We have the barest inkling of how truly vast the Milky Way galaxy is, but looking up on a dark summer night is enough to convince you it must be REALLY big. After all, this garland of hazy light speckled with stars touches both ends of the sky, north and south.
Astronomers have measured the galaxy’s diameter at 100,000 light years which means little until you appreciate that one light year equals 6 trillion miles, the distance a beam of light travels in one year. The fastest spacecraft ever built, the Helios probes, reached 157,000 mph (253,000 km/hr) as they zipped around the sun studying the solar wind from the mid-1970s to 1985. While that’s nine times faster than the International Space Station, it would still take 4,383 years to travel one light year at that phenomenal pace.
Even fleet light takes 100,000 years to cross from one side of the galaxy to the other. A light ray leaving Earth 100,000 years ago, when Neanderthals were the dominate human species in Europe, recently arrived there in our mobile-phone obsessed era. What will Earth look like 100,000 years from now?
Vast as the Milky Way is, it’s dwarfed by IC 1101, a faint galaxy residing in the center of the rich galaxy cluster Abell 2029 in the constellation Virgo. Located a billion light years from Earth, IC 1101 is the largest known galaxy with a diameter of 6 million light years or at least 60 times the size of the Milky Way.
You’ve probably all seen the illustration comparing the size of Earth to the sun. We sure do look tiny. Now multiply our one star by 200-400 billion – that’s the number of stars in the Milky Way – and consider that many of them likely harbor planets. Impressive place this Milky Way … until you park it alongside IC 1101 with its 100 trillion stars.
Galaxies can be broken down into three basic types: spirals (like the Milky Way), ellipticals and irregulars. Spiral galaxies’ cores glow yellow from billions of older stars that formed in the galaxy’s youth that have since aged and evolved. Hot, new stars, which are generally bluer in color, coalesce from dust and gas within the spiral arms that wind around the central hub.
Ellipticals are spherical or flattened like a footballs and generally featureless. Most appear like foggy patches of amorphous star-haze. At a young age, they quickly converted their dust and gas into billions of stars that have since aged and yellowed like the ones in the Milky Way’s core. No spiral arms or fresh-faced hot stars here.
Giant ellipticals like IC 1101 usually start out small, beginning with the merger of a few modest galaxies within a cluster like Abell 2029. But if the process continues unchecked, a monster is born. Over their lifetimes large ellipticals can rack up a lot of mass, and the bigger they get, the more gravitational pull they exercise over their environment, sucking in even more galaxies. Large elliptical galaxies are common features in large, rich galaxy clusters.
If you could put IC 1101 in place of our Milky Way it would encompass a volume of space big enough to include our galaxy and its satellites the Large and Small Magellanic Clouds plus the neighboring Andromeda and Triangulum galaxies. That’s I what call supersized!
Every time we look at the sky, we can’t help but be taught a lesson in perspective. Earth’s an atom compared to the Milky Way, and the Milky Way’s a mouse at the feet of IC 1101. Our job is to find our place in this vastitude.
To assist you in your journey, a great place to start, besides the night sky of course, is Cary Huang’s wonderful Scale of the Universe 2.