Life in the Extreme


 
As for the forces, electromagnetism and gravity we experience in everyday life. But the weak and strong forces are beyond our ordinary experience. So in physics, lots of building blocks take 20th or perhaps 21st century equipment to explore. ~ Edward Witten
 
Is there extraterrestrial life out there? What does it look like? We have explored the possibility of plasma-based life (New Myths-September 2009) that can live inside stars and the space in between. We have seen the possibility of life based on chemicals other than our carbon-water-based life here on earth (New Myths-March 2011). Now we have some scientists who are proposing some even more bizarre ideas.
 
On November 28, 1967, British radio astronomer, Antony Hewish and his student, now retired British astrophysicist Jocelyn Bell Burnell who was a postgraduate student at the time, observed a transmission coming from outer space that was happening at regular intervals of 1.33 seconds. Naturally, being conservative scientists, though they may have wished otherwise, they did not suspect extraterrestrial intelligence signaling; however, they could not help but call the signal LGM-1 an abbreviation for “little green men.” In an effort to eliminate their pet possibility of extraterrestrial communication, they looked for alternative explanations for the pulses. They eliminated known stars, instrumental effects and defects and human activity as possible scenarios. Maybe there was something more to this and it really was “Little Green Men.” It was only when they found a second source of pulsating radiation that they truly abandoned their playful LGM hypothesis.
 
Pulsars, short for “pulsating stars,” are actually rotating neutron stars, an idea that was originally and independently put forward by former Cornell astrophysicist Thomas Gold and Italian astrophysicist, Franco Pancini in 1968. Their hypothesis was soon confirmed to be actual fact by the discovery of a pulsar with a very short pulse period in the Crab nebula.
 
When one looks back, maybe Burnell and Hewish were a bit hasty in abandoning their playful theory of Little Green Men. Astronomer Frank Drake, one of the founding fathers of Search for Extraterrestrial Life (SETI) once mused about the possibility of life on a neutron star. Is this something that is really even remotely possible?
 
Life on a neutron seems to stretch the realm of reality when we investigate the nature of a neutron star. When a massive star collapses in a supernova event, one result can be neutron stars. Even though the once-massive star, now a neutron star, is barely larger than a city on earth, they have some of the most unusual and extreme properties of any object in the night sky. For instance, they have the strongest magnetic fields in the known universe, up to 100 trillion times that of the Earth. Such fields are intense enough to distort the atoms that make up matter. There are now known to be neutron stars called magnetars that have magnetic fields that are over a thousand times greater than that of an ordinary neutron star.
 
The extremes of a neutron star do not end with its magnetic field either. The temperature inside a newborn neutron star ranges from 10^11 to 10^12 degrees Absolute; one degree Celsius is the equivalent of -272.15 degrees Absolute. Within a few years, the huge number of neutrinos, which are subatomic neutral particles closely related to electrons, that the neutron star emits, will carry away so much energy in the form of heat, that the temperature will fall to a relatively cool 10^8 Absolute within a few Earth years.The gravitational field at the neutron star's surface is about 2×10 ^11 times stronger than on Earth. As a result, if you were able to land safely on a neutron star (with current technology, you couldn’t) and wanted to launch yourself back into space, you would have to achieve an escape velocity of one hundred thousand kilometers per second, a sharp contrast to the eleven kilometers per second to leave the surface of the Earth. If that were not enough, a neutron star is so dense that one teaspoon of its material would weigh about 100 million tons. Such an extreme would make it kind of difficult to enjoy a morning cup of coffee, black, one sugar. In the interest of obeying the law of preservation of angular momentum (we have a rotating massive star many times the size of our own Sun, collapsing to a size of around ten to fifteen kilometers in diameter-the result is rapid rotation), a neutron star also is a rapid rotator as evidenced by the pulsar discovered by Burnell and Hewish. Burnell’s and Hewish’s pulsar was a real plodder, believe it or not, as there have been pulsars found since that time with rotational periods that are measured in milliseconds.
 
With the extremes of the conditions on a neutron star, scientists can only speculate on the structure of a neutron star. A neutron star has an atmosphere that is hypothesized to be at most several micrometers thick. The only force acting on it would be the star’s intense magnetic field.
 
From the atmosphere, we move down to the surface which is hypothesized to be a solid crust. In fact, a solid crust may be an understatement and here we find another extreme of the neutron star; the crust is estimated to be ten billion times as strong as steel. The crust is probably also very smooth, though there may be irregulartities measuring no more than five millimeters at the greatest imperfection. In order to create this supersolid crust, the matter making up the crust  is probably made up of ordinary atomic nuclei (neutrons and protons) that are crushed into a solid lattice-like framework with electrons flowing between the lattice structures.
 
If we were ever able to land on the surface of a neutron star and actually burrow into the supersolid crust, scientists speculate that we would encounter nuclei made up of an ever-increasing number of neutrons. If nuclei so structured existed on Earth, they would decay very quickly whereas on a neutron star, they are stabilized by the tremendous pressures.
 
