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.
