Download Stellar Evolution and the Search for Extraterrestrial Intelligence and more Exams Nursing in PDF only on Docsity! ASTRO 7N EXAM 2 2024/2025 WITH 100% ACCURATE SOLUTIONS A high-luminosity star... A. is always at a larger distance than a low-luminosity star B. emits more light than a low-luminosity star C. is always redder than a star with a lower luminosity D. is at a lower temperature than a low-luminosity star E. is always at a smaller distance than a low-luminosity star - Precise Answer ✔✔B If a red giant appears the same brightness as a red main sequence star, which one is further away? A. the red giant B. we cannot tell C. it depends on the phase of the moon D. the main sequence star E. they are at the same distance - Precise Answer ✔✔A The heaviest nuclei of all are formed... A. during helium burning B. as part of the p-p chain C. during the carbon burning D. during supernova explosion E. during all stages of stellar evolution of massive stars - Precise Answer ✔✔D Fill in the blank in the following chemical reaction that occurs in the Sun: Hydrogen-2 + proton = + energy: A. hydrogen-2 B. Hydrogen-1 C. Helium-3 D. Carbon-12 E. Helium - 4 - Precise Answer ✔✔C Which of the following has the smallest radius? A. type A main sequence star B. main sequence star with surface temperature 8000K C. type K main sequence star D. white dwarf E. neutron star - Precise Answer ✔✔E Why does the main sequence part of a star's life end? A. the helium in the core is exhausted what makes the sun stable? - Precise Answer ✔✔balance of gravity (inward force) and gas pressure in its hot interior (outward force) What causes gas pressure in sun's core and at what temp is this process occurring? - Precise Answer ✔✔nuclear fusion and 15 million degrees kelvin Relative to earth what is mass and diameter of sun? - Precise Answer ✔✔diameter is 109x earth; mass is 333,000x earth Luminosity = watt light bulbs - Precise Answer ✔✔4x10^24 100 watt light bulbs how much of the solar system's mass is in the sun? - Precise Answer ✔✔99.9% how long has the sun been shining? - Precise Answer ✔✔4.5 billion years How much longer will the sun shine> - Precise Answer ✔✔5.5 billion years Sunspots - Precise Answer ✔✔slightly-cooler regions on the sun's surface due to magnetic activity preventing hot material from rising in that region ; have 11 year cycles Nuclear Fusion - Precise Answer ✔✔long lasting source of energy in stars: 4 protons combine to make helium-4 (2 protons and 2 neutrons) and release energy in gamma rays proton-proton chain - Precise Answer ✔✔step 1: two protons collide at very high speed, and stick together; one of them changes into a neutron; ends with deuterium nucleus (2H: 1 proton and 1 neutron bound together), plus released energy Step 2:deuterium nucleus from step 1 collides with another proton and makes a Helium-3 nucleus (3He: 2 protons and 1 neutron) plus some more excess energy released step 3: two helium-3 nuclei combine to make a helium-4 nucleus (4He: 2 protons and 2 neutrons), releasing back 2 protons in the process and some more extra energy How much energy is required to cause collisions during each step of "p- p chain" - Precise Answer ✔✔a lot of energy what is generated and released at each step of the "p-p chain" - Precise Answer ✔✔energy!! What is the equation that energy output form the p-p chain comes from? - Precise Answer ✔✔E=mc^2 How does the mass of a helium-4 nucleus compare to the mass of 4 protons - Precise Answer ✔✔it is much less that the 4 protons What happens to some of the mass of the helium-4 nucleus? - Precise Answer ✔✔converted to energy in the form of gamma-ray photons The core of the Sun is - Precise Answer ✔✔at the center; high density and temperature; where nuclear reactions occur and gamma rays are produced radiative zone of the sun - Precise Answer ✔✔photons are repeatedly re- absorbed and re-emitted; the energy of an individual photon can take on average 170,000 years to pass through convective zone of sun - Precise Answer ✔✔hot gas rises and cold gas sinks; light traverses in 1 week photosphere of sun - Precise Answer ✔✔temperature 5,780 K; this is the "surface" of the sun that we see; photons have been converted to visible wavelengths; can see "granules" due to convection bringing material up and down in cells chromosphere of sun - Precise Answer ✔✔red or orange color; temperature about 4,500 K; we see through this, down to the photosphere How many parsecs away is a star with a measured parallax angle of 0.1 arcsecs? - Precise Answer ✔✔10 parsecs away. (1/0.1) how many parsecs away is a star with a parallax angle of 0.02? - Precise Answer ✔✔50 parsecs away (1/0.02) Hertsprung-Russell diagram (H-R diagram) - Precise Answer ✔✔A graph that plots luminosity v. temperature of stars. The y-axis displays increasing luminosity and the x-axis displays decreasing temperature. Hertsprung-Russell diagram (H-R diagram) - Precise Answer ✔✔ H-R Diagram horizontal axis - Precise Answer ✔✔stars' surface temperature; increasing from left to right what color are cooler stars? - Precise Answer ✔✔redder (around 2,300 K) What color are hotter stars? - Precise Answer ✔✔bluer (around 40,000 K) Major spectral classes of stars (run hotter to cooler) - Precise Answer ✔✔O - B - A - F - G - K - M O - B - A - F - G - K - M - Precise Answer ✔✔oh be a fine guy kiss me How is spectral class determined? - Precise Answer ✔✔using the absorption spectrum, where absorption lines from different chemical elements with different