A Journey Through Stellar Collapse and Spacetime Curvature
A black hole is a region of spacetime where gravity is so intense that nothing—no particles or even electromagnetic radiation such as light—can escape from it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole.
The boundary of no escape is called the event horizon. Although it has an enormous effect on the fate and circumstances of an object crossing it, it has no locally detectable features according to general relativity.
Black holes form through the gravitational collapse of massive stars. To understand this process, we must first examine the life cycle of stars:
Stars spend most of their lives fusing hydrogen into helium in their cores (main sequence phase). When hydrogen is exhausted, the star's fate depends on its initial mass:
In massive stars (>20 M☉), fusion continues through progressively heavier elements until an iron core forms. Iron cannot be fused to release energy, so the core becomes inert.
When the core exceeds the Chandrasekhar limit (~1.4 M☉), electron degeneracy pressure can no longer support it against gravity. The core collapses at nearly 25% the speed of light.
The collapsing core rebounds when it reaches nuclear density, sending a shock wave through the star's outer layers. This causes a Type II supernova explosion, briefly outshining entire galaxies.
The explosion ejects the star's outer layers into space, leaving behind either a neutron star or, if the remaining core is sufficiently massive, a black hole.
If the remaining core mass exceeds ~3 M☉ (Tolman-Oppenheimer-Volkoff limit), neutron degeneracy pressure cannot halt the collapse. The core continues collapsing indefinitely, forming a singularity.
The event horizon forms when the escape velocity at a given radius exceeds the speed of light. This marks the birth of a black hole.
Formed from collapsing stars
Mass: 3-100 M☉
Common in binary systems
Mass: 100-10⁵ M☉
Formation mechanism debated
Possibly from merged stellar black holes
Mass: 10⁵-10¹⁰ M☉
Found at galaxy centers
Formation may involve direct collapse or mergers
The spherical boundary marking the point of no return. For a non-rotating black hole, its radius (Schwarzschild radius) is:
Where G is the gravitational constant, M is the mass, and c is the speed of light.
At the center lies a gravitational singularity where density becomes infinite and spacetime curvature becomes infinite.
General relativity predicts its existence, but quantum gravity effects are expected to modify this picture.
Matter spiraling into a black hole forms a hot, luminous disk due to:
Quantum effects near the event horizon cause black holes to emit thermal radiation:
Where ħ is the reduced Planck constant and k is Boltzmann's constant.
Since black holes don't emit light directly, we detect them through their effects on nearby matter and light:
The first direct image of a black hole's shadow (M87*) was captured in 2019 by the Event Horizon Telescope.