Astro 130 Practice Questions for Final – Flashcards

Which is NOT a characteristic of an AGN? A) existence of a "star-like" object at the center that dominates the galaxy's luminosity. B) all are much more luminous than normal galaxies. C) their spectra show radiation over a wide range of wavelengths. D) their host galaxy is always elliptical.

Which of the following does NOT imply that there is a supermassive black hole in the center of a galaxy? A) We see a positive and a negative spike in velocity (the "zigzag" in the plot) of the gas close to the center of the galaxy. B) The number of stars close to the center of the galaxy increases. C) Velocities of stars increase very close to the center of the galaxy. D) The center of the galaxy appears completely dark.

Which one of the following is NOT true about the relationship between the supermassive black holes (SMBHs) and their host galaxies? A) More massive the SMBH, more massive the host galaxy. B) More massive the SMBH, larger the host galaxy's bulge. C) Galaxies with SMBHs in their centers contain less gas as most of the gas was consumed by the black hole. D) A SMBH can influence properties of its host galaxy by feedback - jets and high-energy radiation from the accretion disk can suppress star formation in other parts of the galaxy.

Which of the following statements about an accretion disk is NOT correct? A) The outer part of the accretion disk orbits slower than the inner part. B) Accretion disk converts gravitational potential energy to heat energy, then to radiation. C) Because energy is transferred outward, the inner part of the accretion disk is cooler than the outer part. D) There is a gap between the innermost radius of the accretion disk and the event horizon of the central black hole.

How did astronomers measure the mass of Milky Way's supermassive black hole? A) They saw X-ray emission coming from the vicinity of the central black hole. B) By using MASERs. C) By tracing the orbits of gas clouds within the accretion disk. D) By tracing orbits of about a dozen stars near the center of the galaxy.

The best evidence for the existence of a supermassive black holes is A) large quantities of high-energy emission such as X-rays and gamma rays, and radio emission from relativistic electrons. B) huge dark regions in the centers of galaxies, where black holes have been sucking in the galaxy from the inside out. C) very high orbital velocities in a very compact region. D) evidence for jet velocities that approach the speed of light.

The mass of a supermassive black hole thought to power a typical bright active galactic nucleus is roughly A) 3 solar masses. B) 10 solar masses. C) 1 million solar masses. D) 1 billion solar masses. E) 1 trillion solar masses.

bservations show that supermassive black holes in centers of galaxies form from one very massive star that collapses into a black hole (about tens of masses of the sun) and it then grows by accretion. A) True B) False

How much mass does it take to power a quasar by accretion, where does the gas come from? A) It takes about 10 Msun per year; gas comes from the host galaxy itself. B) It takes about 1 Msun per year; gas comes from the host galaxy and from collisions with other galaxies. C) It takes about 100 Msun per year; gas comes from the host galaxy and from collisions with other galaxies. D) It takes about 1 million Msun per year; gas comes from the host galaxy itself. E) Quasars can only be powered by huge amounts of gas produced by many supernovae within the galaxy

Why do jets produce such large lobes, larger than the host galaxy of the SMBH that they come from? A) The material from the jet encounters the interstellar or intergalactic medium. B) Lobes and jets are actually not related and are a completely separate phenomenon. C) Because they carry a huge amount of gas from the vicinity of the black hole. D) The material carried by the jet is so hot that it has to travel very far from the SMBH in order to finally cool and expand.

Superluminal motion of jets coming from AGN can be explained: A) The jets encounter radiation from the surrounding material and this induces the knots in the jets to move at higher speeds, similar to MASERs. B) Radiation from the jet and radiation from the core of the galaxy travel along paths of different lengths are therefore take different amounts of time to reach us. C) The extreme gravity of the supermassive black holes accelerates the jets to move faster than the speed to light. D) The twisted magnetic field lines that produce the jets can actually accelerate the gas within the jets to move a little faster than the speed of light.