If we move deeper still into the neutron star, we would come to a point  where a process called “neutron drip” is happening. Neutron drip is exactly what it sounds like. Neutrons actually leak out of atomic nuclei due to the extreme pressures being exerted on them. In addition to these neutrons, in this region, we would also potentially find free atomic nuclei and free electrons.
 
Ultimately we will reach the core of the star. Scientists have no idea of what form of matter the core is made of. They do have a few models to consider though. One model describes the core as being made of degenerate matter made mostly neutrons, with some protons and electrons. More exotic forms of matter are also hypothesized such as degenerate strange matter which contains quarks, quarks being the subparticles that make up protons and neutrons or matter that is made up of pions and kaons, which are other atomic subparticles. The jury is still out as to which model represents reality or is it something that scientists have not even thought of?
 
If neutron stars in themselves were not mind-boggling enough, scientists have come up with a number of other types of neutron stars. One is the quark star which is a hypothetical neutron star made up of quark matter. There are three suspected candidates that astronomers know of.
 
Another hypothetical star is the electroweak star which is a type of neutron star in which the quarks are converted to leptons through the weak nuclear force; weak nuclear force is the force responsible for radioactive decay. Currently they are a theoretical possibility only as there is no evidence that such stars actually exist.
 
Then there is the possibility that there are preon stars in our universe. Preon stars are neutron stars made up of preons; preons are hypothesized to be subparticles making up subparticles such as quarks and leptons. No evidence, however, has been found for these hypothetical stars.
 
With the extreme bizarre characteristics of a neutron star, how could life possibly survive, let alone evolve?  We do know that astronomer Frank Drake mused that it may be possible. If so, what would that life be like?
 
Life, if it exists on a neutron star, would be as strange as the star itself. For one, observers of life on a neutron star would be able to observe a rapid evolution and if there were intelligent life, rapid cultural development. Almost like a rapid succession fruit fly colony.
 
The reason for the rapid pace of evolution is that the time scale for the strong nuclear force, which would be the dominant force on the star (it is the attraction that keeps atoms together), is much shorter than our time scale that is dominated by electromagnetic forces. Put into perspective, if life arose on a neutron star, a civilization could rise in the time millions of times faster than here on Earth. The life would also, like the star, be extremely dense.
 
Science fiction author and physicist Robert Forward developed an entire ecosystem on a neutron star in his books Dragon’s Egg and its sequel, Starquake. The star's most intelligent species are called cheela that are about the volume of a sesame seed but have the mass of a human being. The main part of the story takes place in about a month on a human timescale. During this time, the human explorers are witness not only to the discovery of a life form on a neutron star, but one that evolves intelligence to a point where their technology exceeds that of the human observers.
 
Another writer that has imagined neutron star-based life is Stephen Baxter, in his short story, "Flux", part of his Xeelee Sequence. Gregory Benford, in his short story, "Bow Shock", an astronomer finds a fast-moving neutron star that is not all that it seems. Larry Niven’s Integral Trees and its sequel, Smoke Ring, take place in a ring of gas in orbit around a neutron star. He also wrote the short story, "Neutron Star", about a space traveler that gets to a neutron star only to experience its enormous gravitational pull.
 
If life on or near a neutron star is not weird enough for you, how about life in a black hole? Believe it or not, there is at least one physicist who believes it possible and notes a number of advantages of residing there. Living in a black hole would provide an ideal shelter from the external forces of the universe and it provides a limitless supply of energy. A number of science fiction authors have also imagined the possibility.
 
A black hole is an object with a gravity field so intense that it prevents anything, including light, which travels at the ultimate speed limit of the universe, from escaping. If light cannot escape how do we would we see it, let alone know that they exist? The presence of a black hole can be detected through its interaction with other matter such as orbiting stars and energy such as visible light. In fact, when large amounts of matter fall into a black hole, it will be heated via friction that a black hole could be among the brightest object in the universe, also known as a gamma ray burster.
 
The term "black hole" was first publicly spoken by American physicist John Wheeler during a lecture in 1967. Although Wheeler is usually credited with coming up with the term, humbly he insisted that it was suggested to him by somebody else. Whatever the source, the name stuck.
 
Though the term is relatively new, the concept of an object with such an enormous gravitational field that it would appear dark is not. In 1783 in a letter to the Royal Society, English geologist John Michell put forth his idea of what would become known in our century as a black hole.
 
Independently and later in 1796, French mathematician Pierre Simon Laplace proposed the same thoughts and published them in the first and second editions of his book Exposition du système du Monde (his hypothesis was removed from later editions). Readers of the later editions did not miss anything either as the physics of the day was premature and the idea of black holes remained strictly a mathematical anomaly.
 
It was only when Einstein came up with his General Theory of Relativity, published in 1916, that all of that changed.  Soon after Einstein came up with the general theory of relativity, friend and colleague Karl Schwartzschild  came up with the first solution to the field equations of general relativity.
 
A few months after Schwarzschild, student physicist Johannes Droste independently came up with the same solution as Schwartzschild but he wrote more extensively about the properties of his solution. He described the bending of known physical laws at what was to be called the Schwartzschild radius. In 1958 physics professor, David Finkelstein identified the Schwarzschild radius as an event horizon. He coined the term “event horizon” because if an event occurs within this boundary, information from that event cannot reach an outside observer, thereby making it impossible to determine if such an event occurred.
 
