Stars

Stars, Galaxies, and the Universe

Ch 30

SOL 13

Objective ES 1 and 2

What is a Star?• A ball of energy that gives off a massive

amount of electromagnetic energy

Stars Spectrum

• These can tell you the

stars composition and

temperature

Spectra of Stars• Stars are assigned spectral types of O,B,

A, F, G, K, and M which are based on their temperature

• Each type is subdivided into the numbers 0-9

• Provide information about the stars composition and temperature

Apparent Motion

Motion of Stars

• They rotate on an axis

• They may revolve around another star

• They move toward or away from our solar system.

• The Doppler Effect can determine their direction…works just like sound in the apparent shift because of motion!

The same shifting happens with the light from a moving star.

Lower Frequency Higher Frequency

The spectrum of hydrogen that is from a stationary source.

When the star is moving closer...

Stationary Hydrogen

“Blue Shifted” Hydrogen from star moving towards Earth.

And when a star moves away from us...

Stationary Hydrogen

Lines are shifted to the red end.

And when a star moves away from us...

Stationary Hydrogen

Lines are shifted farther to the red end.

Faster

Since the universe is expanding...

•All distant objects have a red shift.•The farther the object, the more extreme the red shift

Astronomers use this relationship

between distance and speed to measure

the distance to distant stars and galaxies.• .

Positions and Distances of Stars

• Distance is measured in light years

• 9,461,000,000,000 km in one year

• To account for the motion of the Earth when viewing the stars, the apparent shift in position of the star is called parallax

Measurements

• Distances to the closest stars can be determined through measurement of the trigonometric parallax. The parsec is defined to be the distance at which1AU subtends an angle of 1 arc second.

Stellar Brightness• Apparent Magnitude:

the brightness of a star as seen from Earth, does not take into account the distance.

• Absolute Magnitude: the actual brightness of a star

Hertzsprung-Russell diagram

• The properties of mass, luminosity (total energy output), temperature, and diameter are closely related

• Each star has specific characteristics related to each of the properties

• 90% of all stars fall along main sequence

http://lcogt.net/en/book/stages-stars-life

Stellar evolution• Mass and composition determine nearly all

of a star’s properties.• Fusion occurs to generate the energy from

the star• Not only can Hydrogen be fused to make

helium, other elements can also be made He into C, C + He to make O, then Ne, then Mg, then Si.

Birth of a Star

All stars start life as a nebula of gas and dust. Over millions of years gravity pulls these closer together.

Gravitational force

Birth of a starBirth of a star

NebulaNebula

Pressure builds up and the core starts to heat up giving out infra red radiation.

Birth of a starBirth of a star

ProtostarProtostarStarStar

The gravity eventually gets so big and the temperature gets so high that nuclear fusion starts, it becomes a star

The dust and gas from the nebula is added to the protostar, it gains mass. As mass is gained gravity increases and the temperature within the protostar increases

Life of a star

Radiation PressureFrom the energy of fusion

Gravitational forceFrom the mass of the material

A Stable Star like our SunA Stable Star like our Sun

Nuclear fusion4 Hydrogen 1Helium + ENERGYNuclear fusion4 Hydrogen 1Helium + ENERGY

The force of the radiation pressure from nuclear fusion is balanced with the gravitational force in a stable star.

Death of a Star

Star like our Sun A large Star

StarStarRed GiantRed GiantWhite dwarfWhite dwarfBlack DwarfBlack Dwarf

Eventually a star the size of our sun becomes a Red Giant.

The star keeps increasing in size until the gravitational force causes it to collapse into itself creating a White Dwarf

This cools down to become a black dwarf.

Life Cycle of a Star: Small and Medium Stars

• Protostar• Medium sized star becomes a red giant then

a white dwarf then become black dwarfs

Large StarLarge StarRed

SupergiantRed

SupergiantSupernovaSupernovaNeutron StarNeutron StarPulsarPulsarBlack HoleBlack Hole

A larger star eventually becomes a super Red Giant.

This then collapses, heats up and explodes in a supernova.

The small core becomes a neutron star. This can turn into

a pulsar

If a star is large enough it’ll become a black hole.

Massive Stars• Massive stars can become a supernova and

blow up, its core can become a neutron star or a Black hole

Ultra-Massive Black Holes• Researchers theorized the potentially

ultra-massive black holes, which lie in galaxies at the centers of massive galaxy clusters containing huge amounts of hot gas, may generate the energy outbursts that keep this hot gas from cooling and forming huge numbers of stars.

The larger the star the more fusion can take place and form many

elements

Closest Star to Earth: Alpha Centauri

Groups of Stars• There are 88 constellations that were named

by ancient people• They appear to move around the poles• They can be seen only during

certain times of the year.

They are not gravitationally

bound together

Dividing the Sky

 Zenith ( Position directly Overhead ) andAzimuth ( Angle from North along the Horizon )

Binaries and Novas• Two stars that are

gravitationally bound together

• Orbit a common center of mass

• Most appear as a single star

• Star Clusters- spherical arrangements of hundreds of thousands of stars

Galaxies• Large gathering of stars, gas, and dust that

is bound together gravitationally.

Types of Galaxies• Spiral Galaxies: Spiral shaped with

normal spirals and barred spirals

• Elliptical Galaxies: not flattened into a disk shape, no arms, similar to a football in shape

• Irregular Galaxies: no distinct shape

• Most galaxies are located in groups rather than being spread throughout the universe

Galaxy types

Elliptical

Spiral

Irregular

Milky Way Galaxy

• Side angle looks like a fried egg, flat edges and bulging in the middle

• Spiral shape with arms rotating off the sides, circulates around the center bulge

• Center of galaxy has a high concentration of stars

• Our solar system is located in the arm of Orion

Quasars

• Most distant objects in the universe, they give off a tremendous amount of energy

• May be related to black holes

• Stands for quasi-stellar radio source

COSMOLOGY• The study of the universe, its nature, its

origin and its evolution

Big Bang Theory

• All matter and energy was compressed into a small volume.

• About 14 billion years ago it expanded and has been expanding ever since

• Support: The Red Shift of Galaxies and Cosmic Background Radiation (low level energy that formed shortly after the BB)

Dark Matter• Dark matter and energy accounts for

96% of the mass in the universe, it is invisible

• This is what makes the sky dark, it does not give off, reflect or absorb any light

Dark Energy

• Nothing is really known about dark energy

• Hypothesized to oppose gravity

• Force that is pushing galaxies away from each other.

Will we ever travel to other Galaxies?

• The nearest galaxy to ours is called the "Sagittarius Dwarf" and it is about 60 000 light years away from our own galaxy (the Milky Way). Assuming we can get a vehicle to reach the speed of light, it would take 60 000 years for a vehicle to travel to this galaxy.

•  Given current technology, it is unlikely that we will ever visit another galaxy.

Twinkle Twinkle