A Spectrum of Darkness

Black holes span an enormous range of sizes:

• Stellar-mass (5–100 solar masses): the collapsed cores of dead massive stars.
• Intermediate-mass (100–100,000 solar masses): rare and hard to confirm.
• Supermassive (millions to billions): anchors at the centers of large galaxies.
• Primordial: hypothetical relics of the Big Bang that could explain some dark matter.

Across this whole range, a black hole's mass tends to track the size of its host galaxy — a tight link that suggests the two grow up together.