As soon as his mom left the room, George jumped off his bed and gathered together all the bits of paper that had fallen out of the back of the Black Holes book. They were covered in spidery handwriting and little doodles, and numbered pages 1 to 7. He started to read.
My Difficult Book Made Simple for Annie and George (version 3), it began.
WHAT YOU NEED TO KNOW ABOUT BLACK HOLES
SECTION 1 What Is a Black Hole?
SECTION 2 How Is a Black Hole Made?
SECTION 3 How Can You See a Black Hole?
SECTION 4 Falling into a Black Hole
SECTION 5 Getting out of a Black Hole
SECTION 1
What Is a Black Hole?
A black hole is a region where gravity is so strong that any light that tries to escape gets dragged back. Because nothing can travel faster than light, everything else will get dragged back too. So you can fall into a black hole and never get out again. A black hole has always been thought of as the ultimate prison from which there’s no escape. Falling into a black hole is like falling over Niagara Falls: there’s no way of getting back the same way you came.
The edge of a black hole is called the “horizon.” It is like the edge of a waterfall. If you are above the edge, you can get away if you paddle fast enough, but once you pass the edge, you are doomed.
As more things fall into a black hole, it gets bigger and the horizon moves farther out. It is like feeding a pig. The more you feed it, the larger it gets.
SECTION 2
How Is a Black Hole Made?
To make a black hole you need to squash a very large amount of matter into a very small space. Then the pull of gravity will be so strong that light will be dragged back, unable to escape.
One way black holes are formed is when stars that have burned up their fuel explode like giant hydrogen bombs called supernovas. The explosion will drive off the outer layers of the star in a great expanding shell of gas, and it will push the central regions inward. If the star is more than a few times the size of our Sun, a black hole will form.
Much larger black holes are formed inside clusters and in the center of galaxies. These regions will contain black holes and neutron stars as well as ordinary stars. Collisions between black holes and the other objects will produce a growing black hole that swallows anything that comes too near it. Our own galaxy, the Milky Way, has at its center a black hole several million times the mass of our Sun.
NEUTRON STAR
When stars much more massive than the Sun run out of fuel, they usually expel all their outer layers in a giant explosion called a supernova. Such an explosion is so powerful and bright it can outshine the light of billions and billions of stars put together.
But sometimes not everything is expelled in such an explosion. Sometimes the core of the star can remain behind as a ball. After a supernova explosion, this remnant is very hot: around 180,000 degrees Fahrenheit (100,000 degrees Celsius), but there is no more nuclear reaction to keep it hot.
Some remnants are so massive that under the influence of gravity they collapse in on themselves until they are only a few dozen miles across. For this to happen, these remnants need to have a mass that is between around 1.4 and 2.1 times the mass of the Sun.
The pressure is so intense inside these balls that they become liquid inside, surrounded by a solid crust about 1 mile (1.6 km) thick. The liquid is made of particles that normally remain inside the core of the atoms—the neutrons—so these balls are called neutron stars.
There are also other particles inside neutron stars, but they really consist mostly of neutrons. To create such a liquid on Earth is beyond our present technology.
Stars like the Sun do not explode in supernovae but become red giants whose remnants are not massive enough to shrink under their own gravity. These remnants are called white dwarfs. White dwarfs cool down over a period of billions of years, until they are not hot anymore.
Many neutron stars have been observed by modern telescopes. Since the cores of stars are made of the heaviest elements forged inside stars (like iron), although white dwarfs can be quite small (about the size of the Earth) they are extremely heavy (about the mass of the Sun).
Star remnants that are less heavy than 1.4 times the mass of the Sun become white dwarfs. Neutron stars are born from supernovae remnants that have between 1.4 and 2.1 times the mass of the Sun. Remnants more massive than 2.1 times the size of the Sun never stop collapsing on themselves and become black holes.
SECTION 3
How Can You See a Black Hole?
