Development of the Black-Hole Concept

A black hole became a physical concept only after several different questions were answered: Which exact geometries solve Einstein’s equation? Is the Schwarzschild radius a true singularity or a coordinate boundary? Can matter actually collapse through it? What global structure results? Does rotation admit an exact solution? And can astronomical data identify such an object? No single paper answered all of them.

This chronology follows nine bounded milestones. Primary papers establish what was constructed, proved, named, or observed. Retrospective histories are used only where later interpretation and terminology must be reconstructed. The date in the first column is the relevant historical act, not the date of a translation, archive copy, or later account. The final column prevents modern black-hole language from being projected backward into a narrower result.

Milestones from exact solution to physical object

Date	Source class and record	What changed	What it did not establish
1916	Primary paper: Schwarzschild 1916, §§1–7, original pp. 189–196; English trans. PDF pp. 1–7	Schwarzschild gave the exact static, spherically symmetric vacuum exterior field of a point mass in Einstein’s new theory. It became the prototype geometry for nonrotating compact objects.	The paper did not present the modern global black-hole region, a regular horizon-crossing extension, gravitational collapse, or an astrophysical object. The later translator foreword is not evidence for Schwarzschild’s own claims.
1939	Primary paper: Oppenheimer and Snyder 1939, pp. 455–459, especially Eqs. (27)–(39) and pp. 458–459	An idealized homogeneous, pressureless sphere was followed through continued relativistic contraction. The calculation showed that collapse need not halt at the Schwarzschild scale and that finite comoving proper time can coexist with an asymptotic exterior-time description.	This was not a theorem about generic initial data or every star. It neglected pressure, rotation, inhomogeneity, radiation, and realistic stellar microphysics, and it did not formulate the modern global event-horizon definition.
1958	Primary paper: Finkelstein 1958, §II, Eqs. (2.1)–(2.4), Figs. 1–2, pp. 965–967	A horizon-regular, time-asymmetric extension made $r=2GM$ a one-way causal boundary rather than a curvature singularity. Ingoing trajectories could cross it smoothly.	One regular one-sided extension is not the complete maximal analytic extension. The construction did not model stellar formation or establish that such objects occur in nature.
1960	Primary paper: Kruskal 1960, Tables I–II and Figs. 1–2, pp. 1743–1745	Kruskal coordinates displayed the maximal analytic Schwarzschild extension, including two exterior regions, black-hole and white-hole regions, regular horizons, and the spacelike singular boundaries.	The maximally extended eternal vacuum solution is not the global spacetime of an ordinary star formed by collapse; its second exterior and white-hole region need not occur in a collapse geometry.
1963	Primary paper: Kerr 1963, complete paper, especially Eq. (5), pp. 237–238	Kerr found an exact stationary, axisymmetric, rotating vacuum metric. This supplied the geometry needed to move beyond the nonrotating Schwarzschild prototype.	Constructing the metric did not prove black-hole uniqueness, nonlinear stability, or that realistic rotating collapse approaches a member of the Kerr family. Its full global and horizon interpretation required later work.
1964-01-18	Primary news report: Ewing 1964, Science News Letter 85, p. 39	Ann Ewing’s report contains the earliest verified occurrence in print of “black hole” found in the inspected record, in reporting on a 1963 AAAS meeting about collapsed stars.	The article did not identify who first said or invented the phrase. Earliest verified print use is not proof of earliest oral use or unique coinage.
1965	Primary theorem paper: Penrose 1965, complete theorem and proof, pp. 57–59	Penrose replaced exact spherical models with a global argument: under the stated causal and null-convergence hypotheses, a closed trapped surface in a spacetime with a noncompact Cauchy surface implies that there exists at least one future-directed null geodesic that is future-incomplete—it cannot be extended to arbitrarily large affine parameter within the spacetime.	The conclusion is existential, not a claim that every future null geodesic is incomplete. The theorem did not conclude that curvature must diverge, locate a singular point, prove an event horizon exists, establish cosmic censorship, or show that every collapsing star forms a black hole.
1967 lecture; 1968 article	Primary public exposition and retrospective naming history: Wheeler 1968, “The Black Hole,” pp. 8–10; Herdeiro and Lemos 2018, §§IV–VII, PDF pp. 7–13	Wheeler adopted the compact term in a 1967 public lecture and used it prominently in his 1968 article, helping make “black hole” the standard name for complete gravitational collapse.	Influential adoption and popularization are not evidence that Wheeler uniquely coined the phrase. The surviving record leaves earlier oral use and individual priority uncertain.
1971–1972	Primary observational papers: Murdin and Webster 1971, p. 110; Webster and Murdin 1972, pp. 37–38; Bolton 1972, pp. 271–273	A precise optical/radio association connected Cygnus X-1 with HDE 226868, while independent radial-velocity studies identified a spectroscopic binary with a heavy unseen companion. Under the orbital and stellar models, a black hole became the compelling compact-object candidate.	The observations did not image or directly detect an event horizon. The inference depended on counterpart identification, orbital dynamics, the visible star’s properties, and alternatives allowed by the compact-object model.

