Q&A Hero

Q: For a white dwarf to explode entirely as a Type I supernova, its mass must be A) at least 0.08 solar masses. B) 1.4 solar masses, the Chandrasekhar limit. C) 3 solar masses, the Schwartzschild limit. D) 20 solar masses, the Hubble limit. E) 100 solar masses, the most massive known stars.

Q: If it gains sufficient mass from a binary companion, a white dwarf can become a A) brown dwarf. B) Type II supernova. C) Type I supernova. D) planetary nebula. E) black dwarf.

Q: Type II supernovae occur when their cores start making A) carbon. B) oxygen. C) silicon. D) iron. E) uranium.

Q: Which of the following best describes the evolutionary track of the most massive stars? A) diagonally to lower right, then vertical, then horizontal left B) horizontally right, diagonal to lower left, then horizontal right C) horizontal right, then a clockwise loop D) horizontal right E) vertically left, then straight down

Q: As a 6 solar-mass star leaves the main sequence on its way to becoming a red supergiant, its luminosity A) decreases. B) first decreases, then increases. C) increases. D) remains roughly constant. E) first increases, then decreases.

Q: As a star's evolution approaches the Type II supernova, we find A) the heavier the element, the less time it takes to make it. B) the heavier the element, the higher the temperature to fuse it. C) helium to carbon fusion takes at least 100 million K to start. D) photo disintegration of iron nuclei begins at 10 billion K to ignite the supernova. E) All of the above are correct.

Q: A 20-solar-mass star will stay on the main sequence for 10 million years, yet its iron core can exist for only a A) day. B) week. C) month. D) year. E) century.

Q: An iron core cannot support a star because A) iron is the heaviest element, and sinks upon differentiation. B) iron has poor nuclear binding energy. C) iron cannot fuse with other nuclei to produce energy. D) iron supplies too much pressure. E) iron is in the form of a gas, not a solid, in the center of a star.

Q: Of the elements in your body, the only one not formed in stars is A) hydrogen. B) carbon. C) calcium. D) iron. E) aluminum.

Q: You observe a low-mass helium white dwarf. What can you conclude? A) It is over 100 billion years old. B) It will soon be a Type II supernova. C) It is part of a binary star system. D) Its core is mostly carbon. E) It was once a blue supergiant.

Q: Virtually all the carbon-rich dust in the plane of the galaxy originated in A) low-mass stars. B) high-mass stars. C) planetary nebulae. D) white dwarfs. E) brown dwarfs.

Q: Black dwarfs are A) very common, making up the majority of the dark matter in the universe. B) often made from very low mass protostars that never fuse hydrogen. C) rare, for collapsing cores of over three solar masses are uncommon. D) rare, for few binary systems are close enough for this merger to happen. E) not found yet; the oldest, coldest white dwarf in the Galaxy has not cooled enough yet.

Q: The initial mass of a protostar generally determines the star's future evolution. But in some cases, what can alter this process? A) The star may be isolated in space, far from other influences. B) The star may be in a spectroscopic binary system. C) The star may gain mass by passing through a dark cloud. D) The star may collide with another, unrelated star. E) The star may drift away from the other stars in its formation cluster.

Q: When the outer envelope of a red giant escapes, the remaining carbon core is called a A) black dwarf. B) white dwarf. C) planetary nebula. D) black hole. E) brown dwarf.

Q: Which of these evolutionary paths is the fate of our Sun? A) brown dwarf B) supernova of Type II C) pulsar D) planetary nebula E) nova

Q: A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object? A) hypernova B) nova C) gamma ray burstar D) Type I supernova E) Type II supernova

Q: A(n) ________ represents a relatively peaceful mass loss as a red giant becomes a white dwarf. A) nova B) emission nebula C) supernova remnant D) planetary nebula E) supernova

Q: Compared to our Sun, a typical white dwarf has A) about the same mass and density. B) about the same mass and a million times higher density. C) a larger mass and a hundred times lower density. D) a smaller mass and half the density. E) a smaller mass and twice the density.

Q: Which of these is true of planetary nebulae? A) They are expelled by the most massive stars in their final stages before supernova. B) They are rings of material around protostars that will accrete into planets in time. C) They are ejected envelopes surrounding a highly evolved low-mass star. D) They are the envelopes that form when blue stragglers merge. E) They are the material which causes the eclipses in eclipsing binary systems.

Q: The outward pressure in the core of a red giant balances the inward pull of gravity when A) the electron orbits are compressed so much they are all in contact. B) the electrons and protons have combined to form neutrons. C) hydrogen begins fusing into helium. D) carbon fuses into heavier elements. E) iron forms in the inner core.

Q: A white dwarf has the mass of the Sun and the volume of A) Jupiter. B) Earth. C) Mars. D) the Moon. E) Eros.

Q: A solar-mass star will evolve off the main sequence when A) it completely runs out of hydrogen. B) it expels a planetary nebula to cool off and release radiation. C) it explodes as a violent nova. D) it builds up a core of inert helium. E) it loses all its neutrinos, so fusion must cease.

Q: Can a star become a red giant more than once? A) yes, before and after the helium flash B) yes, before and after the Type II supernova event C) no, the planetary nebula blows off all the outer shells completely D) no, it will lose so much mass as to cross the Chandrasekhar Limit E) no, or we would see them as the majority of naked-eye stars

Q: During the hydrogen shell burning phase A) the star grows more luminous. B) the star becomes less luminous. C) helium is burning in the core. D) the core is expanding. E) hydrogen is burning in the central core.

