Concept art of an accretion ring and jet around a supermassive black hole. Image credit: NASA / JPL-Caltech.

Ask Ethan: How Do Hawking Radiation And Relativistic Jets Escape From A Black Hole?

If nothing can escape from beneath the event horizon, where do these phenomena come from?

The most important feature of a black hole is that it has an event horizon: a region of space where the gravitational field is so strong that nothing, not even light, can escape from it. How, then, do we explain the matter and radiation that we both see and predict should come from them? That’s what Russell Sisson wants to know, as he asks:

Everything you read about a black indicates that “nothing, not even light, can escape them”. Then you read that there is Hawking radiation, which “is blackbody radiation that is predicted to be released by black holes”. Then there are relativistic jets that “shoot out of black holes at close to the speed of light”. Obviously, something does come out of black holes, right?

Matter and radiation can definitely come towards us, originating from the black hole’s location. But does that mean something escapes from a black hole? Let’s find out!

While distant host galaxies for quasars and active galactic nuclei can often be imaged in visible/infrared light, the jets themselves and the surrounding emission is best viewed in both the X-ray and the radio, as illustrated here for the galaxy Hercules A. It takes a black hole to power an engine such as this, but that doesn’t necessarily mean that this is matter/radiation escaping from inside the event horizon. Image credit: NASA, ESA, S. Baum and C. O’Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA).