THE hustle and bustle of daily life is a stark contrast to the tranquillity of the night sky. Many of the names we use for the constellations are thousands of years old. Ancient Greek and Arabic astronomers had almost exactly the same view that we have today: the stars do not seem to change.
But this is a lie.
We now know that the night sky is a seething, bubbling tableau. Look up, and unseen by your eye a vast number of stars are erupting, exploding or being torn apart. With our limited human vision we see only the tiny brightest tip of what the cosmos has to offer. Look deeper, and violence abounds.
A growing number of astronomers now devote their careers to what is known as “time-domain astronomy” – the search for celestial bodies that appear, disappear or change with time. The goal is to catch stars in the very act of brightening or fading, and to use these changes to learn more about the cosmos.
Flashes and flares in the sky usually represent catastrophic releases of energy, under conditions far more extreme than we could ever hope to reproduce in laboratories here on Earth. The catch is that time-domain astronomy is a cosmic guessing game, with seemingly impossible odds stacked against us. The fundamental problem is that we don’t know in advance where the next change in the heavens is going to happen. For example, suppose that once a night, somewhere in the universe, a star abruptly ends its life in a colossal supernova explosion. We cannot possibly know which of billions of stars will be the next to go.
Maybe we should just stare through our telescopes, night after night? Unfortunately, most modern telescopes have tiny fields of view.
The Hubble Space Telescope, arguably the most powerful telescope ever built, has a field of view that covers just 0.000008 percent of the sky at any one time.
Patiently point Hubble in a random direction once every 24 hours, hoping that you’ll see the one supernova in the universe that happened to occur that night, and you’ll average tens of thousands of years before you’re lucky enough to catch one in the act.
Astronomers have thus had to come up with a range of clever solutions.
Perhaps unique in all fields of research, astronomy is built on strong partnerships between amateurs and professionals. Thousands of amateurs patrol the skies with their own modest-sized telescopes night after night. Astronomers have also built new types of telescopes, with spectacular fish-eye lens capabilities to image enormous swathes of the sky at once. For example, the forthcoming Large Synoptic Survey Telescope will utilise a 3 200-megapixel camera to provide a field of view more than 3 000 times larger than that of Hubble. And a new radio telescope, the Murchison Widefield Array, has a view of the sky larger than Hubble’s by a factor of 500 000.
While we will still don’t know exactly where to look to see the next explosion or disruption, the odds are greatly increased when you’re looking through a massively wide- angle lens.
Once an astronomer finds something unexpected in the sky, the most urgent thing is to let everyone else know too. Sophisticated electronic alert networks have thus been developed, which allow any registered user to instantly notify everyone else. The truly dedicated sleep with their phones by their beds, ready to be awakened by an automatic alert.
Upon receiving such an alert, astronomers will swing their telescopes to the relevant patch of the sky, eager to capture their own contribution to the aftermath of the event before it fades away.
Every day, a global game of “whack-a-mole” takes place as these alerts criss-cross the globe and call stargazers to action.
What have we learnt from time-domain astronomy? We have seen colossal distant star quakes, releasing more energy than the sun can produce in a quarter of a million years.
We have seen stars cry out their final farewell in a flash of light as they fall into the maw of a giant black hole. We have seen invisible noodle-like tubes of gas, drifting in front of galaxies, flaring and distorting their light like a fun-house mirror.
And we have borne witness to the birth cries of newborn black holes, formed when a star’s nuclear furnace shuts down and gravity takes over.
We have begun a heady new era in which the sky changes in real time as we watch with amazement.
l Gaensler is director, Dunlap Institute for Astronomy and Astrophysics, University of Toronto. This article initially appeared in The Conversation.