LOVE this pictureeeeee
Stellar evolution is one of my favorite subjects to discuss…
NGC 7026. Yes, there are so many objects in the sky that not every one of them has a cute name like, “Seahorse Nebula”. This beautiful feature of the cosmos is a Planetary Nebula and is the result of a low-mass star ending its life that has lasted for billions of years. The subject of stellar evolution is of particular importance to me and has inspired me to write about its complexity, and how we have all benefited from the behavior of stars, particularly high-mass stars. Our vast knowledge of them, especially given the distances is truly remarkable. We have SO many at our disposal just to observe. Every type of star you can imagine is catalogued by the brilliant Astronomers of our past and today. At a distance of 6,000 light years and located in the constellation of Cygnus, NGC 7026 once was a star that has released its outer shells of elements heavier than hydrogen, created over its multi-billion year lifetime through proton fusion. It does not explode into a supernova because it is a low-mass star and will never attempt to fuse iron in its core. Instead, it releases its outer shells of elements, one by one. The most furious this star got was at its Red Giant phase, which is the beginning of the end for low-mass stars. Lastly, and perhaps even more amazing is that at the center of this nebula lies a solid dense core of carbon, known as a white dwarf. This core is very dense and is the result of billions of years of stored heat and will glow, but very faintly compared to a living star. Even though it is dead, the white dwarf will still emit intense radiation and stellar winds that drive the outer shells out into space. Eventually, the white dwarf will cool down and will turn into a brown dwarf. It is not brown however and in fact, it has been recently discovered that a cooled white dwarf most likely turns into crystallized carbon. What’s special about that? That’s basically your cosmic version of a diamond in space. A diamond that is 10 billion trillion trillion carats. We have evidence of this actually in the 2,500-mile diameter burned out star called, Lucy. A diamond that large is incomprehensible. Stars are truly amazing and continue to teach us new things about them.
The Death Of High-Mass Stars(15 Solar Masses and Above)
The previous lesson discussed fusion between hydrogen atoms into helium atoms(proton-proton chain), thus creating energy. A star of heavy mass also does this but produces energy in another way that smaller mass stars do not. This process is called the CNO Cycle. This is a six-step process that produces the same result as the proton-proton chain, which is four protons fusing, turning into a helium atom, and releasing energy. This cycle produces energy 1,000 times faster than the proton-proton chain does. The massive star needs to create a lot more energy to counter the immense force of gravity pushing down on it. It is important to recall that the more mass you have, the more gravity you have pushing down. On the moon you can float in mid air practically, on Earth, you fall back to the ground at the same speed no matter how heavy you are. (See Galileo’s Tower of Piza experiment). If you were on a neutron star, the weight of gravity pushing down is so strong that you would be flattened thinner than a piece of paper.
If you have a star that is 100 times the mass of our own sun for example, it is going to have 100 times the force of gravity trying to crush and destroy it. So in order to counter this immense force, the massive star has to produce A LOT more energy than a smaller star would. This causes massive stars to not live nearly as long as smaller stars because their fuel is exhausted much faster. The average lifetime for a massive star 15 solar masses or larger is in the millions of years, not billions of years.
The CNO cycle is only capable because massive stars contain large amounts of carbon, which was created from Helium atoms fusing with eachother. Whereas our small mass star no longer created a core of any elements higher than carbon because its mass was insufficient, the heavy mass star does not have this problem and will continue to create heavier and heavier elements in its core via fusion. When the core reaches 17 X 10 ^6 kelvin, or roughly 30,000,000 degrees Fahrenheit, the CNO cycle becomes the dominant force of energy production.
C-N-O Cycle:
In sum, a Carbon atom captures one proton and becomes Nitrogen, emitting what is called a Gamma-ray(An electromagnetic particle of radiation). The nitrogen created is unstable and decays back to a carbon atom. The carbon atom has a slightly heavier mass and after capturing another proton, creates a slightly heavier Nitrogen atom once again, emitting another gamma-ray. This slightly heavier nitrogen atom then captures a proton and becomes Oxygen, emitting another gamma-ray. This oxygen atom decays into a slightly heavier nitrogen atom, and the last step of this stage involves the nitrogen atom capturing a proton and emitting an alpha-particle(consisting of two protons and two neutrons), which turns out to be the nucleus of a helium atom. This closes the cycle and with Helium being produced, energy is created. This part is a little overwhelming, but is important to understanding how massive stars create the energy needed to withstand the force of gravity.
