Stars Huge spheres of very hot gas that emit light and other radiation. They are formed from clouds of dust and gas, or nebulas, and go through different stages as they age. We use light years to describe the distance a star is from the earth. ○ A light year is the distance that light travels in one year or 9.5 x 10^12 km.

Globular Cluster (M15)

Stars are powered by Nuclear fusion ○ Stars are huge spheres of very hot hydrogen and helium gas that emit light. ○ Stars are held together by gravity. ○ The core of the star is under tremendous pressure and is over 15 million Kelvin. ○ They get their energy from nuclear fusion. Fusion combines hydrogen nuclei into helium. Each time particles fuse, energy is released.

Young Stars

Some stars are brighter than others ○ Brightness depends on temperature. The hotter, the brighter. ○ Brightness depends on the stars distance from the earth. The closer, the brighter.

Betelgeuse  Red giant  Surface of star would extend until Jupiter’s orbit  6000 F

Rigel  85,000 time luminosity of sun  36,000 F  Blue Giant

Orion

Brightness of a star

A star’s color is related to its temperature ○ The hottest stars are blue ○ Average temperature stars are yellow (sun) ○ The coolest stars are red

The life cycle of a star In a way that is similar to natural cycles, stars are born, go through stages of development, and eventually die. Stars begin as a cloud of gas and dust known as a nebula. It collapses inward by its own gravity. As the nebula collapses it begins to spin and form a protostar. Soon nuclear fusion begins within the protostar. At this point, a star is born. The fusion reactions convert hydrogen to helium. Eventually, hydrogen is used up and the star begins to die. (Scientists estimate our sun will last another 5 billion years.)

The life cycle of a star continued. As the nuclear reactions decrease the pressure from the release of energy begins to decrease. The stars outer limits expand and it becomes a red giant (A large reddish star lat in the life cycle). The star appears red because its surface is cool, but its core is really hot. Helium is being converted to carbon. As the star depletes its helium it begins to expand again. The outer limits of the star begin to leave the star and a white dwarf (a small, dim, and very dense star about the size of the earth) is the result.

Life Cycle of a Star  er/starslife/. er/starslife/  Watch life cycle of a star 1 and the lives of stars.

Bubble Nebula

Cat’s eye nebula – Planetary Nebula with White Dwarf

Saturn Nebula – Planetary Nebula with White Dwarf

Eskimo Nebula – planetary nebula with white dwarf

Blinking Nebula – planetary nebula with white dwarf

Nebulas  er/hm_helix_twist/. er/hm_helix_twist/

Supernovas Massive stars evolve faster than smaller and produce heavier elements during fusion. These stars produce iron cores. Fusion producing iron requires more energy. The energy required for fusion is more than fusion produces. The core collapses on itself because of its own gravity. It rebounds and sends out a shockwave. The result is a huge explosion. This is called a supernova.

Supernova

Crab Nebula – Remnant of Supernove explosion

 Watch supernova explosions.

Neutron Stars Sometimes big supernova explosions form neutron stars. Neutron stars are a few dozen kilometers thick, but they are very massive. They are extremely dense. 1 teaspoon of matter from a neutron star would weigh 100 million tons on the earth.

Black Holes The most massive supernovas will form a black hole. In a black hole matter is so massive and compressed that nothing, not even light, can escape its gravitational pull. Therefore, black holes cannot be seen directly. They must be detected by observing radiation and x-rays.

Black Hole

Black Holes  black_holes/. black_holes/  html. html

Galaxies A galaxy is a collection of millions to billions of stars. If you counted 1000 galaxies a night it would take 275,000 years to count them all!

Galaxies Gravity holds galaxies together. Galaxies are often grouped together by gravity in clusters. The Milky Way galaxy (the one we live in) is closely linked to Andromeda galaxy. The two galaxies are part of a cluster of 30 galaxies. Some galaxy clusters can be as large as 100 million light-years across.

Sombrero Galaxy

Barred Galaxy

Pinwheel Galaxy

Galaxy Cluster Abell

Colliding Galaxies  er/hm_quintet/. er/hm_quintet/  er/lookdeep/. er/lookdeep/

 Show size of universe 1 and 2.

Origins of the Universe The universe is all of the space, matter, and energy that exists – past, present, and future. It takes time for light to travel. Some things are so far away that we don’t see the present. For example, it takes 8 light minutes to get to the sun. Therefore, we see the sun as it was 8 minutes ago. That is crazy to think about! So we see things in the universe as they were long ago.

Origins of the Universe One theory of how the universe began is called the big bang. The big bang states that the universe began with a gigantic explosion 13 billion to 15 billion years ago.

Origins of the Universe  According to the theory, nothing existed before the big bang. There was no time and no space. But out of this nothingness came the vast system of space, time, matter, and energy that now makes up the universe. The explosion rereleased all the matter and energy that still exist in the universe today.

Hubble Deep Field

The Universe  hudf/. hudf/  The universe is estimated to be 13 to 15 billion years old.  Watch the size of the universe