Black holes captivate scientists worldwide, with supermassive ones at galaxy centers remaining one of cosmology's greatest puzzles.
Researchers are actively exploring their formation, and the innovative model of black hole stars—or quasi-stars—offers promising insights into this cosmic mystery.
Supermassive black holes (SMBHs) range from hundreds of thousands to billions of solar masses and reside at the hearts of most galaxies. Sagittarius A* at the Milky Way's center, for instance, weighs about 4 million solar masses (1).
Their origins remain elusive, requiring immense matter compressed into tiny volumes. Leading theories include primordial black holes from the Big Bang's high-energy densities, merging into SMBHs (2); Population III stars collapsing shortly after the Big Bang (z=20) from pre-galactic halos (3); and stellar clusters collapsing due to relativistic velocities (4).
Another compelling explanation is the black hole star, or quasi-star, model.
This theory proposes ultra-massive stars forming early in the universe via Jeans gravitational instability in giant gas clouds. The protostar's core becomes extraordinarily dense under gravity.
Instability arises from electron-positron pair production and neutrino fluxes, leading to core collapse into a black hole while outer layers hold firm, preventing supernova explosion.
The released energy is absorbed by the envelope, maintaining the star's structure. Thus, a quasi-star features a central black hole surrounded by stellar material.
The black hole accretes envelope gas, releasing energy that expands the star to 50-100 times a red giant's size—about 10 billion km across—with a surface temperature around 3700°C (5). This mimics normal stars' hydrostatic equilibrium.
Lifespan is roughly 7 million years (6). The black hole grows to ~10,000 solar masses, potentially seeding SMBHs if starting massive enough (7).
