The Mystery of Dark Matter
If you look at the night sky, you'll often see stars moving very quickly. In fact, they move much more quickly than they should according to their size and the laws of physics. Scientists do not completely understand why the speed of these stars is so high. But many believe the reason is that much of the universe is made up of something called "dark matter". Groups of stars called galaxies, such as the Milky Way, might even consist of ninety per cent dark matter.
How much something weighs depends on where it is. The same object weighs only half as much on Mars as it does on Earth and almost three times as much on Jupiter. So scientists prefer to talk about the mass of something rather than how much it weighs, because mass does not change. They can work out the mass of galaxies by measuring the distance between them and the speed they move. Recently, Dr. Jorge Penarrubia and a team from Edinburgh University discovered something interesting. The mass of the Milky Way is only half as much as the mass of another nearby galaxy, Andromeda. This seems strange, but dark matter may explain why.
Finding out more about dark matter could help us understand how the universe began, but this is not easy. Lots of scientists with different types of expert knowledge are working on the problem. The Edinburgh team is working with many other universities like the University of British Columbia.
We can't see dark matter, it's very difficult to measure and we can't find out its mass. Unlike stars, dark matter doesn't produce or reflect light. But we can make a good guess that it is there because of the way things move and the way light bends. Experts now think dark mater may be very different from the mater which we find on Earth. There may also be five times as much dark matter in the universe as ordinary matter.
The Swiss scientist Fritz Zwicky first gave dark matter its name in the nineteen-thirties. Researchers have been looking for it ever since. Today, technology such as the Large Hadron Collider is collecting more and more information but this technology cannot tell us everything. New ways of finding dark matter will be needed. Investigating dark matter may even mean we will need to start asking questions about the way we look at the universe, including the ideas of Albert Einstein.
Astronomers have taken the first ever image of a black hole, which is located in a distant galaxy (星系).The black hole is 500 million trillion km away and was photographed by a network of eight telescopes across the world. It was captured by the Event Horizon Telescope (EHT).
The announcement was made in Washington, Brussels, Santiago, Shanghai, Taipei and Tokyo. Details have been published today in Astrophysical Journal Letters.
Prof Heino Falckc, of Radboud University in the Netherlands, who suggested the experiment, told BBC News that the black hole was found in a galaxy called M87. "What we see is larger than the size of our entire Solar System," he said. "It has a mass 6.5 billion times that of the Sun. And it is one of the heaviest black holes that we think exists. It is an absolute monster, the heavyweight champion of black holes in the Universe."
The image shows an intensely bright "ring of fire", as Prof Falckc describes it, surrounding a perfectly circular dark hole. The bright halo is caused by very heated gas falling into the hole. The light is brighter than all the billions of other stars in the galaxy combined - which is why it can be seen at such distance from Earth. The edge of the dark circle at the center is the point at which the gas enters the black hole, which is an object that has such a large gravitational pull (万有引力),not even light can escape.
"It is remarkable that the image we observe is so similar to that which we get from our theoretical calculations. So far, it looks like Einstein is correct once again." said Dr Ziri Younsi, of University College London -who is part of the EHT cooperation.
Chinese scientists were involved in the observation through a telescope in Hawaii. They were also highly involved in follow-up data processing and theoretical analysis, said Shen Zhiqiang, head of the Chinese Academy of Sciences' Shanhai Astronomical Observatory and a member of the EHT international team.
Shanghai and Taipei were selected as two of the cities to hold news conferences, together with Washington, Brussels, Santiago and Tokyo, recognition of China's contribution.
"In the fields of astronomy, radio astronomy, and space astrophysics, China has made a significant contribution to this global project," Falcke said.
Today, I was sitting with some other students and teachers as the judges of the annual singing contest of Beijing National Day School (BNDS). Watching the wonderful performances on stage, I could not help1what happened last year.
Last year was the first year I came to the BNDS International Department. The first month at BNDS was almost a (n)2: Curiosity quickly3, replaced by a heavy workload. To make matters worse, I was 4a total stranger in a new environment. When I was in trouble, I was too5to turn to anyone for help. I shut the door to the outside world.
I thought I might continue to6in darkness by myself, until one day, I saw the7of the annual singing contest. If I was not brave enough to communicate in words, maybe I could8my heart out. Having made my decision, I joined the audition (试镜). Luckily, I9among more than 100 contestants and entered the top 32. After another three rounds of competition, I made10to the finals together with three other contestants.11more and more students knew that I joined the contest, they went to watch my performance, volunteered to12for me and then shared my singing videos on social media. It seemed that I became well-known overnight.
Finally, the big day came. When I13the nerve to walk onstage, I could not believe my eyes. The dark theater was suddenly lit up by14sticks, which were like stars in a dark sky. “Come on, Becky!” A shout broke the silence, followed by kind laughter. When it became15again, I began to sing.
The music started, which drew me back to16. Now I might not remember clearly what songs I sang last year, but I would never forget the17in the darkness. From then on, I had my18, made friends, and I even joined the singing club. Singing opens the door19a brand-new world. I know I will stay at BNDS, and I won't be20.
