White Dwarf Star X-ray Explosion Was Caught On Satellite For The Very First Time

Sci Tech Daily

Stars in the solar system eventually use up all of their fuel, and when that happens, they end up shrinking to form what’s called white dwarfs. But there are times when these dead stars flare back up to life in an extremely hot explosion, which produces a fireball of X-ray radiation.

Incredibly, a research team managed to observe one of these explosions of X-ray lights for the first time in history.

According to astrophysicist, Ole König, from the Astronomical Institute at FAU, “It was to some extent a fortunate coincidence, really. These X-ray flashes last only a few hours and are almost impossible to predict, but the observational instrument must be pointed directly at the explosion at exactly the right time.”

The instrument used for this particular case is the eROSITA X-ray telescope, which is currently located one and half million kilometers from Earth – approximately 932000 miles – as it surveys the sky for soft X-rays, something it has been doing since 2019.


On July 7, 2020, it managed to measure a strong X-ray radiation in an area of the sky that was completely unobtrusive just four hours before that. Four hours later, when the X-ray telescope surveyed the same area in the sky, the radiation had disappeared. What follows is that ‘the X-ray flash that had previously completely overexposed the center of the detector must have lasted less than eight hours.’

Theoretical research done more than 30 years ago predicted that X-ray explosions such as this, but they have actually never been observed directly, until this time. These fireballs of X-rays happen on the stars’ surface which were originally comparable in size to the sun before they used up most of their fuel, which is made of hydrogen and later on helium deep within their cores.

These ‘stellar corpses’ shrivel up until all that remains are “white dwarfs,” which are usually similar in size to the Earth but have a mass that can be similar to that of the sun.

Explained by Jörn Wilms, “One way to picture these proportions is to think of the Sun being the same size as an apple, which means Earth would be the same size as a pin head orbiting around the apple at a distance of 10 meters.”

These Stellar Corpses Look Like Gemstones

The scientists also explained that on the other hand, if you shrink an apple to the same size of a pin head, this small particle would still keep it’s comparatively large weight of the apple. Wilms shares, “A teaspoon of matter from the inside of a white dwarf easily has the same mass as a large truck.”

They also explain that since these burnt out stars are mostly made up of oxygen and carbon, which can be compared to gigantic diamonds that are the same size as Earth as they float around in space. These objects, which are in the form of precious gems, are so hot that they actually glow white. Yet, the radiation is so weak, making it hard to detect from Earth.

That is, unless the white dwarf is accompanied by a star that happens to still be burning, or when the massive gravitational pull of the white dwarf draws hydrogen from the shell of the accompanying star.

FAU astrophysicist Wilms says, “It time, this hydrogen can collect to form a layer only a few meters thick on the surface of the white dwarf.” At this layer, the massive gravitational pull produces such huge pressure that’s so great, it makes the star reignite. In a chain reaction, it eventually becomes a major explosion where the layer of hydrogen is blown off. The X-ray radiation of an explosion this huge is what managed to hit the eROSITA detectors on July 7, 2020, which produced the overexposed image.


“Using the model calculations we originally drew up while supporting the development of the X-ray instrument, we were able to analyze the overexposed image in more detail during a complex process to gain a behind the scenes view of an explosion of a white dwarf, or nova,” explains Wilms.

The results, which were published in the Nature journal, the white dwarf has around the same mass as the sun, making it relatively large. The explosion produced a fireball with a temperature of around 327,000 degrees, which makes it almost sixty times hotter than the sun.

These novae tend to run out of fuel quite fast, and they also cool rapidly, which makes the X-ray radiation becomes weaker until it becomes visible light eventually. This is what reached Earth half a day after the detection was made by the eROSITA which was seen by the optical telescopes.

Ole König said, “A seemingly bright star then appeared, which was actually the visible light from the explosion, and so bright that it could be seen on the night sky by the bare eye.”

Apparently “new stars” such as this one have been observed in the past, and they were named “nova stella” or “new star” precisely because of their unpredictable appearance. But because these novae are only visible after the X-ray flash, it’s quite hard to predict such outbreaks, left mostly to chance when these flashes hit the X-ray detectors.

König said, “We were really lucky.”

Take a look at the video below to see more on this amazing discovery.

 

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