- Email: [email protected]
How a 3000-year-old code unmasked a stellar cannibal
Secrets of the
demon star
Has an ancient Egyptian papyrus exposed the ghoulish habits of a baleful stellar cannibal? Stephen Battersby investigates
F
ROM 93 light years away in the constellation of Perseus, the Demon Star winks at us. Roughly once every three days its bright blue light turns bloodshot as it reddens, fades for a few hours and then blazes out once more. For the ancient Greeks, it marked the blinking eye of the Gorgon Medusa, whose head was severed by Perseus. The star’s more common name, Algol, derives from the Arabic al-ghul – the ghoul. Modern astronomy suggests that the Demon Star has a grisly habit to match that reputation: it should be eating itself. Yet oddly, our observations have never quite matched our expectations. That might now have changed – thanks not to modern telescopes, but to information encoded on an Egyptian papyrus 3000 years ago. Algol’s baleful blinking has been systematically observed since at least the 17th century. In 1783 the 19-year-old amateur astronomer John Goodricke suggested in a communication to the Royal Society of London that the cause might be a darker body passing in front of the star. But it was only in 1881 that a University of Harvard astronomer called Edward Pickering confirmed the fact: there is more than one of Algol. A dense, brilliant blue star and a diffuse, bloated red star orbit perilously close to one another, merging into a single point of light. The two bodies are aligned to form an eclipsing binary, with the red star periodically passing in front of the blue, blocking it from our view.
Christian Larrieu/The Bridgeman Art Library
Two’s a crowd That explains the blinking, but according to current theories two such muscular stars cannot peacefully cohabit in so small a space. Algol’s diffuse red star should have only a weak grip on its outer layers of gas, and the dense blue star should be pulling this gas away and devouring it. This stellar cannibalism should act as a drag on the stars, gradually slowing their orbit and reducing the frequency of the blinking. But in centuries of observations we have been unable to see that. Algol’s current period > is 2.867 days, or 68 hours 48 minutes, 15 December 2012 | NewScientist | 43
with each eclipse lasting about 10 hours. It has changed a little over centuries, but apparently at random. If there is any long-term slowing trend, it has been masked by shorter-term variation – perhaps caused by magnetic fields. In 2006, Sebastian Porceddu was unaware of this mystery. He was studying for two degrees, one in astronomy and one in Egyptology, at the University of Helsinki in Finland. His astronomical speciality was looking for hidden periods in sequences of impact craters, sunspots and the like. Helsinki Egyptologist Jaana Toivari-Viitala thought of another place he could apply this expertise. “She suggested I look into the calendars of lucky and unlucky days,” says Porceddu. In ancient Egypt, these mystical calendars, often drawn on papyrus, assigned good and bad prognoses to days and parts of days. A bad prognosis could mean hunger, thirst or
disease. It was unlucky to be born on such a day, and foolish to make a journey or lay the foundation for your house. Good omens meant health and success, and were times to feast and make sacred offerings. Some prognoses are predictable – the first day of a month is always good, for example. Others seem to be scattered at random. ToivariViitala wondered whether some pattern was hidden, perhaps obscured by statistical noise such as one-off prognoses tied to religious festivals and seasonal changes. To further muddy the waters, many calendar entries are missing – perhaps eaten by ants, says Porceddu. To search for such hidden patterns, Porceddu reached for a statistical tool called the Rayleigh test. This is a bit like using the calendar to direct someone’s movements. The person looks through the calendar at regular intervals, say every four days. They read
the prognosis, use it and the date as inputs of a fairly simple algorithm that spits out a direction, and then take a step in that direction. If the chosen interval does not match any hidden periodicity, the steps tend to cancel one another out. “Imagine a person leaving the pub who is totally drunk,” says Lauri Jetsu, Porceddu’s astronomy supervisor at Helsinki. “They do not get very far.” If the sampling matches a hidden period, however, the person begin to moves more purposefully. Porceddu applied this test to a papyrus called the Cairo Calendar, which dates from Egypt’s New Kingdom, between 1550 and 1069 BC. He found a clear period of 29.5 days, equal to the lunar month – and a second, less obvious cycle. “It did not have such a high statistical significance, and initially we didn’t pay much attention,” says Porceddu. But checking and reanalysing the data confirmed
While pharaonic priests may have looked to the stars to determine their high days and holidays (see main story), tantalising evidence indicates that another sort of extraterrestrial body had a special place in ancient Egyptian society. The idea was sparked by a sprinkling of artefacts found in ancient tombs that were made of unusually nickel-rich iron – a metallic composition usually associated with meteorites. The earliest are nine beads from tombs at Gerzeh, on the banks of the Nile south of Cairo, which date to about 3300 BC. The most extensive is a collection of objects including a series of miniature blades found in the tomb of the pharaoh Tutankhamun from about 1320 BC. Even this last find predates archaeological and written evidence for the working of terrestrial iron ores in Egypt by centuries. Couple that with the fact that the nickel-rich iron is found only in ritual spaces such as tombs, and it suggests
that the material’s origin is indeed out of this world, says meteorite specialist Diane Johnson of the Open University, in Milton Keynes, UK. “An observation of a meteorite fireball would have been a dramatic event. That might have given the material from it an extra magic and potency.” It is a theory that was espoused by the British Egyptologist Gerald Averay Wainwright, who opened the Gerzeh tombs in 1911. He observed that many cultures interpreted meteorites as the product of lightning, and put other fossilised rocks that they regarded as “solidified lightning bolts” to extensive ceremonial use. On the north wall of Tutankhamun’s tomb, a painting appears to show one of the iron blades being applied to his mummified head in a ceremony known as the “opening of the mouth”, which reanimated the mummy and allowed it live on in the underworld. Other circumstantial
