Direct collapse to a black hole is when a massive star collapses into a black hole without producing a bright supernova. It works because the imploding core cannot power a strong explosion, most of the energy leaves as neutrinos, and the outer layers largely fall back or are only gently ejected. Astronomers infer these events when a star brightens in infrared light from heated dust, then disappears with no supernova seen.
What is direct collapse to a black hole?
Direct collapse is a pathway for massive stars to form black holes in which the star vanishes with little or no visible supernova, leaving either a faint transient or none at all.
In typical core-collapse supernovae, the stellar core implodes, a shock wave revives, and the outer layers are blasted into space, creating a bright optical display that can outshine a galaxy. In direct collapse, the shock fails to unbind the star. The result is a dim event, often detectable mainly in the infrared where newly formed dust glows, followed by the disappearance of the progenitor star.
How does direct collapse to a black hole work?
As a massive star exhausts nuclear fuel, its iron core becomes unstable and collapses under gravity. The collapse produces a burst of neutrinos and a shock. If that shock cannot overcome infalling material, it stalls. The core then crosses the threshold to a black hole, and much of the envelope falls inward rather than exploding outward.
- Energy budget: most gravitational energy escapes as neutrinos, leaving too little to drive a luminous supernova.
- Fallback: material that briefly moved outward reverses course and accretes onto the newborn black hole.
- Dust and infrared glow: weak outflows and shocks can heat circumstellar gas and create dust that radiates in infrared light for months to years.
Theory has long predicted such failed supernova outcomes for some mass ranges and stellar structures, especially in stars with dense envelopes, certain rotation rates, or metallicities. Until recently, clear observations were scarce.
How was direct collapse observed in Andromeda?
In new research led by Kishalay De of Columbia University, astronomers revisited public infrared survey data and found a massive star in the Andromeda galaxy that brightened for about three years starting in 2014, then faded and vanished without a supernova. The work, published in Science, interprets the signal as a star undergoing direct collapse to a black hole.
A NASA infrared telescope recorded a years-long rise in infrared light, followed by the star’s disappearance and a lingering shell of dust. No bright optical supernova was detected.
The progenitor appears to have started life at roughly 13 times the Sun’s mass and, by the time of collapse, was closer to about 5 solar masses, consistent with heavy mass loss over its lifetime. The infrared emission traces dust heated by a weak outflow or shock, while the lack of optical fireworks points to a failed explosion. Together, these signatures provide the clearest view so far of stellar collapse proceeding directly to a black hole in a nearby galaxy.
This event builds on earlier candidates, such as the “vanishing” red supergiant N6946-BH1 identified by long-term monitoring, which also showed infrared emission and the disappearance of the progenitor but with fewer constraints. The Andromeda case adds multi-year infrared evolution and a resolved dust shell, strengthening the direct-collapse interpretation.
Why is direct collapse important?
- Black hole birth rates: Quantifies how often massive stars make black holes without supernovae, a key input for stellar population models.
- Supernova census: Helps explain why some massive star progenitors are missing from supernova observations.
- Chemical enrichment: Direct collapse ejects little material, so it changes expectations for how galaxies seed heavy elements and dust.
- Gravitational-wave progenitors: Quiet black hole births in binaries can affect the masses and spins of the black holes that later merge.
- Feedback in galaxies: Fewer energetic explosions means different heating and stirring of interstellar gas.
What are the limitations and open questions?
These events are hard to catch. The signal is faint in visible light, the infrared rise can be slow, and the definitive signature is the star’s disappearance. Large, long-baseline surveys in the infrared are essential to find more cases in nearby galaxies.
Key questions remain: which stellar masses and structures most often produce failed supernovae, how metallicity and rotation shift the boundary between explosion and collapse, and how to confirm the newborn black hole. Follow-up at radio and X-ray wavelengths can sometimes reveal accretion or interaction with residual material, but many newborn black holes will be electromagnetically quiet.
Direct-collapse events are likely hiding in archival data. Systematic searches, including machine learning applied to infrared time series, will expand the sample and sharpen theory.
Finally, while popular questions arise about planets surviving such a collapse, very massive stars have short lifetimes and violent mass loss. Their environments are not favorable for long-lived, habitable worlds. The scientific focus is on how stars die and black holes form.