Emergent Universe

January 3, 2011

The most distant object we’ve sent through our solar system is the Voyager 1 probe. Launched on September 5, 1977 it has since reached the very edge of our solar system and will soon pass out of the heliopause, or the point where our sun’s solar wind is weaker than the interstellar wind of other stars, effectively drawing the end of our solar system. Well after its original mission was completed, Voyager 1 continues to collect data on our Sun and its perplexing heliosphere.1 After traveling for 33 years, this probe has only made it 0.002 light years from our planet, but it has flown by everything in our solar system. It’s from this perspective that we begin our story of an alien solar system; from the outgoing point of view of an interstellar probe, the star we are about to discuss looks no bigger or brighter than any other star in the night sky, (and it’s not even visible to the naked eye) but it holds the little-known distinction of an abode for life.

Stars can be classified by their brightness, their size, their composition, and their ability to undergo fusion. Scientists also classify stars based on their spectral characteristics, or what color the star looks like as it burns, which is based on what kinds of heavier elements are getting fused in the star’s interior, which in turn is determined by how hot the star is. We can graph these stars in a diagram that compares the mass of a star with its luminosity. This is called the Hertzsprung-Russell diagram and it shows a band of stars on in the center sloping down and to the right that signifies the stability strip of main sequence stars.2 This strip shows the correlation between the mass of a star and the brightness and temperature with which it burns. Stars generate their heat and light through the process of fusing elements together to form heavier elements called nucleosynthesis. A star maintains its integrity by balancing the inward push of gravity with the outward thrust of nuclear fusion. When the star runs out of fuel to continue fusion, the inward push of gravity overcomes the weakened thrust of fusion and the star collapses, getting hotter as the gravitational collapse causes potential energy to be released, concentrating the heat of the star into a much smaller volume. Eventually, that star releases all of that energy in a nova.3 In our star, mostly hydrogen fuses together under immense temperature and pressure to form helium; in other stars hotter than our Sun, heavier elements can be formed in greater quantities and at a faster rate than our scrawny little star. Stars are the furnaces that create all the chemical elements in the universe and when these gas balls burn out and explode in a nova, releasing the heavy elements that will one day make up the satellites around another solar system. The more massive the star, the bigger the explosion and these supernovas release every known element out into the universe.

The HR diagram plots a star's absolute magnitude versus their spectral characteristics

When the universe began, there was only hydrogen and helium with a smattering of lithium and beryllium in the smallest trace amounts. The first generation planets to form in the afterglow of the Big Bang were only made of hydrogen and helium, more akin to the gas giants in Earth’s solar system rather than a terrestrial planet like Areios. It wasn’t until the first generation stars went supernova that we see any satellite resembling a rocky planet because heavier metals that make up the bulk of our world weren’t forged until a supernova explosion sent those products out into the stars. The second generation planets could have been made of rocky material and may have been habitable for life once elements like carbon, nitrogen, and oxygen were created. Areas of a galaxy with more hydrogen and helium tend to create more bigger stars that create more violent supernova explosions.

Because of this, NGC 772 has areas of more star-building compared to other areas with less star-building and this means that certain regions of NGC 772 is more habitable than other regions, which is conceptualized by the galactic habitable zone.4 The GHZ of NGC 772 looks like a donut; the very center of our galaxy is too close to a super massive black hole at the center of the galaxy; that black hole will spit out dangerous radiation and any planet too close would get irradiated with high-energy particles that could tear apart a cell. Any planet too close to the center would be sterilized. Any star in the center of the galaxy would also be closer to more massive stars and would be subjected to more devastating supernova explosions that might hinder the development of life. Too far out into the edge of the galaxy and there’s not enough gas to form stars and planets and any satellite out there would not have enough metal to build a habitable planet. It’s somewhere in between the outer and inner portions of our galaxy that we find the right space conducive for building habitable planet and stars. This concept of a “goldilocks” zone that’s just right for life will come up again later in our discussion a planet’s orbit around a star. But more on that later…

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