The word Neutron has first been introduced here and it is important to remember this word as it has a lot to do with a massive star’s remnant once it dies.
Supernovas:
Unlike small mass stars, when a massive star has a core of carbon, it does not stop there. It will use its outer shells to burn and create energy. The star seeks to burn its outer layers to create energy just as our smaller stars do. Yet, the more massive stars continue this chain down the periodic table until iron is reached. Pictured below is a diagram of a high mass star. You can see that there are many more layers than a smaller star has. Carbon fuses with carbon to create an oxygen core. Oxygen fuses with oxygen to create neon. Neon fuses and creates magnesium, magnesium fuses with itself and creates Silicon, and Silicon fuses with itself to create Iron. So what happens after Iron is reached is amazing, in my humble opinion. Iron actually cannot fuse with itself and instead causes the star to become “cooler” by absorbing energy instead of releasing any. Its inability to create energy from this fusion ends the star’s life, but not in a slow manner like low mass stars. This end of a star’s life creates an explosion that for a brief moment outshines an entire galaxy. The energy released from this explosion is equivalent to the amount of energy that star produced over its entire lifetime. That is just absolutely surreal. That is A LOT of energy released at once. This is what a supernova is. The extraordinary power released is equal to a trillion atomic bombs or more. Each element burned throughout the various shells provides the star with less and less time before it explodes via supernova. For example, Silicon is only burned for about 3 days in a high mass star and the fusion into iron destroys the star within seconds. Truly amazing considering this star has lived for millions of years. But in any event, once the iron in the core is attempted to fuse together and fails to do so, the core collapses in on itself, the weight of the massive star now entirely unstable. This type of supernova is called a, Core-Collapse supernova.
Neutron Stars:
You might expect the entire star to blow up, but we know now that that is not the case. The overwhelming pressure of gravity pushing inwards on the star’s core actually squeezes together all the protons and electrons that make up the atoms in the core of the star. This creates a solid ball of neutrons, which has a density unlike anything in the universe. This density is one billion tons per cubic meter. In comparison, a tiny square cube of a neutron star weighs as much as an entire mountain. As I mentioned in the beginning, hypothetically, if you were to stand on a neutron star you would be flattened thinner than a piece of paper. Just as we have gravity here on earth, it takes a certain amount of power to leave Earth and travel into space.
Earth’s gravity has an effect on its “Escape velocity”, as first introduced by Sir Isaac Newton. By definition, escape velocity is, “the speed needed to ‘break free’ from a gravitational field without further propulsion.” For example, Earth’s escape speed is 11 kilometers/ second. If you are traveling any slower than that, you will not have the force needed to leave Earth. For Jupiter, the escape speed is 59.5 kilometers/ second, the largest and most dense of the eight planets. The sun has an escape speed of 617.5 kilometers/ second. The escape speed of a Neutron star depends solely on its mass. And considering a Neutron Star and a Black hole are almost the same thing, it can be inferred that the escape speed of a neutron star can span from thousands of kilometers per second up to the speed of light which is 299,792 kilometers per second or for the western folk, 186,000 miles per second. Think about that number for a second. If a neutron star has such incredible densities, then not even light, which is traveling at that unbelievable speed can escape the immense pull of gravity caused by the density of a neutron star.
This bit of information is so vital to our understanding of black holes. We can easily observe the gravitational influence that large objects have in space and infer the object’s density, mass, composition, etc. It explains why Jupiter, the planet with the heaviest mass has 64 moons!! Can you imagine? Its why we are orbiting the sun and it isn’t orbiting around us. It is why the sun in fact is orbiting around the center of the Milky Way Galaxy!! As you’ll see later, there is something lurking in the center of our galaxy that is the perfection of gravity’s immense effect on space.
