented sensitivity. Molecular hydrogen, which is normally invisible to conventional optical telescopes, emits faint infrared signatures that SPHEREx is uniquely equipped to detect.
The new observations show that molecular hydrogen traces the full extent of the bipolar nebula surrounding GK Persei, suggesting that the two structures are directly connected — a significant clue in a cold case that has been open for over a century.
“It is really exciting to see the ways the science community, both around the world and on campus here at ASU, is using SPHEREx data to answer new science questions,” said Sean Bryan, ASU School of Earth and Space Exploration associate research professor, survey lead for the SPHEREx mission and member of the science team.
ASU’s role in NASA mission science
The School of Earth and Space Exploration at ASU maintains strong connections to NASA mission science, with faculty conducting research in areas such as stellar astrophysics, infrared spectroscopy and interstellar chemistry. Discoveries such as the vast envelope of molecular hydrogen around GK Persei highlight ASU’s ongoing commitment to advancing our understanding of the universe's origins and evolution.
Images of the GK Persei nebula from Deep Sky Collective, taken over more than 265 hours, give extra visual context for the SPHEREx findings. These images show that the molecular hydrogen is connected to the supposed planetary nebula structure.
“The numbers just do not add up for the large nebula to be a recent event,” Starrfield said. “A typical planetary nebula lives for only about 30,000 years and would be long gone by the time the white dwarf had faded to its current brightness, which takes about a million years.”
Why it matters
Classical novae are among the most energetic and chemically productive events in the galaxy. Understanding how their remnants evolve and what molecular species survive and form in their aftermath has direct implications for models of stellar evolution, the chemical enrichment of the interstellar medium and the life cycle of stars.
With SPHEREx scanning the whole sky in the infrared, astronomers think GK Persei is only the first of many stellar remnants that will show features that we cannot see with optical telescopes. It seems the universe keeps its secrets for a long time, but new space telescopes are finally starting to uncover them.
Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) is a joint project of the Jet Propulsion Laboratory and the California Institute of Technology, and is funded by the National Aeronautics and Space Administration.
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