A black hole is a region where gravity is so strong nothing, not even light, escapes. How they form, what is inside, the first images, how they end.
By The Orbital Record editorial teamPublished Last reviewed
A black hole is a region of space where gravity is so strong that nothing, not even light, can escape once it crosses the event horizon. Most form when massive stars collapse; supermassive ones, millions to billions of times the Sun’s mass, grow at galaxy centers. We have photographed two: M87* in 2019 and Sagittarius A* in 2022.
Black holes are the most extreme prediction of Einstein’s general relativity, and in the last ten years they went from inferred to imaged, heard and weighed. This guide covers what they are, how they form, how we find them and the open questions, with links to the papers that built the field.
A black hole is matter compressed so much that the escape velocity at its boundary exceeds the speed of light. That boundary is the event horizon: not a surface you could stand on, but a point of no return. Inside it, every possible path leads further in.
Here is one way to picture it. Escape velocity from Earth is about 11 kilometers per second. Squeeze Earth smaller and its surface gravity rises, so the escape velocity rises too. Squeeze it to the size of a marble and the escape velocity reaches the speed of light. That is a black hole.
The size of the horizon for a non-rotating black hole is the Schwarzschild radius, 2GM/c2, about 3 kilometers for every solar mass. It is named after Karl Schwarzschild, who found the first exact solution of Einstein’s field equations in December 1915, weeks after the theory was published, while serving on the Russian front (Schwarzschild’s 1916 solution). At the center, the theory predicts a singularity, a point of infinite density.
Real black holes spin. Roy Kerr found the solution for a rotating black hole in 1963 (the Kerr solution), and it shows that every uncharged black hole in nature is described by just two numbers: its mass and its spin.
Black holes form in three main ways: from collapsing stars, by growing at the centers of galaxies, and possibly from the dense early universe.
When a very massive star runs out of fuel, its core can no longer hold itself up and collapses in a fraction of a second. If the core is below about 1.4 solar masses, the Chandrasekhar limit, it becomes a white dwarf (Chandrasekhar’s mass limit). Heavier cores become neutron stars, and if the remnant is heavier still, roughly above two to three solar masses, nothing stops the collapse.
J. Robert Oppenheimer and Hartland Snyder worked out the process in 1939 (Oppenheimer and Snyder’s collapse). Their paper appeared on September 1, 1939, the day Germany invaded Poland, and the subject sat largely untouched for two decades. Stellar black holes weigh a few to a few tens of solar masses; the heaviest known in the Milky Way, Gaia BH3, has 32.7.
At the center of almost every large galaxy sits a black hole of millions to billions of solar masses. They power quasars, the brightest steady objects in the universe, first identified by Maarten Schmidt in 1963 (the discovery of quasars).
How they grew so large, so early, is one of the biggest open questions. In 2024 Roberto Maiolino and colleagues used JWST to find a black hole of about 1.6 million solar masses in the galaxy GN-z11, at redshift 10.6, feeding at roughly five times the theoretical limit (GN-z11’s early black hole). In July 2026 Euclid and Keck doubled the known number of quasars beyond redshift 7, with the most distant at redshift 7.77 (the earliest quasars).
Intermediate-mass black holes, between about a hundred and a hundred thousand solar masses, should be the seeds of supermassive ones, but convincing examples are rare. Primordial black holes might have formed directly from dense regions in the first second of the universe, an idea Bernard Carr and Stephen Hawking explored in 1974. None has been confirmed, and they remain a candidate for part of dark matter.
Black holes span more than ten orders of magnitude in mass. Here are the main types:
| Type | Mass (Suns) | Example | How detected |
|---|---|---|---|
| Stellar-mass | About 3 to over 100 | Cygnus X-1; Gaia BH1 (9.6) | X-rays from stolen gas, wobbling companion stars, gravitational waves |
| Intermediate-mass | About 100 to 100,000 | Few confirmed candidates | Gravitational waves, star clusters, flares |
| Supermassive | Millions to billions | Sagittarius A* (4.3 million); M87* (6.5 billion) | Stellar orbits, quasars, Event Horizon Telescope images |
| Primordial (hypothetical) | Could be tiny or large | None confirmed | Microlensing, evaporation bursts, gravitational waves |
General relativity predicts that matter crossing the event horizon is inevitably crushed into a singularity. Roger Penrose proved in 1965 that, once a “trapped surface” forms, a singularity follows under very general conditions (Penrose’s singularity theorem). The result earned him half of the 2020 Nobel Prize in Physics.