Lighthouses In the Sky:
So, back to our now dead star…After our massive star has exploded, its remnant, a Neutron star is left behind and has some interesting characteristics. Its density has been discussed but what can we actually observe? Well what happens after this supernova is that the core is left but it is spinning at unbelievable rates. It is believed that the force of the star collapsing on top of this core is what gets the core spinning at such high rates. I would imagine that if one side of the star collapsed more than the other at just a slightly quicker rate, it would result in sending the star in an unbelievably fast spin.
Over 2000 neutron stars have been observed in 2011 and the observations we’ve made were more than just gravitational. Particular types of neutron stars are what you would call, “lighthouses” in space. What occurs as a result of their incredibly fast spin is that a beam of electromagnetic radiation from its poles is observed at rates measured in hundreds of times per second to as slow as one “pulse” every second. We can only observe these beams of radiation if it is aimed at Earth, however, which certainly limits the number of neutron stars we can observe that are pulsating. The name for these neutron stars is called, a Pulsar. It is also important to keep in mind that everything rotates. Earth rotates on its axis and is the reason we have days. There are planets that rotate so slow that it takes over one earth year just for that planet to revolve once on its axis. We observe this throughout our solar system. The pulsars created from these remnant supernova explosions are so regular that they are more accurate than the atomic clocks we use here on Earth. The pulsar is spinning at an incredibly fast and accurate rate. Something also to keep in mind is that with rotation, magnetic fields are created. Earth has its own magnetic field, which is why compasses point due North. It is how we are protected from the sun’s violent storms that reach us. But at our poles, there is a weakness in the gravitational field. We know this because of the Aurora Borealis, The Northern Lights. Particles from the sun interact with atmospheric particles on Earth and this combination creates the beautiful waves of colors we see across the sky. But you would not see this phenomenon at the equator. It will start at the poles and if the sun storm is strong enough, the Northern Lights can be seen further south. I mention this because our neutron star is no exception. And it is at its poles where radiation beams out. After millions of years, the rotation of these pulsars slows, and their magnetic field weakens ever so slightly. This enables Astronomers to calculate how old a neutron star is. If it is young, it will be spinning fast and will produce precise pulses of radiation from its poles. If it is an old neutron star, it will be doing neither.
The Crab Nebula:
One of the first observed and documented supernovas in history began in the year 185, but most are familiar with the beautiful image of the Crab Nebula, observed and documented by Chinese, Japanese, and Arab astronomers in the year 1054. This supernova occurred because a star, roughly 8-10 times the size of our sun reached the end of its life-cycle and created a core-collapse supernova. At the time this supernova occurred, it was described as being seen for over a month in the sky in broad daylight. Its remnants have been traveling through space at several thousand kilometers per second ever since then. I mention this because if you ever want to see exactly what I have written about, just look at the Crab Nebula. Its made of beautiful colors, particularly green, orange, and yellow. These colors, measured with a spectrometer tell Astronomers what elements this once massive star was made of. The heavy elements(> Carbon) we observe in space today were created only by supernova explosions. Gold and silver were created from supernovas. Remember that the next time you put on your jewelry :) At the center of the crab nebula, driving radiation outwards is a Pulsar with a spin rate of 30.2 times per second. This beautiful supernova remnant is pictured below.
The Grand Finale: Black Holes
The greatest mystery of them all. What happens when a star blows up and leaves behind nothing, but we know there is “something”? Strange question yes, but there is firm agreement amongst scientists that considering Einstein’s theory of general relativity has held up after all this time, it can be presupposed based on the predictions his theory makes that yes, there are black holes. Black holes are not black in the literal sense, but they are black because we cannot see this object in the night sky. It surely is there, however. As I’ve discussed, every object we observe is orbiting around something. A planet is orbiting around a star, a star is orbiting around the center of the galaxy…but what explains stars orbiting around nothing?
Black holes were the subject of great debate after pulsars were first detected. They too had been theorized based on the laws of gravity and mass as explained by Albert Einstein. But in 1978, the first major step in detecting black holes was taken; The launching of The Einstein X-Ray Observatory. Quite fitting given that he has had everything to do with the theory of black holes and our subsequent yearning for the discovery of one.
