Outreach

Astronomical Transients: Astronomers use the term transient to refer to anything that emerges unexpectedly in the night sky and then fades away. Every few hundred years, a bright “new star” appears in the sky and disappears, inciting a sense of awe and wonder. These transients, such as supernovae, have long been the subject of myth and mystery. With the advent of modern telescopes, we find the Universe is teeming with violent cosmic explosions that emit light across the entire electromagnetic spectrum, eject highly energetic particles, and generate ripples in spacetime.

We now know cosmic transients represent a wide variety of cataclysmic phenomena. For example, massive stars collapse when they die, leaving behind neutron stars or black holes, and launching relativistic jets of gamma-rays. These explosions can be so bright they can be seen across the Universe, outshining entire galaxies. Other transients include optical and infrared outbursts from tidal disruption events where stars are torn apart by supermassive black holes, energetic fast radio bursts from highly magnetised neutron stars, and X-ray bursts triggered by runaway thermonuclear burning of matter accreted onto a neutron star. Unfolding over timescales ranging from milliseconds to months, these cosmic transients have transformed our understanding of the cosmos.

Cosmic Laboratory to Probe Extreme Physics: Cosmic transients form under the most extreme conditions in nature, reaching temperatures up to trillions of degrees and generating magnetic fields possibly 100 trillion times stronger than anything produced on Earth. These powerful events can reveal nuclear fusion processes within stellar cores and synthesise elements beyond hydrogen and helium that are essential to life on Earth. They offer glimpses into the cosmos shortly after the Big Bang, when the first stars began to form, and reveal otherwise invisible matter across the Universe. Cosmic transients serve as natural laboratories for studying matter and energy at scales far beyond what can be recreated in terrestrial laboratories, reshaping our understanding of the Universe and our place within it.

Transient detections have led to some of the most remarkable discoveries in modern physics. The detection of distant supernovae led to the ground breaking realisation that our Universe is not only expanding, but doing so at an accelerating rate. This discovery was awarded the 2011 Nobel Prize in Physics. In 2015, astronomers were able to detect gravitational waves from the merger of two black holes, an event that lasted just 0.1 seconds. This unveiled an entirely new way to study the cosmos, and was recognised with the 2017 Nobel Prize in Physics. That same year, astronomers observed two neutron stars merging, confirming their long-suspected connection to gamma-ray bursts. The explosion from this merger revealed the signatures of gold and platinum, solving a decades-long mystery of where half of all elements heavier than iron are produced.

The Unique Challenges of Transient Astronomy: Despite these remarkable discoveries, the true nature of many cosmic transients remains a mystery. Transients can appear unpredictably anywhere across billions of galaxies and fade quickly, requiring rapid detection. Vast areas of the Universe must be scanned, generating petabyte-scale datasets that must be swiftly processed. Once detected, tens of telescopes must be rapidly coordinated to study these fleeting events, each class requiring special observational techniques to capture their nature before they vanish. Such an effort is timely as several cutting-edge mega-facilities with significant Australian investment are coming online over the next five years, providing major opportunities for transient discoveries and testing our understanding of extreme physics.