Monday, 8 February 2010

Quasars/Black Holes

An interesting article on Quasars and Black Holes. These are not something we can fully comprehend but it is good to have a general idea of what these are and how they come about. It is also good to know what’s out there - not in the streets, not in another country, not on the other side of the Earth - but out there in the Milky Way. It also gives us a perspective of how small we are - and of the mysteries, the unknown out there.


They are the oldest objects we know of in all the universe. So far out on the edge of creation that their light has taken ten billion years – twice the age of Earth – to reach us, they are one of the great mysteries of modern astronomy. Each of them outshines a hundred galaxies, ten thousand billion stars, and yet may be little larger than our solar system. What makes them shine so brightly? How were they formed? What, in fact, are they? We do not know. 

We call them “quasars,” an abbreviation of “quasi-stellar radio sources.” In other words, they look like stars and they give off radio waves. These stars, in fact, were seen and photographed by astronomers for decades and they seemed to be merely distant members of our own galaxy, the Milky Way. In the early 1960s, however, radio astronomers detected powerful sources of microwaves in the sky. When optical telescopes were turned toward these radio sources, nothing unusual was found – just these seemingly ordinary stars. 

But, with further observations, the seemingly ordinary stars turned out to be quite un-ordinary – not even stars at all … 

Astronomers analyze the light of a star by breaking it up into a “spectrum,” a rainbow, accomplishing with lenses and prisms what nature does with water molecules suspended in the air. By examining this spectrum, scientists can tell how hot a star is, what it is made of, how fast it is rotating on its axis, and so on. However, when astronomers tried to examine the spectra of quasars, they found something surprising. Quasars were unlike any other object observed in the sky; their spectra were completely strange. 

How could this be? Astronomers grasped for explanations, and eventually they found one – but the explanation proved almost as mystifying as the observations. 

When a locomotive is approaching you, and it blows its whistle, the sound of that whistle is higher in pitch than it would be were the locomotive standing still. Conversely, as the locomotive moves on down the tracks away from you, its whistle is lower in pitch. This is the Doppler effect, and it applies to light waves just as it applies to sound waves. By analyzing a star’s spectrum, and noting which way the light waves are shifted, we can determine if that star is approaching us or receding from us. If the “pitch” is raised – if the light waves are shifted toward the blue end of the spectrum – then the object is approaching; if the waves are pitched lower, and shifted toward the red end of the spectrum, the object is receding. An object heading toward us thus shows a blue shift; an object moving away, a red shift. 

Now, as scientists analyzed the light of quasars, they found it had been re-shifted – and re-shifted to an enormous degree. 

Expanding Universe 
Earlier, scientists had found that the entire universe seems to be expanding outward, and they found that almost all the galaxies outside our own display red shifts, and thus are receding. Every other galaxy is not, of course, fleeing from our own; instead, the whole universe is expanding, and every galaxy is moving farther away from every other galaxy. It is as if we are seeing the aftermath of a great explosion – and, indeed, we are. According to some scientists a “Big Bang” took place 15 billion years ago; at that time all the matter in the universe, collected in one “cosmic egg,” exploded outward, and Creation began. 

The greater the red shift a galaxy displays, the farther away it is from us, and the faster it is moving away. The quasars displayed enormous red shifts, and thus they had to be very far away, and receding very quickly. 
In fact, the farthest quasars we have yet observed are over twelve billion light-years away, and are receding at over ninety percent of the speed of light. (A light-year is about six trillion miles. If you cannot imagine twelve billion light-years – or even just one – you are not alone. No one can.) This means that the quasars were formed soon after the birth of our universe. In effect, we are looking into the past as we look outward into the cosmos. And, as we see the quasars twelve billion light-years away, we are viewing the universe as it must have been when it was young. 

But what are quasars? 
They look like stars, but to be seen at such a great distance they must be far brighter than any star. In fact, the average quasar is a hundred times as bright as our galaxy – as bright as ten thousand billion stars put together. But a quasar is not a hundred times as large as our galaxy – far from it. Indeed, most quasars seem to be only a few light-years in diameter. 

Astronomers were perplexed. How can such small objects be so bright? What makes quasars shine? 

We live in a violent universe, a universe of powerful and uncontrollable energies. The quasars, so small and yet so bright, must be powered by these violent energies – and evidence of that violence is visible even at our distant vantage point. Some of the quasars have huge jets of gas spewing out of their cores – evidence of vast energies at play. What, then, is the source of these energies? 

Modern physics have shown that “antimatter” exists – matter that is reversed in electrical charge. When antimatter meets the ordinary matter of our universe, the opposite charges cancel out, both matter and antimatter are destroyed, and pure energy is created. 

Perhaps the quasars are where antimatter and matter meet, in mutual destruction, that would account for the huge amounts of energy created. But there are other theories as well, some even stranger …. 

Black Holes 

A “black hole” is created when a star collapses under the pull of its own gravity. If the gravity is intense enough – thousands of times as strong as the earth’s gravitational field – then the matter of the star will be literally crushed out of existence. Eventually an object will be formed that is so dense with such powerful gravity that not even light can escape from it. This is a black hole. 

Matter can fall into a black hole, but it can never get out; black holes act as cosmic vacuum cleaners, feeding on the dust and gas between the stars. As the dust or gas is pulled into the black hole, it is accelerated to incredible velocities, and as it’s pulled in radiation is emitted – x-rays. Thus a black hole is illuminated by the material it devours. 

Now, the larger a black hole becomes, the stronger its gravitational field grows and eventually it is swallowing not only dust and gas, but entire stars and planets. As the ever-increasing torrent of matter is sucked in, more and more radiation is given off. There is no limit to the size of a black hole; a black hole as massive as a billion suns might occupy the center of galaxy, pulling in more stars all the time. Such a black hole would be little larger than our solar system and yet it would produce more energy than all the rest of its galaxy. 

Such a black hole sounds very much like our description of a quasar – comparatively small, but producing incredible amounts of energy. Could it be then that the quasars are giant black holes greedily devouring their parent galaxies? 

Maybe. It is a bizarre and frightening image. But there is yet another explanation. 

Some astronomers speculate that there are short-cuts through space, “wormholes” in the fabric of the universe. Two points might be separated by billions of light years in space, but they might be connected by a wormhole, a sort of space warp, only a few million miles long … or less. 
Earlier I noted that holes are always drawing matter in, and never letting any of it back out again. That may not be quite true. Some scientists have speculated that a black hole is one end of a wormhole – departure stations for a sort of universal subway system, if you like. Matter would fall into a black hole, travel through a wormhole in space, and emerge – somewhere else. 

Could that “somewhere else” be the quasars? 
This is only speculation; there is no proof. Indeed, there may never be. It is hard to see how we could prove such a theory. 

But it is an awe-inspiring image. Imagine matter being sucked into a black hole here, in this part of the universe, then being carried, somehow, across a short-cut in space, to a point billions of light-years distant where it re-enters our universe in a torrent of light and energy. 

That emergence point, that other end of the worm hole, could be a quasar. If so, we have at least a partial answer to the question of quasars. And yet, as happens so often in astronomy, our answer only poses still more questions, and, in the end, reveals our universe to be a place of strangeness, complexity, and infinite wonder. 

By Dave Stover 

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