Blog Post: Catching the Disappearing Stars That Become Black Holes

When a massive star dies, we usually see a brilliant supernova explosion lighting up the night sky. But what if some of the most massive stars skip this dramatic finale entirely? New research suggests that many massive stars may collapse directly into black holes without any visible explosion—essentially vanishing from our telescopes. This "disappearing star" scenario has profound implications for how we search for black holes and understand the final moments of the universe's most massive objects.

What They Found

Gilkis, Laplace, Drout, and colleagues tackled a fundamental question: what do black hole progenitors actually look like before they collapse? Using sophisticated stellar evolution models combined with atmospheric calculations, they predicted the colors and brightness of stars destined to become black holes. The results challenge conventional wisdom.

The team found that most black hole progenitors are hot and blue at the moment before collapse—not the cool, red supergiants that astronomers have traditionally focused on. Many exist in the Wolf-Rayet phase, a brief but intense stage where massive stars shed their outer layers and shine brilliantly in ultraviolet light. Only a minority are red supergiants. This distinction matters enormously for observational searches. The predicted direct-collapse rate is roughly 0.4 events per century in a galaxy like the Milky Way, meaning these events are genuinely rare but not impossibly so for nearby galaxies.

Why It Matters

This research directly impacts how we detect black hole formation in real time. For decades, searches for "failed supernovae"—supernovae that collapse to black holes instead of exploding—have concentrated on red supergiants in nearby galaxies, assuming that's where the action happens. But if the majority of direct-collapse events come from hot, blue stars, those surveys are systematically missing most of the signal.

This connects directly to the broader landscape of transient astronomy and multi-messenger observations. Just as gravitational wave detectors like LIGO have revolutionized black hole science, electromagnetic observations of disappearing stars could provide a complementary window into black hole formation. Catching a star in the act of vanishing would give us unprecedented insight into the physical processes governing which massive stars explode and which collapse silently.

What's Next

The immediate path forward is clear: ultraviolet-sensitive monitoring campaigns of nearby star-forming galaxies. Missions like Swift and future UV observatories are well-positioned to detect the sudden disappearance of a hot, luminous star. The predictions from this paper provide a crucial roadmap—astronomers now know what to look for, where to look, and how often they might expect to find it.

Open questions remain about the physics connecting core structure to explosion outcome, and how binary interactions might alter these predictions. Each disappearing star detected would be a golden opportunity to constrain these models.

Starithm continuously monitors real-time transient alerts from major surveys, making it an ideal platform to flag candidates matching these predictions and coordinate follow-up observations across the electromagnetic spectrum.