Supernovas are the most powerful and spectacular outbursts known in nature. What is called a Type II supernova is due to the collapse of a massive star, at least eight times as massive as the sun, that has used up its main nuclear fuel and produced a nickel-iron core. When this core can no longer support the pressure of the star’s outer layer, it collapses to form a neutron star of immense density. Over 2,500 million tons of neutron star packed into a matchbox. Its temperature is around 100,000 million degrees centigrade.

   Multitudes of neutrons are produced in the collapsed star, which pass directly through the star into space, and this release of neutrons causes the core to respond with a shock wave that moves outward.

   When it meets the material that is falling inward, the result is a catastrophic explosion. Sometimes most of the star’s material is blown away, leaving only a small, incredibly dense remnant that may be a neutron star or, in extreme cases, a black hole.

   A supernova is often more than 500 million times as luminous as the sun. A supernova remnant (SNR) may be detectable as a pulsar, an example of which is the Crab Nebula, known to be a remnant of the supernova observed in the year 1054. The 1987 supernova in the Large Cloud of Magellan had a low peak luminosity by supernova standards, only about 250 million times that of the sun. As its brightest the supernova shone as a star between magnitudes 2 and 3, even though it was 170,000 light-years away.

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions

What is the main topic of the passage?

Câu hỏi liên quan

• According to the passage, the doers of education are  .....................

• We sometimes think of writing as more real than speech because ..................

• This article is about ...............

ZUNIA12

• In the first paragraph, the word “elements” is closest in meaning to____.

• The author indicates that a hummingbird’s wings are different from those of other birds because .........

• The word “fledgling” in the third paragraph could be best replaced by which of the following?

• The author discusses cows and horses in paragraph 3 in order to_________

• According to paragraph 2, which of the following is not true about fungus growing on or near plants?

• What can be inferred about the government?

• What does the passage mainly discuss?

• The topic of this passage is______________.

• The word "fused" in line 2 is closest in meaning to .......

• Which of the following can be inferred about Moore's poems?

• What is NOT true about the Beatles?

• The word “emaciated” in the passage mostly means .......

• All of the following were mentioned in the passage as detriments to women in the business world EXCEPT .................

• What type of band is NOT mentioned in the article?

• The passage supports which of the following conclusions?

• It can be inferred from paragraph 1 that___________

• When she published her first book, Carson was closest to the age of .........