Greatest Mysteries of the Universe

Do neutrinos hold secrets to the cosmos? For a quarter of a century, Wolfgang Pauli's prediction remained an educated guess. In 1930, the Austrian physicist predicted the existence of a ghostly new subatomic particle. After observing beta decay in a radioac- ered particle must exist to explain the tive nucleus, Pauli noted that an undiscov- resulting spectrum. During beta decay, a proton becomes a neutron by emitting a positron. But Pauli argued the nucleus also emitted an unknown electrically neutral particle. He thought this hypothetical particle had less than 1 percent of a proton's mass. During the 1930s, Italian physicist Enrico Fermi investigated the problem and completed the work Pauli began. Fermi thought the weak nuclear force destabilized atomic nuclei and caused particle transformations. He called Pauli's ghostly particle the neutrino, Italian for "little neutral one." German physicist Hans Bethe, meanwhile, was attacking the question of how stars ...

How many galaxies are in our Local Group? Our Milky Way Galaxy wheels within the Local Group of Galaxies in a relatively quiet corner of the cosmos. The Virgo cluster of galaxies, some 50 million light-years away, plays city center to our boondocks. The Virgo cluster holds an amazing 2,000 "island universes." Our little Local Group, by contrast, contains roughly three dozen galaxies, most of them unimpressive dwarfs. Many, perhaps most, galaxies exist in such small groups scattered throughout the cosmos. The Local Group spans a mere 6 million light-years, and only three large galaxies lie within it. The most significant, the Andromeda Galaxy (M31), is an expansive spiral whose magnificent disk extends 140,000 light-years. Next in size is our own Milky Way, with a disk spanning 100,000 light-years. The third spiral in the group, M33 (sometimes called the Pinwheel Galaxy), measures 55,000 light- years across. The Local Group's remaining members include irregular, elli...

Is Jupiter a failed star? The brilliant planet Jupiter dazzles anyone with a clear sky. Roman observers named Jupiter after the patron deity of the Roman state following Greek mythology, which associated it with the supreme god, Zeus. But when Galileo turned his telescope skyward in 1610, Jupiter took on new significance. Galileo discovered the planet's four principal moons — and witnessed the first clear observation of celestial motions centered on a body other than Earth. Astronomers recognized Jupiter as the largest planet in the solar system long before any spacecraft provided detailed exploration.The planet's mammoth size — 88,846 miles (142,984 kilometers) at the equator — holds 2.5 times the mass of all the other planets combined. This makes Jupiter the most dominant body in the solar system after the Sun. The planet's volume is so great that 1,321 Earths could fit inside it. Jupiter is a magnificent example of a gas-giant planet. It has no solid surface and is c...

hat happens at the cores of galaxy clusters? The centers of rich clusters of galaxies contain the densest concentrations of matter in the universe. They're also among the most violent places we know of. As time rolls on and large galaxies swarm around meeker ones, mergers take place. Big galaxies grow larger by eating small ones. As this happens, worlds are torn apart, stars shredded, and gas clouds compressed into reckless new throes of star formation. We live in a relatively quiet corner of the Milky Way Galaxy. By contrast, the centers of rich galaxy dusters are the universe's most chaotic locations, constantly bustling with activity. Until recently, astronomers thought they understood how galaxy clusters form. As matter collapses inward, pulled by gravity, groups of galaxies and clumps of matter crush together. The monsters of the scene, the big galaxies, fall toward the center, where the most mass resides. Hot gas in the cluster core loses energy and cools by emitting...

How many brown dwarfs exist? In 1975, Jill Tarter, then at NASA's Ames Research Center, coined the term "brown dwarf" Before that time, astronomers hypothesized the existence of so-called black dwarfs, dark objects that were free-floating and lacked the mass to "turn on"as stars. Back then, ideas about low-mass, star-like objects suggested those with masses less than 9 percent of the Sun's wouldn't undergo normal stellar evolution. Instead, they would become "stellar degenerates" heavily laden with dust and characterized by cool outer atmospheres. Various ideas about star formation suggested there should be many brown dwarfs in the galaxy. But being nearly dark, they'd be hard to find. The best strategy would be to look in the infrared part of the spectrum. Lack of success in identifying brown dwarfs, which certainly should have existed, stymied astronomers. They turned to various methods in vain attempts to find them. These included ca...

Galaxies in groups and clusters frequently pass close to each other. They sometimes collide and merge in spectacular fashion. The Milky Way is a dominant member of a tribe of galaxies called the Local Group. Astronomers recognize about three dozen members, most of which are quite small. Although there's a great deal of space between the galaxies in the Local Group, the question arises: Will the Milky Way merge with another galaxy? In fact, our galaxy formed from past mergers, and it will be the scene of many to come. The likeliest scenario of galaxy formation and evolution suggests that galaxies grew in the early universe by merging with many small protogalaxies. Scientists think our galaxy grew during its first few billion years by shredding and cannibalizing as many as 100 small protogalaxies. But the galaxy's merger-mania continues. Astronomers see evidence the Milky Way has gobbled up as few as five and perhaps as many as 11 small galaxies in the past few hundred millio...