But a singularity is where the theory fails, not a description of reality. At the center, the density predicted is infinite, and general relativity must give way to a quantum theory of gravity nobody has completed. So the honest answer is that we know what happens at the horizon and just inside it, and we do not know what is at the center.
What would you experience falling in? For a stellar-mass black hole, tides would stretch you apart well before you reached the horizon. For a supermassive one, the horizon is so large that tides there are gentle, and you would cross it without noticing anything special. Seen from outside, you would appear to slow down and fade at the horizon, never quite crossing it.
Black holes emit no light of their own, so astronomers find them through their effect on their surroundings:
The first image of a black hole was released on April 10, 2019: the shadow of M87*, in the giant galaxy Messier 87, 55 million light-years away, with a mass of about 6.5 billion Suns (the first image of a black hole). The second, of Sagittarius A* at the center of our own galaxy, followed on May 12, 2022 (the image of Sagittarius A*).
How was it captured? The Event Horizon Telescope links radio dishes across the planet so they act as one Earth-sized telescope, observing at a wavelength of 1.3 millimeters. Eight telescopes observed together in April 2017, and their data were combined by supercomputers into a single image. The result is a bright ring of hot gas, bent by gravity around a dark central shadow: 42 microarcseconds across for M87*, far finer detail than any single telescope on Earth could resolve.
The Sagittarius A* image was harder because the gas around it changes within an hour. Both rings match what general relativity predicts for spinning Kerr black holes. If you want to see why the images look the way they do, Veritasium’s “How to Understand What Black Holes Look Like” in our video library is the clearest visual guide.
Sagittarius A* is a supermassive black hole of about 4.3 million solar masses (GRAVITY collaboration, 2022), about 26,000 light-years from Earth. It is quiet compared with quasars, sipping gas rather than feasting.
The proof came from watching stars. For decades, Andrea Ghez’s team at the W. M. Keck Observatory and Reinhard Genzel’s team using ESO telescopes tracked individual stars whipping around an invisible point. In 2008 Ghez’s team used the orbit of the star S0-2 to measure an enclosed mass of about 4.1 million Suns at a distance of about 8 kiloparsecs (stellar orbits around the Milky Way’s black hole). Ghez and Genzel shared half of the 2020 Nobel Prize in Physics.
The work continues. In August 2026 the GRAVITY instrument on ESO’s Very Large Telescope Interferometer reported S301, the fastest known star in the galaxy, reaching about 25,000 kilometers per second, over 8% of the speed of light, on an 8.7-year orbit (S301, the fastest known star). Tracking two full orbits could reveal how fast Sagittarius A* spins within about a decade.
Black holes were discovered in stages over two centuries, by many people:
Black holes can die, very slowly. In 1974 Stephen Hawking applied quantum theory near the event horizon and found that black holes should glow faintly, as if they had a temperature, and gradually lose mass (Hawking’s “Black hole explosions?”). The smaller the black hole, the hotter it is and the faster it evaporates; at the very end, it would release its remaining energy in a burst.
For real black holes the effect is tiny. A black hole with the Sun’s mass has a temperature of about a millionth of a kelvin, far colder than the 2.7-kelvin cosmic microwave background, so today it absorbs more than it emits. It would take around 1067 years to evaporate. Don Page turned Hawking’s prediction into precise rates in 1976 (Page’s evaporation rates). Hawking radiation has never been observed from any astrophysical black hole.
Black holes will probably be the last large objects in the universe. Long after the last stars fade, in about 100 trillion (1014) years, and after even dead stellar remnants decay, black holes will remain. Fred Adams and Gregory Laughlin called this stretch, from about 1040 to 10100 years, the Black Hole Era (Adams and Laughlin’s “A dying universe”). The largest supermassive black holes will be the last to evaporate, after roughly a googol (10100) years. Explore it in the Black Hole Era.
If a black hole evaporates into featureless heat, what happens to the information about everything that fell in? Quantum mechanics says information cannot be destroyed; Hawking’s calculation suggests it is. Resolving the paradox is one of the main goals of quantum gravity research, and there is still no consensus answer.
Since 2023, JWST has found hundreds of compact, very red objects in the early universe. A Nature paper published in January 2026 argued that they are young supermassive black holes buried in dense cocoons of ionized gas, about 100 times less massive than first thought. It is the leading explanation, not a settled one. Read the full story in our explainer on little red dots.
Black holes of a billion solar masses existed less than a billion years after the Big Bang. Either they started as unusually heavy “seeds”, perhaps from collapsing gas clouds, or they grew faster than the standard limit allows. JWST and Euclid are now finding enough early black holes to test both ideas.
