TOPIC: AstronomyAIM: What are stars?

Star •Ball of gases that gives off light and heat

The Big

BangTheory

•Universe began with a giant explosion 13 billion years ago

•Matter stars •It is still expanding•Most accepted theory

What is the Sun?

•Nearest star to Earth

What arestarsmade of?

•Hydrogen and helium gases

How dostarsform?

•1. Nebula (large cloud of gas, ice, and dust) forms

The Orion Nebula, a site of active star formation. From the Hubble

Space Telescope.

The above images show the Eagle Nebula star-forming region in the Infrared (left) compared with a visible light image by Hubble Space Telescope (right).

•2. Nebula contracts (due to gravity) & breaks up into smaller pieces

•3. Temperature increases (1 million K)

•4. Center = protostar forms

•5. Temp reaches 10 million K

•6. H fuses to make He star

H-RDiagram

•Hertzsprung-Russell Diagram

•Higher temp stars radiate more energy

•90% of all stars fall on main sequence (line from upper left to lower right)

Our sun has been a main sequence star for 5 billion years and will stay a main sequence star for another 5 billion years.

How do stars change?

•1. Shrinks•2. Increases in density

•3. Temp increases•4. Moves into main sequence (when fusion starts)

TypesOfstars

•1. Giant = late stage •(When H is used up)•Core contracts, temp increases

•Outer layers expand & cool

•a. Red Giant = large bright star, fairly cool

•b. Super Giant = very large stars

•Example: Betelgeuse

Betelgeuse is located in the constellation of Orion. It’s diameter is larger than the diameter of Jupiter’s orbit around the Sun.

•Can eventually collapse, outer portion explodes SUPERNOVA (giant explosion)

•Supernova can turn into a neutron star OR a black hole

A supernova is a giant explosion in which the temperature in the collapsing core reaches 10 billion K and atomic nuclei are split into neutrons and protons. Protons merge with electrons to form neutrons, and the collapsing core becomes a neutron star. A typical neutron star is the size of a major city on Earth, but has a mass greater than the Sun’s.

Hubble Space Telescope image of a neutron star (identified by the arrow) in the direction of the southern constellation Corona Australis. The star has a surface temperature of 1.2 million degrees Fahrenheit, which is far hotter than that of ordinary stars.

•Black hole = object so dense that nothing can escape its gravity

•Usually results from the supernova of a very massive star

•2. White dwarf = giant that lost outer layers

• Very small, hot star, Hot dense core

• Keeps contracting due to gravity

A giant’s core will continue to contract and become hotter. When it uses up all its helium, it contracts even more. When the temperature reaches 100 million K, helium fuses, forming carbon. Now the star is enormous and its surface is much cooler. Its outer layers escape into space leaving behind a hot, dense core that continues to contract and is now called a white dwarf which is about the size of Earth.

There are many white dwarfs in our galaxy, but most are too dim to be seen. One of the first to be discovered was Sirius B, the dense companion star to Sirius.

Life Cycle of a Star

Nebula

Protostar

Giant

Super Giant

Neutron Star

Black Hole

White dwarf

Black dwarf

(SUPERNOVA)

What is aconstellation

?

•Star pattern that appears to form images

•Used by astronomers to locate and name stars

Telescope •Instrument used to observe objects in outer space using lenses