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02/19/2009

Let's Go Naked

In my last column I noted the 200th anniversaries of the births of Darwin and Lincoln. This year marks another anniverasry, this time of an event that happened 400 years ago and is the reason for this year being designated the "International Year of Astronomy". It was in November and December of 1609 that Galileo pointed his telescope at the heavens, first at the moon where he saw mountains , valleys and "seas". By mid January of 1610 he had discovered four moons orbiting Jupiter and by July of that year he had discovered the rings of Saturn. Thus began the ongoing quest to probe our universe, its scope, its origins and its ultimate fate.

To mark just a few milestones, in 1785 William Herschel and his sister Carolyn proved that the Milky Way is a huge disk of stars with a central bulge. It would take until the 1920s before Edwin Hubble not only found there were galaxies other than our Milky Way but also found the galaxies were moving away from us - the universe was expanding. Now we know that the universe is expanding even faster as time goes by. At the other end of the time scale, it was 1964 when Arno Penzias and Robert Wilson decided it wasn’t pigeon poop that was causing the noise their radio antenna was picking up from all over the sky. The noise was the cosmic microwave radiation left over from the Big Bang, which we now know happened nearly 14 billion years ago.

Of course, with many spacecraft having passed by or orbited planets and their moons and some having dispatched landers or rovers to our solar system neighbors, we now know more about some spots on Mars, for example, than we know about some locations here on Earth. And we even have photographs of planets orbiting stars trillions of miles away.

What of the future in astronomy? Certainly two key questions to be answered are what exactly are dark matter and dark energy, the prime ingredients of our universe? For those, like Galileo, pointing their telescopes at the heavens, the Holy Grail will be finding small planets the size of Earth orbiting stars in zones where life is possible.

Of all the single objects that astronomers have found in the heavens, the weirdest has to be the black hole. In 1783, the same decade that Herschel and his sister identified the Milky Way as what we call a galaxy, there was a rector of a church in Yorkshire named John Michell. A more recent rector of Thornhill, the Reverend Canon Lindsay Dew, is quoted in the book "The History of Astronomy" by Heather Couper and Nigel Henbest as saying that Michell was a professor of geology at Cambridge when he got married. Apparently, one couldn’t be a professor at Cambridge and be married! So, Michell got ordained and became rector of Thornhill.

In 1783, Michell gave a lecture to the Fellows of the Royal Society in which he theorized the existence of black holes. He had figured out that, if a there was a celestial body that weighed a hundred million times as much as the Sun, its gravity would be so great that light couldn’t escape. In other words the heaviest single objects in the universe would be invisible!

Michell’s idea didn’t catch on and it remained for Einstein to come up with the equations that would predict the existence of a black hole. As we’ve discussed earlier, it was Karl Schwartzchild who, in 1916, took Einstein’s equations and showed that if all the matter in a star was compressed into a small enough space, the result would be that light itself could not escape and the equations broke down, with time itself going to zero! If you were watching a space traveler approaching and being sucked into such a black hole, the traveler would appear to "freeze" in place before entering the space where light could not escape. As noted in Walter Isaacson’s book "Einstein. His Life and Universe", Einstein himself did not believe that what his equations predicted could be real and, even as late as 1939, came up with an argument "proving" this point. However, only a short time later, J. Robert Oppenheimer and a student, Hartland Snyder, produced calculations predicting that a star could suffer gravitational collapse and indeed become a black hole.

Now we know that virtually every respectable galaxy contains a black hole, some having masses equivalent to billions of suns. The black hole forms when a sufficiently heavy star burns up most of its nuclear fuel and begins to collapse, generating such pressure that it explodes, i.e., becomes a supernova shedding some much material. After that, the star begins to shrink, becoming more and more compact. The smaller it gets the more intense the gravity and, finally, the gravity is so strong that, inside a certain diameter shell around the black hole, light cannot escape. This shell, called the event horizon, in essence "clothes" the black hole, preventing us from seeing what happens to the matter, which presumably has been compressed into a ridiculously small dot known in the trade as a "singularity".

