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NATS1311 From the Cosmos to Earth

NATS1311 From the Cosmos to Earth. ATOM DEFINITION: The smallest unit of a chemical element that has the properties of the element. The atom consists of a nucleus with orbiting electrons surrounding the nucleus. NATS 1311 From the Cosmos to Earth. Nuclear stability diagram.

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NATS1311 From the Cosmos to Earth

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  1. NATS1311 From the Cosmos to Earth ATOM DEFINITION: The smallest unit of a chemical element that has the properties of the element. The atom consists of a nucleus with orbiting electrons surrounding the nucleus.

  2. NATS 1311 From the Cosmos to Earth . Nuclear stability diagram. Number of neutrons vs. number of protons in a nucleus.

  3. Radioactive Decay Processes • alpha decay • beta minus decay • electron capture • beta plus decay • Changes number of protons and neutrons in decaying nucleus • Type of decay protons neutrons nucleons • -2 -2 -4 • - +1 -1 0 • ec -1 +1 0 • +-1 +1 0 •  0 0 0 •  = gamma ray emission from nucleus NATS 1311 From the Cosmos to Earth

  4. NATS 1311 From the Cosmos to Earth Half life The time required for one half of a group of nuclei to decay into their daughter products. Sometimes called lifetime.

  5. NATS 1311 From the Cosmos to Earth .

  6. NATS 1311 From the Cosmos to Earth

  7. Besides radioactive decay of an unstable nucleus, nuclei undergo two other process to change for one element to another. • These are fission and fusion. • Fission: • Breaking apart a heavy nucleus into two lighter nuclei. • Requres a neutron to activate the process. NATS 1311 From the Cosmos to Earth

  8. NATS 1311 From the Cosmos to Earth .

  9. Besides radioactive decay of an unstable nucleus, nuclei undergo two other process to change for one element to another. • These are fission and fusion. • Fusion: • Combination of light nuclei into a heavier nucleus producing a large quantity of energy. • 4 hydrogen atoms combine into 1 helium atom. • This process requires extremely high temperatures and pressures and occurs in the core of stars. NATS 1311 From the Cosmos to Earth

  10. NATS 1311 From the Cosmos to Earth .

  11. Nuclear fission and fusion • Binding energy • Energy equivalent to missing mass of a nucleus. • Mass of hydrogen atom 1.0078 amu • Add mass of a neutron 1.0087 amu • 2.0165 amu • Mass of deuterium atom 2.0141 amu • Missing mass 0.0024 amu • 1 amu (atomic mass unit) = 931 MeV • from E= m c2 • Therefore 0.0024 amu = 2.2 Mev = 3.5x10-13 Joules • This is called the binding energy of deuterium NATS 1311 From the Cosmos to Earth

  12. NATS 1311 From the Cosmos to Earth • 1 gram of hydrogen produces 1 x 1011 Joules of energy. • Enough to boil 50 tons of water. • Binding energy per nucleon : • (the number of protons and neutrons in the Nucleus) • Total binding energy of atom • Number of nucleons in atom

  13. NATS 1311 From the Cosmos to Earth . Triple alpha process. Three helium atoms combine to form 1 carbon atom.

  14. NATS 1311 From the Cosmos to Earth . C-N-O Process. 4 Hydrogen atoms are added, one at a time to 12C, 13C, 14N, and 15N. The end products are 12C and a Helium atom. The net result is 4 hydrogen atoms form 1 helium atom.

  15. Element building • The process of element bulding continues by • adding the nucleus of one helium atom at a time to • 12C until 56Fe (Iron-56) is obtained. • 12C6 +4He2 -›16O8 • 16O8+ 4He2-› 20Nel0 • 20Nel0+4He2-› 24Mgl2 • • • • • • • 52Cr24 +4He2 -› 56Fe26 • The process stops here. • • maximum stability is reached • • the next element has a lower binding energy • and greater relative nuclear mass. NATS 1311 From the Cosmos to Earth

  16. NATS 1311 From the Cosmos to Earth FIG. 14.16 Figure 14.16 Overall, the average mass per nuclear particle declines from hydrogen to iron and then increases. Selected nuclei are labeled to provide reference points. (This graph shows the most general trends only; a more detailed graph would show numerous up-and-down bumps superimposed on the general trend.)