First to understand what an x-ray is, we must first recognize that any form of energy behaves in a wave-like manner. And depending on the frequency of these waves determines what kind of energy/information it carries. For example, on one end of the spectrum we have radio waves. Their frequencies are much longer. Along the spectrum there are microwaves, infrared waves, visible light(what you and I see), ultraviolet radiation, x-rays, and gamma rays. X-rays have incredibly short frequencies, thus therefore carrying a much higher energy than waves at the other end of the spectrum. We know also that when temperatures reach a certain degree, various electromagnetic waves are detected. It is known that at 10^6 kelvin, or roughly 1.8 million degrees, x-rays are created.
In 1964, a rocket flight into space detected at the time, one of the strongest sources of x-rays ever observed and it was coming from the direction in which the constellation Cygnus resides in the night sky.
Cygnus X-1
Cygnus X-1 is named for the x-ray source that is coming from a “high-mass x-ray binary system” some 6,000 light years from Earth. Binary systems are actually quite common in the universe. As a matter of fact, the majority of stars form in pairs, or even comprise of 3 or more stars! In binary systems for example, it has been discovered that both stars do not form at the exact same time, nor do they acquire the exact same mass. It is when this occurs that scientists have a chance to observe something rather amazing. Imagine that both stars are massive giants, but one is more massive, say 40 solar masses, compared to its companion at 20 solar masses. We know from this entire lesson that the 40 solar mass star will die much quicker than its companion as it will exhaust its fuel faster. Our 40 mass star has just exploded in an unimaginably huge supernova, leaving behind a neutron star with a surface gravity stronger than the speed at which light or any radiation travels(299,792 kilometers/second). This by definition is a black hole. Now, what happens with our 20 solar mass star that once was orbiting around the 40 solar mass star?
The gravitational influence of the black hole and the proximity of the 20 solar mass star is not going to be good for that 20 solar mass star. The gravitational influence of the black hole is immense and unforgiving. It is so strong that the black hole literally pulls the companion star apart, creating what is called an Accretion Disk around the black hole as pictured below. This disk of gases from the companion star spiral inwards, feeding the black hole. Throughout this process, the black hole sometimes devours more than it can handle, and as a result, jets of excess material are launched out of the black hole at speeds half the speed of light, perpendicular to the accretion disk. The accretion disk becomes extremely hot because of friction between gas in the faster inner moving orbits combined with the slower orbits further away from the black hole. The temperatures of the gases in the innermost region of the accretion disk can reach 10^6 kelvin, our magic number for observing x-rays. Hence, the eventual confirmation that Cygnus X-1 was a source of x-ray emission produced from the energy released as a result of a black hole devouring a nearby star. The source of x-rays were detected from an incredibly small region with an estimated diameter of a mere 100,000 kilometers. The sun by comparison has a diameter of 1,000,000 kilometers, roughly. Pictured below also is Cygux X-1, an eerie looking region in space in which a black hole looms.
Singularities, Theories and the Conclusion of Black Holes
To summarize, a black hole is essentially, a supernova remnant with a core of ultra-dense neutrons that created a gravitational force so strong that not even light or radiation produced can escape. There are still many theories as to what else a black hole could be. Einstein’s theory of general relativity begs the question if there could be a high mass star collapse resulting in an object with infinite density, and therefore an infinite gravitational influence, resulting in what is called, a singularity. A singularity is basically the end or breakdown of logical explanation of certain laws of physics. The fact is, is that we really don’t know what a black hole leads to. Theories from Einstein suggest the presence of wormholes. We know that black holes create a massive indentation in space, a hole in space perhaps that can be traveled through? Highly doubtful. I think that if we were to see a black hole with our own two eyes, we would see chaos. A gravitational influence of this kind creates pressures and speeds of gases and particles that would destroy anything anywhere near it. Black holes are dangerous. They are rogue, meaning that they roam the universe with no restrictions or boundaries. Any star that is captured by its gravitation is doomed. It will lose all of its mass slowly but surely. Mass that will disappear once it makes it within the event horizon, the boundary surrounding the black hole which light can not escape…If our estimations are correct and there really are trillions of stars, then just how many of those stars attained a mass of 15 solar masses, large enough to one day explode in a supernova leaving behind a black hole? I think some basic mathematics would conclude that there is an eerily large amount of black holes in the universe. They would be hard to detect unless you know where you were looking. They don’t produce light and are incredibly small. However, the laws of gravity do give them away. Objects near a black hole spin very fast, objects too close get devoured, turned into an accretion disk, and are slowly digested by the black hole.
