1. Stellar-Mass Black Holes:
- Rapidly Rotating: Stellar-mass black holes, which typically range from a few times the mass of our Sun to tens or hundreds of solar masses, can have very high rotation rates. Some of these black holes are classified as "rapidly rotating" or "Kerr black holes," meaning their rotation is close to the theoretical maximum allowed by general relativity.
- Rotation Period: The rotation period of rapidly rotating stellar-mass black holes can be extremely short. Observations of stellar-mass black holes in X-ray binaries suggest rotation periods on the order of milliseconds to seconds.
2. Supermassive Black Holes:
- Slower Rotation: In comparison to stellar-mass black holes, supermassive black holes, which can have masses ranging from millions to billions of times the solar mass, tend to have slower rotation rates relative to their maximum allowed spin.
- Rotation Periods: The rotation periods of supermassive black holes are typically longer, often on the order of minutes, hours, or even days. However, some observations have indicated faster rotation rates in certain supermassive black holes.
3. Quasi-Periodic Oscillations (QPOs):
- Stellar-mass black holes can exhibit quasi-periodic oscillations (QPOs) in their X-ray emission, which are fluctuations in brightness that occur at fairly regular intervals. These oscillations are thought to be related to the black hole's innermost accretion disk and provide insights into the black hole's spin.
It's worth noting that estimating the spin of a black hole is a complex task and requires detailed observations and modeling. Additionally, the theoretical understanding of black hole spins continues to evolve, particularly in the context of extreme astrophysical environments.