A singularity is quite something. Einstein’s equations break down and we are prevented by the clothes, the event horizon, from peering into the hole and watching what happens to all the stuff. In Einsteinian terms, spacetime collapses. Hey, I have no idea what that means! As best I can determine, nobody knows what really happens. In a sense it’s the opposite of the Big Bang, where something emerges from "nothing". (Again, even in the depths of empty space "nothing" is apparently "something", with virtual particles popping in and out of existence.)

With Einstein failing us in such tiny specks of unthinkable density, we are desperately in need of some sort of quantum gravity theory, that holds true for singularities. If all the matter in a black hole gets squashed into an infinitely small speck, the density itself becomes infinitely large! Some theorists say that you can’t just keep on squeezing matter that hard and that there must be some sort of repulsive forces that will stop the squashing at some small but finite size. As a totally naive individual regarding such things, I personally would prefer to think that if I could see inside a black hole, I’d see a ball of stuff in the center. Unfortunately, the hole’s "clothes", the event horizon, won’t allow us in to see what’s really in that singularity.

Which brings us to another possibility, not yet observed and perhaps nonexistent. Suppose we have a singularity that has no clothes, that is, a "naked" singularity. In the February issue of Scientific American, Pankaj Joshi has an article titled "Naked Singularities". Longtime readers of these columns will know that one reason I write about some subjects is that I don’t understand them but nevertheless write about them in hopes that I might con myself into believing that I do understand them! So, let’s go naked.

Joshi describes the event horizon clothing the black hole as a convenient "scientific fig leaf". We know what goes on up to the fig leaf but can’t see what happens to the matter squashed down to our singularity. Famed scientists Stephen Hawking and Roger Penrose proved singularities were unavoidable and Penrose postulated that singularities have to be clothed by event horizons.

However, Joshi and others have made calculations which show that under certain conditions a singularity may form without an event horizon. Such a "naked" singularity would be visible, possibly as a little speck of dust and, unlike a black hole, a naked singularity could not only suck in matter, it could also spit it out. That speck of dust would still be unbelievably heavy but in some cases the gravity would not be superstrong and if you approached in your rocket ship you might be able to turn away from the naked singularity at the last minute and avoid getting sucked in.

One example of an object projected to form a naked singularity would be a collapsing star shaped like a football (an American football). It would collapse to form something akin to a narrow spindle with points at the ends. The gravity never becomes intense enough to trap light but the density of matter becomes highest at the ends of the spindle. Only at these points would a singularity form. Since no event horizon formed, the singularities would be "naked" and would be visible to observers.

OK, you’re right. I don’t know of any stars shaped like a football. But theorists have also calculated the situation for a collapsing star that isn’t uniform in density. Such a star has a structure resembling an onion, with concentric shells of different densities. Their calculations indicate that, under the right conditions, the shells could collapse at different rates and a singularity could form without the formation of an event horizon. In other words, you don’t need a football to get a naked singularity.

Why be concerned about the naked singularity, if any exist? The hope is that if we could find one it would be a lab for studying quantum gravity, which would shed light on what goes on inside a black hole. Even more exciting is the possibility that such an unusual object might provide evidence for or against the ever-so-hard-to-prove string theories. As we’ve discussed previously, string theorists postulate that tiny strings or loops are the ultimate entities making up our universe. The hope is that proving the existence of such fundamental building blocks would provide the link that would tie together the quantum theories of the microscopic world and Einstein’s equations describing gravity and the universe itself. We might have the long-sought theory of everything!

Well, I apologize if this column has been rather obtuse and disjointed and perhaps unintelligible. As I said, I try to con myself into thinking I understand something but I certainly have not succeeded in this case! I promise not to write again about naked singularities unless one is actually discovered somewhere out there in the heavens. Honestly, I’ll be much more excited when they photograph small earth-like planets circling a distant star.

My next column will be posted on March 5 or slightly earlier, depending on whether or not the subject is more easily understood than naked singularities.