The answer is, you can’t, because no light can get out of a black hole. It is like looking for a black cat in a black cellar. But you can detect a black hole by the way its gravity pulls on other things. We see stars that are orbiting something we can’t see but that we know can only be a black hole.
We also see discs of gas and dust rotating around a central object that we can’t see, but that we know can only be a black hole.
SECTION 4
Falling into a Black Hole
You can fall into a black hole just as you can fall into the Sun. If you fall in feetfirst, your feet will be nearer to the black hole than your head and will be pulled harder by the gravity of the black hole. So you will be stretched out lengthwise and squashed in sideways.
This stretching and squeezing is weaker the bigger the black hole is. If you fall into a black hole made by a star only a few times the size of our Sun, you will be torn apart and made into spaghetti before you even reach the black hole.
But if you fall into a much bigger black hole, you will pass the horizon—the edge of the black hole and the point of no return—without noticing anything particular. However, someone watching you fall in from a distance will never see you cross the horizon because gravity warps time and space near a black hole. To them you will appear to slow down as you approach the horizon and get dimmer and dimmer. You get dimmer because the light you send out takes longer and longer to get away from the black hole. If you cross the horizon at 11:00 according to your wristwatch, someone looking at you would see the watch slow down and never quite reach 11:00.
SECTION 5
Getting Out of a Black Hole
People used to think nothing could ever get out of a black hole. After all, that’s why they were called black holes. Anything that fell into a black hole was thought to be lost and gone forever; black holes would last until the end of time. They were eternal prisons from which there was no hope of escape.
But then it was discovered that this picture wasn’t quite right. Tiny fluctuations in space and time meant that black holes couldn’t be the perfect traps they were once thought; instead they would slowly leak particles in the form of Hawking Radiation. The rate of leakage is slower the bigger the black hole is.
The Hawking Radiation would cause black holes to gradually evaporate. The rate of evaporation will be very slow at first, but it will speed up as the black hole gets smaller. Eventually, after billions and billions of years, the black hole will disappear. So black holes aren’t eternal prisons after all. But what about their prisoners—the things that made the black hole or that fell in later? They will be recycled into energy and particles. But if you examine what comes out of the black hole very carefully, you can reconstruct what was inside. So the memory of what falls into a black hole is not lost forever, just for a very long time.
YOU CAN GET OUT OF A BLACK HOLE!
The next day was the day of the big science competition at school. George left home early. He said good-bye to his pig, kissed his mother, put Eric’s book on black holes into his school bag, and scooted out of the door, breakfast in hand. His dad offered to take him to school on the back of his bicycle-made-for-two, but George just yelled, “No thanks, Dad,” and was gone, leaving his parents feeling like a small tornado had just swept through the house.
George ran up the road, and when he got to the main intersection, he looked back to see if either of his parents was waving at him from the
front door. When he saw they weren’t, he turned left at the corner instead of right, the direction he would have taken to go to school. He knew he didn’t have much time, so he hurried along as fast as he could. As he ran, thoughts streamed through his head.
He thought about Eric, who, by now, would be swallowed up by the great dark menace of the black hole, the strongest force in the Universe. He thought about Cosmos and whether George would find him in the place where he was headed. He thought about Annie, whom he would see later at the competition. Would she believe him when he told her that her dad had been tricked by an evil former colleague into taking a journey across outer space that had plunged him into great danger?
Now George understood why Annie told such extraordinary stories—after the wonders of the Universe, real life did seem pretty dull. He couldn’t imagine a life without Annie or Cosmos or Eric now. Or at least he could, but he didn’t want to. He had to save Eric, he had to!
George didn’t know and couldn’t imagine why Dr. Reeper wanted to throw Eric into a black hole and steal his amazing computer. But he could guess that whatever Dr. Reeper was up to, it wasn’t for the good of mankind, science, Eric, or anyone else. Whatever Dr. Reeper’s aim was, George felt sure it was a horrible one.