Nobody knows for certain. General relativity predicts that everything that crosses the event horizon is crushed into a singularity of infinite density at the center, but that prediction marks where the theory breaks down. A future theory of quantum gravity is expected to replace the singularity with something finite but unknown.
Yes, in principle. Stephen Hawking showed in 1974 that quantum effects make black holes emit faint radiation and slowly lose mass. The process is extraordinarily slow: a black hole with the Sun's mass would take around 1067 years to evaporate, and the largest supermassive ones about 10100 years.
As of October 2026, the nearest known black hole is Gaia BH1, about 1,560 light-years away. It has about 9.6 times the Sun's mass and is dormant, revealed only by the wobble of a Sun-like star that orbits it every 185.6 days. Closer, undiscovered ones probably exist.
Not in any realistic scenario. Black holes do not suck things in from afar: at a safe distance their gravity is the same as any object of equal mass. The nearest known one is about 1,560 light-years away. Even if the Sun were replaced by a black hole of the same mass, Earth's orbit would not change.
No single person. John Michell imagined 'dark stars' in 1784, Karl Schwarzschild found the mathematical solution in 1916, and Oppenheimer and Snyder showed in 1939 how a star could collapse into one. Cygnus X-1 became the first widely accepted real black hole in the early 1970s.
No. Hawking radiation from a stellar or supermassive black hole would be far colder than the cosmic microwave background, so it is undetectable with any telescope. Scientists have tested analogous effects in laboratory systems, and searches continue for the final bursts of tiny primordial black holes, but no confirmed detection exists.
Schwarzschild, Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften zu Berlin, 189-196, 1916
Found in 1916 the first exact solution of Einstein's equations, with the radius now known as a black hole's horizon. Karl Schwarzschild's paper, explained.
Oppenheimer and Snyder, Physical Review, 56, 455-459, 1939
Showed in 1939 that a heavy dead star collapses forever and cuts itself off from the universe. Oppenheimer and Snyder's first black hole formation.
Kerr, Physical Review Letters, 11, 237, 1963
Found in 1963 the exact solution of Einstein's equations for a spinning mass, describing real black holes by mass and spin alone. Roy Kerr's letter.
Schmidt, Nature, 197, 1040, 1963
Identified in 1963 the star-like radio source 3C 273 as a distant, enormously luminous object: the first quasar. Maarten Schmidt's Nature paper, explained.
Penrose, Physical Review Letters, 14, 57-59, 1965
Proved in 1965 that once a trapped surface forms, collapse to a singularity is unavoidable in general relativity. Roger Penrose's Nobel-winning theorem.
Hawking, Nature, 248, 30-31, 1974
Showed in 1974 that black holes glow faintly and evaporate, ending in a burst. Stephen Hawking's two-page Nature letter on Hawking radiation, explained.
Ghez et al., The Astrophysical Journal, 689, 1044-1062, 2008
Weighed the Milky Way's central black hole at about 4 million Suns by tracking the star S0-2 for 12 years with Keck. Andrea Ghez's team, 2008.
Event Horizon Telescope Collaboration, The Astrophysical Journal Letters, 875, L1, 2019
Captured in 2019 the first image of a black hole: a ring of light around the shadow of M87*, 6.5 billion Suns. The Event Horizon Telescope's paper.
Event Horizon Telescope Collaboration, The Astrophysical Journal Letters, 930, L12, 2022
Imaged in 2022 the shadow of Sagittarius A*, the 4-million-Sun black hole at the Milky Way's center. The Event Horizon Telescope's first Sgr A* paper.
Maiolino et al., Nature, 627, 59-63, 2024
Found with JWST a 1.6-million-Sun black hole feeding at five times the usual limit in GN-z11, at redshift 10.6. Roberto Maiolino's team, Nature 2024.
An animated overview of black holes from birth to death: how they form, what happens near the event horizon and how they eventually evaporate. A solid six-minute starting point for beginners. Kurzgesagt - In a Nutshell
Explains what the first image of a black hole, M87*, actually shows, using J.P. Luminet's 1979 simulation of how a black hole with a thin disk should look. Great for understanding the famous ring. Veritasium
Explains the black hole information paradox: whether information that falls into a black hole is truly lost, and why the answer matters for physics. Animated and beginner-friendly, made with physicist Alessandro Sfondrini. Kurzgesagt - In a Nutshell
A 98-minute deep dive into black holes: how they form, how physicists draw them with spacetime diagrams and where they force general relativity and quantum physics into conflict. For viewers who want the full theory. PBS Space Time
New Scientist interviews Oxford astrophysicist Becky Smethurst about what black holes are, how supermassive black holes reach billions of solar masses and how they shape their galaxies. A long, conversational overview. New Scientist