To the Majesty of the Dark Universe
“If the stars should appear one night in a thousand years, how would men believe and adore; and preserve for many generations the remembrance of the city of God which had been shown! But every night come out these envoys of beauty, and light the universe with their admonishing smile.”
¯ Ralph Waldo Emerson
Try it. Next time you’re outside on a clear night, look up. You might see the winking lights of an airplane, the glow of an orbiting satellite, or even the bright trail of a meteor. Of course, you’ll see lots of stars.
What about all the space between the stars? Is something hidden out there in the darkness? Or is it merely empty? There’s nothing for the human eye to see, but astronomers are finding ways to detect what lies between the stars. And they’re discovering that most of the universe is made out of mysterious, invisible stuff.
Why Looking at the Sky
As well as displaying a complete history of our relationship with the universe, to any who can read it, the stars are an unparalleled reservoir of stories. Part of the pleasure of stargazing is sidereal terminology, the language of stars. At Orion’s right shoulder is Betelgeuse, a pulsing red supergiant. (The name is a corruption from the Arabic Yad al-Jauza, hand of the giant.) Alpheratz is in the constellation of Pegasus, and its etymology pays the debt Arab astronomy owed to ancient Greece. Like all the natural sciences, of which it is the oldest, astronomy owes its advances to observers of genius, to a chain of learning passed between scholars across the ages, and to local conditions.
While professional star gazers must now travel to high altitude observatories in Chile and Hawaii to rise above the pollution, their forebears had only to lie on their backs. If you do this in the Sahara, even today, the stars will seem almost within reach, and before the moon rises you will see by starlight, which is indeed as calm as it is bright. You will see so many meteors that you will stop counting before you reach 20.
In their unveiling and fading, their movement, their glitter, their seasons and their witnessing of all we have been and will be, the stars seem alive, as they spin through life-cycles of near incomprehensible scale. (Betelgeuse is expected to explode into a supernova within the next million years.)
We have used them to find our way across our planet, to situate earth within the universe and to determine our origins, in the atoms forged in the nuclear reactions at their incandescent hearts. Through astrology we have tried to use them to predict our destinies, and to explain our natures. You need to know nothing about them to be uplifted by their beauty, awed by their profusion and comforted by the infinities where they voyage.
Why Darkness Matters
The Star Count was an effort to help scientists learn more about how light pollution affects our view of the night sky. Whether participants saw thousands of stars—or just a dozen—depended a lot on whether they were surrounded by darkness or by twinkling city lights.
On a clear night, with no clouds, moonlight, or artificial lights to block the view, people can see more than 14,000 stars in the sky, says Dennis Ward, an astronomer with the University Corporation for Atmospheric Research (UCAR) in Boulder, Colo. He helped coordinate the Star Count. But when people are surrounded by city lights, he says, they’re lucky to see 150 stars.
If you’ve ever driven toward a big city at night and seen its glow from afar, you’ve witnessed light pollution. It occurs when light from streetlights, office buildings, signs, and other sources streams into space and illuminates the night sky. This haze of light makes many stars invisible to people on Earth.
Dust and particles of pollution from factories and industries worsen the effects of light pollution. When these particles float into the atmosphere, light ricochets off of them and scatters even more. “If one city has a lot more airborne pollution than another,” Ward says, “that city will suffer the effects of light pollution on a much greater scale.”
The problem with light
Light pollution doesn’t just put a damper on amateur stargazing. Hazy skies also make it far more difficult for astronomers to do their jobs. Some of the earliest telescopes and observatories were placed as far away from civilization as possible so that astronomers could observe the faintest galaxies without interference by city lights.
But cities are getting larger. Suburbs are growing in once dark, rural areas. Light from all this new development is increasingly obscuring the faint light given off by distant stars and galaxies. And if scientists can’t locate these objects, they can’t learn more about them.
“To get all the way out of the atmosphere and away from light pollution,” Ward says, instruments such as the Hubble Space Telescope are placed in orbit. Still, a lot of astronomical viewing takes place from Earth, where light pollution remains a problem.
Light pollution doesn’t only affect star visibility. It can harm wildlife too.
Scientists don’t entirely understand how animals navigate at night, but it’s clear that artificial light can attract them, making them go off course. There’s increasing evidence, for example, that migrating birds use sunsets and sunrises to help find their way, says Sydney Gauthreaux Jr., a biologist at Clemson University in South Carolina.
“When light occurs at night,” he says, “it has a very disruptive influence.”
Sometimes birds fly into lighted towers, high-rises, floodlit smokestacks, and cables from radio and television towers. Experts estimate that millions of birds die this way every year.
Sea turtle hatchlings also depend on moonlight and starlight to guide them into the water. Artificial lights can disorient these animals. They often end up heading toward lit-up parking lots, beach houses, and hotels by mistake.
