There are many questions associated with the creation and evolution of the major constituents of the cosmos. A basic question astronomers must address is, how did the universe create its first stars and galaxies? Once these entities were created, how did they influence subsequent galaxy, star and planet formation? This is an important question, because these later objects are made of elements that can only have been created by the first generation of stars.
It is still unknown whether the universe created black holes with the first generation of stars or whether these exotic objects were created by the first generation of stars. Because black holes represent the most extreme physical conditions of spacetime and generate some of the most energetic phenomena following the Big Bang, they are the ultimate physical laboratories for testing theories of the universe.
We now know that our universe has a "foamy" structure. The galaxies and clusters of galaxies that make up the visible universe are concentrated in a complex scaffold that surrounds a network of enormous cosmic voids. However, in addition to the "normal" matter that makes up the visible parts of the universe, scientists have discovered that there are vast amounts of unseen matter. This so-called, "dark matter" makes up roughly 27% of the matter-energy content of the universe, while the visible pieces account for only about 5% of the total. Clearly, if we hope to understand the structure of the universe and the processes by which it formed and evolves, we must first understand the distribution of this important but unseen dark matter and the ways in which it interacts with and influences normal matter.
~ Types of Galaxies- Elliptical galaxies are shaped like a spheriod, or elongated sphere. In the sky, where we can only see two of their three dimensions, these galaxies look like elliptical, or oval, shaped disks. The light is smooth, with the surface brightness decreasing as you go farther out from the center. Elliptical galaxies are given a classification that corresponds to their elongation from a perfect circle, otherwise known as their ellipticity. The larger the number, the more elliptical the galaxy is. So, for example a galaxy of classification of E0 appears to be perfectly circular, while a classification of E7 is very flattened. The elliptical scale varies from E0 to E7. Elliptical galaxies have no particular axis of rotation, Spiral galaxies have three main components: a bulge, disk, and halo (see right). The bulge is a spherical structure found in the center of the galaxy. This feature mostly contains older stars. The disk is made up of dust, gas, and younger stars. The disk forms arm structures. Our Sun is located in an arm of our galaxy, the Milky Way. The halo of a galaxy is a loose, spherical structure located around the bulge and some of the disk. The halo contains old clusters of stars, known as globular clusters, Spiral galaxies are classified into two groups, ordinary and barred. The ordinary group is designated by S or SA, and the barred group by SB. In normal spirals (as seen at above left) the arms originate directly from the nucleus, or bulge, where in the barred spirals there is a bar of material that runs through the nucleus that the arms emerge from. Both of these types are given a classification according to how tightly their arms are wound. The classifications are a, b, c, d ... with "a" having the tightest arms. In type "a", the arms are usually not well defined and form almost a circular pattern. Sometimes you will see the classification of a galaxy with two lower case letters. This means that the tightness of the spiral structure is halfway between those two letters.
It is still unknown whether the universe created black holes with the first generation of stars or whether these exotic objects were created by the first generation of stars. Because black holes represent the most extreme physical conditions of spacetime and generate some of the most energetic phenomena following the Big Bang, they are the ultimate physical laboratories for testing theories of the universe.
We now know that our universe has a "foamy" structure. The galaxies and clusters of galaxies that make up the visible universe are concentrated in a complex scaffold that surrounds a network of enormous cosmic voids. However, in addition to the "normal" matter that makes up the visible parts of the universe, scientists have discovered that there are vast amounts of unseen matter. This so-called, "dark matter" makes up roughly 27% of the matter-energy content of the universe, while the visible pieces account for only about 5% of the total. Clearly, if we hope to understand the structure of the universe and the processes by which it formed and evolves, we must first understand the distribution of this important but unseen dark matter and the ways in which it interacts with and influences normal matter.
~ Types of Galaxies- Elliptical galaxies are shaped like a spheriod, or elongated sphere. In the sky, where we can only see two of their three dimensions, these galaxies look like elliptical, or oval, shaped disks. The light is smooth, with the surface brightness decreasing as you go farther out from the center. Elliptical galaxies are given a classification that corresponds to their elongation from a perfect circle, otherwise known as their ellipticity. The larger the number, the more elliptical the galaxy is. So, for example a galaxy of classification of E0 appears to be perfectly circular, while a classification of E7 is very flattened. The elliptical scale varies from E0 to E7. Elliptical galaxies have no particular axis of rotation, Spiral galaxies have three main components: a bulge, disk, and halo (see right). The bulge is a spherical structure found in the center of the galaxy. This feature mostly contains older stars. The disk is made up of dust, gas, and younger stars. The disk forms arm structures. Our Sun is located in an arm of our galaxy, the Milky Way. The halo of a galaxy is a loose, spherical structure located around the bulge and some of the disk. The halo contains old clusters of stars, known as globular clusters, Spiral galaxies are classified into two groups, ordinary and barred. The ordinary group is designated by S or SA, and the barred group by SB. In normal spirals (as seen at above left) the arms originate directly from the nucleus, or bulge, where in the barred spirals there is a bar of material that runs through the nucleus that the arms emerge from. Both of these types are given a classification according to how tightly their arms are wound. The classifications are a, b, c, d ... with "a" having the tightest arms. In type "a", the arms are usually not well defined and form almost a circular pattern. Sometimes you will see the classification of a galaxy with two lower case letters. This means that the tightness of the spiral structure is halfway between those two letters.
what is a globular cluster?
what universe has a "foamy" structure?
what generation created the black hole?
how did the universe create its first stars and galaxies?
how did they influence subsequent galaxy, star and planet formation?