Dark Matter May Have Powered Universe's First Stars

Dark matter may have fueled the formation of the universe's first stars—vast, invisible giants totally unlike the blazing suns of today—scientists say.

According to a new theory, disintegrating fragments of the mysterious substance could have created "dark stars" hundreds of thousands of times wider than the sun around 13 billion years ago, just after the big bang.

Because these stars weren't fueled by fusing hydrogen and helium like known present-day stars, they would have been completely invisible—but scorching hot.

The findings "drastically alter the current theoretical framework for the formation of the first stars," said study co-author Paolo Gondolo, an astrophysicist at the University of Utah.

Scientists still don't know what dark matter is exactly, so the research could shed light on it and other astronomical mysteries, he added.

"We are always searching for ways to determine the nature of dark matter," Gondolo said.

The paper will appear in next month's issue of the journal Physical Review Letters.

Annihilation Engine

According to some theories of the universe, dark matter likely consists of hypothetical particles called neutralinos.

The new paper suggests that neutralinos annihilated each other in the early universe, producing subatomic particles called quarks and their antimatter counterparts, antiquarks.

The heat from this process was enough to prevent embryonic hydrogen and helium from cooling and shrinking. Such contraction ignites the self-sustaining fusion process that powers conventional stars.

"The heating can counteract the cooling, and so the star stops contracting for a while, forming a dark star" some 80 million to 100 million years after the big bang, Gondolo said.

Dark stars, made up mostly hydrogen and helium, would be vastly larger than the sun and other stars—up to 15,000 times the size of our solar system. And instead of shining, they would glow in the infrared.

"With your bare eyes, you can't see a dark star," Gondolo said. "But the radiation would fry you."

Wide-Ranging Implications

The theory may have wide-ranging implications about the importance of dark matter in the earliest stages of the universe.

For example, dark matter is widely believed to have helped with early galaxy formation, said Rennan Barkana, an astrophysicist at Tel Aviv University in Israel who was not involved with the new paper.

But until now it was thought that "the dark matter does not play any significant role in the formation of the star itself," he said.

That's important, because the substance is believed to make up most of the universe's matter, partly because galaxies rotate faster than can be explained by the visible matter within them.

In total, about 23 percent of the universe is thought to be dark matter, as opposed to 4 percent for the ordinary matter that makes up stars, planets, and moons.

The remaining 73 percent is thought to be dark energy, an even more mysterious force helping the universe to expand at increasing rates.

Search Is On

Emanuele Ripamonti, an astronomer at Universita' dell'Insubria in Como, Italy, said that in order for the new research to be plausible, the formation of stars from dark matter must rely on a cascade of events that are not yet well studied.

"Every time they make a choice, the authors pick the 'most likely' option, but in some cases there is no real consensus" about what would happen, he said.

Barkana called the theory intriguing and novel but agreed that more research is necessary.

"It is unclear whether in the end an observational prediction will come out that will allow the dark star possibility to be clearly distinguished from other scenarios," he said.

If dark stars exist, however, they would likely give themselves away by spewing gamma rays, neutrinos, and antimatter, study author Gondolo said. The stars would also be associated with clouds of cold, molecular hydrogen gas that wouldn't normally harbor such energetic particles.

If found, dark stars wouldn't only provide insights into dark matter, he added. They could also help unravel phenomena like the formation of heavy elements—thought to come from exploding conventional stars—and the rapid formation of black holes, which defies theoretical predictions.

"Without detailed simulations, we cannot pinpoint the further evolution of dark stars," he said. "We have to search for them."

"Zombie" Roaches Lose Free Will Due to Wasp Venom

The parasitic jewel wasp uses a venom injected directly into a cockroach's brain to inhibit its victim's free will, scientists have discovered.

The venom blocks a chemical substance called octopamine in the cockroach's brain that controls its motivation to walk, the study found.

Unable to fight back, the "zombie" cockroach can be pulled into the wasp's underground lair, where an egg is laid in its abdomen. The larva later hatches and eats the still living but incapacitated cockroach from the inside out.

"The whole thing takes about seven to eight days, during which the meat has to be fresh," said study co-author and neurobiologist Frederic Libersat of Ben-Gurion University of the Negev in Be'ér Sheva, Israel.