Why is it that we often see a jet only on one side of an AGN? A) The jet on the other side of the accretion disk is not as fast. B) The jet on the other side is there, it is just emitting light at a different wavelength. C) The jets that are pointed more directly toward us appear brighter and we see them more easily. D) The magnetic field lines of accretion disks around SMBHs are so twisted that they only point a jet in one direction.

Which of the following is NOT a piece of evidence supporting the conclusion that active galactic nuclei are powered by accretion disks around massive black holes? A) Observed radiation from the galactic center varies significantly in brightness in times as short as a few days. B) Infrared observations show that many stars are forming near the centers of active galaxies. C) Radio observations sometimes show long jets of material extending millions of light-years out from the galactic center. D) The total amount of radiation coming from the galactic center is, in some cases, comparable to the amount of radiation put out by 10 billion or more ordinary stars.

Which of the following is NOT true of quasars? A) Some quasars are more than a thousand times more luminous than the Milky Way. B) Quasars were more common in the past. C) Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time. D) Quasars are powered by the energy radiated by matter falling into a central black hole. E) Some quasars can change their brightness every few hours.

What is the difference between a Radio galaxy and a Blazar? A) Radio galaxies are AGN, while Blazars are just what we call a jet of an AGN B) Blazars are AGN, while Radio galaxies just have jets and radio lobes and are not really active. C) Both are AGN, but Blazar's jets are oriented 45 degrees from head-on. D) Both are AGN, but our line of sight is perpendicular to the jet when looking at Blazars. E) Both are AGN, but Blazar's jets are oriented nearly head-on.

According to the theory that active galactic nuclei are powered by supermassive black holes, the high luminosity of an active galactic nucleus primarily consists of A) the combined light of thousands of young, high-mass stars that orbit the black hole. B) light emitted by hot gas in an accretion disk that swirls around the black hole. C) intense radiation emitted by the black hole itself. D) radio waves emitted from radio lobes found on either side of the galaxy we see in visible light.

According to current understanding, what is a quasar? A) a very large galaxy thought to be formed by the merger of several smaller galaxies, typically found in the center of a galaxy cluster B) a galaxy with an unusually high rate of star formation. C) any object with an extremely large redshift is called a quasar. D) an active galactic nucleus that is particularly bright.

In some cases, a supernova in a binary system may lead to the eventual formation of an accretion disk around the remains of the star that exploded. All of the following statements about such accretion disks are true except A) the central object about which the accretion disk swirls may be either a neutron star or a black hole. B) X rays are emitted by the hot gas in the accretion disk. C) the radiation from an accretion disk may vary rapidly in time. D) the accretion disk consists of material that spills off the companion star. E) several examples of flattened accretion disks being "fed" by a large companion star can be seen clearly in photos from the Hubble Space Telescope.

Why does gas get heated when it is accreting? A) Gravity of the black hole stretches gas particles in the inner part of the accretion disk. B) The inner parts of the accretion disk orbit faster than the outer parts causing the gas to loose energy through friction. C) The gas in the inner part of the accretion disk orbits faster and faster moving gas always emits more energy. D) Since black holes are hot, the black hole heats up the gas nearby.

When we see X rays from an accretion disk in a binary system, we can't immediately tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following phenomena in this system. Which one would force us to immediately rule out the possibility of a black hole? A) sudden, intense X-ray bursts B) bright X-ray emission that varies on a time scale of miliseconds C) visible and ultraviolet light from the companion star D) spectral lines from the companion star that alternately shift to shorter and longer wavelengths

From a theoretical standpoint, what is a pulsar? A) a binary system that happens to be aligned so that one star periodically eclipses the other B) a star that is burning iron in its core C) a star that alternately expands and contracts in size D) a rapidly rotating neutron star E) a neutron star or black hole that happens to be in a binary system

How do we know that pulsars are neutron stars? A) We have observed massive-star supernovae produce pulsars. B) No massive object, other than a neutron star, could spin as fast as we observe pulsars spin. C) Pulsars and neutron stars look exactly the same D) Pulsars have the same upper mass limit as neutron stars do. E) none of the above