Allen F. Bortrum

 



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-02/19/2009-      

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Dr. Bortrum

02/19/2009

Let's Go Naked

In my last column I noted the 200th anniversaries of the births of Darwin and Lincoln. This year marks another anniverasry, this time of an event that happened 400 years ago and is the reason for this year being designated the "International Year of Astronomy". It was in November and December of 1609 that Galileo pointed his telescope at the heavens, first at the moon where he saw mountains , valleys and "seas". By mid January of 1610 he had discovered four moons orbiting Jupiter and by July of that year he had discovered the rings of Saturn. Thus began the ongoing quest to probe our universe, its scope, its origins and its ultimate fate.

To mark just a few milestones, in 1785 William Herschel and his sister Carolyn proved that the Milky Way is a huge disk of stars with a central bulge. It would take until the 1920s before Edwin Hubble not only found there were galaxies other than our Milky Way but also found the galaxies were moving away from us - the universe was expanding. Now we know that the universe is expanding even faster as time goes by. At the other end of the time scale, it was 1964 when Arno Penzias and Robert Wilson decided it wasn’t pigeon poop that was causing the noise their radio antenna was picking up from all over the sky. The noise was the cosmic microwave radiation left over from the Big Bang, which we now know happened nearly 14 billion years ago.

Of course, with many spacecraft having passed by or orbited planets and their moons and some having dispatched landers or rovers to our solar system neighbors, we now know more about some spots on Mars, for example, than we know about some locations here on Earth. And we even have photographs of planets orbiting stars trillions of miles away.

What of the future in astronomy? Certainly two key questions to be answered are what exactly are dark matter and dark energy, the prime ingredients of our universe? For those, like Galileo, pointing their telescopes at the heavens, the Holy Grail will be finding small planets the size of Earth orbiting stars in zones where life is possible.

Of all the single objects that astronomers have found in the heavens, the weirdest has to be the black hole. In 1783, the same decade that Herschel and his sister identified the Milky Way as what we call a galaxy, there was a rector of a church in Yorkshire named John Michell. A more recent rector of Thornhill, the Reverend Canon Lindsay Dew, is quoted in the book "The History of Astronomy" by Heather Couper and Nigel Henbest as saying that Michell was a professor of geology at Cambridge when he got married. Apparently, one couldn’t be a professor at Cambridge and be married! So, Michell got ordained and became rector of Thornhill.

In 1783, Michell gave a lecture to the Fellows of the Royal Society in which he theorized the existence of black holes. He had figured out that, if a there was a celestial body that weighed a hundred million times as much as the Sun, its gravity would be so great that light couldn’t escape. In other words the heaviest single objects in the universe would be invisible!

Michell’s idea didn’t catch on and it remained for Einstein to come up with the equations that would predict the existence of a black hole. As we’ve discussed earlier, it was Karl Schwartzchild who, in 1916, took Einstein’s equations and showed that if all the matter in a star was compressed into a small enough space, the result would be that light itself could not escape and the equations broke down, with time itself going to zero! If you were watching a space traveler approaching and being sucked into such a black hole, the traveler would appear to "freeze" in place before entering the space where light could not escape. As noted in Walter Isaacson’s book "Einstein. His Life and Universe", Einstein himself did not believe that what his equations predicted could be real and, even as late as 1939, came up with an argument "proving" this point. However, only a short time later, J. Robert Oppenheimer and a student, Hartland Snyder, produced calculations predicting that a star could suffer gravitational collapse and indeed become a black hole.

Now we know that virtually every respectable galaxy contains a black hole, some having masses equivalent to billions of suns. The black hole forms when a sufficiently heavy star burns up most of its nuclear fuel and begins to collapse, generating such pressure that it explodes, i.e., becomes a supernova shedding some much material. After that, the star begins to shrink, becoming more and more compact. The smaller it gets the more intense the gravity and, finally, the gravity is so strong that, inside a certain diameter shell around the black hole, light cannot escape. This shell, called the event horizon, in essence "clothes" the black hole, preventing us from seeing what happens to the matter, which presumably has been compressed into a ridiculously small dot known in the trade as a "singularity".