It is this event horizon that defines a black hole and is described as a boundary in spacetime through which matter and light can only pass inward towards the mass of the black hole. It truly is a point of no return. However, that is a matter of perspective as well all thanks to general relativity.
 
If you were an outside observer you would find that due to gravitational time dilation predicted by general relativity, time would pass slower near the black hole and speed up as you move further from the black hole.  As a result of time dilation, if you were to watch an object falling toward the event horizon it would appear to take an infinite time to do so. The object would also appear redder and redder to the outside observer while at the same time dim to a point where it could no longer be seen.  
 
However, if you were the one going into the black hole yourself, your observations would be completely different. In fact, you would not notice any of these effects as you cross the event horizon. From your perspective, you would cross the event horizon after a finite time. At the same time, you would never really know when you crossed the event horizon since it is impossible to determine from the inside.  
 
At the center of a black hole according to general relativity lies a gravitational singularity where the curvature of spacetime is infinite. For a non-rotating black hole, the gravitational singularity is a point and if it is a rotating black hole, the singularity appears as a ring. In both cases, the singularity has a zero volume but possesses all of the mass of the black hole. From high school physics we know that density is related to mass and volume so that, as a result, the singularity would have an infinite density.
 
If you were to continue your fall into a black hole no force in the universe could spare you from reaching the singularity once you had crossed the event horizon. Once at the singularity, things would really get messy. You would be crushed into infinite density while at the same time contributing your small mass to the whole of the black hole. At the same time you would be stretched by the growing tidal forces in a process sometimes referred to as the "noodle effect.”
 
There are black holes of stellar size which are the result of the gravitational collapse of heavy stars. However, there are also supermassive black holes, many at the centre of galaxies including our own Milky Way. The source of these massive black holes is somewhat of a mystery but one theory suggests that star formation in the early universe, where matter would have been far more concentrated, may have resulted in the creation of supermassive stars. In turn, these supermassive stars collapsed over time to provide the embryo of the supermassive black holes. In addition to gravitational collapse, it is theoretically possible black holes could be formed in high-energy collisions of matter to a point where they reach a critical density.
 
With the distortions of time and space as well as the physical laws of our universe coupled with the enormous gravitational maw of a black hole, how can life possibly live, let alone thrive there?
 
Russian physicist Vyacheslav Dokouchaev has hypothesized that civilizations of the third type (according to Kardashev scale) may live safely inside a supermassive black hole. The Kardashev scale was developed in 1954 by Russian physicist Nicolai Kardashev to describe the level of a technological civilization based on its ability to use energy. A type I civilization uses energy of its home planet, a Type II would use energy of its solar system and a Type III, the energy of the entire galaxy. Some scientists have expanded the scale to include a Type IV civilization that can harness the energy of an entire universe and a Type V civilization that can harness the energy of multiple universes. We can only wonder why any civilization that advanced would want to hide within the confines of a supermassive black hole.
 
The City and the Stars by Arthur C. Clarke and its  sequel, Beyond the Fall of Night, written by Gregory Benford tells the tale of a galactic Empire that was nearly destroyed by its greatest creation, a pure disembodied intelligence that came to be known as the “Mad Mind.”  Since the immortal “Mad Mind” could not be destroyed it was driven to the edge of the Galaxy and imprisoned in a black sun prison.
 
The first novel of the Heechee Saga, Gateway, by Frederick Pohl, is about hero Robinette Broadhead who signs on to a ten-person crew to fly in a pair of ill-understood starships developed by an alien technology, to an unknown destination. On their first flight, they all fall into stellar mass black hole, though our hero is able to escape. In later tales of the series, the alien Heechee, the creators of the starship technology being exploited by humans, emerge from their home inside the supermassive black hole at the center of our galaxy, having, because of time dilation in their home, spent only a few centuries there.
 
In Gregory Benford’s Eater astronomers detect what appears to be a distant high energy source, probably a gamma ray burster, caused by a black hole engulfing a star light years away. The hole begins its approach  to the Earth, destroying asteroids and interplanetary debris on the way. The black hole is found to house an intelligent being. The intelligence was created by "a very early, intelligent civilization whose planet was being chewed up by the black hole and who had uploaded their consciousnesses to it.”
 
Exhultant  is a novel in the Xeelee Sequence written by Stephen Baxter. In the Xeelee Sequence humanity is spreading out into the galaxy while waging a war on the highly advanced Xeelee. In the sequence, the Xeelee are described as having first inhabiting primordial black holes. When the black holes began to evaporate, the Xeeleee moved to the supermassive black holes at the centres of galaxies—including the one named Chandra in our own Milky Way.
 
With life potentially arising in these extreme environments where even the laws of the known universe are so twisted that they would be unrecognizable to us it truly stretches the boundaries of imagination.  However, with the possibility that life could exist in these environments, is it really even a possibility that we are alone in this universe?
 
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