|The Big Bang||Life cycle of a Star||Quasars||Colliding Galaxies|
The Cosmic Events discussed here are a few of those major events that shape the universe…”the movers and shakers” of the universe. They are not the comets that occasionally pass our way, nor the asteroids that threaten our life…although those are the issues that have the greatest direct impact on us. The ‘movers and shakers” of this universe are those events which define the path for the development of this universe. Some of these major events are discussed here and consist of the following:
|the start of the universe….The Big Bang;|
|followed by the initial formation of stars;|
|then the death of stars, which allowed many other events to take place, like the formation of planets and Black Holes;|
|and finally, colliding Galaxies.|
Of course there are many other cosmic events which have important effects on the universe but the above seem to have a common thread between them which fundamentally defines how our universe has developed.
|Some background physics (you can skip this if you like)
It is interesting to note that there are three fundamental concepts from physics that I like to think of as instrumental to the development of the universe as we know it….gravity, conservation of angular momentum, and temperature:
Gravity. We are well aware of the effects of gravity. It is the universal attraction between all objects…always has been, always will be (except, of course, for love).
Conservation of Angular Momentum. Ever notice how everything in the universe is rotating? Moons around planets, planets around suns, suns around galaxies, galaxies around other galaxies…even asteroids and comets rotate around suns. How does that happen? Conservation of angular momentum! …..in the beginning, when gravity first had that little tug of one particle to another, there was a slight hint of rotation or a slight differential of the velocity component perpendicular to the line of gravity. No matter how slight it was, there was that small, insignificant velocity component. That velocity component is conserved as the particles are drawn closer through the action of gravitational force…as the distance gets smaller, the rotation gets faster. Remember the well known example of the spinning ice skater….begin a spin with outstretched arms and the rotation will increase to a blazing fast spin as the arms and legs are brought into the body. From this law of physics we end up today with a host of spinning structures….and it is because of that we don’t go flying off into oblivion, or, crashing into the sun
Temperature. It is also interesting to note that temperature plays an essential role in the occurrence of the events listed above. Consider this sequence of events:
All of this is dependent on the temperature of the material.
The Big Bang – the First “Cosmic Event”
The universe is expanding. We know this because we can measure the rate at which all major structures in the universe are moving away from one another. It is a well studied and easily measured property of our universe (see Astronomers, Edwin Hubble). By going back in time, astronomers and physicists can identify the sequence of events leading to today’s universe. Most astronomers and physicists see the Big Bang theory as the logical beginning based on observations to date. By observing, measuring, and analyzing data collected over the past hundreds of years, scientists have developed a logical sequence of events leading backwards to a Big Bang event.
The beginning of the universe is now generally accepted as described by the Big Bang Theory. What is the Big Bang? Current science considers the Big Bang to be the beginning ….the First Moment… when all the substance of the universe consisted only of sub-atomic and atomic particles……and lots of energy, at a temperature of trillions of degrees! All the material of today’s universe evolved from a single point of pure energy! Think of it….no material, no stable matter. Nothing to put your hands on! Just elementary particles and an energy field! …a huge energy field….and at a very high temperature. It is hard to imagine such a time and place! From that moment, all we know of today evolved in accordance with the physical laws we know of or have theorized. It is important also to note that the Big Bang Theory requires an infinite density and temperature, which is consistent with Einstein’s General Theory of Relativity.
|Cooling of the Universe immediately after the Big Bang. Today’s temperature is -270°C The Yellow portion signifies the period in which all the matter of the Universe was in the form of a plasma.|
The above chart shows the timeline currently held by today’s astrophysicists and scientists. The chart covers essentially the first 100 seconds after the Big Bang (the last little bit of the chart goes on to 380,000 years but only because nothing much changed between 100 seconds old and 380,000 years! (other than the universe got a lot bigger). You are probably wondering right about now….”How the hell do they know that?” Good question. The answer lies in the experiments that these scientists have performed. The tools they use are big, expensive, and exotic….Particle Colliders. In order to test what happens in very hot, very dense environments, the scientists must create very hot, very dense environments. That is what the Particle Colliders do. The workhorse to date has been the Relativistic Heavy Ion Collider (RHIC). With this instrument, conditions approaching those that are thought to exist about 2 microseconds (μsec) after the Big Bang are created. Yes…at atomic nuclei levels, pressures as high as 15×1030 PSIG and temperatures of several trillions of degrees have been attained. The particles which exist at these conditions can be created and their properties measured. How to go further back in time to that Big Bang? Build bigger and better Colliders. The new Large Hadron Collider (LHC), located in France and Switzerland, is just the instrument. It is expected to reach densities several times larger than the RHIC and temperatures in excess of 10 trillion degrees. If successful this will allow scientists to investigate the conditions existing just 0.3 of a μsec after the Big Bang! Yes…this is definitely exotic science!
