Radio galaxies and quasars--quasi-stellar radio sources--usually

Radio galaxies and quasars--quasi-stellar radio sources--usually display two symmetric, radio-emitting lobes. These sources can stretch more than 10 million light years across--more than twenty times the visible extent of the typical host galaxy, and more than 100 million times the diameter of the Milky Way.

In 1971, Martin J. Rees suggested that hidden engines located within the nuclei of the parent galaxies generate the energy needed to power the giant radio lobes. He proposed that high-speed particles shooting along narrow channels could transport this energy. A few years later other investigators demonstrated that, in many sources, jet-like features do seem to connect a radio-bright core in the galaxy’s nucleus with knots of radio emissions emanating from the outer extremities of the lobes. The nature of the engine that powers the processes in radio galaxies and quasars is still a mystery, but most astronomers think a massive rotating black hole lies behind all the commotion. Theorists commonly suppose that material spiraling toward a black hole becomes compressed and heated to a temperature of millions of degrees before it vanishes into the hole’s interior. The superheated particles circling the hole may be responsible for various exotic phenomena that occur in and around the centers of active galaxies, such as the formation of radio jets.

1. According to the passage, which one of the following is an accurate statement concerning radio-emitting lobes?

A. They are powered by superheated particles spiraling toward black holes.
B. Their exact energy source remains a question for scientists.
C. They stretch more than 10 million light years across.
D. They are probably responsible for the formation of radio jets around the centers of active galaxies.
E. They are always symmetric in their orientation.


2. According to the passage, scientists' hypotheses about black holes and their part in radio-emissions would be best supported if which of the following were found to be true?

A. Some particles become greatly condensed and raised to high temperatures as they near the entrances to black holes.
B. Many exotic phenomena have been observed in and around the centers of active galaxies.
C. High-speed particles do, in fact, shoot along narrow channels and transport energy from quasars and radio galaxies to their lobes.
D. Particles inside black holes have been shown to reach temperatures of several million degrees.
E. Radio emissions of radio galaxies were found to have different wavelengths from those of quasars.


3. The primary purpose of the passage is to

A. point out that scientists have been unable to find empirical proof of the existence of black holes
B. summarize the findings of Martin J. Rees regarding the existence of radio-emitting lobes
C. describe the way in which radio galaxies are formed
D. discuss radio-emitting lobes and possible ways by which they may be powered
E. show that radio galaxies and quasars are more alike than was previously thought


4. According to the passage, some scientists believe which of the following about the formation of radio jets?

A. Only the strong gravity of a black hole can control them.
B. Such emissions are responsible for the symmetric, radio-emitting lobes on radio galaxies and quasars.
C. such processes may be powered by particles at high temperatures circling the outside of black holes.
D. Their energy is so powerful as to preclude destruction by any known astronomical force.
E. They could only be produced from a symmetrically-shaped lobe.


5. The author suggests that although the research of Martin J. Rees helped scientists to form a theoretical model for radio galaxies, it failed to explain

A. why the radio lobes are of such massive size
B. that radio energy is carried by high-speed particles
C. how the energy source that produces radio emissions actually works
D. how radio jets are similar to other exotic phenomena occurring outside entries to black holes
E. what determines the direction in which the radio jets point


6. It can be inferred that the passage mentions the investigators’ demonstration (Text in Red) in order to

A. argue for Martin Rees' theory that a massive, rotating black hole is behind all the commotion
B. discuss the belief that superheated particles circling the black hole may help form radio jets
C. explore the possibility of hidden engines located in the nuclei of parent galaxies
D. support Martin J. Rees's theory that energy could be carried by high-speed particles through narrow channels
E. prove that most astronomers agree with Rees and want to support his work


7. According to the passage, scientists formulated the massive rotating black hole theory in order to

A. explain how radio signals travel from the parent galaxy to the radio-emitting lobes
B. demonstrate how jet-like features connect to a radio-bright core in the galaxy's nucleus
C. account for various unexplained phenomena in the radio emissions of quasars and radio galaxies
D. test the theory that radio emissions must be reduced to superheated particles in order to power themselves
E. provide a possible explanation for a power source in radio galaxies and quasars