Presentation on theme: "Warm Up 6/6/08 If star A is farther from Earth than star B, but both stars have the same absolute magnitude, what is true about their apparent magnitude?"— Presentation transcript:
1Warm Up 6/6/08If star A is farther from Earth than star B, but both stars have the same absolute magnitude, what is true about their apparent magnitude?a. Star B has the greater apparent magnitude.b. Both stars have the same apparent magnitude.c. Star A has the greater apparent magnitude.d. Apparent magnitude is not related to distance.A Hertzsprung-Russell (H-R) diagram shows the relationship between ____.a. temperature and absolute magnitudeb. apparent magnitude and parallaxc. absolute magnitude and apparent magnituded. parallax and temperatureWhich of the following refers to the change in wavelength that occurs when an object moves toward or away from a source?a. spectroscopy c. wave theory of lightb. Doppler effect d. chromatic aberrationAnswers: 1) a. 2) a. 3) b.
3The Birth of a StarThe birthplaces are dark, cool interstellar clouds (nebulae)The initial contraction of the nebula can be triggered by the shock wave from an explosion of a nearby starOnce this begins, gravity squeezes the particles, pulling every particle toward the center
4The Birth of a StarThe Orion Nebula in normal color and infrared
5Protostar Stage The initial contraction can span millions of years The temperature of the nebula slowly rises until it is hot enough to radiate energy from its surfaceProtostar – a developing star not yet hot enough to engage in nuclear fusionWhen the core of a protostar has reached about 10 million K, pressure within is so great that nuclear fusion of hydrogen begins, and a star is bornHeat from hydrogen fusion causes the gases to increase their motion
7Concept Check What is a protostar? A protostar is a developing star not yet hot enough to engage in nuclear fusion.
8Main-Sequence StageMain-Sequence Stage – From the moment of birth until the star’s deathThe internal gas pressure struggles to offset the unyielding force of gravityHydrogen fusion will last for a few billion years and provides the outward pressure to keep the star from collapsingThe more massive a main-sequence star, the shorter its life spanA yellow star, like our sun, can remain in the main-sequence for approximately 10 billion yearsOnce the hydrogen fuel of the star’s core is depleted, it evolves rapidly and dies
10Red-Giant StageOccurs because the zone of hydrogen fusion continually moves outwardWhen all the hydrogen is consumed, the core no longer has outward pressure supporting it, and will contractThe core will grow hotter, the heat is radiated outward and expands the surfaceAs the surface expands, it cools down, producing its reddish colorThe core will eventually reach a temperature which allows Helium to Carbon fusionEventually all the fusion fuel will be consumedThe Sun will spend less than 1 billion years as a Red-Giant
11Red-Giant StageGlobular Star Cluster, some of the oldest stars in the universe
13Concept Check What causes a star to die? A star runs out of fuel and collapses due to gravity.
14Burnout and DeathWe do not know that all stars, regardless of their size, eventually run out of fuel and collapse due to gravityLow Mass Stars – consume fuel at a slow rate, may remain on main-sequence for up to 100 billion years, end up collapsing into white dwarfsMedium Mass Stars – go into red-giant stage, followed by collapse to white dwarf by blowing out their outer layer, and eventually light up planetary nebulaeMassive Stars – these have relatively short lifetimes, end with a large supernova (brighter than the sun if near Earth), this huge explosion blasts apart the starSupernova – an exploding star that increases in brightness many thousands of times
17Concept Check What is a supernova? A supernova is the brilliant explosion that marks the end of a massive star.
18White DwarfsWhite Dwarf – remains of low and medium mass stars, extremely small stars with densities greater than anything on EarthThe sun begins as a nebula, spends much of its life as a main-sequence star, becomes a red-giant, planetary nebula, white dwarf, and finally, black dwarf
20Neutron StarsThe smaller white dwarfs are actually a result of the more massive starsNeutron Stars – remnants of supernova events, stars that are smaller and more massive than white dwarfsElectrons are forced to combine with protons to form neutrons, because of how closely packed the matter is
22SupernovaeThe outer layer of a star is ejected, while the core condenses to form a very hot neutron starAs the star collapses, it rotates faster, and it generates very strong radio waves situated at its magnetic poles creating pulsesPulsar – a variable radio source of small size that emits radio pulses in very regular periods
24Black HolesBlack Hole – A massive star that has collapsed to such a small volume that its gravity prevents the escape of everything, including lightHow does astronomer find a black hole?They look for material that is being gravitationally swept up by a location that we cannot seeMaterial that is swept in should be very hot and emits large amounts of X-rays