  17. NATS 1311 From the Cosmos to Earth FIG. 14.18 Figure 14.18 This graph shows the observed relative abundances of elements in the galaxy in comparison to the abundance of hydrogen. For example, the abundance of nitrogen is about 10-4, which means that there are about 10-4 (=0.0001) times as many nitrogen atoms in the galaxy as hydrogen atoms.

  18. NATS 1311 From the Cosmos to Earth . LAWS OF RADIATION Black body: An ideal object that absorbs all radiant energy that reaches its surface. It also emits radiation, the characteristics of which depend on its temperature. Planck's law: Planck developed a mathematical formula that explained radiation from black bodies. He assumed light existed in small quanta called photons E = hf where h = Planck's constant f = frequency of vibration

  19. NATS 1311 From the Cosmos to Earth . Spectrum: The amount of radiation given off at each wavelength. Stefan's law: (Rule 1) The energy emitted by a black body is proportional to the fourth power of its absolute temperature E ~T4 Wien's law: (Rule 2) The wavelength at which most energy is emitted from a black body is inversely proportional to its absolute temperature.

  20. NATS1311 From the Cosmos to Earth FIG. 6.10 Figure 6.10 Graphs of idealized thermal radiation spectra. Note that, per unit surface area, hotter objects emit more radiation at every wavelength, demonstrating Rule 1 for thermal radiation. The peaks of the spectra occur at shorter wavelengths (higher energies) for hotter objects, demonstrating Rule 2 for thermal radiation.

  21. NATS 1311 From the Cosmos to Earth

  22. NATS 1311 From the Cosmos to Earth . Spectral classes of stars Spectral Intrinsic Effective Class color temperature* O electric blue 38,000 B blue 30,000 A blue white 10,800 F yellow white 7,240 G yellow 5,920 K orange 5,240 M red 3,920 *For the hottest spectral type in class, such as A0 in class A. Each class is divided into 10 subgroups labeled 0 - 9. For example, B0 (hottest), or B9 (coolest) in class B.

  23. LUMINOSITIES • Luminosity: ~ r2T4 • Apparent magnitude: Apparent brightness of a • celestial body based on a • logarithmic scale of luminosity. • Magnitude scale: 1 is 2.5:1 • 2 is 6.3:1 • 5 is 100:1 • Absolute magnitude: Equivalent to the apparent • magnitude if star were • placed 10 parsecs (32.6 light years) from sun. NATS 1311 From the Cosmos to Earth

  24. NATS 1311 From the Cosmos to Earth 13.1. Figure 13.1 The inverse square law for light. At greater distances from a star, the same amount of light passes through an area that gets larger with the square of the distance. The amount of light per unit area therefore declines with the square of the distance.

  25. NATS 1311 From the Cosmos to Earth FIG. 13.8 Figure 13.8 A Hertzsprung-Russell (H-R) diagram, one of astronomy's most important tools, shows how the surface temperatures of stars, plotted along the horizontal axis, relate to their luminosities, plotted along the vertical axis. Note - vertical scale is a logarithmic scale. It has 11 decades of range.

