Neutron stars and stellar black holes are the ultra-dense corpses of massive stars. But a quasar isn't an object at all—it’s a blinding feeding frenzy that outshines entire galaxies.
Neutron Stars
When a massive star between 10 and 29 times the mass of our Sun runs out of fuel, its core collapses under its own gravity. The inward pressure is so immense that protons and electrons are crushed together to form neutrons. The outer layers of the star explode outward in a supernova, leaving behind a dense, glowing sphere. Neutron stars are incredibly small, typically only 12 to 15 miles across, but they contain more mass than our Sun. A single teaspoon of neutron star material would weigh billions of tons on Earth.
Black Holes
If the dying star is even more massive, not even the density of neutrons can halt the core's collapse. The matter crushes inward until it condenses into a singularity—a point of infinite density. This creates a gravitational pull so intense that nothing, not even light, can escape once it crosses a boundary called the event horizon. While "stellar-mass" black holes form from dead stars, galaxies also host supermassive black holes at their centers, which can be millions or billions of times more massive than the Sun.
Quasars
A quasar is the active feeding process of a supermassive black hole. When a galaxy's central black hole pulls in vast amounts of surrounding gas, dust, and stars, that material forms a rapidly spinning accretion disk. Friction and gravitational forces heat this disk to millions of degrees, causing it to emit immense jets of radiation. During this feeding phase, the black hole operates as a quasar, shining so brightly that it can outshine its entire host galaxy. Once the surrounding fuel is consumed, the quasar fades, leaving behind a quiet supermassive black hole.