Hydrogen shell detected around Nova Persei 1901 may be a planetary nebula
by Tomasz Nowakowski, Phys.org
Using NASA's SPHEREx space telescope, astronomers have observed remnants of the eruption of Nova Persei 1901. As a result, they detected a bipolar molecular hydrogen shell around this nova, which may be a large planetary nebula. The finding was detailed in a paper published March 13 on the arXiv pre-print server.
The mystery of a century-old nova eruption
Nova Persei 1901 (or GK Persei) was the first bright classical nova of the 20th century. It has a round overall morphology consisting of almost a thousand cometary-like structures, and currently extends to a radius of about 1.0 arcminute.
Although Nova Persei 1901 has been extensively studied for over a century, it still holds many surprises. Previous observations have found that the remnant of this explosion may be best described as a thick spherical shell or an equatorial barrel feature with polar cones.
New findings from SPHEREx
Now, new SPHEREx observations of Nova Persei 1901 conducted by a team of astronomers led by Dipankar Banerjee of the Physical Research Laboratory (PRL) in Ahmedabad, India, provide more evidence supporting the planetary nebula hypothesis.
"SPHEREx obtained 114 spectrophotometric images of GK Persei and its environs, covering all 102 of its wavelength bands. The exposure time for each image was 113.58 seconds. Emission was detected in about 30 of the images," the researchers explain.
The observations found that Nova Persei 1901 has a bipolar molecular hydrogen shell with a dimension of 18 x 10 arcminutes. This shell is co-spatial with a hydrogen-alpha nebulosity surrounding the nova. The mass of the shell is estimated to be within the range of 0.28–0.38 solar masses.
Planetary nebula or something else?
Given that planetary nebulae, especially the bipolar ones, often host molecular hydrogen shells, the astronomers therefore assume that the detected shell is a planetary nebula. Moreover, the mass of the shell further supports this scenario, as planetary nebulae generally have masses between 0.1 and 1.0 solar masses.
However, the authors of the paper note that the bipolar shape requires a dense equatorial constriction, for instance, a torus, to shape the nebula, but such a torus is not seen in the collected SPHEREx images.
Furthermore, the results suggest that the planetary nebula would have faded below detection level by the time the nova erupted in 1901, making it improbable to observe simultaneously the planetary nebula and the nova remnant.
Another possibility considered by the researchers is that the shell is actually material that existed prior to the eruption in 1901. Afterward, it could have been ionized by the nova outburst and is presently in the recombination phase.
These uncertainties therefore underscore the need for further investigation of Nova Persei 1901. “GK Persei and its environment remain partially understood; the more we discover about it, the more we realize how incomplete our understanding is. There is a need for a spatio-kinematic study of the nebulosity to further test its classification as a planetary nebula, and to understand its relation to the 1901 outburst,” the scientists conclude.
Written for you by our author Tomasz Nowakowski, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.
Publication details
D. P. K. Banerjee et al., Detection of a molecular hydrogen envelope around nova GK Persei, arXiv (2026). DOI: 10.48550/arxiv.2603.12991
Key concepts
Transient & explosive astronomical phenomena, Bipolar nebulae, Gaseous nebulae, Circumstellar shells
