Everything Kids' Astronomy Book (4 page)

M
aybe you have seen comets and meteors speed across the sky or have heard that asteroids sometimes reach the earth. But did you know the universe also contains blinking lights called pulsars? These pulsars flash so regularly that you could almost set your watch by them. There are also black holes that can pull stars to their destruction, and a mysterious, dark unseen matter scattered throughout the universe. At the edge of the solar system are what astronomers think are millions of icy objects just waiting to become new comets.

In the Blink of an Eye

Do you like to read mysteries? Astronomy is one of the biggest mysteries of all because it is all about what happened and why. Do you remember what a supernova can do? If it explodes and nothing is left but stardust, someday it may become another star. But what if part of it collapses inward after the explosion? When it does happen, astronomers think a neutron star is instantly created. A neutron star is an object so massive that half of a teaspoonful could weigh as much as a million blue whales, the largest animal on Earth. If you think the magnets on your refrigerator are strong, imagine if you could squeeze that magnet to the size of a pinpoint. Scientists believe this compression is what really increases the magnetic field of the neutron star. Once the neutron star starts spinning, it sends out a radio signal. You probably think of your AM or FM radio as the only radio signals around, but your TV stations also use them as well as many other people like the police, firemen, truckers, and pilots. Have you ever felt the pulse in the inside of your wrist with your finger? Try to find it and count how many times a minute you can feel that beat. It should be regular like the pulse of a spinning neutron star, called a pulsar. Your heart probably beats at a different rate than your friend's. Each pulsar's signal also sends out a different rate and so its location can be identified if the radio beam is directed toward Earth. Try taking your pulse and the pulse of your friend each day for a week, and write down your numbers. Did they change?

Amazing Quasars

Now that you know that stars can be located by following a radio wave to the star, what would you do if you found a radio wave, but couldn't find the star? Like the astronomers, you would keep searching until you did! The light from the “star,” although viewers on Earth can barely see it at all, is brighter than almost any other object in the sky and this indicates that it is a source of tremendous energy! How bright is this light? Brighter than a trillion suns! Astronomers have found out that they are actually quasars, quasi-stellar radio sources, and many of them are located at the farthest edge of the universe. By measuring the huge red shift in the spectrum of each quasar, they are able to determine how fast it is speeding away from Earth and how far away it is. Can you guess how far the quasar would have traveled in the time it has taken to read this book, especially since the universe is continually expanding? Scientists also wonder what else might be hiding near these mysterious quasars. Many astronomers believe they may be the centers of galaxies that cannot be seen by any type of telescopes. Are there still quasars in the universe today? No one can be sure due to how rapidly light travels; what we are seeing now may have happened billions of years ago! Do you think those quasars have been replaced by black holes? And do you ever wonder if the universe keeps expanding, will the planets also get farther apart? Although that would seem logical, it doesn't appear to be the case. At this point in time the objects in our solar system seem to remain the same distance apart just as they always have been.

The Sky Is Falling

Have you ever watched the whirlpool that is made in your bathtub when the water drains out? A black hole is like a whirlpool in space, dragging any stars that pass close enough to their destruction. Do you know what powers a whirlpool? Gravity does! When a supernova collapses a heavy neutron star is formed. If that same star had been bigger, a smaller, heavier black hole with much more gravity would have been created. Astronomers have been able to prove neutron stars or pulsars exist because they send out radio waves, but a black hole's gravity is so strong it won't even let light escape from it. To be able to find a black hole, astronomers must look for its effect on other objects in the sky. Although X-ray radiation also cannot escape from a black hole, a star that circles it can have its gas pulled away. The radiation generated from the hot gas is transferred into the empty space beside it and this can be measured. Scientists have found the space is very small, but the gravitational pull is incredibly strong, so they believe they are seeing a black hole at work.

Where would you look for the nearest black hole? Many of the stars in other galaxies appear to be orbiting around a huge, empty space. Maybe this is also what keeps Earth's Milky Way Galaxy spinning around.

Seeing in the Dark

Have you ever walked into a theater after the movie has started? Although you know it is filled with seats and other people, you really can't see anything but a big, bright, moving screen! Telescopes have revealed that the universe is filled with endless luminous galaxies, but most astronomers believe that the galaxies are surrounded by a dark halo or circle filled with dark matter. How did they discover the existence of this substance? Numerous calculations seem to prove there is too much gravity beyond the edge of each galaxy and throughout the universe for the amount of bodies of light that we are able to see! Scientists have come to question their original beliefs that all objects with gravitational pull must be visible. At this point in time astronomers can only guess what form this unseen matter might take. It might be dark galaxies, dwarf stars too faint to be seen, or black holes. Most scientists believe the dark matter formed right after the big bang and that it could be particles that are so tiny that they can't be seen or aren't able to send out enough radiation to be measured! Sounds hard to believe, doesn't it? Even after they have totaled up all the light and dark matter, there is still 70 percent of the gravity they can't explain in the universe. They believe that dark energy, the driving force for the expanding universe, accounts for the rest of it. One way to think of it is like magnetism or electricity. Just because you can't see it doesn't mean it isn't there. Until astronomers discover a way to measure it, they just have to believe it is there because they see its effect!

Misplaced in Space

Many years ago if you had asked an astronomer about space debris, he would have thought you were talking about stardust or chunks of planets and moons created when objects in space collided. Today, hazards in space are more likely to be manmade. With all you know about gravity, it is obvious that sooner or later, what goes up, must come down! Have you ever seen a really large meteor? Did you think that maybe it wasn't a meteor at all? Maybe it was junk that was left behind when it could no longer be used, such as:

• A piece of equipment or an item that came off a spaceship or astronaut;

•A rocket booster after it ran out of fuel;

• Or even part of a spacecraft or a satellite.

Old space stations have returned to and burned up in Earth's atmosphere after new, improved models have been lifted into space. Most of the tanks and other containers used for a shuttle liftoff never reach space. They fall into the ocean to be reused on another mission or burn up in the atmosphere. Parts of the rockets that were lifted above the atmosphere will probably drift in space for a long time. Are the remains of probes and spacecraft sent to other planets called interplanetary trash? You can use satellites, the shuttle, the Hubble telescope, and the space station to practice finding objects in space with your telescope. Since they circle the Earth at regular intervals and at certain places in the sky, you can be sure they aren't meteors or junk!

In Search of a Planet!

Did you know that there over a million objects orbiting around the sun and they're not that far away? If you were an ancient stargazer and you found Mars and then Jupiter, you might have wondered why there wasn't another planet between them. When Ceres, an asteroid that is one-eighth the size of the Earth's moon, was discovered, they thought it was. Today's astronomers aren't sure if that space ever held a planet or if there just wasn't enough gravity to form one from the chunks of rock and metal circling in this asteroid belt. Some of these asteroids are as small as a compact car, while others are large enough for a spacecraft to land on them, and one even has a volcano! How would you like to have been in the probe that did land on one called Eros several years ago?