44 | NewScientist | 15 December 2012
linguistic and architectural clues suggest that the ancient Egyptians ascribed magic properties to meteoritic iron. But with a paucity of hard evidence, it’s hard to prove things one way or the other, Johnson says. “We can’t test it beyond looking at the artefacts.” In research soon to be published, Johnson and colleagues from the University of Manchester, UK, have taken our best look yet, using scanning electron microscopy and X-ray and optical imaging to get beneath the skin of a Gerzeh bead held in the Manchester Museum. Like all the ancient samples, it is today heavily oxidised. Analysis of fragments of the original metal, however, indicate an average nickel content of about 9 per cent by weight, which far exceeds anything known from any worked iron of antiquity. That and the distribution of metals within the sample strongly support a meteoritic origin, says Johnson. Richard Webb
JTB Photo/superstock
BOLTS FROM THE BLUE
the conclusion, published in April this year: the calendar showed a clear periodicity at 2.85 days (arxiv.org/abs/1204.6206). A reasonable assumption, given the presence of the lunar cycle, is that this corresponds to something astronomical. And while no planet or moon has a similar period, one clearly visible varying object does: Algol. This would imply that the priests of ancient Egypt were regularly monitoring variable stars, an entirely new suggestion. At first glance the identification seemed scuppered by a simple fact. Although the calendar period and Algol’s period are close, they are not that close. Algol’s observed period today is longer by about 20 minutes. But wait. Such a slowdown is what we would expect from theories of stellar cannibalism. An increase of 20 minutes over 3000 or so years could be caused by a flow of matter
”To further muddy the waters, many entries in the calendars are missing – perhaps eaten by ants”
between the two stars of about three-quarters of the mass of Jupiter in total, or five times the mass of Earth’s moon every year. This mass is close to theoretical estimates for the Algol system. If there is an orbital slowdown that is currently being obscured, this ancient data point from the pharaoh’s priests might show us it is indeed happening. Experts in the astronomy of ancient Egypt have mixed feelings about the claim. One anonymous peer-reviewer of the original paper was dismissive; others are cautiously supportive. “The analysis from the astronomical and mathematical point of view is absolutely correct. I am convinced that there is a signal, and it seems to match Algol’s behaviour,” says Juan Antonio Belmonte of the Astrophysical Institute of the Canaries in Tenerife. But he questions Porceddu’s identification of the Eye of Horus, a representation of a god mentioned repeatedly in the calendar’s text, with Algol. Evidence from temple paintings and carvings leads Belmonte to believe that it refers to the moon. Sarah Symons, a specialist in ancient Egyptian astronomy at McMaster University in Hamilton, Canada, would like direct evidence that Algol was actually observed by the Egyptians. “But it is great to see an interdisciplinary team working on this,” she says. “Egyptologists and astronomers should have more informed conversations.” The Helsinki team had one big doubt themselves. We first got an inkling in 1912 that the Algol system is actually three stars, with the third coasting slowly around the inner pair at a distance. This third party’s gravity could be altering the orbit of the closely bound duo, meaning that 3000 years ago there might have been no eclipses and no baleful variability. But this fear was assuaged in May, when another group of astronomers published images of Algol showing that the third star’s orbit is almost at right angles to the inner pair, where it can have little gravitational influence (arxiv.org/abs/1205.0754). So in the days of the New Kingdom of ancient Egypt, the Demon Star really did flare and subside above the Nile. But did the pharaohs’ priests watch its changing moods, or use its distant eclipses to advise the people on the best times to celebrate? That connection will remain controversial – unless some day some as-yet undeciphered papyrus clearly identifies Algol and confirms that ancient data point for science. n Stephen Battersby is a consultant for New Scientist based in London 15 December 2012 | NewScientist | 45
demon star
Has an ancient Egyptian papyrus exposed the ghoulish habits of a baleful stellar cannibal? Stephen Battersby investigates
F
ROM 93 light years away in the constellation of Perseus, the Demon Star winks at us. Roughly once every three days its bright blue light turns bloodshot as it reddens, fades for a few hours and then blazes out once more. For the ancient Greeks, it marked the blinking eye of the Gorgon Medusa, whose head was severed by Perseus. The star’s more common name, Algol, derives from the Arabic al-ghul – the ghoul. Modern astronomy suggests that the Demon Star has a grisly habit to match that reputation: it should be eating itself. Yet oddly, our observations have never quite matched our expectations. That might now have changed – thanks not to modern telescopes, but to information encoded on an Egyptian papyrus 3000 years ago. Algol’s baleful blinking has been systematically observed since at least the 17th century. In 1783 the 19-year-old amateur astronomer John Goodricke suggested in a communication to the Royal Society of London that the cause might be a darker body passing in front of the star. But it was only in 1881 that a University of Harvard astronomer called Edward Pickering confirmed the fact: there is more than one of Algol. A dense, brilliant blue star and a diffuse, bloated red star orbit perilously close to one another, merging into a single point of light. The two bodies are aligned to form an eclipsing binary, with the red star periodically passing in front of the blue, blocking it from our view.
