The Cosmic Neighborhood

I love space. I love it so much I am going to take time before writing my next article to write this exclusive blog post about the topic of space. Specifically, about how its not a vacuum in the dreaded sense of the word. There is quite a lot of stuff flying around in the nothingness we think of as everything above our atmosphere. Thats a good first approximation but it is often full of stuff. If you were instantly teleported out into space exactly one astronomical unit towards the sun, you wouldn’t say space is a vacuum. You would probably notice how hot the very center of our sun is. A vacuum is defined as a region of space void of all matter, causing regions with greater density to want to expand into it in order to reach equilibrium. Perfect emptiness would correspond to no matter at all and an average temperature of 0 K. Outer space can consist of only a few hydrogen atoms per cubic meter, but is still flooded with enough radiation from stars to achieve an average temperature of 3 K. Regions where stars are currently forming in the Milky Way galaxy have densities of 100 particles per cubic centimeter and an average temperature of 10 K. These clouds of gas, or ‘nebulae’, can become perturbed by nearby events and initiate their star cycles. How it develops is influenced primarily by one factor: how fat it is.

Let’s talk about the fundamental currency of space; matter. The more matter you have, the stronger the gravity field you generate. There exists an entire spectrum of possibilities for celestial superstructures all based on varying degrees of magnitude. To make visualization sorta easier we have coined a unit of measurement called a ‘solar mass’, which is defined as the mass of our sun (named ‘Sol’) or (1.98892 ± 0.00025) × 1030 kg; roughly 332 950 times the mass of the earth or 1 048 times the mass of Jupiter. Lone stars up to four solar masses live long healthy lives lasting in excess of ten billion years, ending in a dense core of helium that cools off and goes quiet after awhile. If the stars have more mass, the star develops faster due to the increased density in the guts of it all. The gas becomes so dense that even helium can be ignited to give off energy, and so on with heavier elements, building up layers of elements like a jawbreaker, until it gets to iron. After only about ten million years, the core of the star is so hot and dense that it radiates its energy into the outer layers, causing a run-away “bounce” and a shedding of roughly three-fifths of the stars mass, known as a supernova. Often, these fast growing stars explode and cause the formation of smaller stars from nearby gas clouds, endowing them with a shower of heavy elements that coalesce into planets. This is the current theory for the formation of the solar system.

After detonation, the remnant of the star is playing a game of cosmic hungry hippos. If the mass of the core is between two and ten solar masses, it will become a neutron star. Neutron stars can attract matter from its shed layers or feed off of a sister star to reach its next checkpoint. Once past ten solar masses, a black hole develops. Stars with twenty-five or greater solar masses will retain enough of a core after the supernova to become a black hole directly. Black holes then merge with other stars and black holes to create larger and larger cores. Eventually, they can become so powerful and massive that entire superstructures can form from the swirling cloud of gas and dust being sucked into a super-massive black hole. The one at the center of the Milky Way galaxy is on the order of four million solar masses.

Everything in our immediate vicinity in space is therefore spiraling inwards like a cosmic maelstrom towards the center. This has in turn given rise to a new unit of measurement, known as the ‘galactic year’. It is the time it takes for the solar system to complete a full rotation around the Milky Way, or roughly 240 million years. Our universe is roughly sixty galactic years old, our sun is about twenty galactic years old, and one galactic year ago, the dinosaurs went extinct. The combined weight of the Milky Way galaxy is roughly 600 billion solar masses. Best guesses by astronomers indicate that there are about 300 billion stars in our galaxy, which is shaped like a large disc so massive it takes light over 100 000 years to cross, and is 1 000 light-years thick. And as we look around, we notice that stars behave in all sorts of ways. Sometimes they come in pairs that orbit each other, sometimes a pair of stars will orbit another larger star, sometimes two binary systems will orbit each other, and so on in an endless stream of possibilities. And that isn’t even counting the roughly 160 billion planets orbiting these stars in the Milky Way and the mind boggling impossible to count planets not bound to a star but free floating in space; vagabond Jupiter-like planets without a star to call home.

Outside of that lies the interstellar medium, a scattering of hydrogen and helium gas, with maybe the odd scrap of dust far-flung from its parent supernova. It is cold, dark, and only visited by the odd hydrogen particle or passing cosmic ray. Beyond our galaxy are a collection of twenty-six satellite galaxies that are gravitationally bound to us. Within the ‘local group’ of galaxies are included the Andromeda galaxy which is about 710 million solar masses, spread out over a diameter of 220 000 light-years, and headed straight for us with its own twenty-one satellite galaxies. Expect the collision in roughly 4.5 billion years, or the same as the age of Earth. It turns out to be common for these groups of loosely affiliated galaxies to ultimately combine to form single shapes. Our local group is about 10 million light-years across and is itself part of a larger arrangement of matter.

The ‘local supercluster’ is made up of over 100 galaxy groups and extends 110 million light-years across. There are millions of superclusters in the observable universe, which extends outwards in any direction from Earth for 46 billion light-years. Attempts to visualize the totality of the visible universe have revealed a meta-structure with most of the matter arranged into walls and filaments. This is still not well understood since matter tends to congregate into points on smaller scales. To further mystify matters, a new monster has arisen at the new frontier of the conceivable universe; the ‘Great Attractor’. This object is roughly 250 million light-years away from us and is so massive that its effects can be observed on entire clusters of galaxies. It is believed to contain as much mass as tens of thousands of Milky Ways and grows like everything else in the blackness of space.

Bringing it all back to our familiar rocky ball we call home, we ask the question: what does it all mean practically? It means that there will never be a shortage of raw materials out there in the distance for us to collect and rearrange like humans do into an existence. The universe is chock full of raw materials, just lying around waiting for some sentient beings to come along and make use of. But that can’t happen until we realize the size of the gold mine we are sitting on and find a way to cope with the scales of space. This all begs further questions in my mind such as “how do stars radiate off the energy and can it be used usefully?”, “how can we create a self-sustaining existence given a new post-Earth domain?”, “what are the theoretical limits to what we can create?” It has always been so. People have stood in awe at edge of the known world, and by expanding it we can come to learn more about our surroundings, our origin, and our destiny. After all, space is the final frontier.