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Astronomers use 4 sizes for the stars. The largest stars in the universe are called super giants . The star Betelgeuse is a super giant star. The next step down in size are called medium stars. The star in our solar system, Sun, is a medium star. White dwarf stars about the size of Earth, and neutron stars are the smallest at about 20km in diameter.
Temperature of stars can be estimated from earth using the color of the star. A star that is red is cool in temperature, around 3,200 ° C . White stars are considered hot at about 5,500 ° C . Blue colored stars are the hottest with temperatures of 10,000 ° C or more .
By definition, brightness is the amount of light given off. Brightness depends on the star’s distance from Earth as well as its actual brightness . Brightness is measured by two methods: absolute magnitude which is difficult, and apparent magnitude which is easier. Absolute magnitude involves mathematically moving the stars to the same distance from earth and then rating how bright they are. Apparent magnitude is comparing from earth, the visual brightness of one star to another’s brightness.
All stars, before they are formed, begin as part of a nebula (a large collection of gas and dust in an area). As more and more matter collects in the area, gravity begins to pull together the dust and gas which creates a protostar. This protostar continues to form until nuclear fusion begins. Once this happens, a star is born.
How long a star will last depends on its mass . Big stars with large mass, will burn up very rapidly and have a short life. Small stars with small mass have a long life because they burn up their fuel slowly . It is a lot like fuel efficiency of vehicles, larger vehicles like suburbans and big trucks take more gas to move than the smaller cars like minis and civics.
Small and medium stars have less violent deaths. The outer layers expand and drift away from the center. The core is left behind, which forms a white dwarf star. The white dwarf then simply stops glowing , and is called a black dwarf.
Super giant stars are considerably more violent. When their fuel runs out, these stars explode in what’s called a supernova . The material that is left behind and not scattered too far can reform into a neutron star.
The most massive stars follow a slightly different path. They exploded into a supernova much like the supergiant stars, but the leftover gases do not reform neutron stars. The incredible explosion creates such a huge force that these gases are pulled inward . Gravity becomes so strong so quickly that everything begins to be drawn in and a black hole forms.
Red Giant or Supergiant Protostar Nebula Supernova Black Hole White Dwarf Black Dwarf Neutron Star
There’s more out there than our Milky Way Galaxies
Side View Top View Sun’s Location About 100,000 light-years
Spiral galaxies consists of twin spirals that slowly rotate. The arms appear to rotate and spiral outward due to its rotation. Spiral galaxies contain lots of dust , and particles . therefore astronomers watch these types of galaxies for new stars to form. Earth is located in a spiral galaxy called the Milky Way.
Elliptical galaxies are oval or look like a football. These galaxies contain very little gas and dust. Astronomers watch elliptical galaxies for black dwarfs or supernovas, since most of the stars here are old stars.