Christian Larrieu/The Bridgeman Art Library
Two’s a crowd That explains the blinking, but according to current theories two such muscular stars cannot peacefully cohabit in so small a space. Algol’s diffuse red star should have only a weak grip on its outer layers of gas, and the dense blue star should be pulling this gas away and devouring it. This stellar cannibalism should act as a drag on the stars, gradually slowing their orbit and reducing the frequency of the blinking. But in centuries of observations we have been unable to see that. Algol’s current period > is 2.867 days, or 68 hours 48 minutes, 15 December 2012 | NewScientist | 43
with each eclipse lasting about 10 hours. It has changed a little over centuries, but apparently at random. If there is any long-term slowing trend, it has been masked by shorter-term variation – perhaps caused by magnetic fields. In 2006, Sebastian Porceddu was unaware of this mystery. He was studying for two degrees, one in astronomy and one in Egyptology, at the University of Helsinki in Finland. His astronomical speciality was looking for hidden periods in sequences of impact craters, sunspots and the like. Helsinki Egyptologist Jaana Toivari-Viitala thought of another place he could apply this expertise. “She suggested I look into the calendars of lucky and unlucky days,” says Porceddu. In ancient Egypt, these mystical calendars, often drawn on papyrus, assigned good and bad prognoses to days and parts of days. A bad prognosis could mean hunger, thirst or
disease. It was unlucky to be born on such a day, and foolish to make a journey or lay the foundation for your house. Good omens meant health and success, and were times to feast and make sacred offerings. Some prognoses are predictable – the first day of a month is always good, for example. Others seem to be scattered at random. ToivariViitala wondered whether some pattern was hidden, perhaps obscured by statistical noise such as one-off prognoses tied to religious festivals and seasonal changes. To further muddy the waters, many calendar entries are missing – perhaps eaten by ants, says Porceddu. To search for such hidden patterns, Porceddu reached for a statistical tool called the Rayleigh test. This is a bit like using the calendar to direct someone’s movements. The person looks through the calendar at regular intervals, say every four days. They read
the prognosis, use it and the date as inputs of a fairly simple algorithm that spits out a direction, and then take a step in that direction. If the chosen interval does not match any hidden periodicity, the steps tend to cancel one another out. “Imagine a person leaving the pub who is totally drunk,” says Lauri Jetsu, Porceddu’s astronomy supervisor at Helsinki. “They do not get very far.” If the sampling matches a hidden period, however, the person begin to moves more purposefully. Porceddu applied this test to a papyrus called the Cairo Calendar, which dates from Egypt’s New Kingdom, between 1550 and 1069 BC. He found a clear period of 29.5 days, equal to the lunar month – and a second, less obvious cycle. “It did not have such a high statistical significance, and initially we didn’t pay much attention,” says Porceddu. But checking and reanalysing the data confirmed
While pharaonic priests may have looked to the stars to determine their high days and holidays (see main story), tantalising evidence indicates that another sort of extraterrestrial body had a special place in ancient Egyptian society. The idea was sparked by a sprinkling of artefacts found in ancient tombs that were made of unusually nickel-rich iron – a metallic composition usually associated with meteorites. The earliest are nine beads from tombs at Gerzeh, on the banks of the Nile south of Cairo, which date to about 3300 BC. The most extensive is a collection of objects including a series of miniature blades found in the tomb of the pharaoh Tutankhamun from about 1320 BC. Even this last find predates archaeological and written evidence for the working of terrestrial iron ores in Egypt by centuries. Couple that with the fact that the nickel-rich iron is found only in ritual spaces such as tombs, and it suggests
that the material’s origin is indeed out of this world, says meteorite specialist Diane Johnson of the Open University, in Milton Keynes, UK. “An observation of a meteorite fireball would have been a dramatic event. That might have given the material from it an extra magic and potency.” It is a theory that was espoused by the British Egyptologist Gerald Averay Wainwright, who opened the Gerzeh tombs in 1911. He observed that many cultures interpreted meteorites as the product of lightning, and put other fossilised rocks that they regarded as “solidified lightning bolts” to extensive ceremonial use. On the north wall of Tutankhamun’s tomb, a painting appears to show one of the iron blades being applied to his mummified head in a ceremony known as the “opening of the mouth”, which reanimated the mummy and allowed it live on in the underworld. Other circumstantial
