Observing the past is certainly the easy part. Glancing at the night sky, you will see history, a lot of history-the stars you see are not in their present state, but in their state of light. As far as we know, Polaris, our loyal partner, actually went out at any time after the beginning of the 4th century in 65438+ 10 last year, or 1854, or 14, because this information has not yet arrived here. The best we can say is that it is still shining 680 years ago today. Stars are dying. What Robert Evans did better than others was that he discovered the moment when celestial bodies held farewell ceremonies.
During the day, Evans is an amiable retired pastor of the Australian Unified Church, doing some temporary work and studying the history of religious movements in the19th century. At night, he quietly became the god of the sky, looking for supernovae.
When a huge star-a star bigger than our sun-collapses, it will explode spectacularly, releasing the energy of 654.38 billion suns in an instant, which is brighter than the brightness of all the stars in our own galaxy combined. Thus, a supernova was born. "This scene is like suddenly detonating 1 trillion hydrogen bombs." Evans said. He also said that if the supernova explosion occurred only 500 light-years away from us, we would be finished-"completely smashed the pot." He said happily. However, the universe is vast, and supernovae are usually far away from us and will not do us any harm. In fact, most of them are unimaginable, and their light is only a faint flash to us. A month or so, you can see them. The only difference between them and other stars in the sky is that they used to occupy a little blank space. Evans is looking for this unusual accidental flash in the night sky.
To understand how superb this skill is, let's imagine spreading a black tablecloth on a standard dining table and then sprinkling a handful of salt. We compare scattered salt particles to a galaxy. Now, let's imagine adding up 1500 such tables-enough to form a 3-kilometer-long straight line-and then sprinkling a handful of salt on each table at will. Now, add another grain of salt to any table and let Robert Evans walk in the middle. He saw a grain of salt at a glance. Salt is a supernova.
Evans is an outstanding genius. In the book Anthropologist on Mars, oliver sacks has a chapter about withdrawn scholars and devoted a paragraph to Evans-but he immediately added: "He never said he was withdrawn." Evans, who has never seen a saxophone, sneers at the suggestion that he is withdrawn or a scholar, but he is not sure why he has such a genius.
Evans' home is in a bungalow on the edge of Brooke village in hazel, with a quiet and picturesque environment. Sydney ends here, and then there is the endless Australian jungle. Once, I visited him and his wife Elaine. "I seem to have the ability to remember the star field." He told me that he was embarrassed. "I'm not particularly good at other things," he added. "I don't even remember my name."
"I don't remember where I put my things." Elaine shouted from the kitchen.
He nodded frankly again, grinned, and then asked me if I would like to see his telescope. I think Evans has a good observatory in the backyard-a little Mount Wilson Observatory or Paloma Observatory, with a sliding dome roof and a convenient mechanical chair. In fact, instead of taking me out of the house, he took me into a crowded storage room not far from the kitchen, which was full of books and documents. His telescope-a white cylinder, the size and shape of which is like a domestic hot water tank-is placed on a rotatable plywood shelf made by himself. During the observation, he carried them to the balcony not far from the kitchen twice. There are eucalyptus trees under the slope, and only a mailbox-sized sky can be seen between the eaves and the treetops, but he said that this is more than enough for his observation work. It was there that he searched for supernovae when the sky was clear and the moon was not very bright.
The name supernova was coined by an extremely eccentric astrophysicist in the 1930s. His name is Fritz Zwicky. He was born in Bulgaria and grew up in Switzerland. He came to California Institute of Technology in the 1920s, and soon became famous for his rough personality and outstanding talent. He doesn't seem particularly clever. Many of his colleagues think that he is just a "disgusting clown". He is a fitness fan. He often throws himself on the floor of the cafeteria of California Institute of Technology or does one-arm push-ups in other public places to show his masculinity to anyone who doubts. He was so aggressive that he finally became so aggressive, even his closest collaborator, the gentle Walter Baade?? Don't want to be alone with him. Zwicky also accused Bader of being a Nazi because he was German. Actually, he's not. Bud works at Mount Wilson Observatory on the mountain. More than once, Zwicky threatened to kill Bud if he met him on the campus of Caltech.
However, Zwicky is smart and has keen insight. In the early 1930s, he turned his attention to a problem that puzzled astronomers for a long time: new stars, which occasionally appeared in the sky and could not be explained. Incredibly, he doubts whether the core of the problem lies in neutrons-subatomic particles just discovered by james chadwick in Britain, so they are novel and fashionable. It suddenly occurred to him that if a star collapses to the density of the atomic core, it will become an extremely solid core. Atoms have actually been pressed into a ball, and their electrons are going to become nucleons to form neutrons. This forms a neutron star. Imagine squeezing 654.38+00000 heavy shells into the size of a marble-alas, this is still far from it. The density of the neutron star core is so great that a spoonful of matter in it will weigh 90 billion kilograms. It's just a spoon However, there is more than that. Zwicky realized that such a star would release a lot of energy after it collapsed-enough to produce the biggest explosion in the universe. He called the resulting explosion a supernova. In fact, they will be the biggest events in the process of creating the universe.