In response to the growing light pollution problem, a number of cities are now running light pollution awareness campaigns. Among these cities is San Francisco, which held its first “Lights Out San Francisco” event on October 20, 2007. That night, the city encouraged people to turn off all nonessential lights for an hour.
Sydney, Australia, and Toronto, Canada, have held similar events. And in March 2008, a program called “Lights Out America” will invite all U.S. residents to turn off all nonessential lights for an hour.
To learn more about light pollution’s effect on the night sky, anyone, anywhere on the planet can participate in activities described on the Web site of the Great World Wide Star Count. There, people can compare the results of their stargazing with what others found during the official event.
Learning the Stuff
Billions of tiny dark matter particles probably just zoomed through your body. They were moving fast — about 560,000 miles per hour. There go billions more. And more still. They’re zipping everywhere, streaming through everything you can see.
Yet we don’t feel these particles. We can’t see them. And we can’t stop them. They blow through atoms like they’re not even there. Unlike the atoms that make up star stuff, dark matter particles don’t reflect light, and they don’t respond to electricity or magnetism.
If seeing is believing, then we shouldn’t believe in most of our universe. We can see the sun, other stars and faraway objects that glow in the dark. With the right tools, we can even see things that would otherwise be invisible, like the air in the atmosphere or hot gas in distant galaxies.
Astronomer Carl Sagan liked to say, “We are made of star stuff.” He meant that everything we know — you and your dog, the Earth and moon — is made of the same kinds of atoms as glittering stars. These atoms form elements like carbon, hydrogen, nitrogen, oxygen and hundreds more.
In recent years, astronomers have shown that “star stuff” isn’t the only stuff in the universe. There’s something else moving galaxies around in unexpected ways. That something else includes dark matter and dark energy. Even though these two things are hidden from sight, or “dark,” they’re very different from each other. Because scientists cannot observe dark matter and dark energy directly, they have to study how dark energy and dark matter affect celestial objects we can see — visible stars and galaxies.
Dark energy makes up most of the universe. Dark matter comes in second. And our familiar star stuff — including Earth and everything on it — is less than 5 percent of the universe. Five percent is not much — it’s a little less than three colored squares on a Rubik’s Cube, or equivalent to a very small ice cube in a tall glass of water. It’s a humbling thought.
The Universal Glue
Gravity is an attractive force, which means it brings objects together. The more mass something has, the more gravity, or pull, there is. Because of gravity, the Earth repeatedly circles the sun instead of flying away. And gravity allowed scientists to discover dark matter.
Swiss astronomer Fritz Zwicky stumbled across dark matter in 1933. He was attempting to tally the total mass of a distant galaxy cluster, a family of galaxies held together by gravity. But his numbers just weren’t adding up. To understand Zwicky’s problem, imagine that you want to know the weight of 10 oranges, and each orange weighs one pound. You guess the weight should be 10 pounds, but when you pile the oranges on a scale, it tells you the weight is 100 pounds, not 10.
That was Zwicky’s problem. When he calculated the mass of the galaxy cluster on the basis of its stars, that number that was way too small to explain the cluster’s gravity. Some mass must be missing, he reasoned. Zwicky called the unseen mass dark matter.
This image of the universe shows the radiation left over from the Big Bang, which occurred 13.7 billion years ago. Maps like these helped scientists determine the amount of dark energy and dark matter in the universe. Credit: NASA/WMAP Science Team.
Over time, more evidence for dark matter would emerge. In the 1970s, for instance, astronomers observed galaxies spinning in unexpected ways. Their strange motions could be explained only by dark matter.
Astronomer Dan Coe studies dark matter at the Space Telescope Science Institute in Baltimore, Md. He recently led a study of a galaxy cluster called Abell 1689. Both the visible galaxies and dark matter add to the gravitational pull in a cluster. These gravitational forces act like a lens, and when light passes through a cluster like Abell 1689, it bends. (Think of how light changes when it passes through an empty glass or a pool of water.) By studying these bending light rays, Coe and his team created a map of Abell 1689 that shows where the dark matter might be hiding in the cluster.
Some Popular Guys
As long as people have been living on Earth, we’ve been looking up at bright stars in the night sky, trying to understand the universe and our place in it. Astronomers have long known that not all stars are alike. Some are almost as old as the universe itself, others are just now being born. They come in different colors: blue, white, yellow and red. Some shine brightly in the sky, and others are visible only with special telescopes. Some stars race through space in pairs or groups; others move alone. Some, like our own 4.8-billion year-old sun, are surrounded by planets.
One of the most important ways that scientists group stars is by size. In the early 20th century, just before World War I, astronomers began to put stars into two main size groups: dwarfs and giants.
“Once they discovered that there was a class of stars really big, called giants, they carved the universe up into dwarfs and giants,” says Jim Holberg, a scientist who studies dwarf stars at the University of Arizona in Tucson. “The giants are enormous stars, and dwarfs are stars like the sun.”
