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Stars
Through the millennia before 1666 when Newton dispersed a pinhole ray of sunlight through a glass prism on the wall of his darkened room yielding a rainbow spectrum, stars were just pinpoints of light which formed the slowly rotating background against which the convolutions of the Sun, Moon and planets were measured.
Seventeenth century astronomers, although fascinated with spectral playthings, saw nothing of interest to them, because not even Newton imagined the vast information on the chemical composition, temperature, and mass of each star encoded in that beautiful spectrum. Even a century and a quarter later Goethe, of considerable standing in geology and natural science, said that the idea of white light being a mixture of colored lights is childish twaddle - quite inconceivable!
In 1802, William Hyde Wollaston, an English mineralogist and chemist, replacing the pinhole by a narrow slit so that each colour imaged the slit across a wide band, noticed many dark lines across the band, but thought that they were merely gaps between successive packets of colour, and thereby missed a fundamental discovery in chemistry.
A decade later, a German optician, Joseph von Fraunhofer (1737-1826), also observed the thin dark lines in the sunlight spectrum, noted that the lines occurred at constant positions with respect to the colors, and he meticulously mapped 600 of them, and then found that they occurred in the same places in moonlight, and in the spectra of Mars and Venus, but were significantly different in the spectrum of the dog-star, Sirius. Fraunhofer concluded that Sun and Sirius were independent lights, but Venus, Mars, and Moon merely reflected sunlight.
Five other bright stars were individually different, like stellar fingerprints. So the spectrum was relevant to astronomy. But what did the colors and lines mean? Fraunhofer next turned his spectroscope to materials, heated to incandescence in his laboratory, but observed not a rainbow spectrum nor any dark lines, but a few narrow bands of bright colored Light, and that particular colored bands corresponded to dark lines in the sunlight spectrum.
He now knew that specific substances emitted specific bands of colour when incandescent, and guessed that in some way many such bands were absorbed on the way from the Sun, leaving dark gaps in the spectrum. But alas, in 1826 Fraunhofer died of tuberculosis, aged only 39.
A full generation passed without significant progress, until a German physicist, Gustaf Kirchoff (1824-1887), and a German chemist, Robert Bunsen (1811-1899), collaborated to pick up the Fraunhofer threads. They established that each chemical element emitted its own specific spectrum consisting of a series of bright colored lines or bands when heated in Bunsen's burner.
Kirchoff went on to examine the Sun's spectrum after the beam had passed through the bright yellow flame of incandescent sodium, expecting the yellow lines to fill in the prominent gap in the solar spectrum. Instead, the sodium flame only intensified the gap, absorbing any residual light still in the sunlight there. He thus established that an incandescent element could both emit its characteristic colored lines, but also absorb those colors from incident light.
Stellar spectroscopy then exploded. In 1863 an English astronomer, William Huggins, demonstrated that the Sun and stars were made of the same familiar elements as the Earth, but with considerable variation. A hitherto unknown element with bright yellow emission lines was found in the, Sun following the eclipse of August 20,1868, and named helium (helios : Sun). Five years later it was found to be identical with the spectrum of an inert gas which had been known for some time to seep from uranium and thorium minerals.
Father Angelo Secchi (1818-1878), of the Vatican Observatory, studied the spectra of 4000 stars and grouped them into four classes:
I, white or blue stars like Sirius with strong hydrogen absorption;
II, yellow to orange stars like the Sun with numerous lines of heavier elements;
lIl, orange to red stars with many fine lines grouped together:
IV. dull red stars with carbon lines.
John Henry Draper, and his son Henry. both New York physicians and hobby astronomers, started a new era by adding a camera to the spectroscope. The elder Draper photographed the Sun's spectrum. Commencing with Vega in 1872, Henry had photographed the spectra of eighty stars before his premature death in 1882.
His widow endowed the Harvard Observatory for the systematic spectrographic survey of the heavens under Edward C. Pickering. Using mass production methods with a team of observers and classifiers, and with Secchi's four classes extended to seven, he produced the 1890 Draper Catalogue of 10,351 northern hemisphere stars, followed later by a spectral classification of 1,100 bright southern hemisphere stars. The final nine-volume Henry Draper Catalogue of 1918 listed the spectra of 225,300 stars. Supplements added a further 130,000.
The Pickering empirical classes, O, B, A, F, G, K, M turned out to be intrinsic, progressing from blue white, through yellow to red; temperatures, from 50,000 K to 3,000 K; mass from more than ten times the mass of the Sun to less than a tenth; and composition from hydrogen dominance to hydrocarbons.
Each class was further subdivided according to special characteristics of the spectra, indicated by small letters, a, b, c. Vast as it was, Pickering's Draper catalogue needed two further properties of each star distance and absolute magnitude.
In 1911, the Danish astronomer, Ejnar Hertzsprung, plotted magnitude against colour for stars in several clusters such as the Hyades (within which stars could be assumed to be approximately the same distance from us). Two years later Henry Norris Russell, of Princeton, plotted absolute magnitude against spectral type (colour) for several stars in the near neighbourhood, whose distances and hence absolute magnitude were known from their parallax and redshift. During subsequent decades, their combined plot has been refined (initially by Pickering) to include some 300,000 stars. (Figure 125).
The luminosity
of a star, which expresses the energy radiated per second, depends on surface
area 4pR2,
Stefan's constant s, and surface temperature T, combined
as 4pp2sT4.