193465438+1October 15, Physical Review published a short abstract of a paper. A month ago, zwicky and Budd of Stanford University published this paper. Although it is very short-only 24 lines-it contains a lot of new scientific knowledge: supernovae and neutron stars are mentioned for the first time; It convincingly explains their formation methods; It accurately calculates the degree of their explosion; As a conclusion, it links the supernova explosion with a mysterious new phenomenon called cosmic rays. Cosmic rays travel through the universe in large numbers, which is only recently discovered. These ideas are revolutionary to say the least. The existence of neutron stars will not be confirmed for 34 years. Although the idea of cosmic rays is considered reasonable, it has not been confirmed. To sum up, in the words of Kip S Thorne, an astrophysicist at California Institute of Technology, this abstract is "one of the most prescient documents in the history of physics and astronomy".
Interestingly, Zwicky hardly knows why all this happened. According to Thorne, "he doesn't know much about the laws of physics, so he can't prove his ideas." Zwicky's talent is used to think about big problems. Collecting data is someone else's business, mainly Bud. "
Zwicky was also the first to realize that the visible matter in the universe is far from enough to connect the universe, and there must be other gravitational influences-we now call it dark matter. What he didn't notice was that the neutron star collapsed so tightly that even light couldn't get rid of its great gravity. This forms a black hole. Unfortunately, most of his colleagues look down on him, so his ideas rarely attract attention. Five years later, when the great Robert Oppenheimer turned his attention to neutron stars in an epoch-making paper, he never mentioned Zwedeki's achievements, even though Zwedeki had been studying the same problem for years, and it was in the office at the end of the corridor. For nearly 40 years, Zwicky's inference about dark matter has not attracted people's attention. We can only assume that he did a lot of push-ups during this period.
Surprisingly, when we put our heads into the sky, we can only see a small part of the universe. Only about 6000 stars can be seen from the earth with naked eyes, and only about 2000 stars can be seen from a certain angle. If we use telescopes, the number of stars we can see from one place can be increased to about 50000; If you use a small astronomical telescope of 5 cm, this number will soar to 300 thousand. If we use a 40 cm telescope like Evans, we can count not only stars, but also galaxies. Evans estimates that 50,000-65,438+million galaxies can be seen from the balcony, and each galaxy consists of tens of billions of stars. This is of course a considerable number, but even if you can see so much, supernovae are extremely rare. A star can burn for billions of years, but death is a sudden thing. Only a few dying stars explode, and most of them go out silently, just like a bonfire at dawn. In a typical galaxy consisting of 654.38+000 billion stars, a supernova appears every two or three hundred years on average. Therefore, looking for supernovae is a bit like standing on the observation deck of the Empire State Building in New York and searching the windows around Manhattan with binoculars, hoping to find, for example, that someone is lighting candles on a 2 1 birthday cake.
Therefore, if a hopeful and gentle priest comes to contact them and asks them if they have a star map for finding supernovae, the astronomical community will definitely think that he has something wrong with his brain. At that time, Evans only had a 5 cm telescope-about the same for amateur astronomers, but not enough for serious study of the universe-but he proposed to look for rare phenomena in the universe. Evans began to observe at 1980. Before that, less than 60 supernovae were discovered in the whole history of astronomy. By the time I visited him in August 2006, he had recorded his 34th visual discovery. Three months later, he made the 35th discovery. At the beginning of 2003, the 36th time. )
However, Evans also has some advantages. Most observers, like most people, live in the northern hemisphere, so in the southern hemisphere, the sky is very large, especially at the beginning. He also has speed and superhuman memory. A large astronomical telescope is a heavy thing, and it takes a lot of operation time to move it into place. Evans can turn a 5 cm telescope like a tail shooter in close air combat, and he can aim at any specific point in the sky in a few seconds. So he may be able to observe 400 galaxies in one night, and a large professional astronomical telescope can observe 50 or 60 galaxies, which is very good.
The search for supernovae is mostly fruitless. From 1980 to 1996, he found it twice a year on average-it is not worthwhile to observe it for hundreds of nights. Once he looked for it three times in 15 days, and it took another three years to find 1 time.