  26. NATS 1311 From the Cosmos to Earth FIG. 13.8 • Blue supergiants: • Bluest, most luminous, hottest; moderately large stars; • low densities and large masses, very rare. • Example: Rigel

  27. NATS 1311 From the Cosmos to Earth FIG. 13.8 • Red supergiants: • Orange to red in color; the largest stars and among the brightest; large masses and extremely low densities; few in number. • Example: Betelguese

  28. NATS 1311 From the Cosmos to Earth FIG. 13.8 • Giants: • Yellow, orange, and red; considerably larger and brighter than the sun; average to larger than average masses and low densities; fairly scarce. • Example: Arcturus

  29. NATS 1311 From the Cosmos to Earth FIG. 13.8 • Middle main sequence stars: • White, yellow, and orange; stars higher than the sun on the main sequence are somewhat larger, hotter, more massive, and less dense than the sun; plentiful in number. • Example: Sirius

  30. NATS 1311 From the Cosmos to Earth FIG. 13.8 • Middle main sequence stars: • Stars below the sun on the main sequence are somewhat smaller, cooler, fainter, less massive, and denser than the sun; plentiful in number. • Example: Eridani

  31. NATS 1311 From the Cosmos to Earth FIG. 13.8 • Figure 13.8 • Red dwarfs: • Coolest and reddest stars on the low rung of the main sequence; considerably fainter and smaller than the sun; small masses and high densities; the most abundant stars. • Example: Barnard's star

  32. NATS 1311 From the Cosmos to Earth FIG. 13.8 • White dwarfs: • Mostly white and yellow; extremely faint and tiny by solar standards; enormously high densities; terminal evolutionary development; quite plentiful. • Example: The binary companion of Sirius

  33. NATS 1311 From the Cosmos to Earth . Life Cycle of a Star 1 Protostar Forms in a solar nebula - A swirling mass of gases and dust particles Gravitational collapse causes pressure and temperature increase. When temperature reaches 10 million degrees, hydrogen fusion in the core begins. Star's position on Hertzsprung-Russell (H-R) diagram: moves onto the main sequence,

  34. NATS 1311 From the Cosmos to Earth FIG. 14.5 Figure 14.5 The life track of a 1 solar mass star from protostar to main-sequence star. Time for the Sun to reach the main sequence is about 50 million years.

  35. NATS 1311 From the Cosmos to Earth . 2. Main Sequence Location on the main sequence depends on the mass of the star. Massive stars lie at the upper left; low mass stars at the lower right. O-type stars, more that 8 solar masses, have very high core temperatures and fuse hydrogen into helium very rapidly. Lifetime on main sequence is relatively short - millions of years.

  36. NATS 1311 From the Cosmos to Earth FIG. 13.10 Figure 13.10 Along the main sequence, more massive stars are brighter and hotter but have shorter lifetimes. (Stellar masses are given in units of solar masses: 1 solar mass equals 2 X 1030 kg.) Stars on the main sequence undergo hydrogen fusion in their cores.

  37. NATS 1311 From the Cosmos to Earth FIG. 14.6 Figure 14.6 Life tracks from protostar to the main sequence for stars of different masses.

  38. NATS 1311 From the Cosmos to Earth FIG. 14.8 Figure 14.8 The life track of a 1 solar mass star on an H-R diagram from the end of its main-sequence life until it becomes a red giant. When fusion ceases, core shrinks and star expands; becomes a sub giant. Luminosity increases and star becomes a red giant 100 times diameter of present sun. For Sun, this takes 1 billion years.

  39. NATS 1311 From the Cosmos to Earth FIG. 14.9 Figure 14.9 After a star ends its main-sequence life, its inert helium core contracts while hydrogen shell burning begins. The high rate of fusion in the hydrogen shell forces the star's upper layers to expand outward.

  40. NATS 1311 From the Cosmos to Earth FIG. 14.10 Figure 14.10 Core structure of a helium-burning star. (Triple alpha process) (b) Approximate relative sizes of a low-mass star as a main-sequence star, a red giant, and a helium-burning star. The scale is not precise; in particular, the size of the main-sequence star is even smaller compared to the others.

  41. NATS 1311 From the Cosmos to Earth FIG. 14.11 Figure 14.11 After the helium flash, the rapid initiation of the triple alpha process, a low-mass star's surface shrinks and heats, so the star's life track moves downward and to the left on the H-R diagram.

