Discovery chasing space station

Shuttle Discovery chased the international space station in orbit Wednesday as its seven astronauts geared up for a laser inspection of their ship's wings.

It was the first full day of what NASA considers to be the most complicated space station construction mission yet. The shuttle was to reach the station Thursday.

NASA's space operations chief, Bill Gerstenmaier, said after Tuesday's liftoff that the astronauts face a tremendous series of challenges, but noted, "I can't think of a better start to this mission than what we got today." It was the third on-time shuttle launch in a row.

At least six pieces of foam insulation came off Discovery's fuel tank during liftoff, but because that occurred after the crucial first two minutes, the debris posed no risk to the shuttle, officials said.

"It's preliminary only, but it did look like a clean ascent," Mission Control informed Discovery's commander Pamela Melroy, only the second woman to lead a shuttle crew.

Astronauts woke up early Wednesday to "Lord of the Dance," which begins with the lyrics "I danced in the morning when the earth was begun, I danced in the moon and the stars and the sun." Melroy said it was one of her favorites songs and thanked her husband, Doug, for tipping off Mission Control.

Melroy and her crew were to use a laser-tipped inspection boom Wednesday to check Discovery's vulnerable wings and nose, standard procedure since the Columbia accident.

They will go extra slow, however, for a thorough check of three wing panels that may have cracks just beneath a protective coating. Even though NASA's own safety group wanted to delay the launch, senior managers decided a week ago that wing repairs were unnecessary.

NASA is extra sensitive about launch debris and the shuttle's thermal shielding ever since a hole in the wing brought down Columbia in 2003, the result of a strike by a slab of fuel-tank foam.

A much smaller piece of foam broke off a bracket on the fuel tank during the last launch in August, possibly along with ice, and gouged Endeavour's belly. That led to changes to Discovery's fuel tank to prevent dangerous ice buildup from the super-cold propellants.

Discovery's primary payload is an Italian-built compartment, about the size of a small bus, that will serve as the docking port for science labs due to arrive beginning in December. Italian astronaut Paolo Nespoli is personally delivering the pressurized chamber, called Harmony.

During their 1 1/2-week station visit, the astronauts must install Harmony, relocate a giant girder and set of solar wings, extend those solar wings and radiators, and test a thermal tile repair kit. Five spacewalks are planned, which will be the most ever conducted while a shuttle is docked at the station.

Astronaut Daniel Tani will move into the station once Discovery docks. He will replace Clayton Anderson, who will return to Earth on the shuttle after five months in space.

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Monster Black Hole Can't Be Explained

Astronomers: Monster Black Hole Can't Be Explained

A stellar black hole much more massive than theory predicts is possible has astronomers puzzled.

Stellar black holes form when stars with masses around 20 times that of the sun collapse under the weight of their own gravity at the ends of their lives.

Most stellar black holes weigh in at around 10 solar masses when the smoke blows away, and computer models of star evolution have difficulty producing black holes more massive than that.

The newly weighed black hole is 16 solar masses. It orbits a companion star in the spiral galaxy Messier 33, located 2.7 million light-years from Earth. Together they make up the system known as M33 X-7.

"We're having trouble using standard theories to explain this system because it is so massive," study team member Jerome Orosz of the University of California, San Diego, told SPACE.com.

The black hole in M33 X-7 is also the most distant stellar black hole ever observed.

The findings, detailed in the Oct. 17 issue of the journal Nature, could help improve formation models of "binary" systems containing a black hole and a star.

It could also help explain one of the brightest star explosions ever observed.

Black hole eclipse

Black holes can't be seen, because all matter and light that enters them is trapped. So black holes are detected by noting their gravitational effects on nearby stars or on material that swirls around them.

The companion star of the M33 X-7 pair passes directly in front of the black hole, as seen from Earth, once every three days, completely eclipsing its X-ray emissions.

It is the only known binary system in which this occurs, and it was this unusual arrangement that allowed astronomers to calculate the pair's masses very precisely.

The tight orbits of the black hole and star suggests the system underwent a violent stage of star evolution called the common-envelope phase, in which a dying star swells so much it sucks its companion inside its gas envelope.

This results in either a merger between the two stars or the formation of a tight binary in which one star is stripped of its outer layers.

The team thinks the latter scenario happened in the case of M33 X-7, and that the stripped star exploded as a supernova before imploding to form a black hole.

However, something unusual must have happened to M33 X-7 during this phase to create such a massive black hole.

"The black hole must have lost a large amount of mass for the two objects to be so close," Tomasz Bulik, an astronomer at the University of Warsaw in Poland, writes in a related Nature article. "But on the other hand, it must have retained enough mass to form such a heavy black hole."

The team estimates the black hole's progenitor must have shed gas at a rate about 10 times less than models predicted before it exploded.

"[M33 X-7] might thus provide both the upper and lower limits on the amount of mass loss and orbital tightening that can occur in the common envelope," added Bulik, who was not involved in the study.

Twin black holes

If other massive stars also lose very little material during their last stages, it could explain the incredible luminosity of 2006gy, one of the brightest supernovas ever observed, the researchers say.

One day, the lone star in M33 X-7 will also disappear, notes study team member Jeffrey McClintock of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

"This is a huge star that is partnered with a huge black hole," McClintock says. "Eventually, the companion will also go supernova, and then we'll have a pair of black holes."

While 16 solar masses is hefty for a stellar black hole, it is miniscule compared with the black holes thought to lie in the heart of many large galaxies, including our own.

Such "supermassive" black holes have masses millions to billions times that of our sun, but they are thought to form by mechanisms different from the stellar variety.

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