How did quasars form? Quasars, short for quasi-stellar objects, were first identified in 1962 by Maarten Schmidt at the California Institute of Technology. They appear as star-like points, but they lie at enormous distances, which means they're emitting incredible amounts of energy. By the 1980s, quasars' prodigious X-ray and radio emissions led most astronomers to believe these objects contain black holes in their centers. In the 1990s, scientists increasingly viewed quasars as young galactic cores where gas, dust, and stars fed a central black hole. One byproduct of the infalling matter is a high-energy jet erupting from near the black hole and hurling material into space. Quasars became part of a spectrum of energetic galaxies called active galactic nuclei (AGN), which also includes Seyfert galaxies, BL Lacertae objects, and radio galaxies. Perhaps these diverse objects, astronomers thought, were similar creatures viewed from different angles. Slowly, the question of wh...

Did comets bring life to Earth? Understanding how life began on Earth engages many fields of science. It's a complex question involving related bits of physics, chemistry, astronomy, and biology. Things OLD WOUND Evidence of ancient impacts still scar Earth's surface. Quebec's Manicouagan Reservoir, some 60 miles <96 kilometers) across, marks the site of an ancient impact crater. Space shuttle astronauts took this orbital image in 1983. nasa have come a long way since the fourth century b.c., when Aristotle taught that life arose on its own from inanimate objects. Critical findings of the past 5 decades all point to a picture of how complex, self-replicating cells could have commenced in Earth's early days. In the 1950s, chemists Harold Urey and Stanley Miller demonstrated that small, life-related molecules, such as amino acids, could have formed under conditions likely present on the young Earth. Phospholipids, components of biological membranes, form cell-like...

What will happen L to the Sun? The Sun is an ordinary star. It bathes the solar system with light and heat, making life possible on Earth. It's as regular as clockwork, and it sets our daily life cycles in conjunction with Earth's spin. Little wonder ancient peoples revered the Sun as a god. Yet the Sun will not always be steady and reliable. Billions of years from now, the Sun's finale will turn Earth — and the entire inner solar system — into a very nasty place. At 4.6 billion years old, the Sun is about halfway through its life. Its adulthood, called the main sequence phase, lasts 10 billion years. When the Sun runs out of hydrogen fuel, it must generate energy by fusing heavier elements. At that point, its main sequence phase is over. In one of the most peculiar transformations we know of, the 5un's helium core, about the size of a giant planet, will contract and heat up. And, in response, the Sun will expand by 100 times. The swollen Sun will consume the plane...

How do massive stars explode? Just as people do, stars have a finite life. Born in dusty gas clouds of a galaxy's spiral arms, stars fuse hydrogen into heavier elements during their energy-producing lifetimes. For stars, mass translates into destiny. The smallest can glow like embers for trillions of years. A middleweight star like our Sun burns steadily for 10 billion years; eventually, it puffs off its outer layers as expanding gaseous shells known as a planetary nebula. The most massive stars — furiously hot, blue-white orbs — shine brightly for a few million years and end their lives in spectacular explosions. Supernova explosions are rare, but incredible. In a mere second, a supernova unleashes as much energy as the sum of all other stars in the observable universe. For weeks, the shattered star may rival the light output of its entire host galaxy. The brightest recent supernova occurred in 1987 in the Large Magellanic Cloud, a satellite galaxy of the Milky Way 168,000 lig...

What happens when galaxies collide? The vastness of space astounds us. Everywhere we look in the night sky, darkness abounds. The distances even to the nearest stars are so vast that caverns of emptiness exist between most objects in the cosmos. And the voids between the majority of galaxies are millions of times larger. Despite the bigness of space, things do go bump in the night. Even on large cosmic scales, in galaxy clusters and groups, whole galaxies slam into each other in ornate dances that last tens of millions of years. Even with relatively small telescopes, examples of merging galaxies are visible to backyard astronomers on Earth. In Canes Venatici, the Whirlpool Galaxy's small companion, NGC 5195, is a separate island universe passing it in the night. Centaurus A, the great high-energy galaxy in the southern sky, is the merged debris from a head-on collision of two galaxies. NGC 4038 and NGC 4039 in Corvus, known as the"Antennae"galaxies, provide a beautif...