However, some physicists have recently developed the concept that there was a time before the Big Bang. This concept involves the idea that there was a universe before this one that had collapsed in on itself, to the point where the entire universe occupied a single, finite point in time and space at which point a “big bang” occurred. This alternate theory may be thought of as the Big Bounce. In this scenario the previous universe imploded to a point of finite density, at a given point in time and space, and then explodes to begin the expansion all over. The underlying basis for this concept is that a single point of infinite density (as required by the Big Bang Theory) is not possible, even though Einstein’s General Theory of Relativity requires it. Contrary to the General Theory of Relativity, recent theories of quantum theory of gravity provide for a limit to the density of energy and matter. This limit would then require the present universe to have begun with a finite beginning. The relevant question then is “how did this energy and matter get to that point?”. One possible answer would suggest some sort of process for the accumulation of material, such as a collapse of a previous universe. So expect more theories and adjustments to define this initial state for the Big Bang.
In any event, the universe we know of began with a bang…..and it proceeded to expand and continues to this day. There is a fine point of the Big Bang theory regarding the expansion of the universe…..from the first moment, the universe expanded…it did not expand into something, rather the universe itself simply expanded. There was no edge to the universe as it expanded, nor was there a central point from which the expansion began. The universe simply was the universe and it expanded itself. Yes, this concept is a bit mind-bending because it requires one to visualize a space not only empty (in the truest sense of the word) but also a place which is not a place…..irrelevant! I don’t know about you, but I’ve got a little problem getting my mind around that concept….
So the Big Bang occurred…as some very smart people tell us. Within the first 20 minutes, ¼ of the matter in the universe was converted to helium nuclei. Why helium and not hydrogen?
It was simply too hot for an electron to stick to a single proton, or any proton-neutron nuclei. But the formation of Helium was perfectly suited for this environment! In rapid succession, as the universe cooled slightly in the first few minutes, a proton and a neutron formed, then 2 protrons and a neutrons, then finally 2 protrons and 2 neutrons….a helium nucleus. After some 300,000 years the universe cooled sufficiently for this helium nucleus to attract an electron and the first hydrogen atom was formed.
This is predicted by nuclear physics and confirmed by observations – even today ¼ of the universe is helium. The universe expanded and cooled for the next hundreds of thousands of years and not much changed. After half a million years or so, the temperature had dropped to 3,000°K and this allowed hydrogen to form… the stuff stars are made out of. This opened the door for the existence of molecules as stable matter and allowed the formation of stars and galaxies at a later date. And the formation of stars provided, for the first time, the means to produce elements heavier than hydrogen and helium, through the process of nuclear fusion.
Life cycle of a Star
Stars are born in the enormous gas clouds which occupy the universe. Once born they live their long lives in nuclear fusion and then die. However, even in death the process continues with the remnants of the star…smaller stars, like our sun, leave behind a white dwarf….a white hot mass consisting of mainly carbon, hydrogen, and helium. It will about the size of earth, have no nuclear reactions, and will slowly cool over a period of several thousand million years. Larger stars, greater than 8 solar masses, explode in huge explosions called supernova and leave behind a neutron star, a mass so dense that a teaspoon portion would weigh thousands of tons. It has no nuclear reactions taking place, but emits a narrow beam of electromagnetic radiation which is how the neutron star is detected.
A Star is born…….
Stars depend on fusion of hydrogen for the creation of energy. The hydrogen comes from the abundant supply within the massive gas clouds in the Universe. As these gas clouds cool and condense the atoms come under the influence of gravity and begin to collect and grow in size. As this clump grows larger it attracts, by gravity, more and more hydrogen gas atoms and other, smaller, gas clumps. The increase in mass results in higher gravitational forces, which in turn results in the attraction of more mass, resulting in ever higher gravitational forces. and a continuing cycle. As the mass increases the temperature increases. When the mass is great enough to generate high enough temperatures – 10 million degrees – nuclear fusion results, converting the hydrogen to helium. The helium created is left in the core and the fusion reaction continues from the inside out. Extra large stars (see below) will continue the fusion process to produce heavier and heavier elements. This process takes billions of years. The quantity of hydrogen is so large that the conversion to helium takes a very long time, in spite of the continuous fusion reaction.