I would like to conclude by providing one last tantalizing detail of black holes; they get bigger. MUCH bigger. So big in fact that astronomers are in agreement that at the center of perhaps ALL galaxies lies a super-massive black hole. Its size may be 3 times the size of the sun, but its mass is equivalent to one billion suns!! The gravitational influence of an object like this can cause entire clusters of stars to orbit from millions of miles to many light years away. Our galaxy is 100,000 light years in diameter for example and everything is orbiting around the center in a spiral-like fashion. Studies are still underway to find more evidence for the super-massive black hole theory, but it sure would explain why we have measured millions of stars at the center of our galaxy, orbiting around “something” at unimaginable speeds. It is impossible to see the center of any of the galaxies we observe because there are so many stars at the center, obstructing our view of what may be within the orbits of those stars.
I devoted a lot of time to try to understand the process that stars undergo, from small stars like our sun, to large stars such as Betelguese, a Red Giant that will go “kaboom” one day, producing a spectacle unlike anything seen since the Crab Nebula supernova in 1054. Stars are what created you and I. From a scientific standpoint, we know this to be true. Our universe was once filled with an abundance of Hydrogen, the lightest element. Eventually, stars were created from condensed molecular clouds of Hydrogen and Helium, and through nuclear fusion, heavier elements were created because of the incredibly hot temperatures of the cores of these stars. When the large stars ran out of fuel, they exploded, releasing all of its mass into space at thousands of miles per hour. This mass, made of elements such as Carbon, Silicon, Magnesium, Iron…all make up the things here on Earth, our home planet. Our core of Earth is rich in Liquid iron. Our blood is made of iron! If stars never exploded into supernovas, none of us would be here because there would be nothing to make us up. That is a fact.
There is still much to learn about stars and the galaxies in which they are formed, and I feel it is a natural follow up subject to stellar evolution. I want to learn about the galaxies that create these stars in the first place. How are there so many of them? Why are some galaxies on a collision course with eachother and some are being driven away from one another, by a force yet to be completely identified (Dark energy). There are so many galaxies in the universe, but they are not orbiting around something like everything else seems to. The galaxies in the universe are spread out and most are flying away from our own galaxy at incredible speeds. What could have caused this? I look forward to addressing some of these important questions in the future…
Structure of a high-mass star.
The Crab Nebula. The center of which lies a pulsar.
Illustration of a black hole devouring a star. Seen is the accretion disk around the black hole.
Detailed description of accretion disk.
Cygnus X-1: Location of a large black hole that once was a star that had a mass of roughly 40 solar masses.
Low-Mass Stars (~1 solar mass - 4 solar masses):
Stars of low mass live MUCH longer than stars that are tens if not hundreds of times their size. As a result of this smaller mass, these stars live longer because they dont have to “exhaust” as much fuel in its core to keep the balance of power even within the star. This balance is achieved when the tremendous power of gravity forcing inwards matches the power of energy being forced out, generated in the star’s inner hydrogen core. This is called, equilibrium. When the equilibrium breaks down, the star is in trouble unless it finds a way to match the power of gravity wanting to crush it.
The part of a star’s life-cycle that it resides throughout the majority of its lifetime is called the Main-Sequence. While on the main-sequence, the star uses hydrogen in its core to create energy. This is done only when its core reaches an incredible temperature of 10^6 kelvin. Which is 1,000,000 kelvin. To convert to fahrenheit, you multiply by 9 and divide by 5. So the temperature needed to ignite the hydrogen in its core is just under 2 million degrees fahrenheit. Extremely hot as you can imagine.