Despite their name, most dwarf stars are not unusually small. Or unusual at all: Most stars, in fact, are dwarfs of one kind or another. But within the large category of dwarf stars are other groups of stars. Keeping track of the different kinds of dwarfs can be difficult, but that’s all in a day’s work for astronomers.
A brown dwarf mystery: planets, stars or neither?
Some objects are so strange that even astronomers aren’t sure what to call them. One of these kinds of objects behaves like a star, but it’s not very hot — and it’s too small. Plus, through a telescope, it resembles a planet — but it’s too big to be called one. What would you call it? A star-net? A planet-ar?
An American astronomer named Shiv Kumar first predicted these strange objects might exist in 1963, and he called them black dwarfs. That name didn’t stick, and ten years later another astronomer suggested the name brown dwarfs. That name stuck.
But there was another problem: Even though astronomers like Kumar could use information to imagine how brown dwarfs should behave, no one had ever seen one. It wasn’t until 1995 — just 14 years ago — that astronomers first saw one of these brown dwarfs. Since that first discovery, astronomers have found hundreds more brown dwarfs.
Thanks to more scientists looking for these stars, and better telescopes to see them with, astronomers now know more about brown dwarfs. As it turns out, they aren’t even brown. They are almost totally dark in the sky, producing no visible light. Instead, they emit infrared light, which is so faint it can only be detected by sophisticated telescopes.
Also, brown dwarfs aren’t even stars. Some astronomers even call brown dwarfs “failed stars.”
When you see a star in the sky, it looks like a calm, twinkling light. Your eyes deceive you, however. A star is anything but calm: What you are really looking at it is a giant, fiery ball of burning gas. For most stars, that gas is hydrogen, the lightest element in the universe. Hydrogen is the fuel for stars, just as gasoline is the fuel for most modern cars.
Red dwarf stars: the most popular stars you’ll never see
Objects in space that have just a little more mass than brown dwarfs are called red dwarf stars. Red dwarfs may not be much larger than brown dwarfs, but that small increase in size makes a big difference. Red dwarf stars are massive enough to support hydrogen fusion, like the sun. And they’re also technically stars.
But unlike the sun, red dwarfs don’t shine in the sky. “They’re less massive, and they don’t produce as much energy,” says Holberg. “They don’t have a strong energy source, so they’re burning at a low rate.” Most of the energy red dwarfs produce is invisible to the naked eye but visible to high-powered telescopes.
Despite the difficulty in finding these stars, astronomers believe that most of the stars in our galaxy are red dwarfs. The sun’s nearest neighbor, Proxima Centauri, is a red dwarf more than 20 trillion miles away. Most of our nearest star neighbors are red dwarfs.
White dwarf stars: the end of the line
After a long life of burning hydrogen, a star eventually runs out of fuel. At this point, the star grows and grows and grows into something called a red giant. These giant stars can be hundreds of times as large as the sun, and when theyburn up, all that’s left is the hot core of the star. This hot core is yet another kind of dwarf star.
“The star shrinks to something the size of the planet Earth,” says Holberg. There is no more fuel to burn, but the star is so hot that it blazes as it cools down. Over billions of years, he says, the heat leaks out. “Because the star is so small, it’s like pushing all the water at a dam through a small hole.”
Holberg says that nearly all the stars in our galaxy — about 97 percent — are destined to become white dwarfs. Even among dwarfs, white dwarfs go against expectations. Oddly, the smallest white dwarfs actually have the most mass, and the largest white dwarfs have the least. So the more mass, the smaller the dwarf. For comparison, imagine that you had a magic balloon that deflatedas you blew into it. When a white dwarf cools down, it becomes a black dwarf, a dense, cold object in the sky that astronomers have never seen.
At the end of its life, the sun will become a white dwarf. But before this happens, the sun will expand, like a balloon of fire, into its red giant phase. “The sun will become a giant one day and swallow planets,” he says. “What’s going to survive?”
As a giant, the sun will absorb and disintegrate the closest planet, Mercury. Then, as the sun gets bigger, it will absorb our nearest neighbor, the planet Venus. Bye-bye, Venus. But astronomers aren’t sure what happens then — will the sun finally destroy Earth before becoming a small white dwarf?
Here are the brief notes on the dark majestic universe that has kept us engulfed from the dawn of the creation process. The more you concentrate on these divine darkly constellation, the more you get enlightened. The sky always has encouraged men to think big, to attempt a move beyond their visible abilities- in reality and in imagination. Before we finish, here are few verses for you to ponder from Anna Letitia Barbauld’s pen:
“Is there not
A tongue in every star that talks with man,
And wooes him to be wise? nor wooes in vain;
This dead of midnight is the noon of thought,
And wisdom mounts her zenith with the stars.”