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Daily Archives: April 6, 2008

Smallest black hole proves a giant find for science

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The discovery in our own galaxy of the smallest black hole known in the universe is a feather in the cap for NASA, but it will present new challenges to future space travelers who may venture too close.
Tiny but intense, with a mass 3.8 times that of the sun and a diameter of only 15 miles (24 kilometers), this black hole in the Milky Way galaxy "is really pushing the limits" of our understanding of the phenomenon, according a NASA scientist from Goddard Space Flight Center in Maryland.
"For many years astronomers have wanted to know the smallest possible size of a black hole, and this little guy is a big step forward toward answering that question," said Nikolai Shaposhnikov in a statement by NASA.
He and colleague Lev Titarchuk made the discovery with the aid of NASA's Rossi X-ray Timing Explorer satellite, and presented the findings earlier this week at an American Astronomical Society conference.
A black hole, which can form when a star collapses in on itself to infinite density, sucks in anything in its gravitational pull, including light. Supermassive or stellar-mass black holes can be billions of times the mass of our sun.
The latest black hole was discovered alongside a normal star in a binary system called XTE J1650-500, named for its coordinates in the constellation Ara. The system was discovered in 2001.
Despite its pint-size, this new record-holder packs an astronomical wallop that should force future space travelers in Earth's galaxy to take note, Shaposhnikov said. Small black holes exert a force comparatively far beyond that of larger black holes found at the center of galaxies.
"If you ventured too close to J1650's black hole, its gravity would tidally stretch your body into a strand of spaghetti," Shaposhnikov said.
The black hole cannot be observed directly, but is detected by its effect on its surroundings. Scientists observe matter trapped in its powerful gravity spiraling inward and getting hotter before being swallowed up.
Black holes also emit massive quantities of X-rays of intensity that varies in a pattern that repeats itself over a nearly regular interval, called a quasi-periodic oscillation (QPO).
Shaposhnikov and Titarchuk used the QPO frequency to determine the black hole's mass — 3.8 times that of the sun — with a margin of error half the sun's mass. The result was below the previous smallest black hole mass record of 6.3 times that of the sun.
The black hole's tiny mass approaches the limits astronomers have predicted for such an object, making it very important to research in fundamental physics.
Below some unknown critical threshold, a dying star should produce a neutron star instead of a black hole. Astronomers think the boundary between black holes and neutron stars lies somewhere between 1.7 and 2.7 solar masses (330,000 times Earth's mass).
Knowing this boundary is crucial for understanding how matter behaves under extraordinarily high density.

Sleep more to slim down, scientists say

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An extra hour between the sheets at night might be the key to shedding excess weight and fighting obesity, according to recent research.
"More sleep could be the ideal way of stabilising weight or slimming," said neuro-scientist Karine Spiegel, of France's INSERM, a public organisation dedicated to biological, medical and public health research.
While poor eating habits and lack of exercise clearly play a role in the global rise of obesity, recent data indicates that lack of sleep may also be a factor, and one that is often under-estimated.
Around 30 surveys carried out on wide population samples in seven countries have underlined a link between lack of sleep and excess weight or obesity in both children and adults, Spiegel said.
The first of the studies, carried out in 1992 in France, highlighted the problem in children and teenagers. Spiegel said the increase in obesity in the US in the second half of the 20th century corresponded with a mounting decrease in sleep.
Two key hormones produced at night which help regulate appetite were at play, she said.
Grehlin makes people hungry, slows metabolism and decreases the body's ability to burn body fat, and leptin, a protein hormone produced by fatty tissue, regulates fat storage.
"We have shown that less sleep (two four-hour nights) caused an 18 percent loss of appetite-cutting leptin and a 28 percent increase of appetite-causing grehlin," she said.
Such hormonal changes made people hungry for foods heavy in fats and sugars such as chips, biscuits, cakes and peanuts, she added.
The sleep loss caused a 23 to 24 percent increase in hunger, Spiegel said, translating into an extra 350 to 500 kilocalories a day, "which for a young sedentary adult of normal weight could lead to a major amount of added weight."
It was unclear whether several years of sleep deprivation could lastingly harm the body's ability to restore a balance between the two hormones.
A study released in Washington in February showed children lacking shut-eye faced a greater risk of becoming obese than kids who got a good night's sleep.
Each extra hour of sleep cuts a child's risk of becoming overweight or obese by nine percent, according to an analysis of epidemiological studies by researchers from Johns Hopkins Bloomberg School of Public Health.
By contrast, children who got the least sleep had a 92 percent higher chance of being overweight or obese than children who slept enough, said the study published in the journal Obesity.
"Our analysis of the data shows a clear association between sleep duration and the risk for overweight or obesity in children. The risk declined with more sleep," said Youfa Wang, a senior author of the study.
"Desirable sleep behavior may be an important low cost means for preventing childhood obesity and should be considered in future intervention studies," Wang said in a news release.
The researchers reviewed 17 published studies on sleep duration and childhood obesity.
Some research recommends that children under five years old sleep 11 hours or more a day, while children age five to 10 should get 10 or more hours of sleep, and children older than 10 should sleep at least nine hours.

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