White dwarfs are the dense, hot cores left behind when Sun like stars die. Imagine squeezing the entire mass of our Sun into something the size of Earth, that’s a white dwarf and our Sun will become one in the distant future. These stellar corpses are incredibly dense, with just a teaspoon weighing as much as a large car.
Most white dwarfs slowly fade away over billions of years, but some have more dramatic fates. A new study authored by a team led bby Dr Hila Glanz from the Technion Institute in Israel focused on rare “hybrid” white dwarfs made of helium, carbon, and oxygen. The team used sophisticated computer simulations to study the merger of two of these dead stars which creates some of the most violent explosions in the universe.
A comparison between the white dwarf IK Pegasi B (centre), its companion IK Pegasi A (left) and the Sun (right). This white dwarf has a surface temperature of 35500 K (Credit : R J Hall)
When two of these hybrid white dwarfs spiral into each other, the result is a catastrophic explosion. As the two stellar corpses merge, the lighter one gets partially torn apart while the heavier one undergoes what has been called the “double detonation explosion.”
This isn’t just any explosion, it’s powerful enough to act like a slingshot, hurling the surviving remains of the lighter star into space at speeds in excess of 2,000 kilometres per second. That’s fast enough to be able to escape the gravitational pull from our entire Galaxy and venture into the vast emptiness of intergalactic space.
This discovery solves a long outstanding puzzle about hypervelocity white dwarfs like J0546 and J0927. Both these stellar remnants have been found to be racing through our Galaxy’s outer regions. All existing models were unable to explain both their incredible speeds and their exceptionally high temperature, unlike typical white dwarfs.
“This is the first time we’ve seen a clean pathway where the remnants of a white dwarf merger can be launched at hypervelocity” – Dr. Glanz Hila Glanz from the Technion Institute in Israel.
These explosive mergers also seem to create unusual types of supernovae that are fainter than usual. Understanding these events helps astronomers use them as “standard candles” to probe cosmic distances and the mysterious force driving the universe’s accelerated expansion. Traditional Type Ia supernovae have been used as standard candles for measuring distances across space because they usually explode with the same brightness. However, these hybrid white dwarf mergers produce a new class of underluminous supernovae that are dimmer and more peculiar than their conventional cousins.
G299, a type Ia supernova remnant (Credit : NASA/CXC/U)
As upcoming surveys like the Vera Rubin Observatory and future Gaia data releases discover more of these stellar remnants racing through space, there will be unprecedented opportunities to study both the violent processes that create them and what they reveal about stellar death and rebirth. By continuing this study it may be possible to piece together the physics of stellar explosions, trace the chemical evolution of galaxies, and even test our understanding of fundamental laws that govern our universe.
Source : New study reveals origin of the fastest white dwarfs in the galaxy