Stellar Evolution

Intro

Stellar evolution is a process by which a star changes over time

All stars go through a life cycle

Birth to main sequence old age death remnants

Protostars

Is a type of interstellar cloud

Size and density contribute to regular molecular formation, mostly hydrogen

Its molecular formation helps differentiate it from other interstellar clouds.

E.g (HOPS 383)One of the few known to have an outburst as of 2020 it is the youngest protostar

Protostars

The birth of a young star

They last around half a million years of age

Where common true stars are first made and usually start out as small clumps of gas known as dense cores.

The molecular clouds collapse under gravity

As it collects mass, it collects pressure and inflates

Gravity overwhelms it and it collapses further

After the collapse it forms a low mass protostar and then a proplanteary disk orbiting it

More gas accumulates at the disk and forms an equilibrium

Main-sequence

Most common true stars

A fully mature star which has homogeneous initial composition

-70% hydrogen

28% Helium 2% heavier elements (O2)

Often fuses hydrogen into helium to create energy

Different Main-sequence stars are classified by their nuclear fusion rate to determine their colour and brightness.

Often called yellow dwarfs

Mass of 0.84-1.15 solar masses

Surface temperature of 5300K to 6000K

Its luminosity outshines over 90% of the galaxy, making those that are brighter more rarer

Often has a lifespan of 10 billion years

Supergiants are really rare to find.

The sun is a G-type star

The sun is the constant of solar masses

It is almost halfway into its stage.

The sun is also the constant of luminosity and astronomical

Brown stars are known as failed star and it occurs due to insufficient mass of hydrogen reserves

Somewhat signs of an end of a stellar evolution cycle.

Red Giants

The beginning of its late phase

It forms when a main sequence star exhausted its hydrogen and contracts due to gravity

Fusion continues due to the addition of hydrogen

Continues tug of war with thermal pressure and gravity till it stops expanding.

The radii of the red giant is hundreds of times that of the sun

Nearly 3 times the luminosity

Temperature range from 3000K to 4000K

It’s envelope is low in density despite its volume

Leads to a lack of a defined photosphere

Examples of it are Aldebaran, brightest star in Taurus

Additionally, the body of the star transition into the corona.

White dwarfs also known as degenerate dwarf

Is an emission shell of ionised gas

Is a bit of a misnomer due to inaccurate findings in the 18th century

Is signified as the end of a typical star’s life cycle

Short lived phenomenon.

It also no longer generates energy in its core

Because of this, it will cool and become redder over the course of time.

It is as dense as an olympic sized pool.

Its density is equivalent to a tonne per volume.

Sirius B, a white dwarf over 120 million years

A white dwarf becomes stable

Will cool and form a black dwarf

It is thought that it will live as long as a proton’s lifespan

If consumes, it has a possibility of becoming a diamond planet or a helium planet.

The dumbbell nebula in cons telling Vulpecula

It was noted to have a prolate spheroid shape

Has been expanding over the couple thousand years.

Electron degeneracy matter

Electron degeneracy matter is made out of plasma with unbound nuclei and electrons

Compression of the electrons increases the kinetic energy of the electron and it is only dependant on density.

Black dwarfs are theoretical stellar remnant

If it exists, it is extremely difficult to detect

Emit little to no radiation.

Supernova

Type Ia Supernovas are binary systems

Two white dwarfs spin around each other and collide to form a supernova

Type II Supernovas are esults from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, but no more than 40 to 50 times, the mass of the Sun to undergo this type of explosion. Type II supernovae are distinguished from other types of supernovae by the presence of hydrogen in their spectra.

Stars generate energy by the nuclear fusion of elements. Unlike the Sun, massive stars possess the mass needed to fuse elements that have an atomic mass greater than hydrogen and helium, albeit at increasingly higher temperatures and pressures, causing correspondingly shorter stellar life spans. The degeneracy pressure of electrons and the energy generated by these fusion reactions are sufficient to counter the force of gravity and prevent the star from collapsing