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| SCIENCE TRIBUNE | Thursday, September 13, 2001, Chandigarh, India |
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A colossal black hole at centre of our galaxy Locating hidden treasure SCIENCE QUIZ |
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A colossal black hole at centre of our galaxy MOST of us have grown up believing that black holes are the stuff fit for sci-fi comics. Even when scientists theorised that a huge black hole does lurk at the centre of the Milky Way — as also at the centre of most other galaxies — it was given out that this was only a supposition which would be near impossible to prove because by its very definition a black hole is invisible since even light cannot escape it. And now, out of the blue, comes the news that astronomers have made certain startling observations that represent what may be the most direct evidence for the black hole’s existence, that too right at the centre of our Milky Way galaxy. That in astronomical terms means finding something right in your own backyard. Obviously, the development will take sometime to register, and a final answer may still be a decade away, but the fact remains that this is an epochal discovery. To fully comprehend the importance of the landmark detection, some background knowledge about the black holes is necessary. Black holes are the end result of the stellar evolution of the stars that are at least 20 times more massive than the sun. When such a star exhausts its nuclear fuel, fusion reactions in the core die out. Since it is left with no source of energy to offset the inward pull of gravity, the star’s core quickly collapses and a black hole is born. The matter inside it is so dense and its gravity so strong that not even a beam of light can escape it. A black hole is invisible; its gravitational effects are not. Whenever a black hole gobbles up matter, it is accelerated to extreme velocities. Radiation is emitted as the material spirals inward, increasing in energy. Telltale X-rays burst forth powerfully. NASA’s two-year-old, $1.5-billion orbiting Chandra observatory, the world’s most powerful X-ray telescope, found exactly such a flare coming from the direction of the black hole recently. “It is as if the material sent us a postcard just before it fell in,” says an ecstatic Fred Baganoff, an astronomer at the Massachusetts Institute of Technology (MIT) who is the lead author of the report published in the journal Nature. The monster packs the mass of 2.6 million suns in an area no bigger than the distance from the sun to the earth (just 93 million miles across, or one Astronomical Unit). It is 24,000 light years from the earth. (Light travels about six trillion miles in a year.) While the Milky Way is 100,000 light years in diameter, the area where the black hole might be is about 10 light minutes across. It devours everything in its close proximity. In fact, the voracious black hole was found right while it was snacking matter that came near it. Physics theory says that the hole is surrounded by a mysterious boundary or membrane, which the scientists call the event horizon. This imaginary surface separates the inside and outside of the black hole. Once something crosses this point of no return, it can never escape the black hole. The new observations provide clinching proof that those theories are correct and astrophysicists can now probe near the event horizon. “Modern physics does not have a theory that could account for this object if it is not a black hole,” says Fulvio Melia, a University of Arizona astrophysicist who is not directly involved with the new research. Even if the sighting does not provide clinching evidence about the existence of the matter-sucking drains, it does rule out any other explanation that scientists can imagine for the weird cosmic behaviour. The same group of astronomers had pointed the telescope towards the centre of the galaxy on September 21, 1999, also. It did detect X-rays coming from there, but their intensity was disappointingly low. It was giving out the energy of only one sun when it could have been spitting out the energy of millions of suns, says a member of the team. But this time when they turned Chandra towards the centre of the galaxy on October 26-27, 2000, the powerful fireworks took their breath away. “It suddenly started belting out a great deal of energy, 40 times as bright as our sun,” Gordon Garmire, a member of the team from Penn State University, remembers. These burned brightly and then receded in a matter of hours. “When we saw that light curve, everybody was dancing up and down in the hallways.” The flare lasted about three hours but dropped in intensity by a factor of five for a period of about 10 minutes right at its apparent peak. This drop gave the researchers the evidence they needed to compute the size of the black hole. The Milky Way galaxy is well spaced out. For instance, the nearest star to our sun is 4.2 light years away. But more than 10 million stars are known to orbit within a light year of the galaxy’s centre, dashing along at phenomenal speeds of up to 3.1 million miles per hour. Scientists are divided on what is causing the flares. Many are of the view that the fast swirling of stars is proof enough that something very massive is pulling them in. According to them, it is some combination of sudden heating of gas as it enters the black hole and the vagaries of the unstable magnetic field that interacts with the hot gas at the hole’s event horizon. But there are some astronomers who wonder whether it might only be a bunch of superdense dark stars, another kind of mysterious cosmic object. Chandra will be pointed towards the black hole (the area known as Sagittarius A+) in April again to determine whether flares are common or rare events. Either these take place all the time or we are the luckiest people in history to capture the events in a few hours of viewing time. Incidentally, Chandra is named after Indian scientist Chandrasekhar. Launched into orbit two years ago, it uses four cylindrical nesting mirrors to funnel incoming X-rays. No other instrument in the world can boast of such resolution and sensitivity. Since the atmosphere absorbs