44 | NewScientist | 15 December 2012
linguistic and architectural clues suggest that the ancient Egyptians ascribed magic properties to meteoritic iron. But with a paucity of hard evidence, it’s hard to prove things one way or the other, Johnson says. “We can’t test it beyond looking at the artefacts.” In research soon to be published, Johnson and colleagues from the University of Manchester, UK, have taken our best look yet, using scanning electron microscopy and X-ray and optical imaging to get beneath the skin of a Gerzeh bead held in the Manchester Museum. Like all the ancient samples, it is today heavily oxidised. Analysis of fragments of the original metal, however, indicate an average nickel content of about 9 per cent by weight, which far exceeds anything known from any worked iron of antiquity. That and the distribution of metals within the sample strongly support a meteoritic origin, says Johnson. Richard Webb
JTB Photo/superstock
BOLTS FROM THE BLUE
the conclusion, published in April this year: the calendar showed a clear periodicity at 2.85 days (arxiv.org/abs/1204.6206). A reasonable assumption, given the presence of the lunar cycle, is that this corresponds to something astronomical. And while no planet or moon has a similar period, one clearly visible varying object does: Algol. This would imply that the priests of ancient Egypt were regularly monitoring variable stars, an entirely new suggestion. At first glance the identification seemed scuppered by a simple fact. Although the calendar period and Algol’s period are close, they are not that close. Algol’s observed period today is longer by about 20 minutes. But wait. Such a slowdown is what we would expect from theories of stellar cannibalism. An increase of 20 minutes over 3000 or so years could be caused by a flow of matter
”To further muddy the waters, many entries in the calendars are missing – perhaps eaten by ants”
between the two stars of about three-quarters of the mass of Jupiter in total, or five times the mass of Earth’s moon every year. This mass is close to theoretical estimates for the Algol system. If there is an orbital slowdown that is currently being obscured, this ancient data point from the pharaoh’s priests might show us it is indeed happening. Experts in the astronomy of ancient Egypt have mixed feelings about the claim. One anonymous peer-reviewer of the original paper was dismissive; others are cautiously supportive. “The analysis from the astronomical and mathematical point of view is absolutely correct. I am convinced that there is a signal, and it seems to match Algol’s behaviour,” says Juan Antonio Belmonte of the Astrophysical Institute of the Canaries in Tenerife. But he questions Porceddu’s identification of the Eye of Horus, a representation of a god mentioned repeatedly in the calendar’s text, with Algol. Evidence from temple paintings and carvings leads Belmonte to believe that it refers to the moon. Sarah Symons, a specialist in ancient Egyptian astronomy at McMaster University in Hamilton, Canada, would like direct evidence that Algol was actually observed by the Egyptians. “But it is great to see an interdisciplinary team working on this,” she says. “Egyptologists and astronomers should have more informed conversations.” The Helsinki team had one big doubt themselves. We first got an inkling in 1912 that the Algol system is actually three stars, with the third coasting slowly around the inner pair at a distance. This third party’s gravity could be altering the orbit of the closely bound duo, meaning that 3000 years ago there might have been no eclipses and no baleful variability. But this fear was assuaged in May, when another group of astronomers published images of Algol showing that the third star’s orbit is almost at right angles to the inner pair, where it can have little gravitational influence (arxiv.org/abs/1205.0754). So in the days of the New Kingdom of ancient Egypt, the Demon Star really did flare and subside above the Nile. But did the pharaohs’ priests watch its changing moods, or use its distant eclipses to advise the people on the best times to celebrate? That connection will remain controversial – unless some day some as-yet undeciphered papyrus clearly identifies Algol and confirms that ancient data point for science. n Stephen Battersby is a consultant for New Scientist based in London 15 December 2012 | NewScientist | 45