A singularity is quite something. Einstein’s equations break down and we are prevented by the clothes, the event horizon, from peering into the hole and watching what happens to all the stuff. In Einsteinian terms, spacetime collapses. Hey, I have no idea what that means! As best I can determine, nobody knows what really happens. In a sense it’s the opposite of the Big Bang, where something emerges from "nothing". (Again, even in the depths of empty space "nothing" is apparently "something", with virtual particles popping in and out of existence.)

With Einstein failing us in such tiny specks of unthinkable density, we are desperately in need of some sort of quantum gravity theory, that holds true for singularities. If all the matter in a black hole gets squashed into an infinitely small speck, the density itself becomes infinitely large! Some theorists say that you can’t just keep on squeezing matter that hard and that there must be some sort of repulsive forces that will stop the squashing at some small but finite size. As a totally naive individual regarding such things, I personally would prefer to think that if I could see inside a black hole, I’d see a ball of stuff in the center. Unfortunately, the hole’s "clothes", the event horizon, won’t allow us in to see what’s really in that singularity.

Which brings us to another possibility, not yet observed and perhaps nonexistent. Suppose we have a singularity that has no clothes, that is, a "naked" singularity. In the February issue of Scientific American, Pankaj Joshi has an article titled "Naked Singularities". Longtime readers of these columns will know that one reason I write about some subjects is that I don’t understand them but nevertheless write about them in hopes that I might con myself into believing that I do understand them! So, let’s go naked.

Joshi describes the event horizon clothing the black hole as a convenient "scientific fig leaf". We know what goes on up to the fig leaf but can’t see what happens to the matter squashed down to our singularity. Famed scientists Stephen Hawking and Roger Penrose proved singularities were unavoidable and Penrose postulated that singularities have to be clothed by event horizons.

However, Joshi and others have made calculations which show that under certain conditions a singularity may form without an event horizon. Such a "naked" singularity would be visible, possibly as a little speck of dust and, unlike a black hole, a naked singularity could not only suck in matter, it could also spit it out. That speck of dust would still be unbelievably heavy but in some cases the gravity would not be superstrong and if you approached in your rocket ship you might be able to turn away from the naked singularity at the last minute and avoid getting sucked in.

One example of an object projected to form a naked singularity would be a collapsing star shaped like a football (an American football). It would collapse to form something akin to a narrow spindle with points at the ends. The gravity never becomes intense enough to trap light but the density of matter becomes highest at the ends of the spindle. Only at these points would a singularity form. Since no event horizon formed, the singularities would be "naked" and would be visible to observers.

OK, you’re right. I don’t know of any stars shaped like a football. But theorists have also calculated the situation for a collapsing star that isn’t uniform in density. Such a star has a structure resembling an onion, with concentric shells of different densities. Their calculations indicate that, under the right conditions, the shells could collapse at different rates and a singularity could form without the formation of an event horizon. In other words, you don’t need a football to get a naked singularity.

Why be concerned about the naked singularity, if any exist? The hope is that if we could find one it would be a lab for studying quantum gravity, which would shed light on what goes on inside a black hole. Even more exciting is the possibility that such an unusual object might provide evidence for or against the ever-so-hard-to-prove string theories. As we’ve discussed previously, string theorists postulate that tiny strings or loops are the ultimate entities making up our universe. The hope is that proving the existence of such fundamental building blocks would provide the link that would tie together the quantum theories of the microscopic world and Einstein’s equations describing gravity and the universe itself. We might have the long-sought theory of everything!

Well, I apologize if this column has been rather obtuse and disjointed and perhaps unintelligible. As I said, I try to con myself into thinking I understand something but I certainly have not succeeded in this case! I promise not to write again about naked singularities unless one is actually discovered somewhere out there in the heavens. Honestly, I’ll be much more excited when they photograph small earth-like planets circling a distant star.

My next column will be posted on March 5 or slightly earlier, depending on whether or not the subject is more easily understood than naked singularities.

Allen F. Bortrum