Q: The helium flash converts helium nuclei into A) boron. B) beryllium. C) carbon. D) oxygen. E) iron.

Q: A star is on the horizontal branch of the H-R diagram. Which statement is true? A) It is burning both hydrogen and helium. B) It is about to experience the helium flash. C) It is burning only helium. D) The star is contracting. E) The star is about to return to the main sequence.

Q: When a low mass star first runs short of hydrogen in its core, it becomes brighter because A) it explodes as a nova. B) helium fusion gives off more energy than does hydrogen. C) its outer, cooler layers are shed, and we see the brighter central core. D) the core contracts, raising the temperature and extending the hydrogen burning shell outward. E) the helium flash increases the size of the star immensely.

Q: What temperature is needed to fuse helium into carbon? A) 5,800 K B) 100,000 K C) 15 million K D) 100 million K E) one billion K

Q: When a star's inward gravity and outward pressure are balanced, the star is said to be A) in gravitational collapse. B) in thermal expansion. C) in rotational equilibrium. D) in hydrostatic equilibrium. E) a stage 2 protostar.

Q: A star (no matter what its mass) spends most of its life A) as a protostar. B) as a main-sequence star. C) as a planetary nebula. D) as a red giant or supergiant. E) as a T-Tauri variable star.

Q: The spectra of the oldest stars show the most heavy elements.

Q: Supernova 1987A matched the theoretical predictions for Type I supernovae well.

Q: Blue stragglers are among the first stars formed in a cluster.

Q: The blue stragglers represent the horizontal branch for globular clusters.

Q: Globular clusters are dominated by bright red supergiants at the top right of the H-R diagram.

Q: A 100 million-year-old open cluster will no longer contain any O-type stars.

Q: Novae and Type II supernovae are essentially the same phenomena.

Q: Type II supernova spectra are poor in hydrogen because stars that explode this way use up all their hydrogen before they leave the main sequence.

Q: Most of the energy released during a supernova is emitted as neutrinos.

Q: A carbon-detonation supernova starts out as a white dwarf in a close binary system.

Q: If a white dwarf gains enough mass from a nearby star to exceed its Chandrasekhar limit it will become a nova.

Q: Novae are more closely related to Type II than to Type I supernovae.

Q: Neutrinos can move faster than c, the speed of light, as was discovered in SN1987A in 1987.

Q: The number of Type I and Type II supernovae observed are approximately equal.

Q: Because they all involve the detonation of a carbon-rich white dwarf at the Chandrasekhar limit, all Type I supernovae are approximately equally luminous.

Q: Because they all involve formation of iron in the cores of massive stars, all Type II supernovae are approximately equally luminous.

Q: Chandrasekhar's limit is 1.4 times the mass of our Sun.

Q: Gold is rare since the only time it can be formed is during the core collapse of a supernova.

Q: While luminous enough to be seen with the naked eye, Supernova 1987A was, in fact, in our companion galaxy, the Large Magellanic Cloud.

Q: Supernova 1987A was the first supernova observed by astronomers since Galileo first turned a telescope to the heavens.

Q: The helium flash is followed within a few million years by the Type II supernova.

Q: A massive star can fuse only up to the element silicon in its core.

Q: A star system can become a Type I supernova several times.

Q: Our Sun will likely die as a Type I supernova in about five billion years.

Q: Supergiant stars are burning different fuels in several shells around the core.

Q: The formation of carbon requires a core temperature of about 100 million K, but iron takes much higher temperatures and pressures.

Q: A massive star may change its color and size notably, but its high luminosity remains fairly constant.

Q: Only low mass stars experience the temporary instability of the helium flash; high mass stars go directly into heavier element formation.

Q: Elements heavier than iron are formed mainly in supernovae.

Q: In the cores of the most massive stars, the electrons and protons fuse together and form neutrons.

Q: It is the formation of iron in an evolved giant's core that triggers a Type II supernova event.

Q: Solar mass stars eventually become hot enough for carbon nuclei to fuse together.

Q: White dwarfs were once the cores of stars that produced planetary nebulae.

Q: Contrast open and globular star clusters.

Q: What do all the stars in the Orion Association have in common?

Q: How does the mass of the protostar impact its future evolution?

Q: Why is infrared much better than visible light in studying star formation?

Q: Relate bipolar jets to the T-Tauri phase and Herbig-Haro objects.

Q: Why is M-42, the Orion Nebula, so important to us?

Q: Name four ways that the interstellar medium reveals its presence.

Q: How does the interstellar gas change the light of stars passing through it, even if no dust is also present?

Q: Why are emission nebulae ideal places to go hunting for brown dwarfs?

Q: How could we determine the amount of interstellar dust between us and a distant star?

Q: Why are star clusters ideal sites to study stellar evolution?

Q: Contrast the appearance of the H-R diagrams of a young open and old globular cluster.

Q: Contrast open clusters and associations.

Q: Contrast the brightest stars of young open and old globular clusters.

Q: Compare and contrast Jupiter and the brown dwarf in the Gliese 229 system.

Q: Jupiter and the Sun have almost the same composition and density; why isn't Jupiter also a star?

Q: What is a brown dwarf?