Type Ia supernovae are some of the most rare and dazzling phenomena in the Universe, and yet astronomers were recently lucky enough to catch a glimpse of one in action. And now, their discovery is shedding light on the mysterious origins of such spectacles, according to a new study.
These explosive events are produced when small dense stars called white dwarfs burst with ferocious intensity. At their peak, these supernovae can outshine an entire galaxy. Although thousands of Type Ia supernovae have been found in the last few decades, the process by which they occur has long been debated by scientists.
That is, until a team of Caltech astronomers working on a robotic observing system known as the intermediate Palomar Transient Factory (iPTF) observed a Type Ia supernova, named iPTF14atg, in a nearby galaxy located 300 million light-years away. The data, described in the journal Nature, lends support to one of two popular theories about the origin of white dwarf supernovae.
First off, it is generally believed that when it comes to Type Ia supernovae, the white dwarf that eventually explodes is one of a pair of stars orbiting around a common center of mass. However, it's the interaction between these two stars where scientists tend to disagree.
One theory - referred to as the double-degenerate model - contends that the companion to the exploding white dwarf is also a white dwarf, and when the two objects merge it causes a stellar explosion. (Scroll to read on...)
The so-called single-degenerate model, on the other hand, claims the second star is a Sun-like star - or even a red giant. In this model, the white dwarf's powerful gravity pulls material from the second star, thereby increasing its own temperature and pressure to the point that it stirs a nuclear reaction and explodes in a supernova.
But how are scientists supposed to determine which theory is the correct one if Type Ia supernovae are few and far between? After all, these events only occur about once every few centuries in our galaxy, and the stars involved are extremely dim before the explosions erupt.
That's where the iPTF comes in. From atop Palomar Mountain in Southern California, where it is mounted on the 48-inch Samuel Oschin Telescope, this high-tech system scans about 1,000 square degrees of sky each night. It mainly looks for transients - objects whose brightness changes over timescales that range from hours to days, including Type Ia supernovae.
With its remarkable images - along with other satellite imagery using UV radiation - the Caltech team not only found iPTF14atg, but also determined how it formed.
The discovery "provides direct evidence for the existence of a companion star in a Type Ia supernova, and demonstrates that at least some Type Ia supernovae originate from the single-degenerate channel," researcher Shrinivas Kulkarni, who led the iPTF project, said in a statement.
Although it seems that this rare supernova was created with a white dwarf and companion star, that doesn't necessarily mean that the double-degenerate model doesn't hold water. It's possible that other Type Ia supernovae may result from double-degenerate systems, researchers say.
"The news is that it seems that both sets of theoretical models are right, and there are two very different kinds of Type Ia supernovae," concluded Caltech professor of theoretical astrophysics Sterl Phinney, who was not involved in the research.
There is still much to be learned from supernovae, but this discovery is at least a step in the right direction.
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