Black Holes
Regions where gravity is so strong not even light escapes.
Overview
A black hole is a region of spacetime where gravity is strong enough that no path — for matter or for light — leads back out. They form from collapsed massive stars and grow by accretion and by merging, and they are described by general relativity in terms of just mass and spin.
- The event horizon is a causal boundary, not a physical surface.
- Horizon size scales linearly with mass: roughly 3 km per solar mass.
- Accreting black holes are among the brightest objects in the universe — the light comes from infalling matter, not the hole.
- Both gravitational-wave detection and direct horizon imaging confirmed key predictions within the last decade.
The event horizon
In general relativity, mass and energy curve spacetime and objects follow the straightest available paths through it. A black hole is a configuration where the curvature within a region is extreme enough that every future-directed path leads inward — the event horizon marks that boundary.
Nothing marks the boundary locally — no surface, no barrier, no measurable jolt for an infalling observer crossing a supermassive one. What changes is which futures remain reachable. For a non-rotating black hole the horizon radius is proportional to mass, at roughly 3 kilometres per solar mass, which is the number every catalogued size on this platform is derived from.
Populations
- Stellar-mass black holes, typically a few to a few tens of solar masses, form from the collapse of massive stellar cores. Many are found in X-ray binaries or through gravitational-wave detections of mergers.
- Supermassive black holes, millions to billions of solar masses, occupy the centres of most large galaxies. Sagittarius A* at the Milky Way's centre is about four million solar masses.
- The intermediate mass range, roughly a hundred to a hundred thousand solar masses, is the sparsest part of the catalogue: candidates exist and some merger events land in it, but no formation route is established, so records here carry lower confidence than either population above or below.
- How supermassive black holes reached their masses so early in cosmic history, given the quasars observed at high redshift, is an open problem.
How they are detected
Nothing escapes a black hole, so detection is always indirect or, in the imaging case, based on the shadow it casts. Stellar orbits around the Galactic centre revealed a compact four-million-solar-mass object in a volume no star cluster could occupy — work recognised with the 2020 Nobel Prize in Physics.
Two detection channels now populate the catalogue directly. Gravitational-wave observatories have recorded merger events since 2015, each yielding component masses and spins. The Event Horizon Telescope published horizon-scale images of M87's black hole in 2019 and of Sagittarius A* in 2022 — the only two objects for which a resolved horizon-scale image exists, which is why image coverage on every other black-hole record is honestly empty.
Accretion, jets, and feedback
Accretion is what makes black holes catalogable at all: the infalling material radiates, and that radiation is the observable. Its efficiency far exceeds nuclear fusion, which is why an accreting black hole can outshine its entire host galaxy and be recorded across cosmological distances.
Many systems also launch relativistic jets along the spin axis. On galactic scales these jets deposit enormous energy into the surrounding medium, heating gas and suppressing star formation — a feedback process now understood as an important regulator of galaxy evolution rather than a curiosity.
Open questions
General relativity predicts a singularity at the centre, where its own equations cease to give meaningful results. That is generally taken as a signal that quantum gravity is required, not as a physical description of a place.
No catalogued black hole has ever been observed to lose mass. Hawking's predicted thermal emission is far colder than the cosmic microwave background for any astrophysical example, so every real object absorbs more than it emits — which is why no record on this platform carries an evaporation timescale.
Continue in the data
Catalogues, hubs, and reference pages that hold the underlying records for this topic.
Frequently asked
- How big is a black hole?
- Its event horizon radius is proportional to its mass — roughly 3 kilometres per solar mass for a non-rotating black hole. A ten-solar-mass stellar remnant has a horizon about 30 kilometres in radius; the four-million-solar-mass black hole at the Galactic centre has one about 12 million kilometres in radius, which fits comfortably inside Mercury's orbit — that orbit is nearly five times wider.
- If nothing escapes, how do we detect black holes?
- Through their effects. Stars orbiting an invisible compact mass reveal it dynamically; matter falling in radiates intensely before crossing the horizon; mergers emit gravitational waves; and the Event Horizon Telescope images the dark shadow the horizon casts against surrounding bright emission.
- Could the Large Hadron Collider create a dangerous black hole?
- No. Any microscopic black hole producible at accelerator energies would, under the theoretical frameworks that allow them at all, evaporate essentially instantly via Hawking radiation. More directly, cosmic rays strike Earth's atmosphere at far higher energies continuously and have done so for billions of years without consequence.