You probably know that the most powerful god in Greek mythology was Zeus. This story, together with the story about neutron stars, tell you a little of how the heaviest ELEMENTS are made, generally inside a few special kinds of stars called supernovae, including some that you can quite easily recognize on a clear night. Some of these special stars happen to lie in constellations where according to the ancient Greeks, Zeus was depicted as being extraordinarily violent and hurling thunderbolts - even though they didn’t know that atoms are being made in stars that are exploding violently!
The image here shows a constellation called LUPUS, meaning “wolf” in Latin. It appears on a celestial globe, made for a ruler of seventeenth-century Persia, and decorated with silver dots representing stars in the sky. Zeus knew about a very wicked king and decided to disguise himself as a poor working man. When he knocked on the door of the palace of the king, whose name was Lycaon, Zeus was welcomed and offered some soup. Unfortunately for King Lycaon, the soup had the disgusting taste of a murdered and butchered boy called Arcas - one of the sons of the disguised Zeus! - who instantly recognised the taste of his own son. Zeus exploded with rage, his thunderbolts struck and burnt up all the king’s vicious sons. King Lycaon ran away screaming but as he ran, his screams turned to howls, his arms and legs grew fur and yellow fangs pierced through his mouth – so as you can still see in the sky, he had turned into a wolf (“Lupus”).
Even if we don’t really believe in Zeus’s thunderbolts, in the year 1006 there was a star in the constellation Lupus which really did violently explode. For at least three days, people in Europe, China, Japan, Iraq, Egypt, and possibly North America (according to some Native American rock carvings) saw the brightest star ever recorded in history. Its light was as bright as the moon.
In the first chapter, we read that “supergiant” stars including Betelgeuse, Aldebaran, Deneb, Antares, Rigel and so on use nucleosynthesis to generate elements in increasing order of mass – but that once one of the largest supergiant reaches the point of producing iron, it can become a type of exploding star, maybe even bright enough to be visible in daylight. This type of stellar explosion we call a SUPERNOVA.
So although the supernova in Lupus was the brightest ever known, there have been other ones that were spectacular and made people wonder what on earth would happen next. The last one seen without needing a telescope was in 1604. It was described in a book by an astronomer called Johannes Kepler, famous for having used planetary sightings to find, by trial and error, an algebraic formula connecting the length of a planet’s year with its distance from the sun (he didn’t know the reason why this formula works – that had to wait for the great Isaac Newton’s theories, more than eighty years later). In fact the supernova that he saw is known as Kepler’s star: it is in a constellation called OPHIUCHUS. You can find Ophiuchus in the sky between Hercules, Serpens, Scorpius, and Sagittarius, northwest of the center of the Milky Way. In the northern hemisphere, it is best visible in summer, since in winter, Ophiuchus is in the daytime sky and thus not visible at most latitudes.
For a few days that year, Kepler’s star was the brightest in the sky, but once any supernova had faded away, it was always assumed that there remained no star or anything left to see. However, recently astronomers had a big surprise: although at the spot where Kepler’s star had been there was no light detected, instead there was indeed a different type of image formed by X-rays. This was detected using a very special kind of space telescope, NASA’s “Chandra X-ray Observatory”, which was launched aboard the space shuttle Columbia in 1999. In the image above, red, green and blue colours have been used to represent low, intermediate and high energy X-rays.
Perhaps it’s disappointing that since Kepler’s star, no further supernovae have since been observed: clearly the chance of any of us seeing one in our lifetime is small. But actually, for one to be bright enough, presumably it would have to happen somewhere in our own galaxy (As I'm sure you know, if you have seen the Milky Way — that beautiful band of light that's visible on a dark, clear night — you have been looking towards the edge of a huge disk of billions of stars, which is the galaxy where we live). But what about seeing a supernova in some other galaxy? There are so many other galaxies that astronomers can see with powerful telescopes, so that even though the chance of a supernova in any one of them is small, there are so many billions of galaxies that supernovae in other galaxies have been detected quite often. Centaurus, Cassaeopea, Aries, and Cetus are some of those constellations that contain such galaxies.
Centaurus Aries Cetus
Of course, if any supernova bursts into view, it will last only a few days at most, so the astronomer has to be lucky.
The picture of a man struggling with two serpents, from a celestial atlas printed in 1753, shows Asclepius, the god of medicine, otherwise known as Ophiuchus. Before being placed in the sky, he had been struck by a thunderbolt hurled by Zeus. This was because he’d been given two vials of Medusa's blood, by the goddess Athena. One could be used to destroy, the other to bring people who’d recently died back to life. This infuriated Hades, the god of the dead, who argued that souls were being stolen from him. You may have noticed the symbol of either one or two twisted snakes on the logo of various emergency services: traditionally snakes were thought to be connected to healing and rebirth, because they shed their skins every year before growing new ones.
It’s not only the professional astronomers, in big expensive research establishments, who have all the luck. You can be TEN YEARS OLD and still discover a supernova! Kathryn Gray was aged ten when she was studying images of stars in the constellation CAMELOPARDALIS which had been sent to her father, an amateur astronomer. One good way of searching the sky for a rare event like that is to use a computer program that compares two different images, an older picture and a more recent picture, looking for anything bright that had appeared recently. That’s just was Kathryn was doing, when suddenly there it was: a bright spot, that was confirmed to be a supernova, which she saw in the second image but not in the first.
Here is a mythological drawing of that constellation: the name Camelopardalis means giraffe. In the winter months the Giraffe appears upside down. It might be easier to study Camelopardalis in the summer, when it’s the right side up.
As described in the “Supergiants” chapter, these high-mass stars are rare and have very short lifespans: when this happens, a vast amount of energy is releases in a matter of seconds, fifty times more than the sun will release in ten billion years. By a very complicated series of nuclear reactions and processes of collapse, the massive star is ripped apart. It turns out that the key to solving the puzzle of how the heaviest elements are formed, came from working out this complicated and very rare, but extremely important, process.
You will remember that a well-behaved star, if massive enough, can generate chemical elements in increasing mass up to the element IRON. To make even heavier elements, we have to look at what happens when the supergiant is massive enough to end its life as a supernova…..
During the final destruction of the star in a supernova explosion, a high flux of neutrons is released as iron nuclei are ripped apart. These neutrons can be captured by unstable nuclei before the nuclei have had a chance to decay. In this way nuclei of elements such as copper and tin are created.
However, calculation show that even the fantastically high temperatures reached in a supernova explosion are unable to synthesize the heaviest atoms of all, such as gold or lead. One clue to answering this puzzle lies in the understanding of what happens when there is a collision between what are called neutron stars, and you will find an outline of this process in a different story (“neutron stars and their collisions”).
To choose another story, first click on giantsandsupergiants.com/blog to see the list of stories.
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