THE TEAR OF SIRIUS──Color Change Mystery
Sirius rises late in the dark, liquid sky
On summer nights, star of stars,
Orion’s Dog they call it, brightest
Of all, but an evil portent, bringing heat
And fevers to suffering humanity. 【1】
Homer, the greatest ancient European epic poet of the four poets, composed the above poem in <Homer>, which described the approach of Achilles toward Troy. Sage Homer foreboded portent from Sirius color change, and used it to describe sign of the fall of Troy. The age for Homer to live was about 12th to 7th century B.C., when modern astronomy knowledge wasn’t formed.
I. Sirius Mystery of Color Change
From the beginning of recorded astronomy observation history of humanity, there were red controversies (color change mystery) about Sirius at all times. The Sirius luminosity is second only to the sun, and it is the brightest star in night sky. It can be seen with naked eye. Nowadays the observed color of Sirius A is blue-white, while historical records of the color of Sirius that seen by astronomers and sages were red. To the color of the star itself, it is impossible to change color obviously during any stage of the evolution of the star in thousands of years.
The issue of the color of Sirius aroused general interests in 1980s. In top comprehensive journal in the world, more than ten articles were accepted on Sirius. Up till now, the issue hasn’t been solved (civil subject leader). Journals do not accept radical viewpoints on Sirius under general conditions.
II. The Historic Material of Sirius Color Change Mystery (Red Controversy)
Around 150 AD, the Hellenistic astronomer Claudius Ptolemy described Sirius as reddish, along with five other stars, Betelgeuse, Antares, Aldebaran, Arcturus and Pollux, all of which are clearly of orange or red hue.The discrepancy was first noted by amateur astronomer Thomas Barker, squire of Lyndon Hall in Rutland, who prepared a paper and spoke at a meeting of the Royal Society in London in 1760. The existence of other stars changing in brightness gave credence to the idea that some may change in colour too; Sir John Herschel noted this in 1839, possibly influenced by witnessing Eta Carinae two years earlier. Thomas Jefferson Jackson See resurrected discussion on red Sirius with the publication of several papers in 1892, and a final summary in 1926. He cited not only Ptolemy but also the poet Aratus, the orator Cicero, and general Germanicus as colouring the star red, though acknowledging that none of the latter three authors were astronomers, the last two merely translating Aratus’ poem Phaenomena. Seneca, too, had described Sirius as being of a deeper red colour than Mars.
However, not all ancient observers saw Sirius as red. The 1st century AD poet Marcus Manilius described it as “sea-blue”, as did the 4th century Avienus. It is the standard star for the color white in ancient China, and multiple records from the 2nd century BC up to the 7th century AD all describe Sirius as white in hue.
In 1985, German astronomers Wolfhard Schlosser and Werner Bergmann published an account of an 8th century Lombardic manuscript, which contains De cursu stellarum ratio by St. Gregory of Tours. The Latin text taught readers how to determine the times of nighttime prayers from positions of the stars, and Sirius is described within as rubeola — “reddish”. The authors【2】 proposed this was further evidence Sirius B had been a red giant at the time. However, other scholars replied that it was likely St. Gregory had been referring to Arcturus instead.
A lot of ancient astronomy literatures recorded Sirius as dark red, while Sirius is blue-white in the naked eye of modern people. The possibility that stellar evolution of either Sirius A or Sirius B could be responsible for this discrepancy has been rejected by astronomers on the grounds that the timescale of thousands of years is too short and that there is no sign of the nebulosity in the system that would be expected had such a change taken place.
To the naked eye, it often appears to be flashing with red, white and blue hues when near the horizon. It is because the absorptivities of red and blue in atmosphere are a little bit different when lights pass through the thick flowing gas and diffuse; in the beginning of the Christian era, the discrepancy of main viewpoints of Sirius in red in Europe and main viewpoints of Sirius in blue-white in China was caused by latitude difference (this is as if different latitude regions would see different color of total lunar eclipses).
III. SN1987A——Sharp Decline of Stellar Wind Intensity in the Stellar Final Stage
Two Japanese professors successfully reproduced the rings scene of SN1987A by using one computer. Due to the effect of magnetic field pressure, the spherical shaped gas turned into flat circles, upon which the rings received force from north pole and south pole of the star, peeling off into three rings. In the lightened gas it formed hollow because of lacking stellar winds. The ring shaped high density matter was thought to have taken shape 20,000 years before supernova outburst【3】【4】.
