Black Holes:
- formed from the cores of super massive stars
- best described as regions of space where so much mass is concentrated that nothing, not even light, can escape the gravitational pull
- are where the escape velocity(the more massive the object, the faster you have to travel away) is greater than the speed of light
- Einstein's general theory of relativity provided the first clue to understanding black holes- GRAVITY AFFECTS TIME= the more massive an object is, the more it can slow down time. The gravity is so big near a black hole that time appears to stand still.
- they will suck in matter within a certain distance from them
- Einstein's Theory of Relativity describes gravity as a curvature of space-time
- Stars burn hydrogen in a process known as fusion, which produces pressure that pushes out from the center of the star. This counteracts the force of gravity
- Most massive stars leave behind a small core known as a white dwarf star, surrounded by an expanding shell of gas
- singularity- an infinitely small and dense point
- the singularity is surrounded by the event horizon, the point where the escape velocity is greater than the speed of light
- the distance between the singularity and the even horizon is known as the Schwarzschild radius.
- one indicator of a black hole is an are that exhibits a large amount of mass in a small, dark space
- they have been found in the centers of galaxies and in binary star systems within our own galaxy
Dark Matter
- cannot be seen
- scientists say that 90% of the matter in the universe is invisible. This matter is referred to as dark matter
- dark matter can be detected through its gravitational influence on other objects, or even on life
- can affect the motion of stars and galaxies
- dark matter can also affect the path of light- gravitational lensing, dense objects can cause the light of distant object to bend around it, which cause distorted images and duplicate images of stars and galaxies
- some dark matter may exist in MACHOs (Massive Compact Halo Objects)= believed to be made up of baryonic matter (includes planets, moons, brown dwarfs, dust clouds, white dwarfs, neutron stars, and black holes)
- this matter would be composed of exotic particles called neutrinos, axions, super-symmetric dark matter, and WIMPs (Weakly Interactive Massive Particles)
Quasars
- brightest and most distant objects in the known universe...referred to as radio stars because of the strong presence of radio waves
- can burn with the energy of a trillion suns or 10 to 100 times the energy of our galaxy
- have the largest red shift of any other objects in the cosmos
- quasars are thought to be produced by super massive black holes consuming matter in an acceleration disk. the friction between the particles give off enormous amounts of light such as X-Ray
- the first identified quasar was called 3C 273 and was located in the constellation Virgo.
- more than 2000 quasars have been identified
Pulsars
- named pulsars because of their rapidly pulsing nature
- bright pulsars have been observed at almost every wavelength of light
- some can be seen in visible light
- basically a rapidly spinning neutron star (highly compacted core of a dead star left behind in a supernova explosion)
- the magnetic field around this star is a trillion times stronger than the one surrounding Earth. The magnetic field causes the neutron star to emit strong gamma rays called gamma ray pulsars
- formed when a massive star collapses it exhausts its supply of fuel, which causes it to supernova
- "forms an object composed primarily of neutrons packed so tightly that they no longer exist as normal matter. A physicist named Chandrasekhar Subrahmanyan theorized that if the mass of the core of the collapsing star was 1.4 times the mass of the star itself, the protons and electrons would combine to form neutrons in a neutron star. This number is known today as the Chandrasekhar limit."
- found by using large radio telescopes
Galaxies
- large groupings of stars, dust, and gas held together by gravity
- contain stars, planets, moons, comets, asteroids, nebulae, dust, neutron stars, and black holes
- Spiral Galaxy - characterized by a distinct flattened spiral disk with a bright center called the nucleus ex: Milky Way
- Barred Spiral Galaxy - A barred spiral galaxy is very similar to a spiral with one important difference. The arms spiral out from a straight bar of stars instead of from the center
- Elliptical Galaxy - vary in shape from completely round to extremely flat, no bright nucleus at the center
- Irregular Galaxy - no discernible shape or structure
- Edwin Hubble was the first to figure out the distance of a galaxy
Star Clusters
- multiple star systems
- open clusters (or galactic clusters) are clusters that contain from 12 to 1000 stars. held together by mutual gravitational attraction and have a common center of mass
- globular clusters- much older and contain 10,000 to 1 million stars.
- Charles Messier was one of the first astronomers to observe and categorize star clusters
Nebula
- derived from the Latin word for cloud
- cosmic cloud of gas and dust floating in space
- more than one nebula are called nebulae
- contain the elements from which stars and solar systems are built
- Most nebulae are composed of about 90% hydrogen, 10% helium, and 0.1% heavy elements such as carbon, nitrogen, magnesium, potassium, calcium, iron
- emission nebula- cloud of high temperature gas. tend to be red in color because of the abundance of hydrogen
- reflection nebula- does not reflect radiation of its own. cloud of dust and gas that reflects the light energy from a nearby star or group of stars. frequently the site of star formation. tend to be blue in color because of the way the light is scattered
- dark nebula- cloud of dust that blocks the light from the objects behind it
- planetary nebula- shell of gas produced by a star as it nears the end of its life cycle
- supernova remnant- formed when a star ends its life in a supernova
- all stars, planets, and solar systems are formed from nebulae
- largest object you will find in a galaxy
Stars
- chance alignments are called constellations
- blue stars are HOTTER than red stars
- composed of hydrogen mainly
- create many different elements and give life on this planets
- most plentiful object in the visible universe
- Sirius is the brightest star in the sky
- The lower a star is in the sky, the more it will twinkle because its light must pass through more of the atmosphere
- begin as nebulae
- stars are formed from when a protostar condenses and heats up. this star will live on until it collapses and supernovas and forms a black hole
- life cycle is determined by mass
- main sequence star- point in a star's evolution during which it maintains a stable nuclear reaction, spends most of it's life here
- red giant- star in its late phase of development. reddish or orange in color
- white dwarfs-
The Hertzsprung Russell Diagram (H-R) is a graph showing the relationship between a star's surface temperature and its absolute brightness, along with the color. The lower the number the brighter the star. The higher a star is on the graph, the brighter it is. The more you go to the right on the x-axis the cooler it is. As brightness increases with main sequence, the hotter the star, vice versa.
The main purposes of a H.R. Diagram is-
The main purposes of a H.R. Diagram is-
- Temperature
- Brightness
- Color