Good News for Space Aliens
In July an international team of scientists announced that they had found the oldest planet ever sighted, an important discovery because it suggests that the chances of finding life elsewhere in the universe are much more likely.
Planets had been thought of as latecomers to the cosmic party, created a long time after galaxies and stars and only when heavier elements, like carbon and silicon, had accumulated in the universe. But this 12.7-billion-year-old planet, an enormous
Courtesy of NASA/H. Richer/University of British Columbia |
Astrophysicists have known something was in that spot since 1992, when radio signals suggested a presence. But most assumed the unknown mass was simply a small star or a brown dwarf, especially since it is located in M4, a globular cluster thought not to have heavy elements. Researchers were shocked when astrophysicist Steinn Sigurdsson of Pennsylvania State University concluded that the object was a planet, based on a series of Hubble Space Telescope observations.
Sigurdsson and his colleagues have retraced the unnamed planet’s colorful history in detail. It had formed around a yellow star located at the outer fringes of M4. Then about 2 billion to 3 billion years ago, it and its star migrated toward the crowded center of the cluster and encountered a neutron star paired with a white dwarf. The neutron star captured the planet and its sun, the white dwarf was bounced out, and the entire system was flung toward the outskirts of the cluster. The yellow star eventually evolved into a red giant and transferred its mass to the neutron star, which sped up to become a pulsar. The red giant turned into a white dwarf. Today we can see this white dwarf, along with the planet, orbiting the pulsar.
In another billion years, Sigurdsson predicts, the system will migrate back to the center of the cluster, where encounters with other stars will rip the group apart, “leaving the planet to float, by itself, in the spaces between the stars,” he says.
The presence of the relic suggests that very early planet formation was common, says Sigurdsson. This means that life could well have evolved around 5 billion or 6 billion years earlier than anyone had expected.
—Kathy A. Svitil
Gamma-Ray Burst Source Located
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Images courtesy of Pete Challis/Harvard Smithsonian Center for Astrophysics |
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BIn April a team of astronomers finally confirmed the origin of mysterious high-energy bursts of gamma rays that randomly pervade the universe about twice a day. The discovery began at 6:37 a.m. on March 29, when Harvard astronomer Krzysztof Stanek’s pager beeped. It was NASA’s High Energy Transient Explorer satellite calling. The probe had spotted a powerful flash of gamma rays in the constellation Leo. Within seconds Stanek and other researchers around the world obtained the coordinates so that they could train their telescopes on the burst—the brightest ever detected by the High Energy satellite. At its peak, the burst was so powerful it was almost visible to the naked eye, emitting a 100 million trillion times more radiation than a solar flare. “In just a few seconds, it produced as much energy as our sun would produce in 10 billion years,” Stanek says.
Astronomers had theorized that gamma rays are born when a large supernova, called a hypernova, spits out jets of material that interact with a star’s outer layers. But no one had empirical proof because gamma-ray bursts are so fleeting and difficult to pinpoint. This time, Stanek and his colleagues instructed the 6.5-meter Multiple Mirror Telescope, atop Mount Hopkins in Arizona, to collect a detailed spectrum over 12 days following the event. Astronomers calculated that if a supernova spawned a gamma-ray burst, a distinctive type of light would appear during the following week. “That is exactly what happened,” Stanek says. “And each day, as the supernova got stronger, the lines [in the spectrum] evolved. There is no doubt there is a supernova there and that it caused the burst. This clinches the case.”
—Kathy A. Svitil
Signs of Primordial Star Ignition Detected
Late in 2002, Wolfram Freudling and two colleagues grabbed some observing time on the Hubble Space Telescope to study the universe’s pristine early days, before exploding stars seeded interstellar space with heavy elements. The results, announced in April, confounded their expectations. Less than a billion years after the Big Bang, the cosmos already showed notable signs of stellar contamination, meaning that the first stars lit up much sooner than astronomers believed.
Hubble’s infrared camera enabled Freudling, an astronomer with the European Southern Observatory in Garching, Germany, to analyze the elements in three quasars—clouds of hot gas swirling into giant black holes—that were up to 12.8 billion years old. According to standard models, the first stars needed at least 500 million years to begin lighting up and another 700 million to 1 billion years to manufacture heavy elements such as iron and spread them through space. Freudling therefore expected that gas around the quasars, which were shining when the universe was just 900 million years old, would be metal-free.
Instead, he and his colleagues found the quasars are surrounded by copious amounts of iron. That means the first stars must have lit up just 200 million years after the Big Bang, a number that dovetails nicely with new results from the WMAP satellite (see “Probe Reveals Age, Composition, and Shape of the Cosmos,” page 37). Together, the two sets of data show that the universe is unexpectedly efficient at building stars. “The next step will be to find and measure quasars farther in the past,” Freudling says. Eventually he hopes to discover when the first stars ignited.
—Kathy A. Svitil
