Q&A Hero

Astronomy & Astrophysic

Q: Why do some radio galaxies appear to have lobes while some do not?
Q: How does Hubble's law relate cosmological redshift to distance?
Q: What is meant by a cosmological distance?
Q: Why do rich clusters of galaxies contain a larger fraction of ellipticals than normal?
Q: Contrast the sizes and membership of the Local Group and Virgo Cluster.
Q: What is the Tully-Fisher relation?
Q: Contrast Irr I and II in terms of structure.
Q: The elliptical galaxies are most like what part of our Milky Way? Explain.
Q: Is Hubble's tuning fork diagram a real evolutionary tool? Why?
Q: To which portion of the Milky Way are the Magellanic Clouds most similar? Why?
Q: What type of galaxy are the two Magellanic Clouds? How do we know this visually?
Q: Distinguish an E0 from an E7 galaxy.
Q: Distinguish an Sa from an Sc galaxy.
Q: Who invented the galaxy classes, and what three major groups did he invent?
Q: Hubble divided the spiral galaxies up in what six subtypes?
Q: Like Herbig-Haro objects associated with protostars, the lobes around radio galaxies are the result of ________ streaming from the active nucleus. Describe their alignment.
Q: The size of a quasar can be measured by ________.
Q: If the central engine for our Milky Way is a black hole of 3 million solar masses, then it has an event horizon about ________ kilometers across.
Q: The spectrum of radio galaxies indicates the energy is in ________ radiation.
Q: The central engine for active galaxies is believed to be a ________.
Q: The minimum period of light variations are used to find the ________ of the central engine in galactic cores.
Q: A possible evolutionary sequence is quasar to ________ to normal spiral galaxy.
Q: The most luminous quasars can give off ________ times more light that our own Galaxy.
Q: The radio lobes of active galaxies can span ________ of light years.
Q: Of all the active galactic nuclei, the ________ is the most energetic.
Q: Fast-moving electrons, moving close to c, in a strong magnetic field generate ________ radiation.
Q: The spectrum of radio galaxies matches ________ radiation, and is produced in strong magnetic fields.
Q: Active galaxies emit most of their energy in ________ wavelengths than visible.
Q: Most radio galaxies belong to Hubble's class ________.
Q: The most luminous objects known in the universe are ________.
Q: Dividing a distant galaxy's velocity by its distance will give you ________.
Q: A property common to active galaxies is that their energy is primarily ________.
Q: According to Hubble's Law, the larger a galaxy's redshift, the greater its ________.
Q: A galaxy with a blueshift is moving ________ Earth.
Q: The Tully-Fisher relation uses the ________ of the spiral to find its luminosity.
Q: For a galaxy 200 Mpc away, a useful standard candle would be the ________.
Q: The combined ________ of the Local Group binds them together.
Q: The Local Group consists of about ________ galaxies.
Q: The Tully-Fisher relation uses the rotational speed of the galaxy to measure its ________.
Q: At the top of the distance ladder sits ________.
Q: For measuring the distances to galaxies within 17 Mpc, we rely primarily on ________ variable stars.
Q: The largest nearby cluster of galaxies lies about 17 Mpc distant in ________.
Q: Some giant elliptical galaxies are found to have disks of gas and dust with star forming regions, and are probably the result of ________.
Q: The Milky Way and M31 in Andromeda both belong to the ________.
Q: The elliptical galaxies have compositions and shapes like the ________ of the Milky Way.
Q: Intermediate between E7 and Sa galaxies, ________ have a disk but no gas or dust.
Q: The vast majority of galaxies in the universe are ________ and ________.
Q: In the Hubble Classification scheme, the three main types of galaxies are ________, ________, and ________.
Q: The flattest of all the ellipticals are class ________.
Q: A tightly wound barred spiral would be classified as ________.
Q: Hubble divided the spirals into normal and ________ categories.
Q: In going from Sa to Sc, the size of the ________ reduces significantly.
Q: The optical classification of galaxies was pioneered in the 1930s by ________.
Q: Galaxies that look like huge globular clusters are Hubble type ________.
Q: The classical pinwheel-shaped galaxies are ________, according to Hubble.
Q: Our own Milky Way's Hubble class, according to the best data, is ________.
Q: X-ray observations of elliptical galaxies reveal large amounts of very hot ________ in their interior.
Q: The Magellanic Clouds are good examples of the ________ type of galaxy.
Q: The dustiest and flattest spiral galaxies are in Hubble's class ________.
