The Dark Energy Camera Captures the Remains of an Ancient Supernova

Chinese astronomers first described an explosion in writing in the year 185. According to those documents, a "guest star" illuminated the heavens for about eight months. Now that we know, it was an explosion.

The only thing left is a band of debris known as RCW 86, which was studied by scientists using the DECam (Dark Energy Camera) to study the supernova's aftermath.

SN 185 was noted by Chinese astronomers in The Book of the Later Han, or Hou Han shu as it is known in Chinese. Ancient accounts of astronomical events are subject to ambiguity, and in the case of the Hou Han shu, the uncertainty is heightened by the fact that the text was penned 200 years after the actual events took place. It's possible that the stellar detonation was also observed by ancient Romans, but this is less certain.

Because comets and supernovae are often confused, historical accounts of celestial occurrences may also be suspect. There is no mention of the guest star traveling in the Hou Han shu, and the Chinese record's location matches that of RCW 86, the SN debris band. Modern scientists are confident that the Hou Han shu captured SN 185, particularly in light of the fact that high-tech readings in the present day support this.

More than 8,000 light-years distant, roughly in the direction of our closest stellar neighbor Alpha Centauri, SN 185 erupted. Astronomers can view the wake of a supernova explosion, one of nature's most dramatic occurrences, making it an intriguing object. RCW 86 is now nothing more than a frail band of gas and detritus that once belonged to SN 185. SN 185 was a Type 1a supernova, which means that, in contrast to other supernovae, it only left behind an expanding, dissipating band of material.

However, none of that was initially known by scientists. RCW 86 was confusing due to its length, and they had to work it all out.

Astronomers assumed that SN 185 was a core-collapse supernova due to its enormous magnitude. It would take that kind of explosion roughly 10,000 years to leave behind the residue we can see today. Therefore, it was uncertain whether RCW 86 was connected to SN 185 by scientists. Over 8,000 years separated the timeline from reality.

Then, in 2006, a study revealed that RCW 86 had a very fast expansion velocity behind it, indicating that it was temporally connected to SN 185. Based on x-ray measurements, that research. They demonstrated that there was an odd admixture of thermal and synchrotron x-ray emission along some stretches of the growing disk. Briefly stated, movement produces synchrotron x-rays while heat produces thermal x-rays. Given that synchrotron x-rays can only be produced by charged particles moving at relativistic velocities, the existence of them indicates a much greater velocity in the shell.

This research changed the age of RCW 86 to be roughly 2,000 years old, which is exactly in accordance with SN 185. The calculated shock velocity "strengthens the argument that RCW 86 is the remnant of SN 185," according to the authors of the 2006 article.

That didn't, however, explain why RCW 86 is growing so quickly. Once more, an answer was provided by x-ray measurements. Iron content in the shell remnant was greater than anticipated, according to X-ray measurements. Due to their physics, Type 1a supernovae generate an excessive quantity of iron. In fact, type 1a supernovae are responsible for producing two-thirds of the iron in our bodies and in the Earth itself. Astronomers concluded that RCW 86 is the remains of SN 185 because the increased iron can only be explained by a type 1a supernova and because of how quickly it is spreading.

A binary couple, consisting of a white dwarf and another star that could be anything from a lesser white dwarf to a giant star, makes up a type 1a supernova. The white dwarf takes material from the partner star as they get closer to one another. The white dwarf experiences an increase in pressure and warmth along with a rapid outpouring of material. This substance is a component of the RCS 86 extending casing.

The white dwarf continues heating up until it bursts, unlike a main sequence star, which can expand and cool to make up for this. Around the white dwarf, the previously expelled material left an empty shell, which allowed the material from the supernova detonation to spread. The outcome is the ragged, disheveled ring of detritus that we can still see today, 1800 years later.

Of course, none of this was known to the ancients. They had just seen a bright light in the heavens that blazed for eight months before going out of sight. Who knows how it affected common people?

When contemporary astronomy and what the ancients saw collide, it is intriguing. It resembles a monologue between the past and the future. One instance of it is SN 185/RCW 86.

In order to comprehend the evolution of the Earth's magnetosphere, a 2021 research looked at ancient literature for 3,000 years' worth of accounts of auroras. A 2018 study found that the Bible account of Sodom could be explained by a meteor detonation that occurred over the Dead Sea 3,700 years ago. There are numerous additional instances.

Modern viewing techniques allow us to decipher the intricate physics underlying phenomena like supernovae and comprehend them in great detail. We can easily connect to them thanks to the wide-angle picture provided by the Dark Energy Camera. Our displays display the fallout in fascinating detail.

If you want to go even deeper, download the full-size .tif from NOIRLab’s website.