Listen to part of a lecture in an astronomy class.
Okay, so we've been talking about the formation of stars, and today I want to focus on a specific type: brown dwarfs. Now, brown dwarfs are often called 'failed stars' because they never achieve the internal pressure and temperature needed to sustain hydrogen fusion. They form from collapsing clouds of gas and dust, just like regular stars, but they lack sufficient mass. Typically, a brown dwarf has a mass between about 13 and 80 times that of Jupiter. If they were less massive, they'd be planets. If they were more massive, they'd ignite fusion and become true stars. So what happens to these objects? They slowly cool and fade over time, emitting mostly infrared radiation. This makes them difficult to detect, which is why we only started finding them in significant numbers in the 1990s with infrared telescopes. One interesting recent discovery is that some brown dwarfs have weather patterns, like clouds and storms, similar to giant planets such as Jupiter. So they're kind of a bridge between stars and planets.
❓ Вопрос What is the main reason brown dwarfs are called 'failed stars'?
A. They are too small to be detected by optical telescopes.
B. They do not have enough mass to sustain hydrogen fusion.
C. They form from clouds of gas and dust instead of from stellar remnants.
D. They cool down too quickly and disappear into space.
✅ Правильный ответ
They do not have enough mass to sustain hydrogen fusion.
TOEFL Listening Tips
Skim the questions first to predict the content
Watch for signal words in lectures and conversations (however, actually, in fact)
For main idea questions, focus on the beginning; for detail questions, focus on examples and data
For attitude questions, pay attention to the speaker's tone and word choice
Take notes on keywords; don't try to write down every word
