An international team of astronomers used a database combining observations from the best telescopes in the world 【小题1】(detect) the signal from the active supermassive black holes of dying galaxies (星系) in the early universe. The 【小题2】(appear) of these active supermassive black holes is related to changes in the host galaxy. This means a black hole could have far reaching effects 【小题3】 the evolution of its host galaxy.

The Milky Way Galaxy 【小题4】 we live includes stars of various ages, including stars still forming. But in some other galaxies, 【小题5】(know) as elliptical (椭圆的) galaxies, all of the stars are old and about the same age. This indicates that early in 【小题6】(they) histories elliptical galaxies had a period of rich star formation that suddenly ended. Why this star formation stopped in some galaxies 【小题7】 not others is not well understood. One possibility is that a supermassive black hole disrupts(瓦解) the gas in some galaxies, 【小题8】(create) an environment unsuitable for star formation.

To test this theory, astronomers look at distant galaxies. Due to the limited speed of light, it takes time for light to travel across the void of space. The light we saw last night from an object 10 billion light years away 【小题9】(travel) for 10 billion years to reach Earth. Thus the light we see today shows us what the galaxy looked like when the light left that galaxy 10 billion years ago. So looking at distant galaxies is like looking back in time. But the longer distance also means that distant galaxies look 【小题10】(small), making study more difficult.

Have you ever wondered what happens to all of the old objects launched into space, such as rockets and satellites? It's called space junk, and much of it is still out there now. One large piece of space junk,   【小题1】 disused rocket, hit the dark side of the moon on March 4. The rocket's origin is not clear, but scientists know that it was massive— 【小题2】 （weigh）about 3 tons.

What is 【小题3】 （significance）about this space junk crash is that it draws attention to some of the potential 【小题4】 （danger）of space junk. First, the accumulation of space junk in Earth's orbit means that satellites and the International Space Station（ISS）are at risk. In 2016, tiny space debris（残骸）,   【小题5】 measured smaller than a millimeter, caused a tiny chip in the ISS' window. Imagine the damage that a 【小题6】 （large）piece of debris could cause. The European Space Agency website states that objects “up to 1 cm in size could 【小题7】 （able）an instrument or a critical flight system on a satellite” while objects over 10cm “could shatter a satellite or spacecraft into pieces”. In addition to potential damage 【小题8】 spacecraft and satellites, space junk also poses a threat to the Earth 【小题9】 （it）. Crashes can send debris into the atmosphere where it can remain for many decades. Some powerful collisions can even send large debris hurtling（猛冲）toward Earth's surface where it can affect the local environment. Leftover rocket debris can contain toxic materials that 【小题10】 （be）harmful to plants and animal life. Some people in Siberia have even reported serious health problems after rocket debris landed in their regions in 2012, a local doctor told the BBC.

Here’s the reality: humans will never live on an exoplanet (外星行星). That’s according to Michel Mayor, a physicist who was a winner of the Nobel Prize in physics this year.

“ 【小题1】 we are talking about exoplanets, things should be clear: We will not move there,” he told Agence France-Presse(AFP). He said he felt the need 【小题2】 (kill) all the statements that say, “OK, we will go to a livable planet if one day life is not possible on Earth.”

All of the   【小题3】 (know) exoplanets, or planets outside of our solar system,   【小题4】 (be) too far away to travel to, he said. “Even in the very optimistic case of a livable planet 【小题5】 is not too far, the time to go there is considerable,” he added.

Mayor shared half of the Nobel Prize this year along with Didier Quelos for   【小题6】 (discover) the first exoplanet in October 1995, over 4,000 other exoplanets   【小题7】 (find) in the Milky Way, but 【小题8】 (apparent), none of them can be reached.

Since the distance to the 【小题9】 (near) star outside of our solar system is about 70,000 times greater than the distance to Jupiter, all stars are effectively out of reach.

Mayor told the AEP: “We must take care of our planet; 【小题10】 is very beautiful and still absolutely livable.