Among the series of nuclear fusion in the star, the binding energy of forming iron is at maximum. That forming elements heavier than iron couldn’t produce energy, but absorb energy instead. It can be inferred from strong stellar wind hollow that the stellar wind intensity should be rather low before supernova outburst. For detail, see <Sirius Issues——Red Controversy>.
IV. The Fundamental Reason of the Mystery of Sirius Color Change
After sorting out materials, the color of Sirius A is mainly as follow: Sirius appeared to be mainly dispersed dark red for about at least two thousand years; and appeared to be blue-white again in the nearest several centuries.
1. Eliminated Causation of Color Change(Civil Subject Leader Viewed)
In main-sequence evolving course, the time that Sirius appeared to change color in thousands of years was too short, which has already been overthrown by astronomers;
The assumed third star Sirius C in the system, whose induced mass limit is approximately 0.1-0.25 solar mass, as a brown dwarf or red dwarf, is not capable of directly relevant to abnormal red phenomenon of Sirius【5】;
The theory that red giant Sirius B once appeared accounting for red Sirius is also overthrown, for most astronomers think that it would last at least 100,000 years for red giant evolving into white dwarf;
The time scale which Sirius changes from red to blue itself is also greatly larger than thousands of years (even if for the situation of red giant or pre-supernova star), so it is not possible that the color change of Sirius is caused by stellar color completely.
2. The Fundamental Causation of Color Change Mystery（Civil Subject Leader: Possible）
In the final stage of a star, since the stellar center couldn’t generate enough nuclear fusion and degenerate pressure to withdraw gravitation, the nuclear fusion rate upgrade further. The nuclear fusion of forming iron and elements heavier than iron require absorbing tremendous energy, so the sharp decline of temperature directly leads to sharp decline of stellar luminosity and stellar wind intensity, accompanying the production of numerous neutrinos.
1. Firstly, the luminosity of star itself descends rapidly, so the luminosity of blue-white Sirius descends. The color of the surrounding low temperature red gas occupied the dominant position. The color of Sirius turned from blue-white to the controversial dispersed dark red in thousands of years.
2. Together with the rapid descending of luminosity is the sharp decline of the intensity of strong stellar winds. However, the descending of strong stellar winds would not appear immediately. Through changes of several centuries, the dark red stellar winds whose intensity descended gradually escaped Sirius A. The vast majority of red stellar winds accreted onto Sirius B. The stellar blue-white color occupied the dominant position again. The color of Sirius changed from the controversial dispersed dark red to blue-white in hundreds of years.
Appendix: Supplement Historic Materials of Sirius Color
1. Every July in ancient Rome, when Sirius rise from horizon in dawn lights for the first time, people would always respectfully present red dogs as their sacrificial offerings. Their poetry wrote: “Mars shines mild red, while Sirius is redder than that.” Lots of famous classical writers described Sirius as red. Even before 1000 B.C., ancient Babylonians recorded the star is red in their Wedge text. 【6】
3. In the late Qing Dynasty, Wang Tao and A. Wyile translated (1890), among which referred the Sirius color: “The ancients always said Sirius as red, today it is white, why?”【7】
【1】Homer (1997). Iliad. Trans. Stanley Lombardo. Indianapolis: Hackett. ISBN 9780872203525. 22.33–37.
【2】Wikipedia (English version,written and sorted by experts) http://en.wikipedia.org/wiki/Sirius
【3】Thomas Morris，Philipp Podsiadlowski，“The Triple-Ring Nebula around SN 1987A:Fingerprint of a Binary Merger”， Science 23 February 2007: Vol. 315 no. 5815 pp. 1103-1106，DOI: 10.1126/science.1136351
【4】A. Tziamtzis et al, “The outer rings of SN 1987A”, arXiv:1008.3387, August 14, 2011
【5】D. Whittet, “A Physical Interpretation of the ‘Red Sirius’ Anomaly” Mon. Not. R. Astron. Soc., 310, 355-359(1999)
【6】, Xiaolong Wang, Science Friends,2005(3).
【7】, Xiaoyuan Jiang, Astronomy 1992.12. Vol 33. (4)v 1.0