Astronomy

Sun Facts

-Formed 4.6 Billion years ago. -Currently halfway through its Main Sequence for approximately 5.4 billion years. -Sun does not have enough mass to explode into a supernova-will become a red giant. -The sun will become large enough to engulf the current orbits of the solar system's inner planets, possibly earth.

Cause of a Supernova

-Fusion of iron uses up energy instead of releasing energy, -Gravity is greater than pressure. -Collapse of this core-which occurs in a fraction of a second-results in a supernova that nearly obliterates the star just leaving behind a black hole or neutron star.

High Mass Stars VS Low Mass Stars

-High mass stars have shorter lives. -High mass stars die in supernovae, low mass die in planetary nebulae. High mass stars can fuse heavier elements than carbon. -High mass stars can fuse heavier elements than carbon. -High mass stars leave behind a neutron star or black hole-low mass leaves behind a white dwarf. -High mass is less common than low mass.

Not all Stars Join the Main Sequence

-If the protostar has a mass less than 8% of the sun this does not happen. -It does not contain enough gravitation energy to reach a core temperature of 10⁷ kelvin. -No fusion reactions occur. -The star is stillborn (brown dwarf).

Stellar Nursery

-Interstellar giant molecular clouds. -Extremely cold and dense Nebulae. -Much too cold and too low density to ignite thermonuclear processes. -Clouds need to contract and heat up in order to form stars. -External trigger needed for the collapse.

Galaxy

-Large group of stars, planetary nebulae, and interstellar gas (hydrogen and helium are the primary gases in our universe) and dust. -Formed from huge clouds of primordial gas pulled together by gravity. -Formation begins when there is gravitational attraction between distant particles. -Contraction is then accompanied by an increased rational rate, which usually causes the galaxy to flatten as a disk.

Three Groups of STars

-Low Mass -Intermediate Mass -High Mass

Spiral Galaxies

-Milky Way. -Spiral arms that wind outward through the disk. -They are bright and made out of newly formed stars, making them easy to see from great distances. -2/3 of all galaxies formed. -We know the most about spiral because of our own galaxy, the Milky Way. -Acquire information using infrared telescopes.

Elliptical Galaxies

-Most common in the universe. -However, most are very dim and cannot be seen. -Don't make new stars, contains older stars. -Generally yellow-red in color, do not have spiral arms, and contains little interstellar dust or gas.

Evidence of Star Formation

-Nebula contains many massive, very young stars, including T Tauri Stars: strongly variable; bright in the infrared. -Smaller, sunlike stars, probably formed under the influence of the massive star. -Large masses of giant molecular cloud where stars do not form, isolate, but in large groups, called open clusters of stars.

Irregular Galaxies

-No common shape and are less common. -Normally small and faint-diffcult to detect. -Contain both new and old stars. -As common as spiral galaxies. -Most form when two galaxies collide into each other.

Protostars

-Pre-birth state of stars. -Hydrogen and helium still have not ignited. -Enclosed in opaque "cocoons" of dust→barely visible in the optical, but bright in the infrared. -As it contracts, it heats up.

Shocks Trigger Star Formation

-Previous star formation can trigger further star formation through: 1) Shocks from supernova (explosions of massive stars): massive stars die young→supernovae tend to happen near sites of recent star formation. 2) Ionization fronts of hot, massive O or B stars which produce a lot of UV radiation. Massive stars die young and B stars only exist near sites of recent star formation. 3) Collisions of giant molecular clouds. Molecular clouds are very large and may occasionally collide with each other. 4) Spiral arms in galaxies like our Milky Way: Spirals' arms are probably rotating shock wave patterns.

Supergiants

-Shells increase. -Thermal pressure overbalances the lower gravity in the outer layers. -Star expands. -Star cools. -The star moves toward the upper right of the H-R diagram. -It becomes a red supergiant. -If the core evolves too quickly for the outer layers to respond, they explode before even becoming a red supergiant.

Three Types of Galaxies

-Spiral -Elliptical -Irregular

Stars Birth

-Stars are born in nebulae which are huge clouds of dust and gas collapse under gravitational forces. -The outward thermal pressure force must exactly balance the weight of gravity outside the star. This is called Hydrostatic Equilibrium. -This condition uniquely determines the interior structure of the star. -These young stars undergo further collapse, forming main sequence stars. -This balancing of forces is why we find stable stars in a narrow strip called the Main Sequence.

Star Evolution

-Stars are like people in that they are born, grow up, mature and die. -A star's mass determines what life path it will take.

Supernova

-The amount of energy released is so great, that most of the elements heavier than iron are instantly created. -In the last millennium, four supernovae have been observed in our part of the Milky Way Galaxy.

Contraction of Giant Molecular Cloud

-Thermal energy (pressure) -Magnetic fields -Rotation -Turbulence -External trigger required to initiate the collapse of clouds to form stars.

When Stars Leave the MS

-Toward the end of hydrogen burning, the number of particles drop in the core and it shrinks and burns hotter. -Hydrogen shell heats up and hydrogen fusion begins. -There is less gravity from above to balance this pressure. -So the outer layers of the star expand. -The star is now in the subgiant phase of its life.

Center of the Milky Way

26×10³ light years away.

Earth-Moon Via Spacecraft

8 hours

Light Year

A measurement of length or distance, not imd. It is approximately 6 trillion miles.

Star Formation

Collapse of the cores of giant molecular clouds: dark, cold dense clouds obscuring the light of stars behind them.

Neutron Star/Black Hole

Comes from high-mass stars.

White Dwarfs

Comes from low-mass stars.

Globules

Contracting to form protostars.

Mass

Determines a how a star will live and how a star will die.

Gravity

Holds stars together.

High Mass Stars

Interstellar cloud→protostar→massive star→pulsating yellow giant→red giant→supernova explosion→black hole or neutron star

Low and Intermediate Mass Stars

Interstellar cloud→protostar→sun today→red giant→yellow giant→second red giant stage→planetary nebula→white dwarf

Evaporating Gaseous Globules (EGGs)

Newly forming stars exposed by the ionizing radiation from nearby stars.

Pressure

Supports stars against gravity.

Main Sequence Stars

The mass of the protostar determines: -How long the protostar phase will last. -Where the newborn star will land on the MS. -The newborn star's lifetime. -O stars are most massive, M stars are the least massive. -OBAFGKM-oh be a fine girl, kiss me.

Thermal Pressure

The pressure that opposes the inward pull of gravity, owing to heat produced by fusion or gravitational contraction opposed gravity during most of a stars life.

Brown Dwarf

Very faint, emits infrared and has a hydrogen core,