Words that prompt mental images
SOME words really do conjure up mental images, and that can drive you to distraction - literally.
Zachary Estes at the University of Warwick, UK, and his team asked students to identify a target letter appearing briefly at the top or bottom of a computer screen. Just before the letter appeared, some saw the word "hat" in the centre of the screen. Those students were slower and less accurate at identifying the target letter if it then appeared at the top of the screen (Psychological Science, DOI: 10.1111/j.1467-9280.2008.02051.x).
Estes thinks the brain associates "hat" with the "up" position, and conjures up a mental picture of a hat high on the screen. This distracts you from identifying a letter occupying the same space. "It's like putting two pictures on top of each other - it's difficult to see either of them clearly," he says.
Black hole still a heavyweight
The heaviest black hole formed from the collapse of a single star weighs as much as 33 Suns - double the previous record, new measurements confirm.
Black holes come in a range of sizes, from "supermassive" behemoths weighing billions of Suns to "stellar-mass" objects weighing a few times the Sun's mass.
These stellar-mass black holes form when a massive star dies, sending its outer layers exploding outwards in a supernova and collapsing its core into a black hole. There are limits to how massive the objects can become, based on the mass and chemical composition of the parent star.
The previous record holder is a black hole in the nearby galaxy M33. Called M33 X-7, it was measured to have 16 times the Sun's mass.
In late 2007, astronomers led by Andrea Prestwich of the Harvard-Smithsonian Center for Astrophysics in Cambridge, US, suggested a black hole called IC 10 X-1 was even heftier, with between 24 and 33 times the Sun's mass
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First Stars may have been Dark
The Dark Matter debate is fascinating.
Here is the next saga in the chapter.
The first stars to appear in the Universe may have been powered by dark matter, according to US scientists. Normal stars are powered by nuclear fusion reactions, where hydrogen atoms meld to form heavier helium.
But when the Universe was still young, there would have been abundant dark matter, made of particles called Wimps: Weakly Interacting Massive Particles.
These would have fused together and obliterated each other long before nuclear fusion had the chance to start.
As a result, the first stars would have looked quite different from the ones we see today, and they may have changed the course of the Universe's evolution - or at least held it up.
The theory, published in the journal Physical Review Letters, depends on particles that astronomers can't see, but are certain exist, and physicists have never detected. But the indirect evidence for their existence is overwhelming.
"Dark matter particles make up more than three-quarters of the mass of the Universe," says theoretical physicist Katherine Freese from the University of Michigan.
"In fact, billions of them are passing through each of us every second."
In the early Universe, there would have been even more.
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