The renowned Tycho supernova, first observed by Danish astronomer Tycho Brahe in 1572, has recently been reexamined, revealing a surprising origin. Contrary to long-standing beliefs that it exploded in a vacuous region of space, new analyses indicate that it detonated within a planetary nebula, which is the gaseous remnant of a star that has reached the end of its life cycle.
This nebula, often described as ghostly, consists of gas and dust expelled by dying stars, and while they typically fade away over a few hundred thousand years, this timing is particularly relevant to Tycho”s story. The supernova likely occurred while this nebula was still intact, leading researchers to coin the term “supernova inside a planetary nebula,” or SNIP.
Key evidence supporting this theory includes two distinctive protrusions, referred to as “ears,” observed in the remnant”s structure. These features resemble similar structures found in three other known Type Ia supernovae: Kepler, SNR G299-2.9, and SNR G1.9+0.3. Past studies had already suggested that these remnants were SNIPs, and the new findings bolster the idea that Tycho belongs to this category, echoing a hypothesis first proposed in 1985.
Type Ia supernovae result from the explosive death of white dwarfs, which are the remnants of burnt-out stars. The mechanism behind these explosions has been a topic of extensive debate. However, identifying Tycho as a SNIP aligns with the “core-degenerate” model. In this scenario, a white dwarf merges with the core of a companion star, triggering an explosion that occurs well after the initial interaction, yet while the planetary nebula remains visible.
If Tycho”s explosion conforms to this model, it could imply that a significant majority—between 70 and 90 percent—of standard Type Ia supernovae might actually occur within planetary nebulae. This revelation suggests that such supernovae are not merely sporadic events over extended timescales but can also arise from younger stellar populations, where the nebula is still present.
Despite the four centuries that have passed since Tycho”s supernova was first observed, this groundbreaking analysis continues to reshape our understanding of stellar evolution and the lifecycle of supernovae.