How the milestones fit together

An exact line element, a regular horizon, a maximal extension, a collapse spacetime, and a global incompleteness theorem answer different questions. Finkelstein and Kruskal changed the interpretation of the Schwarzschild radius; Oppenheimer–Snyder supplied a formed-collapse model; Penrose showed that the incompleteness conclusion survives far beyond exact spherical symmetry. Kerr opened the rotating branch without settling its later uniqueness and stability questions. Bičák 2000, §§2 and 4, pp. 19–30 and 42–51 gives modern exact-solution context, while Lehmkuhl 2025, pp. 176–190 and 198–205 reconstructs the changing interpretation. Neither later account replaces the primary results.

Naming and observation added two further evidential layers. Ewing documents a verified print occurrence; Wheeler’s public use documents influential popularization, not unique coinage. Cygnus X-1 then required counterpart association, spectroscopy, orbital inference, and compact-object comparison. That chain made a black hole compelling under a physical model, not directly visible or assumption-free.

Modern definitions and derivations belong in Black-Hole Geometry and Mechanics. This chronology records which narrower result arrived when and which later conclusions must not be credited to it.

References

• Bičák, Jiří. “The Role of Exact Solutions of Einstein’s Equations in the Developments of General Relativity and Astrophysics: Selected Themes.” arXiv:gr-qc/0004016v1 (2000). Open PDF.
• Bolton, C. T. “Identification of Cygnus X-1 with HDE 226868.” Nature 235 (1972) 271–273. DOI.
• Ewing, Ann E. “‘Black Holes’ in Space.” Science News Letter 85, no. 3 (18 January 1964) 39. Science News archive.
• Finkelstein, David. “Past-Future Asymmetry of the Gravitational Field of a Point Particle.” Physical Review 110 (1958) 965–967. DOI.
• Herdeiro, Carlos A. R., and José P. S. Lemos. “The Black Hole Fifty Years After: Genesis of the Name.” arXiv:1811.06587v1 (2018). Open PDF.
• Kerr, Roy P. “Gravitational Field of a Spinning Mass as an Example of Algebraically Special Metrics.” Physical Review Letters 11 (1963) 237–238. DOI.
• Kruskal, Martin D. “Maximal Extension of Schwarzschild Metric.” Physical Review 119 (1960) 1743–1745. DOI.
• Lehmkuhl, Dennis. “The Prediction and Interpretation of Singularities and Black Holes: From Einstein and Schwarzschild to Penrose and Wheeler.” Physics in Perspective 27 (2025) 176–209. DOI.
• Murdin, Paul, and B. Louise Webster. “Optical Identification of Cygnus X-1.” Nature 233 (1971) 110. DOI.
• Oppenheimer, J. Robert, and Hartland Snyder. “On Continued Gravitational Contraction.” Physical Review 56 (1939) 455–459. DOI.
• Penrose, Roger. “Gravitational Collapse and Space-Time Singularities.” Physical Review Letters 14 (1965) 57–59. DOI.
• Schwarzschild, Karl. “On the Gravitational Field of a Mass Point according to Einstein’s Theory.” Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften (1916) 189–196. Inspected English translation, arXiv:physics/9905030.
• Webster, B. Louise, and Paul Murdin. “Cygnus X-1—a Spectroscopic Binary with a Heavy Companion?” Nature 235 (1972) 37–38. DOI.
• Wheeler, John Archibald. “Our Universe: The Known and the Unknown.” American Scientist 56, no. 1 (1968) 1–20. JSTOR record.