chapter 14 the universe. the night sky a light year is the distance that light travels in one year,...
TRANSCRIPT
Chapter 14
The Universe
The Night Sky
• A light year is the distance that light travels in one year, about 6 x 1012 mi. This is 8 times the distance around the earth traveled in 1 second.
• Celestial coordinates are similar to earth coordinates. The celestial sphere is the space that extends from the earth’s sphere.
• There is a celestial equator. It is adjacent to the earth’s equator.
• The earth’s north pole touches the celestial sphere at the north celestial pole and the earth’s south pole at the south celestial pole.
Stars
• There are billions of stars in the universe.
• The sun is only one of many. It is a star of average brightness.
• All stars are massive, dense balls of gases with a surface heated to incandescence by energy released by fusion reactions deep within.
Origin of Stars• Stars are born from swirling clouds of hydrogen
gas in the deep space between other stars.• Interstellar (between stars) clouds are called
nebulae. They consist of random, swirling atoms of gases that have little gravitational attraction for one another because they have little mass.
• Complex motions of stars can produce a shock wave that causes particles to move closer together into a growing cluster and as the mass increases the gravitational attraction of the particles for each other increases.
• Eventually you end up with a protostar, an accumulation of gases that will form a star.
A star is born
Nebulae - Swirling clouds of hydrogen gas away from other stars, eventually forms protostar.
A protostar
Origin of Stars
• The protostar becomes more dense. As the atoms accelerate towards the center of the star they gain in kinetic energy which causes the temperature to increase.
• After about 10 million years of contracting and heating the temperature and density conditions at the center of the protostar are sufficient to start nuclear fusion reactions.
• After about 17 million years of this a star is born and it will exist for the next 10 billion years.
Sections of a star
Sections of a Star-The Core
• The core is a dense, very hot region where nuclear fusion reactions release gamma rays and X-ray radiation.
• The density of the core is about twelve times that of solid lead.
• Because of plasma conditions, however, the core remains in a gaseous state even at this density.
Sections of a Star- Radiation Zone
• The radiation zone is less dense than the core, it has a density like water’s.
• Energy in the form of gamma and X-rays from the core is absorbed and reemitted by collisions with atoms in this zone.
• The radiation slowly diffuses outward because of the countless collisions over a distance comparable to the distance between the earth and the moon. It could take millions of years before this radiation finally escapes the radiation zone.
Sections of a Star-Convection Zone• The convection zone begins about 7/10 of
the way to the surface, where the density of the gases is about 1% of the density of water.
• Gases at the bottom of this zone are heated by radiation from the radiation zone below, expand from the heating and rise to the surface by convection.
• The temperature is maintained at about 5500oC
The Sun• At an average the sun converts about
1.4 x 1017 kg of matter to energy every year as H nuclei are fused to produce helium.
• The sun was born about 5 billion years ago and has sufficient hydrogen in the core to continue shining or another 4-5 billion years.
Other Stars• Other stars have masses that are much greater or much
less than the mass of the sun so they have different life spans.
• More massive stars generate higher temperatures in the core because they have a greater gravitational contraction from their greater masses.
• Higher temperatures mean increased kinetic energy, more collisions between hydrogen nuclei and therefore more fusion reactions.
• A more massive star uses up its hydrogen more rapidly than a less massive star and vice versa.
• The life spans of stars range from a few million years for large, massive stars, to ten billion years for an average star, to trillions of years for small, less massive stars.
A star
Fusion fuel for all stars. (10,000,000K required).
Larger stars burn up fuel faster.
Sun’s lifetime - 10 billion years (we’re half through).
4 Hydrogens combine to form Helium
Brightness of Stars
• The brightness of stars is related to: 1. The amount of light produced by the stars. 2. The size of each star. 3. The distance to a particular star.• The apparent magnitude scale indicates the relative
brightness of stars. It goes from 1-6 with 1 being the brightest. The stars are said to be first through sixth magnitude stars.
• The sun has an absolute brightness of 4.8, which is the brightness of a faint star.
• The absolute brightness is an expression of luminosity, the total amount of energy radiated into space each second from the surface of a star.
Luminosity of Stars
• If the sun is assigned a luminosity of 1, then other stars range from a low of 10-6
sun units to a high of 105 sun units.
• The sun is somewhere in the middle of the range of star luminosity.
Star Temperature
• The temperature of the stars is reflected in their color.
• The hotter stars are bluish white, the in between ones are yellowish, like the sun, and the cooler ones are reddish.
• This is the same situation that we have with any incandescent object.
The distribution of radiant energy emitted is different for stars with different surface temperatures. Note that the peak radiation of a cooler star is more toward the red part of the spectrum, and the peakRadiation of a hotter star is more toward the blue part of the spectrum.
The mid mass stars eventually become planetary nebulae after a violent explosion. They eventually add to the dust and gases between stars.Both mid and low mass stars eventually becomes cold clumps of carbon in space.The higher mass stars eventually collapse and rebound to a catastrophic explosioncalled a supernova.
The blown-off outer layers of mid mass stars form ringstar structurescalled nebulae.
Supernova
• http://images.google.com/imgres?imgurl=http://heasarc.gsfc.nasa.gov/Images/rosat/slide_gifs/rosat06.gif&imgrefurl=http://heasarc.gsfc.nasa.gov/docs/snr.html&h=600&w=750&sz=215&tbnid=Ac4nCSENUcFVCM:&tbnh=113&tbnw=141&prev=/images%3Fq%3Dpicture%2Bof%2Ba%2Bsupernova&start=2&sa=X&oi=images&ct=image&cd=2
• http://www.spaceimages.com/kesuph.html
Galaxies
• The basic unit of the universe is the galaxy.• The sun is but one of about one hundred million
stars that are held together by gravitational attraction in the Milky Way galaxy.