  42. NATS 1311 From the Cosmos to Earth FIG. 14.11 Figure 14.11 (b) This H-R diagram plots the luminosity and surface temperature of individual stars in a cluster, that is, those stars that have about the same luminosity (i.e., it does not show life tracks, just the location of these stars).

  43. NATS 1311 From the Cosmos to Earth . 3. Red Giant A star ends its main-sequence life when all the hydrogen in its core is fused into helium; core collapses raising its temperature to 100 million degrees. Its inert helium core contracts while hydrogen fusion in a shell outside the core begins. The high rate of fusion in the hydrogen shell forces the star's upper layers to expand outward causing the star to expand greatly in size, moving location on H- R diagram up and to the right to the giant region. Star becomes a red giant. 3. Red Giant When hydrogen in core is used up, core collapses raising its temperature to 100 million degrees. Triple alpha process converts 3 alpha particles into carbon nucleus releasing more energy. This is a rapid process, called helium flash, that causes core collapse to stop. Outer region of star cools. H to He fusion occurs in shell outside the core causing star to expand greatly in size, moving location on H-R diagram up and to the right to the giant region. Star becomes a red giant. Massive stars move to the supergiant region. Triple alpha process continues.

  44. NATS 1311 From the Cosmos to Earth . 3. Red Giant Outer region of star cools. The core collapses further until the triple alpha process which converts 3 alpha particles into a carbon nucleus begins, releasing more energy. This is a rapid process, called the helium flash, that causes core collapse to stop. More massive stars move to the supergiant region. Triple alpha process continues. 3. Red Giant When hydrogen in core is used up, core collapses raising its temperature to 100 million degrees. Triple alpha process converts 3 alpha particles into carbon nucleus releasing more energy. This is a rapid process, called helium flash, that causes core collapse to stop. Outer region of star cools. H to He fusion occurs in shell outside the core causing star to expand greatly in size, moving location on H-R diagram up and to the right to the giant region. Star becomes a red giant. Massive stars move to the supergiant region. Triple alpha process continues.

  45. NATS 1311 From the Cosmos to Earth FIG. 14.12 Figure 14.12 The life track of a 1 solar mass star from main-sequence star to white dwarf. The dashed line represents the rapid transition from planetary nebulae to white dwarf as the ejected outer layers dissipate, revealing the hot core.

  46. NATS 1311 From the Cosmos to Earth . 4. Planetary nebula When Helium fusion is complete and the core is carbon, helium fusion moves to the shell outside the core. A second expansion occurs. The star becomes unstable and eventually blows away all its outer layers, which are called the planetary nebula, leaving just the core.

  47. NATS 1311 From the Cosmos to Earth FIG. 14.13 Figure 14.13 Planetary nebulae occur when low-mass stars in their final death throes cast off their outer layers of gas, as seen in these photos. The hot core that remains ionizes and energizes the richly complex envelope of gas surrounding it. Ring Nebula Helix Nebula (c) Twin Jet Nebula

  48. NATS 1311 From the Cosmos to Earth . 5. White dwarf Remaining core of star that is less than 1.4 solar masses. Core cools slowly and becomes a black dwarf.

  49. NATS 1311 From the Cosmos to Earth FIG. 14.12 Figure 14.12 The life track of a 1 solar mass star from main-sequence star to white dwarf. The dashed line represents the rapid transition from planetary nebulae to white dwarf as the ejected outer layers dissipate, revealing the hot core.

  50. NATS 1311 From the Cosmos to Earth . Stars initially having more than 3 time the solar mass. Life cycle is similar to that of sun. Elements beyond carbon formed in core due to extremely high temperature. Alpha particles fuse with carbon nucleus to build heavier elements up to iron. Star eventually becomes unstable and explodes in a supernova event. During supernova event, elements heavier than iron are formed.

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