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Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
Thousands of scientists in the Russian Academy of Sciences (RAS) are about to lose their jobs as a result of the...
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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Black Hole's Galactic Loop-the-Loop
13 September 2001 7:00 pm
Astronomers have for the first time charted the path of a black hole, by measuring energy from a star perpetually circling it. The black hole's trajectory suggests that the tightly bound pair was ejected from an ancient cluster of stars billions of years ago, according to a report in the 13 September issue of Nature.
The binary system, called x-ray nova XTE J1118+480, was first spotted by the Rossi X-ray Timing Explorer last year. The satellite detected x-rays from hot gas that passes from a faint companion star into the lightweight black hole. The system, 6000 light-years away, flared brightly enough for astronomers to pinpoint its position in May and July 2000 with the Very Long Baseline Array, a network of 10 radio dishes across the U.S. and its territories. The researchers also found the companion star on older sky-survey photos taken 43 years apart.
These positions allowed astronomer Vivek Dhawan of the National Radio Astronomy Observatory in Socorro, New Mexico, and his colleagues to trace out the black hole's orbit. It is radically different from those of the sun and most other stars in the Milky Way. Rather than circling within the flat plane of the galaxy's disk, the pair dives above and below the disk. This giant loopy path resembles the motions of globular clusters, ancient swarms of stars that wander in random patterns around the Milky Way. The team's data, published in Nature, suggest that the system was born in a globular cluster and then spat out via gravitational encounters with other black holes, propelling it onto a new orbit through the galaxy.
Astrophysicist Shrinivas Kulkarni of the California Institute of Technology in Pasadena admires the calculation of the orbit, but he doesn't think it was kick-started inside a globular cluster. His research suggests that when black holes fling each other out of globular clusters, they probably don't pair up with tiny companion stars. Instead, Kulkarni suspects that the black hole and its partner were blasted out of the galaxy's disk by an unbalanced supernova explosion.
Whatever got it started, XTE J1118+480 probably isn't alone: At least 10,000 ejected black holes may wander through the galaxy on similar paths, says Dhawan, although most are farther away and may not have companion stars to reveal their presence.