From collisions to stellar cannibalism—the surprising diversity of exploding white dwarfs - UNIVERSE

The Palomar 48 inch telescope at the Palomar Observatory in California with an image of the Milky Way in the background. The stars represent the number of supernovae discovered in each direction and the inset is an image of a galaxy after (left) and before (right) the supernova exploded. Credit: Mickael Rigault.

Astrophysicists have unearthed a surprising diversity in the ways in which white dwarf stars explode in deep space after assessing almost 4,000 such events captured in detail by a next-gen astronomical sky survey. Their findings may help us more accurately measure distances in the universe and further our knowledge of "dark energy."

The dramatic explosions of white dwarf stars at the ends of their lives have for decades played a pivotal role in the study of dark energy—the mysterious force responsible for the accelerating expansion of the universe. They also provide the origin of many elements in our periodic table, such as titanium, iron and nickel, which are formed in the extremely dense and hot conditions present during their explosions.

A major milestone has been achieved in our understanding of these explosive transients with the release of a major dataset, and associated 21 publications in an Astronomy & Astrophysics special issue.

This unique dataset of nearly 4,000 nearby supernovae is many times larger than previous similar samples and has allowed crucial breakthroughs in understanding how these white dwarfs explode. The sample was obtained by Zwicky Transient Facility (ZTF), a Caltech-led astronomical sky survey, with key involvement of researchers at Trinity College Dublin, led by Prof. Kate Maguire in the School of Physics. 

Each star is a SN exploding with the size indicating how bright it appears and the color indicating the color of the supernova, they go from blue (hotter) to yellow (cooler) as they grow older and cool. Credit: Mickael Rigault

"Thanks to ZTF's unique ability to scan the sky rapidly and deeply, it has been possible to discover new explosions of stars up to one million times fainter than the dimmest stars visible to the naked eye," says Prof. Maguire.

One of the key results, led by the group at Trinity, is the discovery that there are multiple exotic ways that white dwarfs can explode, including in collisions of two stars in luminous stellar spectacles, as well as the cannibalism of stars by their companions in double star systems.

This is only possible with this sample due to the ability to discover very faint blips combined with large sample sizes. And the surprising diversity may have implications for the use of these supernovae to measure distances in the universe, since the constraints on the properties of dark energy crucially demand that these explosions can be standardized.

"The diversity of ways that white dwarf stars can blow up is much greater than previously expected, resulting in explosions that range from being so faint they are barely visible to others that are bright enough to see for many months to years afterwards," says Prof. Maguire. 

by Trinity College Dublin

Source: From collisions to stellar cannibalism—the surprising diversity of exploding white dwarfs