For a long time, Gaia20ehk seemed like just another star, quietly hanging out 11,000 light-years away in the constellation Puppis. Its light was steady, like an ordinary main-sequence star. But in 2016, things changed. Astronomers noticed three unexpected dips in its brightness. By 2021, the star’s flickering transformed into something bizarre, grabbing the attention of researchers.
One of those intrigued was Anastasios Tzanidakis, a PhD candidate at the University of Washington. While exploring old data, he observed Gaia20ehk’s curious behavior. “It started off stable, but then those three dips appeared, followed by chaotic flickering,” he explained.
Now, Gaia20ehk is a key player in understanding planetary collisions. Tzanidakis and his colleague, James Davenport, think the strange flickering isn’t from the star itself, but rather from a heated, clumpy cloud of debris created by a catastrophic collision between two planetary bodies. They detail their findings in a study in The Astrophysical Journal Letters, where they dub it a possible “planetesimal collision afterglow.”
The breakthrough came when researchers used infrared data alongside visible light measurements. Instead of fading like the star, the infrared light actually brightened. This suggested that the obscuring material was hot enough to glow. Tzanidakis noted, “In infrared, while the visible light dimmed, we saw a spike, indicating that something hot was blocking the star.”
This pattern is crucial to their argument. The authors suggest that new circumstellar dust can absorb visible light and reradiate it as infrared. Current measurements indicate the temperature of this dust is around 900 Kelvin and it has a significant mass, comparable to a small icy moon like Enceladus.
The timing of the events also adds to the evidence. Before the infrared brightening began, Gaia20ehk displayed a 380.5-day periodic signal. This implies that the debris is orbiting at about 1.1 astronomical units from the star, similar to Earth’s distance from the Sun. This positioning reveals that the debris resides in the region where rocky worlds are known to form.
The initial dips in brightness may hint at the lead-up to the collision. Tzanidakis speculates that the two planets were spiraling closer together, experiencing minor impacts before a major collision occurred, unleashing a surge of infrared energy.
Significantly, Gaia20ehk mirrors theories about our own solar system’s chaotic beginnings. The leading model posits that a Mars-sized body collided with Earth, creating a debris cloud that eventually formed the Moon. Though Gaia20ehk is not a direct replay of that event, it offers a rare glimpse into the giant impacts theorized to shape many planetary systems. Studies suggest that rocky planets often form through such collisions in their early stages and catching Gaia20ehk in this evolving aftermath is extraordinary.
Gaia20ehk might not be alone for long. Researchers predict that with ongoing infrared monitoring, especially with advanced observatories like the James Webb Space Telescope (JWST), more planetary impacts will be captured. According to Davenport, the Vera C. Rubin Observatory’s upcoming sky survey may uncover about 100 similar events in the next decade. “Understanding how often these impacts happen is critical to astro-biology,” he said.
As it stands, Gaia20ehk continues to shimmer in infrared light while flickering unpredictably. What once seemed like background noise has transformed into a vibrant picture of a planetary system in the throes of creation and destruction.