"In fact, nothing is valuable," he said. "It helps cosmologists to calculate the speed of galaxy evolution. In areas that are rarely discovered, no sign is a sign. "
On a table next to the telescope, there are photos and documents related to his research. Now he showed me some. If you have read the popular publications of astronomy, you must have read them at some time, and you will know that most of them are color photos such as distant nebulae-colorful clouds formed by the skylight, which are gorgeous, moving and spectacular. The images taken by Evans can't be compared with them at all. They are just fuzzy black and white photos with small bright spots and rings on them. He showed me a photo, which described a large group of stars. There was a little flame on the stars, so I had to get close to see it clearly. Evans told me that this is a star in Zenith constellation, which is called NGC 1365 in astronomy. (NGC stands for "new general catalogue" and records these materials. It used to be a heavy book on someone's desk in Dublin; Needless to say, it's a database now. ) For 60 million years, the light from the magnificent death of this star kept traveling through space, and finally reached the earth in the form of a little light on a night in August 20001year. It was, of course, found in Robert Evans, on the hillside where eucalyptus is fragrant.
"I think it's quite satisfactory," Evans said. "Think about it. Light has been walking in space for millions of years. When it reached the earth, someone happened to look up at the sky impartially and saw it. It seems good to witness such a major event. "
Supernovae don't just give you a sense of surprise. They are divided into several types (one was discovered by Evans), and one of them is called Ia supernova, which is particularly important for astronomy because this kind of supernova always explodes in the same way and has the same critical mass. Therefore, they can be used as "standard candlelight"-a standard for measuring the brightness of other stars (and therefore the relative distance), thus measuring the expansion speed of the universe.
1987, Saul saul perlmutter of Lawrence Berkeley Laboratory in California began to look for a more systematic search method, because he needed more ia supernovae than visual inspection could provide. Perlmutter used advanced computers and charge-coupled devices to design a wonderful system-a first-class digital camera in essence. It automatically searches for supernovae. Now, astronomical telescopes can take thousands of photos, and then use computers to find the bright spots that can explain the supernova explosion. In five years, Perlmutter and his colleagues used this new technology to discover 42 supernovae in Berkeley. Nowadays, even amateurs are using charge-coupled devices to discover supernovae. "With CCD, you can aim the telescope at the sky and then walk away to watch TV," Evans said unhappily. "That magical smell no longer exists."
I asked Evans if he wanted to adopt this new technology. "Oh, no," he said, "I like my own method very much, and," he nodded and smiled at a recent photo of a supernova. "Sometimes I can surpass them."
Naturally, the question arises: What happens if a star explodes nearby? We already know that the nearest star is Alpha, which is 4.3 light years away. I once imagined that if there was an explosion there, we could all see the light of the big explosion spilling into the whole sky within 4.3 years, just like it was spilled from a big jar. What if we have four years and four months to watch an inevitable doomsday approaching us and know that when it finally comes, it will scrape all our meat off our bones? Will people still go to work? Will farmers still grow crops? Does anyone else transport agricultural products to the store?
A few weeks later, I returned to a small town in New Hampshire, where I lived, and asked these questions to Dartmouth astronomer John Thorstenson. "Oh, no," he said with a smile. "The news of such an important event will spread at the speed of light, and its destructiveness will scare you to death. However, you can rest assured that this kind of thing will not happen. "
As for the question that the shock wave of the supernova explosion will kill you, he explained that you have to be "ridiculously close"-about within 10 light years. Danger comes from all kinds of radiation-cosmic rays and so on. Radiation will produce amazing aurora, like a shiny strange light curtain, filling the whole sky. This will not be a good thing. Anything that can perform this scene will sweep away the magnetosphere-the magnetic field that usually protects us from ultraviolet rays and other cosmic rays at high altitudes of the earth. Without the magnetosphere, anyone who unfortunately stepped into the sun would soon look like a burnt pizza.
Thorsteinson said that there is reason to believe that this kind of thing will not happen in this corner of our galaxy, because, first of all, a supernova needs a special star. A star must be 10-20 times the size of our sun to qualify, and "there are no planets around us that meet this condition." Fortunately, the universe is very big. He went on to say that the closest thing to us, which is likely to be qualified, is Orion; Over the years, it has been spewing out all kinds of things, indicating that it is unstable there and has attracted everyone's attention. However, Orion is 50,000 light years away.
In recorded history, only five or six supernovae are close enough to be seen by the naked eye. One was the explosion of 1054, which formed the crab nebula. The other time was in 1604, and it created a very bright star, which could be seen in the daytime for more than three weeks. The last time was in 1987, a supernova exploded in an area called the Large Magellanic Cloud in the universe, but it was almost invisible, and it could only be seen in the southern hemisphere-it was 169000 light years away, and it was not dangerous for us.