• The Milky way is but one of billions of galaxies that are associated with other galaxies in clusters, and these clusters are associated with one another in superclusters.
The Milky Way galaxy
The Milky Way Galaxy
• Contains 3 parts: 1. Galactic Nucleus- Spherical concentration of
stars. 2. Galactic Disk-Rotating disk which contains the
bright, blue stars along with much dust and gas. 3. Galactic Halo-Spherical area with 150 globular
clusters located outside of the galactic disk.• The sun is located in one of the arms of the
galactic disk, about 25-30 thousand light years from the center.
• The galactic disk rotates and the sun completes one full rotation every 200 million years.
The Structure of the Milky Way Galaxy.
The Milky Way (cont.)• The diameter of the galactic disk is about 100,000 light-years.
• In spite of the one hundred billion stars in the Milky Way, it is mostly full of emptiness.
• If the stars were the size of tennis balls the distance between them would be the size across the state of Texas.
• The space between the stars is not actually empty, since it contains a thin concentration of gas, dust, and molecules of chemical compounds.
• The gas outnumbers the dust 1012 : 1.
• The gas is mostly hydrogen, and the dust is is mostly solid iron, carbon, and silicon compounds.
• Over forty different chemical molecules have been discovered in the space between the stars, including many organic molecules (contain C, H, and/or O and N).
• The gas plays an important part in the formation of new stars and the dust plays an important part in the formation of new planets.
Other Galaxies• The nearest galaxy is a dwarf spherical galaxy
80,000 light years from the solar system. • It is a dwarf galaxy because its diameter is about
1,000 light years as opposed to the Milky Way with about 100,000 light years in diameter.
• It is in the process of being pulled apart by the gravitational pull of the Milky Way, which is now known to have 11 satellite galaxies.
• The nearest galactic neighbor similar to the Milky Way in size and shape is Andromeda, with about 100 billion stars, gas, and dust turning in a giant spiral pinwheel.
The Big Bang Theory• This is the current model of how galaxies form and of
the creation of the universe.• According to this theory the universe had an
explosive beginning.• According to this theory all matter in the universe was
located together in a dense state from which it began to expand, even today.
• This theory indicates that the universe was all together at one point in time and the masses that move faster are now further from the center.
Big Bang Theory• A “big bang” of energy created a plasma of protons and neutrons.
This led to the formation of H nuclei.
• The H nuclei were pulled together by gravity into masses that would become the stars. The H nuclei fused into He nuclei, releasing enough energy that the star began to shine.
• The fusion process continued for billions of years, releasing energy as heavier and heavier nuclei were formed. Eventually the star materials were fused into nuclei around iron, the element with the lowest amount of energy per nucleon and the star used up its energy source.
• Larger, more massive dying stars explode into supernovas. Such an explosion releases a flood of neutrons, which bombard medium weight nuclei and build them up to more massive nuclei, all the way from iron up to uranium. These elements are then spread into space as dust which became the materials of which planets were made.
• The force of gravitational attraction provided the initial energy for the whole process.
As the universe expands the expansion carries galaxies away from each other at speeds that are proportional to their distances from each other. It doesn’t matter within which galaxy an astronomer resides, the other galaxies all appear to be moving away.
Hubble Space Telescope
• Images never before seen due to absence of atmosphere.
• An astronomical reflecting telescope with a mirror 94.5 inches (2.4 meters) in diameter; placed in orbit above the Earths atmosphere in April 1990.
Age of the Universe
• It is believed that the big bang occurred some 13.7 billion years ago expanding as an intense and brilliant explosion from a primeval fireball with a temperature of some 1012 K.
• The separation of the galaxies is actually accelerating, pushed by a mysterious force known as “dark energy”.
Review Exercises Chapter 14
• Applying the Concepts p. 372-373:
# 9, 10, 12, 16
• New Book:
p. 406-409 # 2, 4, 5, 6, 10, 13, 16, 17, 28, 29, 30, 31, 38, 39, 41, 48, 49, 50.
Review Chapter 14
• Light year, celestial equator, north and south poles.
• Nebulae and protostars, what are they?
• 3 sections of a star: core, radiation zone and convection zone. The densest is the core, the least dense is the convection zone.
• The larger the mass of the star the lower the lifespan of the star. They use fuel faster.
• Fusion reactions occur in stars-4 Hydrogen atoms are converted to Helium. This is how the energy is produced.
• Brightness of stars: light, magnitude and distance.
• Luminosity-brightness is a measure of this. Scale is 1-6 with 1 the brightest. The sun has a brightness of 4.8.
• The sun is of average luminosity, temperature, size, and mass.
• The color of the stars is related to their temperature, like other luminous objects. Form bluish white for the hottest to yellowish and then reddish for the coolest.
• Supernovas-Explosions of stars that leads to their destruction.
• Galaxies-Clusters of stars. The Milky Way is our galaxy.
• Parts of the Milky Way: Nucleus, disk and halo. The Sun is in one of the disks.
• The Andromeda galaxy-similar to the Milky Way.
• There is dust and gas in space. The gas gives rise to stars, the dust to planets.
• The Big Bang Theory-The faster moving galaxies are now further away. Everything originated at the same point.
• The Hubble Space telescope-Is out in space, there is no interference from the atmosphere.