Scientists Uncover Planets That Devour Stars

In 2020, the Zwicky Transient Facility observed a location in the night sky that suggested the merging of two stars. This phenomenon was identified as a bright red nova, known as Submin’s Red Nova, or slrn. Two years later, astronomers revisited the same area and discovered indications that the star had engulfed nearby planets, referred to as ZTF SLRN-2020.

Earlier observations made using near-infrared telescopes revealed chemical traces such as titanium oxide and carbon monoxide. The event’s brightness was primarily in low-energy wavelengths rather than visible light, indicating a merger event involving bodies between the masses of Neptune and Jupiter.

The stars in this system are not active; the planet did not actively approach but was instead consumed by the star. This raised questions about the physical mechanisms that caused the interaction. The team examined two scenarios: one where a star expanded during its lifecycle to reach the planet’s orbit, and the other where a planet lost energy and spiraled inward toward the star, a phenomenon termed orbital attenuation.

To evaluate these scenarios, the team conducted follow-up measurements on ZTF SLRN-2020 using instruments onboard the JWST, specifically the Near-infrared Spectrometer and Mid-infrared Instrument. They also performed ground-based observations with the Gemini North Telescope Near-Infrared Imager. By combining data from these instruments, the team obtained a comprehensive understanding of the low-energy light emission patterns from ZTF SLRN-2020, revealing insights into the system’s current structure and dynamics.

In their analysis, astronomers identified four key characteristics. The remaining stars displayed a reddish hue, highlighting a significant presence of high-energy electrons in the star’s hydrogen, along with substantial carbon monoxide. There were also traces of phosphine, a compound typically found around gas giants and in the vicinity of young stars. Using computer modeling, the team evaluated which scenarios could realistically produce these observed patterns.

Measurements of star color indicated that ZTF SLRN-2020 is quite similar to the Sun but is roughly 70% of its size. The star is too young to have undergone the expansion associated with its later life stages. Consequently, the planet’s orbit became destabilized, leading to its gradual engulfment by the star. This collision likely released energy, igniting the star’s brightness in 2020 and stimulating the hydrogen in its outer layer.

The team theorized that during the collision, the star would have expelled material from the planet. The emissions of phosphine and carbon monoxide suggested that the ejected material originated from two different layers of dust around the star: a cold outer shell and a hot inner disk. Observations did not reveal any remnants of the planet’s core still orbiting the star, indicating that it was entirely consumed, losing even its outer layers.

The researchers deemed this event a new frontier in physics, as it marks the first observed case of planetary engulfment. The data collected from various instruments can provide future researchers with essential insights when investigating similar instances.

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