Components of the Universe
Galaxies: Galaxies are collections of stars, dust, and planets. Galaxies are classified into 3 categories by their shape.
-Spiral- shaped like a spiral and are classified by a bright bulge in the center of it.
-Elliptical- vary in shape from stretched ovals to completely round. Unlike spirals, ellipticals don't have the bulge at the center.
-Irregular- Irregular galaxies have no specific shape or structure.
Our solar system is on the outer edge of the Milky Way galaxy which is a spiral galaxy.
-Spiral- shaped like a spiral and are classified by a bright bulge in the center of it.
-Elliptical- vary in shape from stretched ovals to completely round. Unlike spirals, ellipticals don't have the bulge at the center.
-Irregular- Irregular galaxies have no specific shape or structure.
Our solar system is on the outer edge of the Milky Way galaxy which is a spiral galaxy.
Clusters: Star clusters are groupings of stars held together by a common gravitational bond.
- Open clusters contain anywhere from a dozen to a thousand stars. The stars are new and hot. Many of these can be found in our own Milky Way galaxy. Open clusters are young because they don't last vey long. The gravitational pull between stars and other objects cause the clusters to eventually disperse.
-Globular clusters are much older and they contain from around ten thousand to a million stars. They don't disperse because the gravitational bond is so strong. The clusters are found just outside our galaxy.
Nebulae:
Nebulae is plural for nebula. A nebula is a cosmic cloud of gas and dust floating in space.
- Emission Nebula- cloud of high temperature gas. Within this nebula, a star energizes atoms with UV radiation. As the atoms fall back to a lower energy state, they give off radiation. This causes the nebula to glow.
- Reflection Nebula- does not create its own glow but reflects the glow of nearby stars.
- Dark Nebulae- cloud of dust that blocks light from objects behind it. Similar to reflection nebulae in composition but different because of the positioning of the light source.
-Planetary Nebulae- shell of gas produced by a star as it nears the end of its life cycle. Nothing to do with planets but often look like planets because of their round shape.
-Supernova Remnant- created when a star dies and creates a massive explosion called a supernova. Nebula glows with the remains of the star.
Quasars:
Quasars have the largest red shift of any object in the cosmos. Quasars are the most distant objects ever to be detected in the universe. Scientists aren't exactly sure what a quasar is but the closest guess is that quasars are created by super massive black holes consuming matter in an acceleration disk. As the matter spins faster, it heats up. The friction gives off a lot of light and other types of radiation.
Another possible explanation is that quasars are very, very young galaxies. It is possible that quasars represent the earliest formation of a galaxy.
Stars:
A star is like a giant nuclear furnace. The nuclear reactions convert hydrogen into helium by a process called fusion. This gives the star its energy. Stars begin their lives as nebulae. The gravity of a passing star or the shock of a nearby supernova may cause the nebula to contract. As it condenses, it is called a protostar. It continues to condense and after it reaches a critical mass, fusion begins. That is how the star is formed.
Dark Matter:
Dark matter cannot be seen but it makes up 90-99% of the universe. Scientist have found that there is not enough visible matter to account for all the gravity that holds the universe together. They have also found many galaxies rotating faster than they should. Normally they would fly apart, but because of dark matter, they don't.
Black Holes:
A black hole is formed when a super massive star dies. When the star collapses, it becomes very small but it still has the same amount of mass as the original star. In few cases, the gravity in that thing goes crazy, and it implodes occupying a single point in space. It fades out of existence but its mass and gravity remains, known as a black hole.
Pulsars:
A pulsar is a rapidly spinning neutron star. A neutron star is the highly compact core of a dead star left behind after a supernova explosion. The magnetic field of a pulsar is about a trillion times that of earth. The field causes it to emit strong pulses of radio waves from both its poles.
The H+R diagram is the way to classify stars by temperature and brightness.