The process by which fuel is created is a complicated one, but put “simply”, it occurs when hydrogen atoms, at 10^6 kelvin are flying around so fast that instead of repelling, they actually fuse together. This does not occur if the temperature is not 1,000,000 kelvin. When hydrogen atoms with one proton fuse together, they create a new atom, helium, now made of two protons. Helium “ash” builds up and is condensed within the star’s core, essentially replacing the hydrogen. What is most important about this process is that when 2 hydrogen atoms bind, a tiny amount of energy is released. This tiny amount of energy is called a Photon and is responsible for heating our planet today. This process of nuclear fusion occurs many many times over again until eventually the Hydrogen core runs out of fuel. This will take billions of years depending on the size of this low mass star, but Astronomers can clearly tell when a star has run out of hydrogen because the star expands and turns red, otherwise known as a Red Giant.
Keep in mind that these very Astronomers have a plethora of stars to observe and this enables them to examine stars all throughout different stages of their life cycle.
So how does a star continue to burn if the core no longer has hydrogen to burn? This is the most interesting part. As I’ve mentioned, gravity and pressure are in a battle. If the star is no longer pushing pressure outwards due to its energy produced via the core, then the gravity will begin its crushing of the star. By doing this, the center of the star now made of Helium ash begins to get very very hot as it is condensed by gravity. Once the central temperature reaches 1 million kelvin again, the outer layers of the star begin to heat up and the hydrogen layer surrounding the core begins to ignite in a furious fashion. This re-ignition expands the outer layers, causing the star to grow by about 50 times its original size! The first picture below shows the inner structure of our low mass star. The layer of hydrogen, otherwise known as the hydrogen shell is now fusing and the star reaches equilibrium once again. Eventually the star reduces in size as the pressure balances out the force of gravity for the second time. This balance occurs for a much less time as there isnt as much hydrogen in the outer shell compared to the amount it had in its core. This stage will last 100 million years.
When the hydrogen shell runs out of hydrogen, the core then attempts to ignite the shell of helium surrounding the once hydrogen shell. To fuse helium atoms together, a higher temperature must be attained because helium atoms carry one more proton than hydrogen. As a result, the repelling of these atoms is even more difficult and requires higher temperatures for fusion to occur. This temperature is 10^7 kelvin or 18,000,000 degrees fahrenheit.
The fusion of Helium within the stars outer layer thus creates the next element on our periodic table which is carbon and the carbon, with a higher density, settles to the inner core as Helium fuses, releasing energy and leaving behind carbon ash. The fusing of the helium shell will last approximately 100,000 years, a small portion of a star’s lifetime. This stage is the most violent of all as the star tries to keep up with the abundance of energy the helium-fusing star creates. Eventually it does and equilibrium is again maintained by expanding to a Red giant for the second time, but this time will be its last.
Once the helium is completely used up, a core of dense carbon ash remains. The central temperature of a low mass star will never reach the 600,000,000 kelvin needed to fuse carbon atoms together to produce energy.
Its central temperature is extremely hot though and produces intense radiation at 300,000,000 kelvin from the carbon core. This forces its outer layers away and produces a Planetary Nebula. This name does not imply any planets involved but was confused by early astronomers as what they were first witnessing was misinterpreted as a planet. This beautiful feature is a star’s last breathe. The outer layers of a dying star pushed out into space tell astronomers what elements the star had produced in its core. There are often times hints of heavier elements such as Oxygen and Neon. All depend on how much mass the star once had. The heavier the mass of the core, the hotter the central temperature. The hotter the central temperature, the more elements created within the star.
What is left after our now dead star is depleted of its outer layers? The answer is a white dwarf. It shines brightly for billions of years but only because it is a product of billions of years of stored heat. The surface temperature of a white dwarf is near 24,000 kelvin, is the size of Earth roughly, but has the mass of half the size of our sun. To put it in perspective, one cubic centimeter of this star’s core equals one ton here on Earth. That type of density is simply unheard of.
