Very massive stars, often exceeding 20-30 times the Sun’s mass, undergo extreme processes before collapsing into black holes. As they exhaust their nuclear fuel, these stars experience intense core fusion, generating heavy elements. This leads to violent outbursts, ejecting vast amounts of matter—sometimes several solar masses—into space via stellar winds, supernovae, or other explosive events like pair-instability supernovae in the most massive cases (100+ solar masses). These eruptions enrich the surrounding interstellar medium with heavy elements. Eventually, the core, unable to support itself against gravity, collapses into a black hole, often accompanied by a final, cataclysmic supernova or direct collapse, depending on the star’s mass and metallicity.
Stellar Winds: Massive stars, particularly those like O-type and B-type stars and especially the later-stage Wolf-Rayet stars, experience powerful, continuous outflows of gas from their surfaces known as stellar winds. These winds are driven by the intense radiation pressure from the star's core. The rate of mass loss can be incredibly high, significantly altering the star's evolution and reducing its total mass by the time it reaches its final collapse.
Pulsational Pair-Instability Supernovae (PPISN): For some very massive stars (in certain mass ranges, particularly for low-metallicity stars), a phenomenon called pair instability can occur. This leads to pulsations that cause the star to eject large amounts of mass in repeated outbursts before a final, often weaker, supernova or direct collapse into a black hole.
Luminous Blue Variables (LBVs): These are highly unstable, very massive stars that undergo episodic and often dramatic outbursts, ejecting vast amounts of material. A famous example is Eta Carinae, which has ejected tens of solar masses in recent history.
Binary Interactions: If a massive star is part of a binary system, it can lose mass to its companion star through a process called mass transfer, especially if it expands and overflows its Roche lobe.
The amount of mass lost can be significant. For high-metallicity stars (like those in our solar neighborhood), as little as 10% of the star's initial mass might remain in the black hole remnant, with the rest ejected. For very low-metallicity stars (which existed in the early universe), it's possible that up to half of the initial mass could end up in the black hole.
This "vomiting" of matter plays a crucial role in shaping the evolution of massive stars and the properties of the black holes they leave behind. It also enriches the surrounding interstellar medium with heavy elements, which are essential for the formation of subsequent generations of stars and planets.