There is another aspect of supernovae that is absolutely important to us. If there were no supernovae, we wouldn't have come to this world. You will remember that we talked about the mystery of the universe-the Big Bang produced many light gases, but no heavy elements. Heavy elements came later, but for a long time, no one knew how they came into being later. The problem is that you need something with a very high temperature-higher than the temperature in the center of the hottest star-to forge carbon, iron and other elements; Without these elements, we would not exist. Supernovae provide an explanation. This explanation was made by a British cosmologist who was almost as eccentric as Fritz Zwicky.
He comes from Yorkshire and his name is Fred Hoyle. 200 1 Huo Yier, who died, was described as a "cosmologist and debater" in the eulogy of Nature magazine, both of which he deserved. The eulogy in Nature magazine said that he "participated in the debate for most of his life" and "ruined his reputation". For example, he claimed that the archaeopteryx fossils in the Natural History Museum of London were fakes, just like Pierre's scam of human skull, which made the museum's paleontologists very angry. They have to spend a few days answering phone calls from journalists from all over the world. He also believes that the earth not only receives the seeds of life from space, but also accepts many of its diseases, such as colds and bubonic plague. He once suggested that in the process of human evolution, the nose is prominent and the nostrils are downward in order to prevent cosmic pathogens from falling in.
It was he who jokingly coined the name Big Bang in a draft broadcast of 1952. He pointed out that when we understand physics, we can't explain why everything converges into a little bit, and then suddenly and dramatically begins to expand. Huo Yier agreed with the steady-state theory that the universe is constantly expanding, and in this process, new substances are constantly produced. Huo Yier also realized that if a star explodes, it will release a lot of heat-the temperature is above 1 100 million degrees Celsius, which is enough to produce heavy elements in a process called nuclear synthesis. 1957, Huo Yier and others showed how heavy elements were formed in supernova explosions. Because of this work, his collaborator W.A. Fowler won the Nobel Prize. Huo Yier didn't. It's embarrassing.
According to Huo Yier's theory, an exploding star will release enough heat to generate all new elements and disperse them in the universe. These elements will form gas clouds-the so-called interstellar medium-and final gathering will form a new solar system. With these theories, we can finally construct a reasonable hypothesis about how we came into this world. We now think we know the following:
About 4.6 billion years ago, a huge vortex composed of gas and dust with a diameter of about 24 billion kilometers accumulated in our present space and began to accumulate. In fact, all substances in the solar system-99.9% substances-are used to form the sun. Among the remaining floating objects, two particles floated very close and were attracted by static electricity. This is the moment when our planet was born. The same thing is happening throughout the newborn solar system. Dust particles collide with each other to form bigger and bigger lumps. Finally, these clumps are big enough to be called asteroids. As these asteroids collide endlessly, they either break, decompose or recombine in endless random replacement, but every collision has a winner, and some winners get bigger and bigger, and finally dominate their orbits.
It all happened quite quickly. It is believed that it only takes tens of thousands of years to change from a small group of dust particles to a young star with a diameter of hundreds of kilometers. In less than 200 million years, probably less than, the earth was basically formed, although it was still hot, and it was often hit by debris floating around.
At this moment, about 4.4 billion years ago, an object the size of Mars hit the earth and blew up enough matter to form a companion star-the moon. It is believed that within a few weeks, the bombed materials have been reassembled; Within a year, it became the rock circle that still accompanies us today. It is believed that most of the materials that make up the moon come from the earth's crust, not the earth's core, which is why there is little iron on the moon, but there is a lot of iron on the earth. By the way, this theory is almost always put forward recently, but in fact, it was first put forward by Reginald Daley of Harvard University in the 1940s. The only problem with this theory recently is that people pay less attention to it.
When the earth is still about one-third of its final size, it may have begun to form an atmosphere, which is mainly composed of carbon dioxide, nitrogen, methane and sulfur. It is difficult for us to connect these things with life; However, in this poisonous mixture, life was formed. Carbon dioxide is a powerful greenhouse gas. This is a good thing, because the sun was much weaker then. If we don't benefit from the greenhouse effect, the earth will be covered with ice and snow forever. Life may never find a foothold. However, life appeared in some way.
In the next 500 million years, the young earth will continue to be ruthlessly hit by comets, meteorites and other debris in galaxies. This process produces water that fills the ocean and produces the necessary ingredients for the successful formation of life. This is a very unfriendly environment, but life begins in some way. A small bag of chemicals twitched and became alive. We are coming into this world.
Four billion years later, people began to think, how did all this happen? Next, let's tell this story.