A huge flash of ultraviolet light has been spotted deep in the universe, and could potentially help illuminate some of the universe’s deepest mysteries.
The discovery could help shed light on how stars come to explode, and how the universe forms the heavy metals that surround us, as well as enigmatic dark energy, scientists say.
The blast was sent through space following a white dwarf explosion – and astronomers have only ever been able to see such an event once before.
Researchers will now be able to keep watching the blast until, in a year, they will be able to see “all the way into the centre of the explosion”.
As they do, they hope to be able to see how this white dwarf, and all other remnants of dead stars, are able to explode with such powerful force.
A white dwarf is the next stage of a star after it has exhausted its nuclear fuel, whereby its outer material collapses leaving only the core.
Despite being one of the most common explosions in the universe, in this instance the white dwarf exhibited unexpected behaviour.
The rare flash of ultraviolet light suggests that something inside or nearby the white dwarf was expelling a large amount of heat. But that surprised astronomers since white dwarf stars usually cool as they age.
“The simplest way to create UV light is to have something that’s very, very hot,” Adam Miller, an astrophysicist from Northwestern University who led the research, said in a statement.
“We need something that is much hotter than our sun — a factor of three or four times hotter. Most supernovae are not that hot, so you don’t get the very intense UV radiation.
“Something unusual happened with this supernova to create a very hot phenomenon.”
Researchers spotted the supernova in December 2019, one day after the explosion first became visible from a nearby galaxy 140 million light-years from Earth.
The galaxy is located close to the tail of the Draco constellation.
Within hours, astrophysicists at Nasa’s Neil Gehrels Swift Observatory were studying the phenomenon using ultraviolet and X-ray wavelengths.
“As time passes, the exploded material moves farther away from the source”, Miller says. “As that material thins, we can see deeper and deeper. After a year, the material will be so thin that we will see all the way into the centre of the explosion.”
The researchers have four possible explanations for the flash of ultraviolet light that accompanied the explosion:
- A white dwarf consumed its companion star and became so large and unstable that it exploded, and the colliding material caused the flash of ultraviolet light.
- Extremely hot radioactive material in the white dwarf’s core mixed with its outer layers, causing the outer shell to reach higher temperatures than usual;
- An outer layer of helium ignited carbon within the white dwarf, causing an extremely hot double explosion and the flash of light.
- Two white dwarfs merged, triggering an explosion, and the colliding material emitted ultraviolet radiation.
The reason this finding is so vital is because it could reveal the secrets of how planets form.
Most iron in the universe is created by supernovae, and so understanding this event could be key to understanding the formation of our own planet, which has a rich iron core.
It could also be key to understanding dark energy, the effects of which can be measured using supernovae. Astronomers are able to use such explosions as “standard candles”, or measuring sticks that allow them to understand exactly how far a certain phenomenon is from Earth, and was used to first discover dark energy.
Dark energy is the name given to the force that is thought to have caused the rate of our expanding universe to increase over time, rather than slowing down. This energy makes up approximately 70 percent of all the energy in the universe, but still remains largely mysterious.
“We don’t have a direct way to measure the distance to other galaxies,” Miller explained. “Most galaxies are actually moving away from us. If there is a type Ia supernova in a distant galaxy, we can use it to measure a combination of distance and velocity that allows us to determine the acceleration of the universe.
“Dark energy remains a mystery. But these supernovae are the best way to probe dark energy and understand what it is.”
”At the moment, when measuring distances, we treat all of these explosions as the same, yet we have good reason to believe that there are multiple explosion mechanisms. If we can determine the exact explosion mechanism, we think we can better separate the supernovae and make more precise distance measurements.”
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