The other thing that went through George’s head as he ran on toward Dr. Reeper’s house was the science competition later that day. If he won the competition by giving a great talk about the Solar System, even his dad wouldn’t be able to say no to George having the computer in the house. The problem was that the awesome plan George had cooked up to save Eric from being eaten up by a black hole meant he wouldn’t actually be at the competition. So he had no hope of winning. It wasn’t easy for George to give up the idea of entering, but he knew he had no choice if he wanted to get Eric back. There was no other way to do it.
George reached 42 Forest Way and took a few moments to get his breath back. As he panted quietly, he looked at the house in front of him. The driveway led through some dilapidated gates to a huge, old building with weird-looking turrets sticking out of the roof.
George crept up the driveway to the house and stared in through a large window. Through the grimy glass, he saw a room full of furniture covered in yellowing sheets, and cobwebs hanging from the ceiling. Picking his way through a bed of nettles, he tiptoed to the next set of windows. One of the windows was slightly open at the bottom. Looking in, George saw a familiar sight.
In the middle of a crazed mess of pipes, cables, and narrow glass tubes holding brightly colored bubbling liquids, was Dr. Reeper, with his back to him, standing in front of a computer screen that was glowing with green light. Even from behind, George could tell that Dr. Reeper was not at all happy. He watched as his teacher struck the computer keyboard wildly, using all his fingers at once, as though playing a very difficult piano solo. The window was open just enough for George to hear what he was saying.
“See!” Dr. Reeper yelled at the computer screen. “I can keep doing this all day! Eventually I’ll find the secret key, you just see if I don’t! And when I do, you’ll have to let me into the Universe! You’ll have to!”
“Negative,” replied Cosmos. “You have entered an incorrect command. I cannot process your request.”
Dr. Reeper tried some different keys.
“Error,” said Cosmos. “Error type two-nine-three.”
“Grrrrrrr!” cried Dr. Reeper. “I will crack you, Cosmos. I will!” At that moment his phone rang. He snatched it up. “Yes?” he barked into the receiver. “Ahhh,” he went on in a more polite voice. “Hello—you got my message?” He coughed in a very fake way. “I’m not feeling so good today … No, just a bad cold … I think I’ll have to take the day off … Such a shame about the competition …” He coughed a few more times. “Sorry! Have to run—I’m feeling really foggy. Byyyeee!” He slammed the phone down and turned back to Cosmos. “See, little computer!” he said, rubbing his hands. “Now I have all day!”
“I do not operate for anyone who is not a member of the order,” replied Cosmos, sounding very brave.
“Ha-ha-ha-ha!” Dr. Reeper laughed crazily. “So the old order still exists, does it? Those silly busybodies who think they can save the planet and humanity! The fools,” he went on. “They should save themselves while there is still time. That’s what I intend to do. Forget humanity! Humans don’t deserve to be saved.” He spat on the floor. “Look what they’ve done so far to this beautiful planet. I’m going to start again somewhere else, with a new life form. Those silly little boys think I’ll be taking them with me. But I won’t! Ha-ha-ha-ha! I’ll leave them here to die, like the rest of the human race. I’ll be the only one left in the Universe, me and my new life form, which will obey my every word. All I need is to get out there, into outer space. You, Cosmos, are going to help me.”
“Negative,” replied Cosmos. “I refuse to operate for a nonmember of the order.”
“I was a member once,” claimed Dr. Reeper.
“Your membership was canceled,” replied Cosmos firmly. “After you—”
“Yes, yes, yes,” said Dr. Reeper quickly. “Let’s not talk about that. Don’t bring up bad memories now, Cosmos. Surely it’s time to forgive and forget?” He spoke in a horrible, syrupy voice.
“Negative,” said Cosmos, causing Dr. Reeper to rise up in a fury in front of the computer and bring his hands crashing down once more on the keyboard.
“Ouch,” said Cosmos, a few bright sparks flying out from the keyboard.
