快猫短视频

WHEN Richard Gott first became interested in astronomy at the age of 8 we had no proof that there were planets around other stars. Or that the afterglow of the big bang fireball still lingers in today鈥檚 universe. And we certainly had no evidence for black holes.

But that was nearly 50 years ago, and times have changed. Powerful telescopes have uncovered galaxies billions of light years away. A raft of space probes and orbiting observatories have pinpointed distant stars and scanned the sky at almost every wavelength. Thousands of satellites monitor the Earth, relaying signals from one side of the planet to the other and helping us to navigate. As for Gott, he is now a professor of astrophysics at Princeton University.

Thrilled by recent advances in astronomy, Gott wanted to make a map showing everything in the observable universe. But even though he had all the data he needed, it wasn鈥檛 an easy task. The biggest problem is that the universe is simply so big. The most distant object we have spotted is a quasar about 250,000 billion billion kilometres away. Gott realised that if he shrank such an enormous distance to fit on a single page, the entire Milky Way would be crammed into a dot smaller than a speck of dust. On the other hand, if he drew our galaxy to fit on the page, he鈥檇 need another 100 kilometres of paper to show the most distant quasar.

Gott, working with colleague Mario Juric and others, has now found a way to show it all at a glance (see 鈥淗ow to shrink the universe鈥�), and 快猫短视频 is proud to publish the result in the pull-out map at the centre of this issue. Imagine lying on the equator for 24 hours, peering vertically up into the sky with a pair of binoculars that have a 4-degree field of view. As the Earth rotates, that field of view will sweep out a band of universe right the way around the sky. The map shows every significant object in that 4-degree slice as it was on 12 August 2003, right out to the distant edge of space and time. For completeness, Gott and Juric also threw in the planets and a few important stars and galaxies that fell outside the 4-degree slice.

Even though it is only a slice through the universe, it contains an impressive list of objects: 8420 satellites; 14,183 asteroids and 126,625 galaxies. It also shows the largest structure ever found in the universe: a wall of galaxies a staggering 1.37 billion light years long. It is a stunning achievement.

Moving away from the Earth鈥檚 surface, the first striking landmark is a belt of artificial satellites. Among these are the Hubble telescope and the International Space Station, which sit on the edge of the Earth鈥檚 atmosphere. Even though the atmosphere here is thin, there is still enough friction to slow down the telescope and space station as they orbit the Earth. Without the space shuttles and Soyuz craft nudging them back into orbit, Hubble and the space station would eventually re-enter the Earth鈥檚 atmosphere and burn up.

Also shown are the Chandra X-ray Observatory and Vanguard, which was launched as long ago as 1958. The GPS satellites used for navigation and a string of geostationary satellites are in higher orbit, and sit within the Van Allen belts of energetic charged particles trapped by the Earth鈥檚 magnetic field.

Poised 1.5 million kilometres away, between the moon and the sun, is the Wilkinson Microwave Anisotropy Probe. Launched in 2001, WMAP scans the sky, measuring tiny temperature ripples in the cosmic microwave radiation left over from the big bang. Such ripples have already revealed vital clues about the cosmos: they pin down the age of the universe, what it is made of, how fast it is expanding and how it evolved shortly after the big bang.

Further out lie the sun and eight planets, and between the orbits of Mars and Jupiter circles a belt of rocky asteroids. These are so numerous that they would just appear as a black smudge if all 220,000 of them were shown. In the equatorial slice we can see, the belt appears as two giant clouds containing over 14,000 rocks. Two other clumps called Trojan asteroids, which follow Jupiter鈥檚 orbit, are tugged along by the planet鈥檚 huge gravitational pull. Gott and his colleagues also picked out the most famous asteroids, including Ceres, the first such object to be discovered over 200 years ago. In 2000, NASA鈥檚 NEAR probe went into orbit around another of the asteroids on the map, the potato-shaped Eros, and beamed back stunning pictures of its surface before landing on it.

Beyond Saturn lies Halley鈥檚 comet, and next to Pluto sits a huge icy rock called Quaoar. Discovered last year, Quaoar isn鈥檛 big enough to be a planet in its own right. Instead it belongs to the Kuiper belt, a collection of primordial lumps of ice and rock that failed to clump together to form planets.

Near the edge of our solar system the probes Voyager 1 and 2, as well as Pioneer 10, continue their journey into deep space. Beyond this boundary, called the heliopause, lies an expanse of empty space so vast it takes light over a month to cross it. Further away still lies the Oort cloud, a chilled reservoir of billions of comets. We can鈥檛 tell exactly what resides in that frozen domain, but gravitational tugs from passing stars and other Oort cloud objects are thought occasionally to nudge comets out of the cloud and into vastly elongated orbits of millions of years around the sun.

Beyond the Oort cloud lie the stars. Gott and Juric鈥檚 map shows the 10 brightest stars in the sky, including Sirius and Alpha Centauri A. Its neighbour, Proxima Centauri, is our nearest star at only 4 light years away, but even this is too far for astronauts to visit using today鈥檚 technology. Travelling in the space shuttle, which reaches speeds of up to 28,000 kilometres per hour, the crew would be dead 155,000 years before they arrived.

