Astronomy is a subject of exploration. In an age where the Earth has been charted from the Old World to the New, it almost seems like the age of great voyages of exploration and discovery have long passed. That stands true as long as you don’t look up at night. On a clear night it becomes painfully clear there is much more to discover; an entire universe out there, filled to the infinite brim of secrets and discoveries waiting to be uncovered. The age of exploration hasn’t passed, it has simply moved up into the never ending sky with astronomers at the helm.
In astronomy countless voyages are undertaken, not by humans but by light. The light may travel for billions of years at the fastest possible speed of 300,000km/s, passing over distances so vast, and wonders so grandiose, it would put any Earth-bound adventure to shame. It’s an astronomer’s job to greet the courageous light at the end of its journey in a telescope and listen to the stories it has to tell. Decoding the tales of light is the essence of astronomy. With these tales astronomers can explore the universe and uncover its hidden wonders. What stories have we heard from light? What lies out beyond our horizon?
Brave New Worlds
Great tales from light in recent times have been the discovery of new worlds, not “new worlds” like continents, rather new planets, worlds around other stars—exoplanets. These new exoplanets were once a rare discovery, however, with telescopes such as the Kepler space telescope greeting light from distant stars, it became apparent how common planets really are. To date 1,932 exoplanets have been discovered by Kepler, with another 4,696 yet to be confirmed and an untold more to be discovered, with at least 1.4 planets for every star. The sheer number of planets doesn’t devalue the discovery. Each exoplanet is a world. It has an environment. It has a history.
In all the exoplanets discovered some of the most interesting worlds have been found; a world that rain glass; a world with rings 200 times larger than Saturn’s; a world with two stars (yes, just like Tatooine!); a world orbiting a neutron star (the remains of a massive star); and a world being blasted away by its star. With all the exoplanets, the list of eccentricities goes on and on, but are any known as “a world with life”?
So far there are none, but astronomers are trying hard to find light that will tell us about a world with life. The first step is to find exoplanets like Earth, small enough that it’s not a gas giant, large enough that is has an atmosphere and not too hot or cold so that it’s in the Goldilocks zone where liquid water can exist on the surface. Kepler has found just 12 planets no more than twice the size of Earth and in the Goldilocks zone—12 planets that may have life.
As our technology and telescopes improve, astronomers will be able to gleam greater details from the stories of light and find even more planets that may harbour life. The day that life signs on another planet are discovered may not be far away.
An Expansive Sea
If telescopes cast their mirrors towards the far reaches of space, equally fantastic stories can be found. Stories from some of the oldest and greatest voyaged of light. Far off in the universe where light has travelled millions to billions of years to reach us, we find the universe is littered with galaxies. Enormous collections of billions of stars in all shapes and sizes, scattered about the black sea of space. In these far off galaxies, like we see in the Hubble Deep Fields, civilisations may have flourished, catastrophes may have occurred and empires fallen, all stories that we will never hear. But we can learn about the galaxies themselves, explore a realm of giants drifting in the black seas.
Among the myriad of galaxies we can find individual and great clusters of galaxies colliding with one another, moving about in a silent dance. Some galaxies are less graceful, violently spewing energy out into the cosmos as their central black holes gorge on stars and nebula, spitting out great beams of high energy particles into space. Such violent galaxies are known as quazars, and are only heard of from light that began travelling towards us very near to the beginning of the Universe.
We will never know the stars and planets of the far off galaxies. Those stories and wonders will never be charted by us.
Even with the largest telescopes imaginable, there is only so far that astronomers may explore. Using radio telescopes astronomers can see right back to 380,000 years after the Big Bang, to the first light that voyaged across the Universe. These weary travellers have been crossing the expanses of the Universe for about 13.7 billion years, ever since the first atoms formed. This old and far travelled light is known as the Cosmic Microwave Background (CMB).
Emitted as a snapshot of what the universe looked like all those years ago, the CMB is the farthest we can explore with light. In every direction the CMB surrounds us at 46 billion light years away, as a horizon to the Observable Universe—a horizon we may never pass over.
Voyages and Tales Untold
The stories we have heard and the sights we have seen from the voyaging light are unending. Here we have not even scratched the surface of what astronomers have learnt, or will learn from light. The age of exploration and discovery never ended. Above us awaits a universe to discover and understand.
One day it may be humanity who ventures forth on a great voyage, called onward by curiosity and perhaps a story of light that captured our imagination.
Written for Woroni, a shorter version of this article was published in print and online.