George couldn’t bear to watch any longer. As much as he wanted to break in and stop Dr. Reeper from hurting poor Cosmos any more, he knew it was vital to get him out of the house and away from the great computer as quickly as possible. To do that, George needed to get to school.
He ran back until he reached the school gates. Big buses sat in the road outside, hordes of children wearing different-colored school uniforms climbing out of them. These were the other kids from nearby schools arriving to take part in the science competition. George weaved through the crowds, saying, “ ’Scuse me, sorry, ’scuse me, sorry.” He was searching for someone.
“George!” He heard his name and looked around but couldn’t see who was shouting at him. Then he spotted her—a tiny figure in a dark blue uniform, jumping up and down and waving at him. He scrambled over to her as quickly as he could.
“Annie!” he said when he reached her. “I’m so glad to see you! Come on, we haven’t got a minute to spare.”
“What’s up?” said Annie, wrinkling her nose. “Is something wrong with your talk?”
“Is that your boyfriend?” A much older boy in the same school uniform as Annie interrupted them.
“Oh, go away,” Annie snapped at the bigger boy. “And say stupid things to someone else.” George held his breath in fear, waiting to see what the bigger boy would do. But he just turned away meekly and got lost in the crowd.
“Where’ve you been?” George asked Annie.
“I told you,” replied Annie. “At Granny’s house. Mom dropped me back at the school, so I haven’t even been home yet. What’s wrong, George? What is it?”
“Annie,” said George very seriously, “I’ve got something awful to tell you.” But he didn’t get the chance. A teacher blew a whistle very loudly, forcing everyone to be quiet.
“Okay everybody!” the teacher announced. “I want you all to line up in your school groups, ready to go into the great hall, where the science competition will begin. You”—he pointed at George in his dark green uniform among a crowd of kids in blue—“are with the wrong school! Kindly go and find your own group before you confuse people anymore!”
“Meet me just outside the hall!” George hissed to Annie. “It’s really important, Annie! I need your help!” With that he left her and joined his own school group. He started walking toward the hall, looking now for someone—or rather several someones—else. When he saw them—Ringo and his group of friends hovering in the hallway—George knew what he had to do. He grab
bed the nearest teacher and started speaking in a very loud voice.
“Sir!” he yelled. “Sir!”
“What is it, George?” said the teacher, backing off a little at the unexpected volume.
“Sir!” shouted George again, making sure everyone around had stopped what they were doing and was listening to him. “I need to change the topic of my talk!”
“I’m not sure that’s possible,” said the teacher. “And do you mind not shouting?”
“But I have to!” bellowed George. “I’ve got a new title!”
“What’s the title?” said the teacher, who was now worried that the boy had gone a little crazy.
“It’s Cosmos, the World’s Most Amazing Computer, and How He Works.”
“I see,” said the teacher, thinking George was definitely insane. “I’ll ask the judging panel what they think.”
“Oh good, thank you, sir!” George yelled even louder than before. “Did you catch the whole title? It’s Cosmos, the World’s Most Amazing Computer, and How He Works.”
“Thank you, George,” said the teacher quietly. “I’ll do my best for you.”
As he walked off, sighing deeply to himself, George noticed that Ringo had taken out his cell phone and was making a call. All he could do now was wait.
• • •
George stood by the entrance to the hall, watching the long lines of schoolchildren file in past him. He didn’t have to wait long before, out of breath and trembling with excitement, Dr. Reeper rushed up to him.
“George!” he exclaimed, smoothing his hair down with one scaly hand. “Did you manage? To change the topic of your talk, that is?”
“I think so,” George told him.
“I’ll check for you,” said Dr. Reeper. “Don’t worry, you go ahead and give the talk on Cosmos and how he works, and I’ll make sure it’s okay with the judging panel. Good idea for a talk, George. Brilliant!”
Just then the principal came by. “Reeper?” he said curiously. “I heard you were ill today.”
George's Secret Key to the Universe Page 13
