SUNSET: 
0A new survey contains 3,628 Type Ia supernovae — the exploding white dwarfs that astronomers use as cosmological toeholds to gauge our expanding universe.
Palomar / Caltech
A new survey contains 3,628 Type Ia supernovae — the exploding white dwarfs that astronomers use as cosmological toeholds to gauge our expanding universe.
The data release, led by Mickael Rigault (CNRS / Claude Bernard University), came from the Zwicky Transient Facility (ZTF), a wide-field astronomical survey based out of Palomar Observatory in California. The ZTF images the sky again and again to catch transients, or short-lived flashes of light.
Some of these transients are a particular type of supernova known as Type Ia, which mark the demise of white dwarf stars. The explosive ends are diverse, but if astronomers can watch a supernova's brightness as it fades, then they can tell what intrinsic brightness that blast had — and hence at what distance it lies. Type Ia supernovae are thus used as standard candles to help astronomers gauge how fast the universe was (and is) expanding.
But they're also quite rare, occurring only about every 1,000 years in a typical galaxy. Only by probing millions of galaxies — whose light traveled as far as 3.5 billion years to reach Earth — did ZTF detect such flashes at a rate of nearly four per night. Since the facility images the sky so often, it also caught many supernovae within days or even hours of the initial blast.
"For the past five years, a group of 30 experts from around the world have collected, compiled, assembled, and analyzed these data," Rigault says. "We are now releasing it to the entire community."
This "nearby" sample of supernovae samples our universe after it had already become dominated by dark energy — the mysterious repulsive force that started causing space to expand at an ever-accelerating rate some 5 billion years ago. (The discovery of dark energy earned three scientists the Nobel Prize in 2011.) Nevertheless, the thousands of supernovae just released represent an opportunity to test cosmology in the nearby universe. They also give astronomers a chance to better understand how white dwarfs explode — which in itself could influence our understanding of the universe's fate.
Read more about the survey in Lancaster University's press release and in the study published in Astronomy & Astrophysics.
About Monica Young
Monica Young, a professional astronomer by training, is News Editor of Sky & Telescope.
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