Everything in our known universe
By Cazzy Lewchuk, Staff Writer
Renowned sci-fi author Douglas Adams once stated, “Space is big. Really big. You may think it’s a long way down the road to the chemist, but that’s just peanuts compared to space.” Indeed, the observable universe is 13.5 billion light years across, and has an estimated diameter of 93 billion light years. Due to its mind-boggling size and human limitations (we are, of course, limited to this planet for our observations), many elements of the universe remain unknown—even its general size and composition is debated. However, many physical objects are present and easily observable. Here’s a breakdown of what’s what.
Many of these names and definitions come from protocol by the International Astronomer’s Union from as recently as 2006. The astronomy field has advanced tremendously in the last few centuries, and it is likely some of these definitions will be revised as our knowledge of the universe continues to grow.
Small solar system objects: A general term for anything within a solar system that does not meet the criteria of other definitions. These include asteroids, comets, and “minor planets” (solid objects too small to be an actual planet). These objects can be as small as one kilometre across or as large as a few hundred.
Satellite/moon: An object that orbits a planet (or dwarf or minor planet), generally made up of shrapnel from forming planets. While sizes vary, generally they are 1000–6000 kilometres across.
Planet: A body that orbits around a central star with a mass large enough to be nearly spherical. They also “clear the neighbourhood,” meaning they become gravitationally dominant in their areas. Objects that only meet the first two criteria, such as Pluto, are known as “dwarf planets.” The planets in our solar system range from a size of 4,879–142,984 kilometres, with Earth clocking in at 12,742 kilometres in diameter.
Star: The most abundant object in our universe, stars are incredibly hot balls of gases held together by gravity that support nuclear fusion. Both the mass and diameter of stars vary greatly; they also contract or expand depending on what stage of their “lives” they are in. Some stars are as little as 20 kilometres across, but the largest star in our universe is thought to be 2.4 billion (yes, with a b) kilometres across. A rough estimation (it’s difficult to determine such large figures) suggests there are approximately 100 octillion (100,000,000,000,000,000,000,000,000,000) stars in the universe.
Galaxy: A shaped large star system formed by gravity. Dwarf galaxies contain a mere few billion stars, while larger ones, such as Earth’s very own Milky Way, contain an estimated 200-400 billion stars. While the sheer number of galaxies in the universe (detected at 100 billion for now) makes it hard to measure size, we do know that it varies greatly. The smallest detected galaxy is “only” 300 light years across (a light year being equivalent to 9.5 trillion kilometres), with the largest known to be 2 million light years across. Galaxy groups and clusters are currently thought to be the largest observable objects in the universe.
Black hole: Little is known about these areas, which contain more mass and gravity than anything else, so that nothing (even light, the fastest thing in the universe) can escape from their pull. Theorized to be at the centre of many galaxies, they are hypothetically formed from the remains of exploded stars. It’s also thought that they could be literal holes in space time: possible portals across our universe, or even gateways to another.
All in all, space is incredibly big, but also incredibly fascinating. So break out the new terms you’ve learned at parties to impress your friends, or attractive, astronomically-inclined people sitting alone at the bar. Like with space, the possibilities are endless.