Within the Milky Way, the map鈥檚 slice of the universe shows over 3000 stars whose distances have been pinpointed using measurements from the Hipparcos satellite. Among them are 66 stars out of the 100-plus stars known to have giant planets orbiting around them. At a distance of 28,000 light years lurks the supermassive black hole at the centre of our galaxy, which is almost 3 million times the mass of the sun.

Nearby lies a binary system consisting of a pulsar orbiting another neutron star. Discovered in 1974 by Russell Hulse and Joseph Taylor, this binary system is losing energy, an effect their calculations showed was due to the emission of gravitational waves, as predicted by Einstein鈥檚 general theory of relativity.

Beyond the Milky Way, the map shows 52 of our neighbouring galaxies, collectively known as the 鈥渓ocal group鈥�. For years, astronomers thought our nearest galaxy was the Large Magellanic Cloud. But in 1994, a team of British astronomers discovered the Sagittarius dwarf galaxy, which is even closer. And in November 2003, astronomers announced the discovery of an even nearer dwarf galaxy in the constellation of Canis Major. Still within the local group lies M 31, better known as the Andromeda galaxy. It is the most distant object visible with the naked eye.

Further out from the local group lies a smattering of galaxies, including the Whirlpool, famously photographed by the Hubble telescope. Meanwhile, a galaxy called M 87 harbours the biggest black hole ever discovered, a monster weighing 3 billion times as much as the sun.

The most striking feature of the map, however, is the collection of over 125,000 galaxies and quasars that form part of the results of the ongoing Sloan Digital Sky Survey. The survey is the most ambitious of its kind. Using dedicated telescopes at Apache Point, New Mexico, a team of 200 astronomers is creating a detailed three-dimensional map spanning a quarter of the sky. By 2005 the Sloan map will show the location, distance and brightness of 100 million objects, including 1 million galaxies and quasars. Even with just 15 million objects mapped so far, the project dwarfs previous galaxy surveys, which have never studied more than a few hundred thousand galaxies.

Slice of sky

To avoid the thick shroud of dust and stars in the plane of the Milky Way, the survey is scanning two fan-shaped sections of sky, and the survey of the slice of sky along the equator is virtually complete. Plotted on Gott and Juric鈥檚 projection, the two slices show up as two vast plains of galaxies stretching almost 30 billion light years, separated by a 鈥渮one of avoidance鈥�.

The survey reveals enormous clusters of galaxies separated by giant voids of empty space, and has also uncovered the largest structure ever found, dubbed the Sloan Great Wall of galaxies. Until recently that distinction was held by another band of galaxies known as the CfA2 Great Wall, which was found in 1989 by the CfA2 survey led by John Huchra and Margaret Geller. Measuring a staggering 1.37 billion light years long, the Sloan Great Wall overshadows this previous record holder by more than 600 million light years.

To avoid confusing the Sloan data with all the galaxies pinpointed by the CfA2 survey, Gott and Juric decided against displaying all of Huchra and Geller鈥檚 galaxies. Instead they plotted contour lines showing the density of galaxies in the CfA2 Great Wall. At the heart of these lies the Coma cluster, one of the densest clusters of galaxies known.

What cosmologists are most interested in is the sponge-like structure revealed by the Sloan survey. That is because this large-scale structure reflects what happened in the immediate aftermath of the big bang. Within a mere 10^鈭�35 seconds after the cataclysm, the universe underwent a period of hyper-expansion known as inflation. This enlarged any quantum fluctuations that had popped up, turning a smooth distribution of matter and energy into clumps. When inflation ended, the universe continued expanding: the clumps began to collapse under their own gravity, and eventually coalesced into galaxy structures. By studying how the galaxies are distributed, cosmologists hope to get a better idea about the very early universe.

In addition to the Sloan data, Gott and Juric have picked out the most distant known galaxy. Spotted by the Subaru telescope in Hawaii earlier this year, this galaxy is a staggering 250,000 billion billion kilometres away. Near it lies the most distant quasar, a dazzling object at the edge of the universe that pumps out as much light as 10,000 billion stars. Such a huge amount of light is thought to be released by gas being sucked into the supermassive black hole lurking at its heart. Other quasars highlighted include 3C 273, the first such object to be discovered, and QSO 0957, whose light is bent by the gravitational field of a galaxy in front of it.

Beyond the most distant quasar lies the region where astronomers believe the first stars lit up the cosmos. Before then the universe was filled with gas, dust and radiation, and some of this radiation is still detectable as a faint glow of microwaves. This cosmic microwave background dates from a mere 300,000 years after the big bang.

So, what to do with such a wealth of imagery? While you might spread your map out on the kitchen table, or stick it on a bedroom wall, Gott has grander ideas. His team now plans to display the map on a giant video screen at Princeton. Gott says the screen will display a small portion of the universe at a time, and he hopes to create a movie that scrolls up the map. He also hopes one day to project the map on the side of a building, using a laser beam to paint the picture.

Gott鈥檚 ultimate dream is to see his map displayed around the inside of a lift shaft carrying a glass elevator up 20 floors. Standing in the middle of the elevator, you would see the universe all around you. Each floor would reveal objects 10 times further away than those on the floor below. For one short ride, you could truly describe yourself as a time traveller 鈥� a trip to the top floor would take you right to the beginning of the universe.