such rays, ground-based telescopes cannot detect them. The existence of black holes at the middle of most big galaxies was theorised by Albert Einstein in his General Theory of Relativity. In fact, scientists believe that there are billions of black holes in the universe, including many that are thousands of times more massive and vastly more luminous than the one detected at the centre of the Milky Way. Astronomers agree that black holes are extremely important to cosmology. Indirectly they tell us that our relativistic theory of gravity and space-time provided by Einstein’s general relativity is fundamentally correct, so that when we use these same equations to study cosmology we have some confidence that they may be correct. Directly, black holes tell us that the universe can hide much of its matter in a way that still contributes to the total mass of the universe, but may not contribute to the abundances of certain primordial elements such as hydrogen and helium. If enough black holes were produced soon after the big bang but before the first few minutes, this could have an impact on the relationship between how rapidly the universe is expanding and the origin of the primordial element abundances. But it is expected that most black holes formed long after the big bang by stellar evolution, and these black holes may contribute to the missing mass in the universe up to the maximum limit set by the primordial element abundances themselves. Will the black hole at the centre of the Milky Way eventually eat all the matter in our galaxy? If the universe is destined to expand forever, the answer to this is believed to be true, but the time scale for this to happen is... astronomical. According to astronomers, the galaxy will be eaten from the inside out as the orbits of the stars in the galaxy continue to lose energy via the emission of gravitational radiation. The amount of orbital energy a star near the sun’s distance loses is incredibly small, but over the course of an estimated 10 raised to the power of 60 years or so, enough energy will be lost that it will have sunk into the centre of our galaxy and be gobbled up by the 100 billion solar mass black hole that has now formed there by eating up all the other stars interior to the sun’s orbit around the galactic centre. After something like 10 raised to the power of 160 years or so, even this black hole will vanish because, as all black holes are believed to do, it too is radiating energy and evaporating. In the end, all that is left over in the universe will be no black holes and a thinning soup of electrons, anti-electrons and photons. Phew! That may be scary but the small consolation is that nothing cataclysmic is foreseen in the near future. So, don’t lose sleep at all. |
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Locating hidden treasure STUDYING the earth’s past records of continental drifts, scientists are now able to locate hidden treasure troves of gold and diamonds. Delivering the keynote address at an international symposium on “applied Geochemistry” in Hyderabad, Robert Kerrich of University of Saskatchewan, Canada, said one such continental drift and the formation of a new arch was responsible for 500 tonnes of gold found in a region of Canada. Using this process, it would now be possible to locate gold deposits in various parts of the world. Gold formation epochs can be plotted by going back to the earth’s crustal movements, he said. In the Canadian event, there was a supercontinental drift 2.7 billion years ago. Records now indicate that the gold mine was formed in the last stages of this drift. This was about 10-15 million years ago.
PTI |
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SCIENCE QUIZ 1. This Swiss physician and alchemist of the medieval period studied in depth the relationship between medicine and alchemy and laid the foundation of this study called “latrochemistry.” He named himself Paracelsus after the great Roman physician Celsus. What was the actual name of this writer of several books on medicine who also stressed that a physician should be a surgeon as well? 2. EELS is new method that uses an electron beam for detecting very tiny cracks in metals such as those used in pipes, bridges, structures of buildings and railway tracks. What does EELS stand for? 3. Pan masala, abundantly consumed throughout India, is a mixture of areca nut, catechu, lime, cardamom and some flavouring agents. It also contains toxic metals like lead, cadmium and nickel. In addition to mouth, in which other organs of the human body can the prolonged use of pan masala cause cancer? 4. A pine tree with scientific name pinus gerardiana grows in the Himalayas at heights ranging from 2,000 to 5,000 metre. Its cones yield small-sized seeds, which are expensive but very delicious dry fruits. What is the household name of these fruits? 5. A small worm like creature serves as a natural plougher, reduces acidity of the soil, supplements protein and can be used for composting. Which is this creature that is known as a friend of the farmer and is also used by the some for medicinal purposes? 6. When a rock is squeezed by applying stress, it deforms and eventually fractures but before fracturing takes place the rock swells due to opening and extension/widening of cracks in it. What is this phenomenon of increase in size of volume called which occurs when the applied stress is about half of the breaking stress of the rock and may be used in future for predicting earthquakes or volcanoes? 7. YAHOO is a term commonly used in computer technology. What is the full form of YAHOO? 8. Which is the fastest bird? At how much speed can it fly? 9. Some people use oils of lavender, peppermint, rosemary, eucalyptus etc to massage their bodies and to cure certain mild ailments. What is this type of cure called? 10. Scientists at an institute located in Kerala have recently developed a perennial and evergreen variety of a hardly plant cinnamon. This variety, named “Sugandhini”, produces leaves which are rich in oil content and eugenol, used as a flavouring agent and a fragrant in industry. Name this institute. Answers 1. Theophrastus Bombastus von Hohenheim |
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