"If you kill a cockroach, it rots within a day."

The mature wasp emerges from the bug victim's body after about a month.

The study recently appeared in the Journal of Experimental Biology.

Zombie Science

The team of researchers at Ben-Gurion University believe that the octopamine discovery is an important piece of the puzzle of how the tropical wasp's venom turns its victims into the living dead.

Octopamine is a brain substance that places insects in an alert state, inspires them to move, and allows them to perform demanding physical tasks.

"It serves the same functions as noradrenaline, which is involved in the fight-or-flight reaction ... in the vertebrate brain," Libersat said.

The team determined that the wasp injects its venom into a specific area of the cockroach's brain, the protocerebrum.

This region, which contains octopamine-secreting nerve cells, controls the ability to start walking. The venom interferes with the release of octopamine, they found.

The researchers then reversed the process: they injected an octopamine-like substance directly into the protocerebrum of cockroaches that had already been turned into zombies by wasp stings.

The result was significant recovery and restoration of the cockroach's free will.

"This helps us understand how movement is initiated in animals," Libersat said. "We know how movement itself is generated, but to understand what makes an animal decide to move or not to move is a different issue."

Parasite Strategies

The jewel wasp is the only parasite known to inject its venom directly into its host's brain.

But other parasites also control the behavior of their hosts, said David Richman, curator of the Arthropod Museum at New Mexico State University in Las Cruces, who was not involved in the new study.

"This is not uncommon. There are a tremendous number of parasites, and they all have different strategies for survival and for propagation of their species," Richman said.

The behaviors of land snails, grasshoppers, and types of ants, for example, can all be affected by parasites.

"Not only that," Richman added, "[some parasites] can take over certain aspects of the host's biology, particularly as you get into microorganisms."

Shuttle Atlantis Launch Delayed

NASA called off Thursday's launch of space shuttle Atlantis after detecting problems with a pair of fuel gauges in the shuttle's external tank.

Shuttle managers said they would try again Friday—if the problem can be solved before then.

Engineers were testing the four engine-cutoff sensors in Atlantis's liquid hydrogen tank, and two of them failed.

Even though they were commanded to indicate the tank was empty, the two kept showing the tank was full, said NASA spokesman Paul Foerman.

At least three of the sensors must work properly to proceed with a launch.

Officials said the problem might be related to wiring and connectors, rather than the sensors themselves. It was not immediately clear how any repairs might be made.

The sensors are critical to ensure that the shuttle's three main engines don't shut down too soon or too late during liftoff. Problems with the sensors have delayed shuttle launches before, most recently in September 2006. The trouble began cropping up following the 2003 Columbia disaster.

NASA had been hoping for an on-time takeoff. Each of the year's three previous shuttle countdowns had ended with an on-the-dot departure.

Atlantis is loaded with Europe's long-awaited space station lab, named Columbus.

The seven astronauts had yet to board their spaceship when the delay was announced.

About 750 Europeans connected to the scientific laboratory—a 2 billion U.S. dollar project begun nearly a quarter-century ago—were in town for the launch and had begun gathering at the space center.

It was yet another disappointing flight delay for the European Space Agency, which has been working on Columbus for more than 22 years.

Columbus is "our cornerstone, our baby, our module, our laboratory," Alan Thirkettle, the European Space Agency's station program manager, said Wednesday.

Columbus will be the second laboratory added to the international space station. NASA's Destiny lab made its debut in 2001, and Japan's huge lab Kibo—which means "hope"—will go up in three sections beginning on the next shuttle mission in February.

Once Columbus arrives at the space station, scientific work can start almost immediately inside the lab, which is essentially packaged and ready to go.

Aside from the interruption caused by the 2003 Columbia tragedy, the actual building of the space station in orbit has gone well, NASA Administrator Michael Griffin said.

That's in stark contrast to the space station's planning and development, which dragged on for years and contributed to Columbus' prolonged grounding.

"We the United States, as the senior partner in the space station coalition, did not plan it well," NASA Administrator Michael Griffin said Thursday, on the eve of Columbus' originally scheduled launch. "It has taken far too long, and I'll just leave it at that."

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