Eddington limit facts for kids

The Eddington limit is a natural brightness limit for stars. It was first figured out by a scientist named Arthur Eddington. Imagine a star as a giant ball of gas. Its own gravity tries to pull it inward, but the heat and light pushing outward keep it from collapsing. This balance is called hydrostatic equilibrium.

The Eddington limit is the point where the outward push from the star's light becomes so strong that it starts blowing away the star's outer layers. This powerful outflow of gas is called a stellar wind. If a star gets brighter than its Eddington limit, it will lose a lot of its mass very quickly.

Arthur Eddington's ideas helped us understand how stars stay stable. He showed that the pressure from a star's light, called radiation pressure, is super important in keeping the star from collapsing under its own gravity.

Most very big stars are not as bright as their Eddington limit. So, their stellar winds are usually caused by other, less powerful forces. However, the Eddington limit helps explain how bright some very active objects in space can get. This includes black holes that are actively pulling in matter, like the super bright objects called quasars.

What Happens When Stars Get Too Bright?

When a star or other space object shines brighter than its Eddington limit, it's called being "super-Eddington." This can cause huge amounts of material to be blown away from the object.

For example, the star η Carinae had massive outbursts between 1840 and 1860. During these events, it lost a lot of its mass. Scientists think this happened because the star briefly shone much brighter than its Eddington limit. Normally, stars lose a tiny bit of mass each year. But during these super-Eddington events, η Carinae lost as much as half a solar mass (half the mass of our Sun) in a single year! This shows how powerful these radiation-driven winds can be.

Super-Eddington Events in Space

Many exciting events in space involve objects going far beyond their Eddington limit for a short time. These include:

• Gamma-ray bursts: These are the most powerful explosions in the universe.
• Novae: These happen when a white dwarf star in a binary system suddenly brightens a lot.
• Supernovae: These are huge explosions that happen when a star dies.

These events cause very fast and intense mass loss.

Some objects, like X-ray binaries and active galaxies, can stay very close to their Eddington limit for a long time. X-ray binaries are systems where a normal star orbits a very dense object like a neutron star or a black hole, pulling gas from it. Active galaxies have supermassive black holes at their centers that are actively feeding on gas and dust.

For objects that get their energy by pulling in matter, like accreting neutron stars or cataclysmic variables (which are white dwarfs pulling in matter), the Eddington limit can actually slow down or stop the flow of new material. This is because the strong outward push from the light can prevent more gas from falling in.

Scientists also think that super-Eddington brightness from black holes that are pulling in matter might explain some very bright X-ray sources called ultraluminous X-ray sources (ULXs).

Images for kids

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  This diagram shows how bright stars can get. The green line is the Humphreys-Davidson limit, which is like an observed Eddington limit for very massive stars. Stars are usually only seen above this line during short, powerful outbursts.

See also

In Spanish: Límite de Eddington para niños