SPACE#2

Luminosity

The Brightness of a star

Nebula

• Hydrogen particles gradually form clouds of dust and gas in space, the bigger the mass of the cloud, the bigger the gravitational force.

• Gravity continues to pull in more gas, so cloud gets denser, heating up.

Protostar

• Gravity pulls the cloud into a tight, spinning ball, applying extreme pressure and thus heat. Once it is hot enough, nuclear fusion begins.

Star formation sequence

Nebula, then gravity pulls gas into a dense clump, then a protostar heats by compression, then fusion ignites, then a main sequence star.

Main sequence star

• Fusion joins hydrogen atoms together to form helium, releasing energy.

• the energy from fusion pushes particles out, while gravity pushes it in.

• When the two forces balance, it creates a stable star, where the star will remain for 90% of its life cycle.

Red giant/supergiant

• After hydrogen is exhausted, the core contracts under gravity, causing the outer layers to expand.

• The star switches from fusing hydrogen to fusing helium. Helium nuclei are larger, so they release more energy, pushing the outer layers outwards, causing them to spread out, cooling red.

Planetary nebula

Red giant’s fuel runs out, causing outer layers to come loose, drifting through space, leaving the white dwarf.

White dwarf

• When gravity has overcome the nuclear fusion when there is no fuel left, gravity compresses into an incredibly dense white dwarf, that is smaller and denser, but hotter than the red giant, glowing from leftover heat.

Black dwarf

• A mass in space with no heat left, just very dense, cold, and invisible. Universe is not old enough so it is only a theory.

Supernova

• As the red supergiant shrinks due to loss of radiation pressure, and gravity overcoming it, the mass is pushed into one point, causing a sudden burst of fusion. Heavier elements are flung across the universe, while a large mass of neutrons are left behind.

• For a brief time, the light from a supernova can outshine an entire galaxy of billions of stars.

Neutron star.

• The result of a smaller supernova.

• Extremely dense, weighing billions of tonnes.

• The collapsing core due to gravity is crushed so hard the protons and electrons are forced into neutrons. The neutrons resist being crushed any further, balancing the force of gravity, creating a stable neutron star.

Black Hole

• The result of a large supernova

• Densest object in the universe.

• The gravity is so strong no known object can counteract it, and not even light can escape it.