Q: The spiral arms are blue from the presence of Population ________ stars in them.
Q: Elliptical galaxies contain only Population ________ stars and little gas and dust.
Q: A type Sa galaxy has a larger ________ than type Sc.
Q: When mass is accreted into a black hole, what fraction of the total mass-energy can be radiated away? A) 0.007% B) 0.08% C) 1.4% D) 20% E) 50%
Q: Not only does the central engine of active galaxies and quasars require a black hole, but also ________ to provide the radiative energy. A) globular clusters for food B) a very strong magnetic field from neutron stars C) a source of high-energy electrons for synchrotron radiation D) an accretion disk of infalling matter E) a high rate of rotation for the black hole
Q: Although theory says a massive black hole with an accretion disk should be emitting X-rays, many black holes emit A) mostly in the infrared. B) only in the visible. C) mainly in the gamma. D) virtually no radiation at all. E) equally across the entire electromagnetic spectrum.
Q: The energy radiated by a typical quasar requires that its black hole accrete about A) one solar mass a century. B) one solar mass a decade. C) one solar mass a year. D) ten solar masses a year. E) one solar mass a day.
Q: Synchrotron radiation produces a ________ spectrum. A) continuous nonthermal B) emission line C) absorption line D) continuous, with some emission lines E) continuous, with some absorption lines
Q: A billion-solar-mass black hole would still have a radius of only A) 20 AU. B) 15 pc. C) 150 kilometers. D) 3 kpc. E) two million light years.
Q: In the gap between quasars and normal spirals lie A) lobe radio galaxies. B) Irr II galaxies. C) S0 galaxies. D) Seyfert galaxies. E) Fisher-Tully galaxies.
Q: In what sense are the quasars "quasi-stellar"? A) Their energy production is hydrogen-helium fusion, like main-sequence stars. B) They are upscale versions of O stars, yet hundreds of times more massive. C) Their luminosity comes from the millions of supergiants that compose them. D) Their spectra are like those of ordinary stars. E) In short time exposures, their images looked stellar.
Q: What is true of the lobes of a radio galaxy? A) They are perpendicular to the galactic plane. B) They are hotter than the galactic core. C) They radiate primarily in X-rays. D) They extend out along the galactic plane. E) They form close to the edge of the galaxy.
Q: The key to finding quasar's distances was A) a Type I supernova in the spiral arm of 3C87. B) the huge red shifts of the hydrogen lines in 3C273. C) planetary nebula in M51. D) the luminosity of 3C52 from the Doppler shift and the Fisher-Tully relation. E) globular clusters in the halo of M87 in Virgo.
Q: Why is the energy source for active nuclei like Seyferts thought to be compact? A) The sources appear to be single stars in photos. B) Their energy appears to be non-stellar synchrotron radiation. C) The light can vary over short time intervals. D) We know the masses of the black holes that lurk there, and can find their radii. E) They are all strong radio sources, with assigned frequencies by their sizes.
Q: In active galaxies, their central engines may be temporarily fed by A) a sudden surge of star formation. B) a series of supernovae around the core. C) the sudden collapse of the core into a supermassive black hole. D) a close encounter with a neighbor galaxy. E) the fusion of helium into carbon in their cores.
Q: The nearest lobe radio galaxy to our Milky Way is A) the Whirlpool, M51. B) Centaurus A. C) M13 in Hercules. D) M42 in Orion. E) M87 in Virgo.
Q: While examining the spectrum of a galaxy, you find all the hydrogen lines are shifted to longer wavelengths. This galaxy is A) moving away from us. B) moving towards us. C) expanding explosively. D) blue shifted. E) not forming new stars.
Q: According to Hubble's Law, the greater a galaxy's redshift, the A) closer it is to us. B) younger it is. C) faster it's approaching us. D) farther it is from us. E) greater its mass.
Q: According to Hubble's Law, a galaxy with a recession velocity of 25,000 km/s will be A) 100 million pcs away. B) 400 million pcs away. C) 700 million pcs away. D) 1000 million pcs away. E) less than 1 million pcs away.
Q: Which statement about the Local Group is false? A) It contains about 55 member galaxies. B) Its notable spirals include the Milky Way, M31, and M33. C) Most of its members are dwarf elliptical and irregular galaxies. D) It contains the large radio galaxy Centaurus A. E) It is about three million light years across.
Q: What is the mass of the black hole believed to be at the center of the Milky Way? How do we know?
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