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Wolf-Rayet Stars Create Amazing 'Bubbles'

2/25/2011

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Astronomers say that they may have finally found the origins of a series of interesting structural features that can be seen in NGC 2359, a formation also known as Thor's Helmet. 

This is an emission nebula located in the constellation Canis Major, some 15,000 light-years away from our planet. The nebula itself is an estimated 30 light-years in diameter. For comparison, the entire Milky Way is about 100,000 light-years in diameter. 

Inside this cosmic structure, astronomers have identified a number of bubbles and arcs, structures whose existence they could not explain. In a new study, they finally made some headway in this regard.

The experts say that the main culprit is a massive Wolf-Rayet star, that is located in the center of one of the bubbles, as evidenced in the attached image. This category of stars contains celestial fireballs that are both massive and highly luminous.

Wolf–Rayet stars (generally called WR stars) are objects that are relatively old and also very heavy. They tend to be 20 times the mass of our Sun, or more, and their main characteristic is that they are losing mass at very high rates. 

The main mechanism through which this happens is via high-speed solar winds, which take matter out of the star at speeds reaching 2,000 kilometers per second. Average surface temperatures on WR stars are very high, at between 25,000 and 50,000 degrees Kelvin. 

For comparison, the Sun is only about 5,800 degrees Kelvin on its surface. Granted, the corona is significantly hotter, reaching temperatures of millions of degrees, Daily Galaxy reports. 

In the new scientific study, it was revealed that the massive amounts of matter that WR stars lose via solar winds are what cause the bubbles in Thor's Helmet and other similar nebulae. 

However, the data also indicates that other mechanisms are at work inside NGC 2359 that are not visible in other similar locations. According to scientists, the observed differences could be accounted for if we consider the WR star in the nebula is moving at supersonic speeds.

At this point, this is only a supposition. Researchers plan to use advanced space telescopes to get a better view of the entire scene, and perhaps determine whether the star is moving, or if it's staying put.

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Light Can Help Determine if Black Holes Spin

2/25/2011

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For all their “popularity“ with scientists, black holes are still pretty much mysterious in every aspect, including when it comes to their basic properties. For instance, it's still unclear if they spin or not, but that could soon change. A team of scientists is already studying the issue via a new method.

The physics of black holes is still a matter of intense debate, primarily because most studies dealing with the issue are either theoretical, or they deal with the results of computer simulations. 

But a team of investigators believes it may have discovered a way of telling if black holes actually spin or not. They say that this trait could be teased out by analyzing the way in which light is distorted as it moves past sch a dark behemoth. 

Due to their tremendous gravitational pull, black holes not only draw in matter and light from their surroundings, but they also distort the very fabric of spacetime. But the way in which this fabric is distorted is influenced by many factors. 

For example, there is a difference between the gravitational warp caused by a static object and a rotating one. The latter produces an effect called frame-dragging, which was first hypothesized by Albert Einstein in his theory on general relativity.

Its existence was inferred from the theory by Austrian physicists Josef Lense and Hans Thirring back in 1918, and so the phenomenon is also called the Lense–Thirring effect. Detecting it is however a tremendously complex task even around Earth.

However, it's not impossible. The NASA Gravity Probe B (GP-B) mission managed to detect the effect around our planet. Given that Earth deforms spacetime due to gravity and that it also spins, then objects in its orbit should theoretically be slightly drawn into the direction in which it rotates.

The same could be observed by analyzing light bent by black holes. The effect these structures have on light should theoretically differ if they spin, or if they are standing still. 

“Light acquires kind of a spiral motion that carries information about the distorted space-time around a black hole. You can imagine that the light that approaches us from the black hole is not going in a straight line, but in spirals,” says scientist Bo Thidé.

He holds an appointment as a space physicist at the Swedish Institute of Space Physics in Uppsala. The expert, also the coauthor of the new investigation, says that this type of light could be easily analyzed, if astronomers have access to a very large telescope.

“This possibility of direct detection of swirling space and time around black holes is one that we think is quite exciting,” Thidé concludes, quoted by Space. 

Details of the new study appear in the January 13 online issue of the esteemed journal Nature Physics.

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The Universe Is 250 Times Bigger than What's Visible

2/19/2011

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According to a new series of investigations, it would appear that the entire Universe, including both its visible and invisible components, is about 250 times than the visible Cosmos alone is. 

There are several misconceptions going around about how old the Universe is. Cosmologists have been able to refine their results to prove that it is some 13.75 billion years old. This should theoretically mean that we cannot see things that are located further than 13.75 billion light-years away.

And this would be true too, were it not for Universal expansion. The visible parts of the Cosmos are not in fact nearly 28 billion years wide, but 90 billion years wide. This finding was made by analyzing background radiation permeating all space. 

Some photons in the Cosmic Microwave Background (CMB) that have been detected here were determined to have traveled more than 45 billion years before finally reaching our location.

So, we know that the visible Universe is big, but cosmologists have been wondering for a long time how big the rest of it is. They are of course referring to its invisible part, which is undoubtedly much larger than we were led to believe. 

University of Oxford investigator Mihran Vardanyan and his team discovered the answer by creating and studying interesting statistical models of the Cosmos as a whole. The researchers determined that it is some 250 times bigger than the Hubble volume.

This volume is comparable in size to that of the observable Universe. Thus far, conducting studies to analyze the volume of the thing has been very difficult, due to the fact that no one could really determine the curvature of the Universe, Technology Review reports. 

Being able to do so is one of the most important steps in establishing the size of the Cosmos with certainty. Curvature places drastic limitation on size and volume, physicists say. 

There are numerous methods being used in the international astronomical community today for establishing curvature, but the Oxford team used an approach called Bayesian model averaging to take them all into account.

Due to its elegance, this statistical method is bound to be used in other areas of cosmology as well, for placing limitations on a variety of parameters that are currently undetermined.
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    Abraham Samuel

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