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Washtenaw Community College *

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MISC

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Astronomy

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Apr 3, 2024

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docx

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What produces interstellar reddening? Dust grains in interstellar clouds preferentially block blue light from background stars What determines if a cloud will collapse? Compare Gravitational Binding Energy to Thermal Energy.More formally: compare cloud mass to Jeans mass. Gravitationally bound clouds are the ones that can collapse into stars Which of the following changes to a molecular cloud would not increase its chances of forming stars? increase in temperature How did the clouds from which the first generation of stars formed differ from current star -forming clouds? They were hotter Which of the following does not prevent molecular clouds from collapsing? degeneracy pressure How did the first generation of stars differ from stars that form today? They were all high-mass stars. What happens to the energy released by collapse? The binding energy becomes more negative as the cloud collapses (-GM2/R). Total energy is conserved True or False? If you could look inside the Sun today, you’d find that its core contains a much higher proportion of helium and a lower proportion of hydrogen than it did when the Sun was first born. True, the Sun is about halfway through its hydrogen-burning life, so it has turned about half its core hydrogen into helium. Suppose the universe contained only low-mass stars. Would elements heavier than carbon exist? No, the core temperatures of low-mass stars are too low to fuse other nuclei to carbon, so it would be the heaviest element. When the Sun dies, it will make? A White Dwarf What is a neutron star? A neutron star is the ball of neutrons left behind by a massive- star supernova. If the beam from a spinning neutron star hit Earth? we would call it a pulsar How do we know pulsars are neutron stars? Pulsars spin too fast to be as large as a white dwarf. What would happen to Earth’s orbit if our sun suddenly became a black hole? Earth’s orbit would not change. True or False?: We can detect black holes with X-ray telescopes because matter falling into a black hole emits X -rays after it smashes into the event horizon. False, black holes do not have surfaces for material to smash into. The X -ray emission comes from gas as it falls toward the event horizon and heats up. What would it be like to visit a black hole? If the Sun shrank into a black hole, its gravity would be different only near the event horizon How are the lives of stars with close companions different? Star that is now a subgiant was originally more massive. As it reached the end of its life and started to grow, it began to transfer mass to its companion (mass exchange)Now the companion star is more massive About how long does light take to reach us from the nearest star besides the Sun? (The Sun takes 8 minutes.) about four years About how long does light take to cross the Milky Way Galaxy? about 100,000 years Why do orbits of disk stars bob up and down? Gravity of disk stars pulls them toward the disk. How long does it take the Sun to complete one orbit of the Milky Way? 230 million years Gas is added to the interstellar medium by supernovae and planetary nebulae. What kind of gas would you expect that to be? gas that has a mix of heavier elements in it, such as carbon, oxygen, silicon, iron,etc Why do reflection nebulae look bluer than the nearby stars? For the same reason that our sky is blue! When we look at a very distant galaxy, billions of light years away, we see? when it was younger, when the whole universe was younger Why does ongoing star formation lead to a blue white appearance? Short lived blue stars outshine others If you want to find elliptical galaxies, you have better luck looking in clusters of galaxies than elsewhere in the universe. Yes, galaxy clusters have a much higher percentage of elliptical galaxies than do other parts of the universe. Which of the following could be used as a standard candle? a star of known spectral type, a Cepheid variable whose period of pulsation is related to its luminosity what are the three major types of galaxies? elliptical, spiral and irregular How are galaxies grouped together? Spiral galaxies are often found in groups of galaxies, Elliptical galaxies are much more common in huge clusters of galaxies Suppose you tried to determine where we are in the galaxy by looking in different directions to see how many stars you could see. If you did this, you would pinpoint our location? in the center of the galaxy. Where will the gas be in 1 trillion years? locked into white dwarfs and low-mass True or False? : The Sun’s velocity around the Milky Way tells us that most of our galaxy’s dark matter lies within the Sun’s orbit. False, the Milky Way’s rotation curve remains flat well beyond the orbit of the Sun, indicating that the majority of the Milky Way’s mass lies beyond the Sun’s orbit. Where does the energy released by a massive black hole come from? gravity Matter falling into supermassive black holes in the centers of galaxies is thought to be the source of? jets that shoot far into space.active galactic nuclei. strong radio emissions. quasars. Since quasars are mostly found at very great distances? there must have been more of them when the universe was young. we can use their light to study the intergalactic medium between us and them. What is the lookback time of the most distant galaxies we can observe? 13 billion years You observe a galaxy moving away from you at 0.1 light-years per year, and it is now 1.3 billion light-years away from you. How long has it taken to get there? 3 billion years What is likely to happen if two galaxies collide? Their mutual gravitational pull will greatly distort each galaxy. Starbursts –greatly enhanced star formation–may occur. How does the universe’s expansion affect our distance measurements? Distances between faraway galaxies change while light travels. Astronomers think in terms of lookback time rather than distance Expansion stretches photon wavelengths, causing a cosmological redshift directly related to lookback time

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