SOLAR SYSTEM AND STAR FORMATION

Solar System and Star Formation

Both happen at the same time, but we’ll look at the two events separately

Solar System Formation

Ingredients: 1 cold solar nebula (-442°F) made up of dust and gas

left over from the big bang

1 shockwave, perhaps from a nearby supernova

The Eagle Nebula

7,000 light years from

Earth

Solar System Formation

Shockwave causes gas and dust to compress

Even small objects have gravity, so nebula begins to collapse inward and rotate

This forms a protoplanetary (early planet) disk . . . but why?

Solar System Formation

Nebula rotated slowly at first

As nebula collapsed, it rotated faster and flattened out

Solar System Formation

Eventually, a star forms at the center of the protoplanetary disk (more on this in just a bit)

Throughout the disk, small, solid pieces of matter come together through the process of accretion

The resulting small, irregularly shaped planetisimals have constant collisions, eventually becoming protoplanets

Solar System Formation

Eventually, protoplanets become large enough to exert gravity on surrounding objects

With gravity, protoplanets become rounder and continue to grow into true planets

Solar System Formation

Evidence for ‘Disk’ Theory Most planets rotate in the

same direction

All planets revolve in the same direction

Planet’s orbits are all in the same plane (almost)

Star Formation

Ingredients: 1 cold solar nebula (-442°F) made up of dust and gas

left over from the big bang

1 shockwave, perhaps from a nearby supernova

Wait a minute . . .

Star Formation

Shockwave compresses dust and gas

Most of the gas and dust in the nebula clumps together in the center of the protoplanetary disk

Eventually, it gets big enough to get hot through increased friction and becomes a protostar

When the temperature in the star reaches 10 million °Kelvin (~20 million °F), Hydrogen fusion begins

If the star does not have critical mass, the chain reaction does not continue The result is a brown dwarf star with no heat or light

If star does have critical mass, it enters main sequence

Star Formation

Main Sequence Longest portion of the solar life cycle Hydrogen fusion occurs Outward force of fusion equals inward pull of gravity

Star Life Cycle

Main Sequence Fusion continues, gradually forming larger and larger

elements, which sink to the core This happens until Iron (Fe) or Carbon (C) form

and/or Hydrogen fuel runs out, then the star dies For a star like our sun, this takes ~10 billion years

Star Life Cycle

Star Life Cycle

Hydrogen fuel begins to run out, the core cools and contracts

As the core contracts, fusion continues up through Carbon

Hydrogen fusion continues in outer layers

Outer portion of star expands into a red giant Compared to our sun it will be bright, cool and large

Death of a Low Mass Star (Up to 1.5 times the size of the sun)

Eventually, outer layer is blown away in a burst of gas called a nova

All that is left is a planetary nebula and a white dwarf Small, dense, and cool

Death of a Low Mass Star

Hydrogen fuel begins to run out, the core cools and contracts

Due to greater mass, as the core contracts, fusion continues up through Iron

Hydrogen fusion continues in outer layers

Outer portion of star expands into a red super giant Compared to our sun it will be bright, cool and huge

Death of a High Mass Star (More than 1.5 times the size of the sun)

Red Giant vs Red Supergiant

Fusion cannot proceed past Iron

When Iron in core reaches 1.44 times the mass of our sun (Chandrasekhar Limit) there is not enough outward energy, so gravity wins and the star implodes

The implosion continues until gravity creates enough energy for a rebound explosion: a supernova

A Fairly Big Bang: Supernova

Supernova 1987A

Supernova releases as much energy in a few weeks as our sun will release in 10 billion years

Brighter than a galaxy for a short period of time

Energy causes fusion of all natural elements above Iron

Core of star collapses to unimaginable density

A Fairly Big Bang: Supernova

Star Life Cycle

Stars between 1.5 and 25 times the size of our sun become neutron stars

After supernova, electrons and protons of all remaining mass compress and become neutrons

All atomic space is gone

Result is the size of a city

Can be pulsars or magnetars

After the Fact: Neutron Stars

Stars greater than 25 times the size of our sun become black holes

After supernova, all remaining mass collapses into infinitely small point called a singularity

immense mass / 0 volume = undefined (infinite) density

After the Fact: Black Holes

After the Fact: Black Holes

Gravity is so strong even light cannot escape

Surface or edge of black hole defined by event horizon

Point at which nothing can escape

Also a bad movie

After the Fact: Black Holes

Hertzsprung-Russell (HR) Diagram