How did the solar system form? Astronomers and geologists have several techniques for dating Earth, and, therefore, the age of the solar system. From the radiometric dating of rocks, which measures the known decay rates of radioactive elements, we know Earth and the solar system are approximately 4.6 billion years old.The knowledge does not come from Earth rocks, however, the oldest of which are about 3.9 billion years old. (Earth rocks are constantly involved in vigorous erosion — by plate tectonics and volcanism — making the oldest rocks on Earth extremely hard to find.) Instead, meteorites — chunks of asteroids, the Moon, and Mars — make dating the solar system more accurate. These bodies were left in more pristine form. The oldest radiometrically dated thus far are 4.6 billion years old, and so the solar system itself must have formed near this time. While many ideas in astronomy have changed radically over time, the notion of how the solar system formed has changed little in ...

How did the Milky Way Galaxy form? Taking a telescope out on a clear springtime night and scanning the area of the constellation Virgo reveals an amazing sight: Large areas of the constellation are peppered with faint smudges, the light from distant galaxies bound up in a huge swarm, the Virgo cluster. This area of sky gives us our best look at the closest large concentration of galaxies in the universe. Astronomers have understood the basic properties of galaxies, at least that they're large congregations of stars, gas, and dust far beyond the Milky Way, since the 1920s. But really understanding galaxies, the story of their formation in the early universe and how they have evolved over the past 13 billion years, is a tricky struggle that challenges the best researchers. We know our own galaxy, the Milky Way, best. Astronomers have had more than a century to conduct astrophysical research on tens of thousands of objects within the galaxy. Cosmologists have made great strides ov...

Do we live in a multiple universe? For as long as humans have gazed skyward, a question has loomed in the back of our collective mind: How do we know everything that we see is everything there is? Technology's horizon Speed-of-iight horizon TO THE EDGE AND BEYOND. With current instruments, we can see galaxies out to "technology's horizon." We can't observe galaxies past the "speed-of-light horizon," but they may become visible in the future if the universe's expansion decelerates. ASTRONOMY: ROEN KELLY Multiverse Decades of astrophysical research beginning in the late-19th century established the universe as we see it, culminating with the Big Bang theory. We now know the universe is about 13.7 billion years old and at least 150 billion trillion miles across. But in recent years, astronomers have begun to address a staggering possibility — the universe we can observe, and in which we live, may be one of many that makes up the cosmos. The sugge...

Could a distant, dark body end life on Earth? Although we live in relative quiet within the cosmos, going about our lives and seeing the stars as a distant backdrop, we are very much part of the universe that surrounds us. Dangers lurk in space, as any glance at the Moon's cratered surface confirms. Not only must our planet avoid collisions with Earth-crossing asteroids, but more remote threats exist. If a nearby star went supernova, a gamma-ray burst erupted nearby, or a black hole or stream of antimatter somehow wandered into our neighborhood, it could spell disaster. While astronomers say those events are unlikely, another dark, distant interloper could create havoc on Earth by its mere presence. Where could such trouble come from? The Sun hasn't always been a solitary star. It was born in a group of suns, as all stars are, and its native companions have been scattered by the gravitational tug created by orbiting the galaxy's center. Yet some 5 billion years after t...

What created Saturn's rings? A glance through a small telescope at the planet Saturn is often the experience that turns people on to astronomy. Simply walking outside, setting up a little scope, and enjoying a spectacular view of a distant planet, colorful and beautiful, surrounded by razor-sharp rings, is deeply satisfying. Saturn's rings were also one of the first targets of Galileo Galilei's new telescope some 400 years ago, when he revolutionized human observations of the cosmos. Among the most identifiable and familiar symbols of astronomy, Saturn's rings remain almost as mysterious today as they were to that Italian explorer. Scientists don't yet know the origin of the rings. In 1980 and 1981, scientists got their first great view of Saturn's rings when the Voyager 1 and 2 spacecraft conducted scientific operations up close. Saturn's globe measures 74,900 miles (120,590 km) across; its rings span 300,000 miles (483,000 km). The rings are divided i...

How could we recognize life elsewhere in the cosmos? Living things could permeate the universe. With at least 25 thousand billion billion star systems out there, it's an incredible conceit to think Earth is the only planet in the whole universe hosting life. Yet over the history of astronomy, we know of only one planet that hosts life — ours. If we were to find life elsewhere, whether microbes in our solar system or more complex beings farther away, how would we recognize it? It might not be easy. But there are starting points."Astrobiologists argue some properties must be universal to life wherever it occurs,"says Alan Longstaff, an astronomer and chemist at the Royal Observatory in Greenwich, England. First, life is defined as a complex chemical system that uses energy, generates waste, reproduces, and takes part in evolution over time. The successful critters on Earth, and presumably in other places too, exist in huge numbers. They also can replicate themselves succ...