levels of ionization arise at different temperatures H-R diagram vertical axis - Precise Answer ✔✔luminosity, expressed in terms of the luminosity of the sun ( "L⊙" ) What is the closest star and how far is it from the sun? - Precise Answer ✔✔Alpha centauri 4.3 light years (1.35 parsecs) from the sun part of triple star system, with its brightest member similar to sun Properties of nearest stars - Precise Answer ✔✔cool dim fall on the lower right of the H-R diagram What is the brightest star in the nighttime sky? - Precise Answer ✔✔Sirius the Dog Star twice as massive as Sun it has a binary companion star, a white dwarf Properties of "brightest stars" - Precise Answer ✔✔varied properties red and blue, low and high luminosity, some on the lower right of H-R diagram, but others near where the sun is, some on the upper left and some on the upper right ( red giant region) what are the "brightest stars" biased towards? - Precise Answer ✔✔stars that already have high luminosities, so they appear bright to us even at large distances; we simply cannot see low-luminosity stars if they are too far away (even in great number) Properties of a star - Precise Answer ✔✔luminosity, mass, size, temperature, and age sizer and temperature directly affect luminosity, as in: L ∝ R^2 x T^4 - Precise Answer ✔✔- a larger size = larger light-emitting surface area = greater luminosity - higher temperature = much greater luminosity (also peaks in bluer colors) Where are the main sequence stars located on the HR Diagram? - Precise Answer ✔✔in a band from lower right across to upper left - around the slightly -wavy red line in the example H-R diagram What are stars during in their cores on when on the main sequence? - Precise Answer ✔✔Hydrogen and helium (by the p-p chain) For stars on the main sequence higher temp means after helium burning is exhausted, what is burned? - Precise Answer ✔✔carbon burning and then even heavier nuclei burning (turning to red giant) "onion skin" model - Precise Answer ✔✔concentric shells of fusion zones involving different chemical elements, with the heaviest gong on towards the core (after nuclei burning) when does burning in the main sequence stop? - Precise Answer ✔✔stops around iron (Fe) because iron is very stable and reactions involving iron don't produce much energy - instead cost more energy than they release "Type II" supernova - Precise Answer ✔✔a violent explosion with the star's core left behind; the explosion itself creates a short-lived highly- energetic environment which briefly makes possible the fusion of elements heavier than iron - like gold, silver, etc. What happens if the remaining core is about 1.4-3 solar masses? - Precise Answer ✔✔it becomes a neutron star - radius about 5-6km or roughly city sized Blackholes - Precise Answer ✔✔the end state of the highest mass stars (> about 40 solar masses), left behind after a supernova explosion Why can't light escape black holes? - Precise Answer ✔✔because the gravity of these collapsed (very dense) objects is so great Do black holes suck things in? - Precise Answer ✔✔black holes do not suck things in; if you are far enough away from them, they act like normal objects with the same mass event horizon of a black hole - Precise Answer ✔✔the spherical boundary around a black hole from within which nothing can escape - not even light (i.e. the "escape velocity" within this distance exceeds the speed of light - :nature's speed limit" nothing can go faster) what can the speed of the orbit of a star in a binary system with a black hole be used to measure? - Precise Answer ✔✔the black hole's mass the intense gravity around a black hole warps space so that a clock appears to slow down as it falls in; that is, light's delivery of the image of the clock to an observer outside is delayed more and more as the clock nears the event horizon - Precise Answer ✔✔ what do strong tidal forces that operate near the black hole do - Precise Answer ✔✔cause objected to be stretched out because the force on the nearer part can be so much greater than the force on the farther parts singularity (black hole) - Precise Answer ✔✔at the center of the black hole; a point of infinite density if a star begins with a mass <about 8 solar masses (fate of star) - Precise Answer ✔✔- the core becomes a white dwarf - collapse stops because of degeneracy pressure of electrons; core radius same as earth's - the white dwarf is surrounded by released outer layers - a planetary nebula if a star begins with about 8-40 solar masses (fate of stars) - Precise Answer ✔✔- final core-collapse is preceded by a Type II supernova - the core becomes a neutron star - collapse stops because of degeneracy pressure of neutrons; radius 5-6 km (city-size) If a star begins with > about 40 masses (fate of stars) - Precise Answer ✔✔- final core-collapse is preceded by a type II supernova - the core becomes a black hole -- collapse does not stop; all the mass becomes concentrated at a singularity habitable zone - Precise Answer ✔✔the region around a star where liquid water could be present on a planet's surface - not too hot as to be boiled off or dried out, and not too cold as to be permanently frozen over - a less massive star would have habitable zone closer to the star - a more massive star would have the habitable zone farther from the star can life exist in extreme environments? - Precise Answer ✔✔yes: deep underground; in near or total darkness; high acidity; high radiation; in methane ice; extreme heat and/or pressure