Probe Reveals Age, Composition, and Shape of the Cosmos

Courtesy NASA/WMAP science team

WMAP’s all-sky map shows temperature fluctuations from relatively warm (red) to cool (blue) in the microwave light that bathed the universe some 13 billion years ago.

 

Before the first detailed full-sky map of the early universe was unveiled in February, astrophysicists could offer only approximate answers to some fundamental questions: How old is the universe? What exactly does it contain? What is its shape?


The map was compiled from data collected by the Wilkinson Microwave Anisotropy Probe, or WMAP, a NASA orbiting laboratory that was launched June 30, 2001. WMAP has provided an unprecedented overview of the universe as it was 380,000 years after the Big Bang, just after an opaque soup of atom fragments combined for the first time into actual atoms. That process sent out radiation. The probe measured the faint glow of this radiation, known as the cosmic microwave background, across the entire sky.

With this data, the WMAP research team calculated that the universe is 13.7 billion years old (plus or minus 1 percent) and determined that the first stars appeared 200 million years after the Big Bang, far earlier than most previous estimates. They also reconstructed the exact proportions of the contents of the cosmos: 4 percent normal matter, 23 percent dark matter, and 73 percent dark energy. Those figures indicate that the universe is flat and will most likely continue to expand forever.

“The WMAP results are a turning point,” says astrophysicist Charles Bennett of Goddard Space Flight Center, the probe’s lead scientist. “Now we need to ask a whole new set of questions, like what happened in the very first moments of inflation and what is dark matter.”

—Kathy A. Svitil

New Matter Detected at Japanese Accelerator

Take one up quark, add two down quarks, and you’ll have yourself a neutron. Take one regular quark and add an antiquark and you’ll get a meson. Such simple recipes may seem strange, but they are the basis of all matter in the universe. Although theoretical physics allows for much more exotic recipes, physicists have so far only found quarks arranged in pairs (mesons) and trios (baryons, such as neutrons and protons). But in July, Takashi Nakano of Osaka University reported that he had detected a pentaquark, a bizarre subatomic particle built from five quarks: two ups, two downs, and an antiquark.

The particle was found at the SPring-8 particle accelerator in Hyogo, Japan, thanks to the advice of Dmitri Diakonov, a theorist at the St. Petersburg Nuclear Physics Institute in Russia. “He gave me a very concrete prediction of the mass at which it might be found,” Nakano recalls. The experiments were designed to study a particle called the K meson, formed by smashing high-energy gamma rays into the neutrons of carbon atoms. Nakano was searching through the debris data when he found a telltale sign of pentaquarks at precisely the mass—1.54 GeV—Diakonov had predicted.

Two other labs confirmed the pentaquark’s existence. One was a team at the Thomas Jefferson National Accelerator Facility in Virginia led by nuclear physicist Ken Hicks of Ohio University. Although the pentaquark’s life span is rather long by subatomic standards (10-20 seconds), it’s so unstable that it can be created only by high-energy cosmic rays striking Earth’s atmosphere or by the forces at work within the center of a neutron star. “In a sense, it is really a new kind of matter,” Hicks says. “For all we know it could have played some role in the early universe, very close to the Big Bang.”

—Kathy A. Svitil

Sparks Fly From Fusion Reactor

Four or five decades from now, physicists say, nuclear fusion may provide nearly limitless cheap, clean electricity. Then again, that is exactly what physicists said four or five decades ago. But in April, Jim Bailey and his team at Sandia National Laboratories in Albuquerque announced that their experimental device, called the Z-machine, had successfully unleashed a brief burst of fusion power.

Courtesy Randy J. Montoya/Sandia National Laboratories

Electrical discharges illuminate the air and shake the floor around the Z-machine, a fusion experiment in New Mexico. The light show, which lasts a fraction of a second, is a side effect of a huge pulse of current intended to trigger sunlike nuclear reactions.

The $73 million Z-machine, built primarily to test nuclear-weapon physics, is shaped like a 36-spoke wagon wheel. On command, huge capacitors at the end of each spoke discharge a total of 20 million amps of electricity toward an array of tungsten wires at the hub. As the current flows through the wires it sets up a powerful magnetic field and produces a brilliant flash of X-rays. The rays strike a BB-size capsule of heavy hydrogen. If everything goes right, the energy causes the capsule to implode, fusing together the hydrogen nuclei into helium nuclei and releasing energy along with a characteristic spray of neutrons. This is a very different approach from that of most fusion experiments, which use magnetic fields to hold together a cloud of hydrogen while it is heated by lasers or radio waves.

In a series of experiments carried out over a year and ending in March, the Z-machine worked exactly as planned. The amount of energy generated was minuscule. “It was only enough to light up a small lightbulb for a few milliseconds,” Bailey says. “What was significant is that we demonstrated we could produce implosions hot enough and dense enough for a fusion reaction.” To serve as a power plant, the machine would have to churn out more energy than it consumes. It now eats up a million times more energy than it makes, but Bailey is optimistic—as fusion researchers always are—that an upgraded reactor, scheduled for completion in 2006, might within a decade permit reactions that produce more energy than they absorb.

—Kathy A. Svitil