Astronomers in Germany have discovered a fiery white dwarf ‘nova explosion’ for the first time.
Researchers observed the event thanks to data from the joint German-Russian X-ray telescope eROSITA, stationed in space about 900,000 miles away.
The X-ray flash – dubbed YZ Reticuli – completely outshined the center of eROSITA’s detector, which records emitted photons.
White dwarfs are the incredibly dense remnants of Sun-sized stars after they have exhausted their nuclear fuel and shrunk to about the size of Earth.
Sometimes such dead stars come back to life in a superheated explosion, creating a fireball of X-rays.
These nova blasts occur from white dwarfs in a binary system – a system composed of two stars that are gravitationally bound.
Astronomers have discovered for the first time a fiery explosion on a white dwarf dubbed a nova explosion. Pictured is the replica of the event that took place in 2020
Overexposed image taken by the eROSITA X-ray telescope launched in 2019 of the Nova explosion
The researchers have now been able to observe such an explosion of X-ray light for the first time, which came from a white dwarf in the constellation Reticulum.
WHAT IS A WHITE DWARF?
A white dwarf is the remnant of a smaller star that has run out of nuclear fuel.
While large stars – those with more than ten times the mass of our Sun – suffer a spectacularly violent peak as a supernova explosion at the end of their lives, smaller stars are spared such dramatic fates.
As stars like the Sun reach the end of their lives, they exhaust their fuel, expand as red giants, and later eject their outer layers into space.
The hot and very dense core of the former star – a white dwarf – is all that remains.
White dwarfs are about the mass of the Sun but about the radius of Earth, meaning they’re incredibly dense.
The gravity on the surface of a white dwarf is 350,000 times that on Earth.
They get so dense because their electrons are smashed together, creating what caused “degenerative matter.”
This means that a more massive white dwarf will have a smaller radius than its less massive counterpart.
Although the observation of eROSITA was made back in July 2020, it has only just been detailed in a new study led by astronomers from Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) in Erlangen, Germany.
“It really was a kind of lucky coincidence,” said study author Ole König from FAU. “We were really lucky.
“These X-ray flashes last only a few hours and are almost impossible to predict, but the observation instrument must be pointed directly at the explosion at exactly the right time.”
eROSITA is floating in space at Lagrange Point 2 (L2), an area of balanced gravity between the sun and the earth 900,000 miles (1.5 million km) away.
eROSITA has been scanning the sky for soft X-rays since 2019, although the instrument stopped collecting data on February 26, 2022 due to the collapse of cooperation between Germany and Russia following the invasion of Ukraine.
Less than a year after going live, on On July 7, 2020, eROSITA measured strong X-rays in an area of the sky that was completely unremarkable four hours earlier.
When the X-ray telescope surveyed the same position in the sky four hours later, the radiation was gone. Accordingly, the X-ray flash must have lasted less than eight hours.
X-ray explosions like these were predicted by theoretical investigations in a study as early as 1990, but have never been directly observed to date.
These fireballs of X-rays occur on the surface of white dwarfs, stars that were originally comparable in size to the Sun before consuming most of their hydrogen and later helium fuel deep in their cores and shrinking.
Composed mostly of oxygen and carbon, white dwarfs are similar in size to Earth but contain a mass that can resemble that of our Sun.
Pictured here is eROSITA, a joint German-Russian X-ray telescope, before its launch in 2019
eROSITA is stationed in space approximately 900,000 miles away at Lagrange Point 2 (L2), an area of gravity balance between the Sun and Earth (artist’s impression)
WHITE DWARF WILL “TURN ON AND OFF” IN 30 MINUTES.
A white dwarf star was spotted in just 30 minutes of “turning on and off,” researchers reported in 2021.
Using data from NASA’s Transiting Exoplanet Survey Satellite (TESS), the Durham University team observed the phenomena in the TW Pictoris star system, 1,400 light-years from Earth.
They found that it didn’t take months for the brightness to increase and then fall again, but only about half an hour, likely due to a fast-moving magnetic field.
Read more: White Dwarf Star Sighted ‘Turning On and Off’ in 30 Minutes
“One can visualize these proportions by imagining that the sun is the same size as an apple, which means that the earth is the same size as a pinhead orbiting the apple at a distance of 10 meters.” , said Professor Jörn Wilms. also at FAU.
When trying to explain a white dwarf, the researchers said to introduce yourself shrink an apple to the size of a pinhead. This tiny particle would retain the comparatively large weight of the apple.
Just a teaspoon of matter from inside a white dwarf easily has the same mass as a large truck.
White dwarfs are so hot that they glow white, but their radiation is so weak that it is difficult to see them from Earth.
In a binary star system (a solar system with two stars), white dwarfs can be accompanied by another star that is still burning.
In this case, the white dwarf’s enormous gravitational pull pulls hydrogen from the companion star’s envelope.
Over time, this hydrogen can accumulate in a layer just a few meters thick on the surface of the white dwarf.
In this layer, the enormous gravitational pull creates an enormous pressure so great that the star reignites, resulting in a violent explosion that blasts off the hydrogen layer.
X-rays from one such explosion hit eROSITA’s detectors on July 7, 2020, producing an overexposed image.
White dwarfs are the incredibly dense remnants of Sun-sized stars after they have exhausted their nuclear fuel and shrunk to about the size of Earth (artist’s impression).
White dwarfs are so hot that they glow white, but their radiation is so weak that it is difficult to see them from Earth
“Using model calculations that we originally created while accompanying the development of the X-ray instrument, we were able to analyze the overexposed image in more detail in a complex process to get a behind-the-scenes look at an explosion of a white dwarf, or nova,” said Professor Wilms.
The blast created a fireball with a temperature of about 327,000 degrees Kelvin, making it about sixty times hotter than the sun.
As these novae run out of fuel fairly quickly, they cool rapidly and the X-rays weaken, eventually turning into visible light.
This visible light reached Earth half a day after eROSITA detection and was observed by optical telescopes.
“Then what appeared to be a bright star, which was actually the visible light from the explosion, appeared and was so bright that it could be seen in the night sky with the naked eye,” King said.
Apparently “new stars” like this one have been observed in the past and called “nova stella” or “new star” because of their unexpected appearance.
Since these novae are only visible after the X-ray flash, it is very difficult to predict such outbursts and it is mostly up to chance when they hit the X-ray detectors.
The new study was published in the journal Nature.
WHAT HAPPENS TO THE EARTH WHEN THE SUN DIES?
In five billion years, the sun is said to have grown into a red giant star more than a hundred times its current size.
Eventually, it will eject gas and dust to form a “shell” that accounts for up to half its mass.
The core becomes a tiny white dwarf star. This will glow for millennia, illuminating the envelope to create an annular planetary nebula.
In five billion years, the sun is said to have grown into a red giant star more than a hundred times its current size
While this metamorphosis will change the solar system, scientists aren’t sure what will happen to the third rock from the sun.
We already know that our sun will get bigger and brighter, so it will likely destroy every form of life on our planet.
But whether the rocky core of the earth will survive is uncertain.