SPHEREx reveals a molecular hydrogen shell around nova GK Persei

Star system: Nova Persei 1901 A | Distance from the Sun: 1414 light years

GK Persei, a nova that erupted in 1901, continues to surprise astronomers more than a century later. Using data from the SPHEREx space telescope, researchers discovered a large, bipolar shell of molecular hydrogen surrounding the nova. This shell, measuring 18 by 10 arcminutes, matches the shape and location of the known H-alpha nebulosity around GK Persei, which was previously thought to be an ancient planetary nebula.

The hydrogen shell is most strongly detected in a specific infrared emission line, and a filament of this emission is seen southwest of the nova, coinciding with regions of X-ray and radio emission where the nova’s ejecta interacts with surrounding material. The study suggests that the hydrogen emission comes from a neutral zone between shock fronts created by the nova explosion. While such hydrogen envelopes are common around planetary nebulae, the evidence shows that the nebulosity around GK Persei is not a typical planetary nebula, but rather pre-existing material ionized by the 1901 eruption. The ionized gas is now slowly recombining, which explains why the nebulosity remains visible after more than a century.

Key findings
- SPHEREx detected a large, bipolar molecular hydrogen shell around GK Persei
- The shell matches the H-alpha nebulosity, previously thought to be a planetary nebula
- A filament of hydrogen emission coincides with X-ray and radio features from shock interactions
- The emission likely comes from a neutral zone between shock fronts
- The nebulosity is pre-existing material ionized by the nova, not a true planetary nebula

Scientific study

Detection of a molecular hydrogen envelope around nova GK Persei (external link)