Take a moment and appreciate the tremendous process that is taking place in our own Sun. We have all seen the video of a hydrogen bomb detonation…..this is a relatively small amount of material that creates a huge amount of energy in an instant. In our Sun this same process has been going on continuously for 5,000 million years, and will continue for another 5,000 million years!
A Star dies…..
Stars come in different sizes….pretty much divided into 4 groups….small, medium, large, and massive. The massive stars are capable of producing the heavier elements. Each of these groups have a unique characteristic of their death, they behave differently depending on their size. But for each group the first step in the death of a star is he same…they become a …….Red Giant.
The first step in the death…. a Red Giant. As the hydrogen runs out and the fusion reaction slows, the star begins to collapse upon itself. This collapse continues until the temperature rises (due to the collapse) and then the star expands outward to many times its original size. For our sun this Red Giant phase will last for several thousand million years and will encompass the Inner planets. It stays this way for millions of years, slowly shedding layers of helium…
For low-mass stars….less than 0.4 times the mass of our sun…..as the Red Giant cools the core this star will collapse to a white dwarf. Its size shrinks to several thousand miles in diameter and remains that way for 1,000,000 million years, eventually losing all it’s mass to the space around. Note that the life of a low-mass star can be longer than the age of the universe as we know it. Therefore, it may be said that no low-mass stars have completed their life.
For medium-mass stars…. between 0.4 and 1.4 times the mass of the sun…..just as with a low-mass star, it will expand over a period of 100 million years to become a Red Giant, encompassing the Inner Planets. Then, over a period of 0.1 million years, it will shed it’s outer layers until only a white hot core (30,000 degrees) remains, a white dwarf, about the size of earth. It is very dim but has a very high surface temperature. It remains that way for thousands of millions of years, eventually cooling to a cold, cold object in space.
For large-mass stars... from 1.5 to 8 times the mass of the sun….. the completion of burning the hydrogen fuel does not result directly in a Red Giant. Rather, it will contract slightly, the core temperature will increase (100 million degrees) and additional fusion will occur, converting helium into carbon. The star will continue to expand towards the red super giant phase. At this point the physics is not certain but it is expected that thermonuclear processes continue, temperatures decrease as fuel runs out, collapse occurs resulting in an explosion during which huge amounts of energy are released within seconds as the star destroys itself (except for the super-dense core). The super-dense remnants make-up a neutron star in which the density, and therefore gravity is so great that electrons and protons are combined to neutrons. The size of the neutron star is very small….on the order of 10 km!
For massive stars…greater than 8 times the mass of our sun (and up to 20 times the mass) these stars may become Black Holes. The massive stars do not live as long as our Sun and the other smaller stars, maybe 10 million years before running out of nuclear fuel, but they burn brighter and hotter. Because they are hotter they can generate the internal temperatures (over a billion degrees) necessary to sustain successive nuclear reactions which produce heavier elements. This is how the heavier elements, such as gold, lead, and uranium, are formed. Note that all heavy elements found on earth were formed in the successive nuclear reactions within these massive stars.
As these massive stars progress through successive stages of nuclear reactions they balloon to enormous size until they eventually run out of fuel at which point gravity takes over and they suddenly collapse, in a matter of seconds. During the sudden collapse the core becomes more and more dense, it reaches a point where the material rebounds and explodes outward to become a Supernova, exploding in a huge flash and shining as brightly as 10 million of our Sun, if only for a short time….a matter of weeks. The remaining core is usually a neutron star or small, Stellar mass Black Hole. It is during this Supernova process when the interstellar space is littered with the heavier elements.
While many Supernovas are observed each year, only five (5) Supernovas have been observed with the unaided eye…..4 in our galaxy and 1 in the nearby galaxy, Large Magellanic Cloud. A Supernova is a rare sight, but one which can be seen with the unaided eye…so consider yourself fortunate indeed should you one night suddenly see a much brighter than normal object in the sky.
Quasars are currently a theory. They are sources of tremendous amounts of energy from the core of galaxies. The central engine of a Quasar is theorized to be a super massive Black hole which is actively consuming material at a tremendous rate. (Note that most galaxies are thought to contain a super massive Black Hole but most do not actively consume large amounts of material, as in the case of a Quasar.) As the Super massive Black Hole consumes material, the objects reach tremendous temperatures (millions of degrees) and extreme speeds before entering the Black Hole and, in the process, give up large quantities of energy in the form of x-rays and visible light, which can be detected here on earth. Quasars are millions of times more massive than our sun and would contain most of a galaxy’s nucleus. At the end of their life they would remain Black Holes.
Galaxies do collide…..and result in a new galaxy of larger size.