Answer These Astronomy Of Interstellar Gas Flashcards

The Predominant color of an emission nebula is A)Red, from the hydrogen Balmer H(alpha) line. What proccess makes an emission nebular glow C) light emitted when electrons jump between energy states in hydrogen atoms. Where are H II regions found A) around hot stars What radiation ionizes the hydrogen in an H II region? A) altraviolet radiation from O and B stars The bright stars at the center of an H II region (an emission nebular) are mostly A) young O and B stars Star clusters of the same type and structure appear to become fainter than expected, on the basis of the inverse square law alone, as distance from the sun increases. this is because C) some of the light is scattered and absorbed by interstellar dust and gas between distant clusters and Earth What is the most abundant element in the universe B) Hydrogren What is a protostar? A) a contracting sphere of gas produced by the collapse of an interstellar cloud with, as yet, no nuclear reactions occuring in its interior. In what region of the Hertzspring-Russell diagram will a newly formed protostar first appear when it begines to shine at visible wavelength? D) upper right side--relatively large luminosity but cool What places a limit on the lifetime of a star? B) amount of available nuclear fuel it contains What particular feature of stellar behavior is associated with the fact that a star is on the main sequence in the Hertzsprung-Russell diagram? A) The star is generating internal energy by hydrogen fusion in its core. Why does the core of the sun contain more helium and less hydrogen than the surface material of the sun? A) thermonuclear reactions have converted much of the original hydrogen in the core into helium What is the most important quantity on which the lifetime of a star depends? D) star's speed of rotation The event which marks the end of the main sequence lifetime of a star is c) the end of the hydrogen fusion in the core What is a red giant? D) a star burning hydrogen into helium in a shell around the core In the helium burning stage of a star's later life, the major chemical element produced in this process is D) Carbon After the helium flash in a low mass star D) helium burning begins in the core and hydrogen burning continues in the layers around the core A star ascending the red giant branch for the second time has A) no nuclear reactions in the core but a helium-burning shell outside the core, the whole surrounded by a dormant hydrogen shell A planetary nebula is C) an expanding gas shell surrounding a hot, white dwarf star The diameter of a typical neutron star of 1 solar mass is predicted to be approximately C) that of an average city, about 30 km What range in the electromagnetic spectrum was being observed when the first pulsars were discovered C) radio Neutron stars are believed to be created primarily by C) Type II supernovae (explosions in high mass stars) A pulsar is C) a rapidly spinning neutron star As time progresses, the pulse rate for most solitary pulsars is A) slowing down, because rotational energy is being used to generate the pulses. The fastest pulsars, called millisecond pulsars, have periods of about 1/1000 second. The reason they pulse so much faster than (for example) the Crab and Vela pulsars is that they D) were spun up by mass transferred on to them from a companion in a binary star system. A nova is a sudden brightening of a star that occurs when A) material from a companion star is transferred onto the surface of a white dwarf in a binary system and is subsequently blasted into space by a runaway thermonuclear explosion, leaving the white dwarf intact to repeat the process. An electromagnetic wave leaves the surface of a neutron star and travels outward. As the wave gets farther from the star's surface C) the frequency decreases and the wavelength increases. What are black holes called black holes A) Nothing, not even electromagnetic radiate, can escape from inside them. What is the likely final fate of a star that has a mass of 15 solar masses after completing its nuclear fusion burning phases? D) It collapses and becomes a black hole. If the sun were replaced by a 1-solar-mass black hole, then the Earth would A) continue to orbit the black hole precisely its present orbit If a black hole is truly black and has an escape velocity greater than the speed of light such that no light can escape it, where do the x-rays come from in the black hole candidates so far indentified? D) from the matter surrounding the black hole, which is highly condensed and hence very hot because of the intense gravitational field In the eighteenth century, Sir William Herschel used star counts in regions of the sky along the Milky Way to estimate the position of the center of the galaxy. He incorrectly concluded that the Sun was close to the galaxy's center. The reason for this erroneous conclusion was C) that he had no knowledge of the large quantity of dust between stars, that obscured the more distant regions of the galaxy Variable stars, such as Cepheid variables and RR Lyrae stars, are used in what important measurement in astronomy? C) distance measurement The method used by Harlow Shapley in 1917 to estimate the Sun's location in our galaxy was the measurement of A) the locations of globular clusters around the galaxy. Where is the solar system located in our galaxy C) in the galactic disk The spiral-arm structure of the Milk Way galaxy has been measured and evaluated most effectively by observtions of C) 21-cm radiation from the interstellar hydrogen and the positions of young stars The event that eventually settled the Shapley-Curtis debate about the "spiral nebulae" was C) Edwin Hubble measuring the distance to the Andromeda galaxy The method used by Hubble to determine the distance to the Andromeda Galaxy (M31), thereby establishing the concept of separate and individual galaxies throughout the universe, was the D) observation of Cepheid variable stars What is a barred spiral galaxy D) a galaxy with a bar through the nuclear bulge, and the spiral arms starting from the ends of the bar Which of the following galaxy types contain little or no interstellar dust or gas A) ellipticals What is a lenticular (S0) galaxy? D) A galaxy with a disk and central bulge like a spiral galaxy, but the no spiral arms The Hubble relationship shows a proportionality between the distance to a galaxy and the D) overall redshift of a galaxy's spectrum What is believed to be the origin of giant elliptical galaxies A) They grew by devouring smaller galaxies in galactic cannibalism As much as 90% of the matter in the universe may be unseen "dark matter." Where is this dark matter? D) It appears to be concentrated in spherical haloes around galaxies, but extending several times the radius of visible matter An intense radio source is found to coincide with a starlike object whose spectrum contains a pattern of intense emission lines in the visible range that matches that of the Lyman UV hydrogen spectral lines, but is very redshifted. What is this object? A) a quasar The fact that quasars can be detected from distances where even the biggest and most luminous galaxies cannot be seen means that A) they must be intrinsically far more luminous than the brightest galaxies How do we determine the distance to a quasar D) the Hubble velocity-distance relation is used once spectroscopy gives a redshift value An electron moving in a magnetic field in space is forced to follow a spiral pattern. As it does so it will emit B) synchrotron radiation, mostly radio waves Which observational fact about quasars and their behavior is perhaps the most extraordinary D) Energy output equivalent to 1000 galaxies from a volume as small as our planetary system. Why are there no nearby (and thus "young") quasars A) Eventually, most of the accretion disk falls into the black hole and the "central engine" runs out of fuel. void void