Ancient ‘White Dwarf’ stars explode and die in more ways than was thought, and observing these violent cosmic deaths could help scientists to discover the invisible ‘dark energy’ that is powering the acceleration of the Universe.
“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 Professor Kate Maguire. School of Physics TCD, author of research published today in Astronomy and Astrophysics.
“Up to now it was thought that the white dwarf stars exploded in a particular way,” said Prof Maguire. “There are lots of different ways that the stars can die, and we can measure how many different types are occurring.”
The violent explosive deaths of white dwarf stars have for decades played a pivotal role in the scientific study of dark energy, an invisible force that remains elusive, but is thought to permeate right through the Universe.
The Sun is our nearest star. Stars are held together by gravity, and what differentiates them from a planet like Earth is that they have got fusion going on in their core. The fusion of hydrogen into helium provides the light and heat that we benefit from here on Earth
“Stars change how they look as they go through life; when our Sun gets older in a few billion years it’ll become what we call a white dwarf,” said Prof Maguire.
“That’s a very small star that has a radius of about the same size as the Earth. It is an extremely dense type of star mainly made up of carbon and oxygen. All stars that are like our sun will end up like this in the future.”
The white dwarf explosions can be thought of as being like cosmic light bulbs, said Maguire. Measuring how bright the ‘bulbs’ are, and the distance to them, can enable physicists to calculate how fast the Universe is expanding.
“We are interested in how stars explode, the mechanics of how that happens, the extreme physics involved, and how you can use them as measurement tools in the Universe to measure distances,” said Prof Maguire.
The data for the TCD-led research was based on observations of about 4,000 white dwarf supernova star explosions captured by a Caltech-led astronomical survey called the Zwicky Transient Facility, based in San Diego, USA.
In 1929, Edwin Hubble, the famous astronomer whom the Hubble Telescope was named after, discovered that the Universe was expanding, and that stars, planets and galaxies were steadily moving further away from the Earth.
Scientists assumed that the Universe’s expansion would slow, in response to gravity, similarly to how a thrown tennis ball falls back to Earth. However, in 1998, scientists found – by observing ‘white dwarf’ star explosions – that the Universe was continuing to expand, and at an accelerating rate.
“Nobody has a clue what this dark energy is, and that’s one of the key things that we want to try and measure with these white dwarf explosions,” said Maguire.
Science Spinning 
This is a test