## What is the significance of the photon sphere?

The photon sphere is a region near a black hole where the gravity is so strong that light itself can orbit around the black hole. The orbits in that region are unstable; the photons can loop around the black hole a few times, but they will not stay forever.

**Is a photon a sphere?**

The photon sphere is located farther from the center of a black hole than the event horizon. Within a photon sphere, it is possible to imagine a photon that’s emitted from the back of one’s head, orbiting the black hole, only then to be intercepted by the person’s eyes, allowing one to see the back of the head.

**What is the difference between a black hole photon sphere and its event horizon?**

The photon sphere is the point where a photon could, in theory, orbit a black hole. The event horizon (EH) is the last point that a photon could be released and escape the black hole.

### Are black holes holes or spheres?

A black hole is a sphere in the sense that everything that goes within its Schwarzschild radius (the distance from the center of the black hole to the event horizon) cannot escape its gravity. Thus, there is a dark sphere around the infinitely dense center, or singularity, from which nothing can escape.

**Can photons escape black holes?**

Light particles can’t escape a black hole but that doesn’t mean they are destroyed. Once a particle of light (‘photon’) passes the ‘event horizon’ of a black hole, it can no longer escape, but there’s nothing to suggest that it is destroyed.

**What is the ring around a black hole called?**

light echoes

The burst created the high-energy rings from a phenomenon known as light echoes.

#### What is Photon Star?

PhotonStar LED Group plc is a leading British designer and manufacturer of intelligent lighting and intelligent building solutions. Within the group are two divisions. PhotonStar LED Ltd. is an LED lighting fixtures businesses focussed on the new build market.

**What happens to photons in a black hole?**

Once a particle of light (‘photon’) passes the ‘event horizon’ of a black hole, it can no longer escape, but there’s nothing to suggest that it is destroyed. Like matter, the photon is rapidly sucked towards the ‘singularity’ at the centre of the black hole, where a huge mass is packed into an infinitely small space.

**What is underneath a black hole?**

The size of an event horizon of a black hole depends on the gravity, so really the event horizon is a sphere surrounding the black hole. They sometimes don’t get that black holes are spheres, and there is no underneath.

## Are black hole hot?

Black holes are freezing cold on the inside, but incredibly hot just outside. The internal temperature of a black hole with the mass of our Sun is around one-millionth of a degree above absolute zero.

**What is the difference between counterrotating and corotating photon spheres?**

Between the counterrotating and the corotating photon spheres are the different photon spheres for light rays approaching the black hole not quite on the equator. This is confusing, so perhaps I should use another example. Imagine that you’re floating above the Earth in a spaceship.

**What is the photon sphere and how does it work?**

No unaccelerated orbit with a semi-major axis less than this distance is possible, but within the photon sphere, a constant acceleration will allow a spacecraft or probe to hover above the event horizon. Another property of the photon sphere is centrifugal force (note: not centripetal) reversal.

### What is the radius of the photon sphere of a black hole?

The radius of the photon sphere, which is also the lower bound for any stable orbit, is, for a Schwarzschild black hole : where G is the gravitational constant, M is the black hole mass, and c is the speed of light in vacuum and rs is the Schwarzschild radius (the radius of the event horizon) – see below for a derivation of this result.

**Are there any stable free fall orbits that cross the photon sphere?**

There are no stable free fall orbits that exist within or cross the photon sphere. Any free fall orbit that crosses it from the outside spirals into the black hole. Any orbit that crosses it from the inside escapes to infinity or falls back in and spirals into the black hole.