Why did Venus turn itself inside-out? Years ago, planetary scientists thought of Venus as Earth's sister planet. Similar in size, both close to the Sun, both rocky bodies, Earth and Venus were practically considered two of a kind. That abruptly changed, however, when astronomers got their first close- up look at Venus. The moment arrived in 1962, when Mariner 2 flew by the planet, and far more forcefully in 1970, when Venera 7 touched down on the hellishly hot surface. Not only do surface temperatures on our sister planet exceed 750° F (400° C), but Venus'thick carbon- dioxide atmosphere produces a greenhouse effect that hosts sulfur- dioxide and sulfuric-acid clouds. It's not a friendly environment for living things of any sort. VOLCANIC VENUS. Volcanoes in a region on Venus called Guinevere Planitia lowland suggest thick, sticky lava oozed from a point at the surface here. The center volcano spans 31 miles (50 km). Scientists'understanding of Venus and its geology...

Should Pluto be considered a planet? Ever since Neptune's 1846 discovery by German astronomer Johann Galle, discrepancies in its orbit suggested another planet existed far beyond it. Thus, the search for Planet X began, with "X" representing "unknown." Astronomers at many institutions responded, but none with the vigor of American philanthropist Percival Lowell, who determined his observatory should be responsible for finding the next new world. In 1930, an extensive search at Lowell Observatory in Flagstaff, Arizona, by the young American astronomer Clyde Tombaugh paid off when he found images of the new planet on two sepa rate photographic plates, revealing its motion against the background stars. Astronomers had found Planet X, now called Pluto (after the Roman god of the Pluto's planetary death blow came August 24, 2006, at the IAU meeting. underworld). However, after analyzing the new planet's orbit, astronomers declared Pluto had too little ma...

Does inflation theory govern the universe? Ever since the Big Bang theory of the origin of the universe was proposed in 1927, the idea has had its skeptics. The radical concept stated that the universe is expanding; run time backwards, and al! matter and energy intersect at a point in time 13.7 billion years ago, the moment of the "bang." Big Bang cosmology has received enormous support from observational tests. In 1929, American astronomer Edwin Hubble observed galaxies generally recede from us; that was the lynchpin of the evidence. In 1964, Bell Laboratories physicists Arno Penzias and Robert Wilson discovered the faint echo of the Big Bang — the cosmic microwave background radiation (CMB). Along with the expansion of the universe and the CMB, nucleosynthesis, the process by which light elements formed in the early universe, is explained by the Big Bang model. But the Big Bang does not yet explain it all. Although by the MINUSCULE TIME. How much is 10 34 second? To...

Does every big galaxy have a central black hole? In the early 1960s, astronomer Maarten Schmidt of the California Institute of Technology made a breakthrough discovery. Looking at several stars that were strangely bright at radio wavelengths, Schmidt obtained a spectrum of the"star"3C 273 and found its distance to be extremely large. It wasn't a star at all, but a remote, extraordinarily energetic object that looked like a star — a quasi-stellar object, or quasar. For many years, the mystery of exactly what quasars were remained unsolved.They baffled astronomers at every turn: Their spectral lines were shifted by an incredible amount toward the red end of the spectrum; because of their great brightnesses, they must represent the brightest objects in the universe, astronomers deduced. But what could be causing such an amazing outpouring of energy, apparently so early in the cosmos' history? The first quasar identified, 3C 273, lies in the constellation Virgo 2 bil...

Are there other planets like Earth? One of the astonishing breakthroughs in observational astronomy of the 1990s was detecting the first planets outside our solar system. As of November 2006, astronomers had found 210 extrasolar planets in 180 different planetary systems. The bulk of these planets are massive Jupiter-sized worlds. As of yet, technology does not allow astronomers to find distant earthlike planets around other stars. But that's not to say the search for such worlds hasn't begun. Despite the fact that earthlike planets have not yet been found, astronomers feel there's good reason to think many exist.The history of extrasolar-planet discoveries around ordinary stars reaches back to 1995, when astronomers detected a planet circling the star 51 Pegasi.The planet is a gas giant more massive than Saturn that orbits its star every 4.2 days. The planet is so dose to its star {Mercury orbits the Sun every 88 days), that astronomers termed it and many other massive...

Why does antimatter exist? In the earliest days of the universe, shortly after the Big Bang, the cosmos was awash in particles. Not all of them were normal particles of matter, however. Corresponding with each type of particle is an antiparticle with the same mass and spin. The nature of our universe results from the fact that matter exists in slightly more quantity than antimatter. The difference is slight, however: For every billion particles of antimatter, there must have been a billion and one particles of matter in the early universe. Everything that exists — galaxies, stars, planets, trees, people — owes its existence to the slight surplus of matter. The question of why antimatter exists and why matter is slightly more abundant dates to 1928, when British physicist Paul Dirac described the behavior of electrons, Dirac worked with quantum mechanics and relativity and worked out an equation governing how electrons should interact with other particles. Dirac's equation pred...