Our white dwarf will shine, but not nearly as bright as a star undergoing nuclear fusion. Eventually the stored heat will be no more and the star will cool, becoming a black dwarf and basically undetectable in the night sky. The vast majority of stars live and die in a similar fashion.
It is the heavier mass stars who’s destruction isn’t nearly as calm. A heavy mass star explodes, producing a supernova. What star’s like this leave behind will baffle you. It’s remnant is detectable but you can’t see it. Astronomers, Particle Theorists and the like have dedicated their whole lives to understanding how a “Black Hole” functions. A stellar supernova remnant that has such a powerful gravitational influence that light cannot escape it and any light near it is literally bent around it, proving its strength on light particles. Any star near it is completely devoured, as Astronomers have actually witnessed.
To be continued in the conclusion of Stellar Evolution: Part III The Death of High Mass Stars and Black Hole Formation
Giggity.
Before I attempt to explain this unbelievably amazing feature of stars, I will first tell you that just like every living thing on this planet that will one day meet its demise, the same holds true for every star we see in the sky, every star that lived before we existed, and every star that will be born long after our sun has run out fuel, leaving behind its incredibly dense core, known as a white dwarf. This topic is of particular interest to me because the evolutionary process that stars undergo over the course of millions to billions of years, pathes the way for all the elements that we as humans have discovered that make up everything around us, including ourselves.
A star is born:
Stars are born in a nursery if you will, and these nursuries are called galaxies. We see as many galaxies in the sky in 2011 as the number of stars discovered in 1995. And it is widely accepted, and even considered factual that each galaxy holds billions upon billions of stars. Galaxies span for hundreds of thousands of light years across so this is possible. The last I checked, 99% of the night sky was black. Theres a lot of space out there. No pun intended.
To get an idea of the distance of our own galaxy, The Milky Way, consider that it is 100,000 light years across. If we were at one end of the galaxy and wanted to communicate with the other side, it would take 100,000 years for that message to reach, and that’s not counting the very real possibility that the signal wont make it that far because it will be absorbed by the cosmic dust and gas that is all around the galaxy. And did I mention that the center of the galaxy holds the most abundant collection of stars? Its not even close. It is believed that at the center of most galaxies are super-massive black holes. And the immense gravitational force of these black holes is causing millions of stars near it to spin around the black hole at unbelievable speeds. Futher away from the galaxy, there are still more stars rotating around the center and our sun is doing just that. We are approximately 28,000 light years away from the center of our galaxy. Think about how it takes 365 earth days to travel one lap around our sun; for the planet Neptune, which is the farthest away of our eight planets, it takes 164.79 Earth YEARS or 60,190 days to make one lap around the sun. So given the vast distance between the sun and another planet which is in our cosmic backyard, then how many years would it take to make one lap around the center of the galaxy? Nearly 250 million years. We have made about 20 laps around the center of our galaxy since the inception of our sun, and the resulting planets.
If one looks at a galaxy, you don’t just see stars rotating around the center of a bunch of other stars. Intermixed with all of this are massive clouds of gas and dust. The dust by definition is simply “any element with a higher atomic number than Helium”, which are again, by definition, “formed in the core of stars via stellar nucelosynthesis and supernova events.” Damn it I ruined the ending already. You’ll have to forgive me.
My point is that within these gases at the center is where a star is being created. This cloud of gas however needs to condense and become compacted in some way first. This can happen if either two clouds of gas collide or if the pressure of a nearby supernova within the galaxy causes it to compact. Once the first step occurs, the now more dense gas cloud gets a little help from gravity. Ok, it gets A LOT of help. Gravity is what causes the gases around this dense area to get sucked into the potential star, only helping it get bigger and stronger. The bigger it gets, the more dense; the more dense, the more gravitational influence. This happens until all the surrounding gas is sucked up and a new star is formed. Given the amount of the surrounding gas is what will naturally determine the size of the star. And this is where separate paths lead. Some are calm, others are unimaginable and still escape our complete understanding of the cosmos.
Artist’s depiction of the immense force a black hole exerts on a companion star.