The absolute magnitude of a star is the ratio of its energy output to that
of the Sun (4x1026 watts).
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X. About 100 stars within the Milky Way galaxy which radiate most of their energy as X-rays, while in visible light they are inconspicuous.
W. A few ultraviolet stars with temperatures up to 100 kilokelvin, including Wolf Rayet stars with strong excitation lines of He+ and ionized oxygen up to 0+++++.
O. Some very bright very hot blue stars, with temperatures ~40 kilokelvin, masses more than ten times that of the Sun, radiating energy at 1035 watts (10,000 times the output of the Sun).
B. Blue-white helium stars: with strong absorption- lines of helium and hydrogen, temperatures ~20 kilokelvin, and 4 to 10 times as massive as the Sun, but rapidly losing mass by radiation and strong stellar winds, for example (Beta Centauri (B0.5), Spica (B1), Algol (B7), and Castor (B9)
A. White hydrogen stars: with strong hydrogen lines, but weaker helium lines, temperatures ~9 kilo-kelvin and 1.7 to 3 times as massive as the Sun, e.g. Vega (A0), Mizar (A1.5), Sirius (A1), and Altair (A7).
F. Yellow-white calcium stars: H and K lines of calcium, "metallic" lines present (in this stellar context "metals" include all elements heavier than helium), temperatures ~7 kilokelvin and 1.1 to 1.7 times as massive as the Sun, for example Procyon (F5).
G. Yellow solar stars: Calcium lines dominant, with many "metallic" lines, and much fainter hydrogen lines, temperatures ~6 kilokelvin, and 0.7 to 1.1 times the mass of the Sun, for example Sun (G0) and alpha Centauri (the Sun's twin in mass and luminosity).
K. Orange stars, "metallic" lines: the spectrum shows a multitude of lines dominated by "metals", although calcium lines are still I strong. The violet cnd of the spectrum is distinctly weaker, temperatures ~4.5 kilokelvin and 0.5 to 0.7 times the mass of the Sun, for example, 61 Cygni (K6).
M. Red stars with molecular compounds (including hydrocarbons) contributing many lines, with lines of calcium and many metals, temperatures ~3 kilokelvin, and only 0.09 to 0.5 of the mass of the Sun, for example Krueger 60A (M4), and Proxima Centauri (M5), the nearest star to the Sun, and most of the stars within 20 light years from the Sun - others of this class farther away are too faint to be seen.
N and R classes (now replaced by C) are "carbon" stars with temperatures similar to K and M classes. Some other anomalous spectra with similar moderate temperature are classified as S. Prefixes and suffixes are added: e for emission lines, n for broad lines caused by rotation, q for nova-like, d for dwarf, D for white dwarf, g for giant, E for Super-giant, and s for sub-giant.
One third of a million stars have been classified by their spectra. about 3.2% as B, 27% as A, 10% as F, 16% as G, 37% as K, and 7% as M. Other classes are rare. These abundance's are skewed because the more luminous stars are visible at greater distances.
When absolute magnitude is plotted logarithmically against surface temperature (spectral class) in the Hertzsprung-Russell sequence (1913), the great majority of stars fall in a broad sigmoidal band which rises steeply from the infrared end, curves obliquely across the diagram to rise steeply again in the hot blue and ultraviolet region. (Figure 126).
Hertzsprung called this band "the main sequence". Separate from this main sequence band are some very bright but quite diffuse stars called giants and supergiants, and at the other extreme some very hot but extremely dense stars called white dwarfs, whose absolute magnitude is low because their stellar mass is compressed into a volume similar to the Earth's, so that the radiating surface area is relatively small.
The H-R diagram does not give adequate numerical representation to either the white dwarfs, which fade to undetectability at comparatively short distances, and still less to "brown dwarfs" (small infrared stars), because they are scarcely visible at all.
Both Hertzsprung and Russell believed that the main sequence was precisely that - an evolutionary sequence, as stars increased their masses (as had been assumed by Jarkovski (1888). But current orthodox theory is locked into the arbitrary assumption that a star born with small mass remains a low-mass star, and vice versa and that hot blue stars have short brilliant lives of some 106 or 107 years because they radiate away their energy at prodigious rates, compared with the Sun with a life of 1010 years.
Hence it is assumed that all hot blue stars must be young, all older ones having long since exploded to giants, and then degenerated to white dwarfs, few of which are visible to us. Hot blue stars in globular clusters (for example 47 Tucanae) are anomalous because such cluster stars are assumed to be old and all approximately the same age.
The main sequence originally plotted luminosity against spectral type (colour and temperature) but as luminosity is proportional to the fourth power of the mass, the main sequence is a progression of mass, from 0.1 of the mass of the Sun at M5, 0.5 at M0, equal to the Sun at G0,1.5 times at F5, twice at F3, 4 times at B5, and almost ten times the mass of the Sun at hot blue stars like Spica and Beta Centauri.
As the mass of a star is assumed to change only marginally during stellar evolution, each star is confined essentially to an ordinate of the the H-R diagram, exploding to a short-lived giant stage, and expiring as a white dwarf.
In contrast,
in my model with spontaneous creation of new matter and energy as cancelling
opposites, mass increase proceeds continuously in all stars at rates proportional
to their masses. The main sequence is precisely that, a sequence as Russell
believed, but stellar evolution proceeds with increasing mass (Figure 126).
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Stars commence
like Jupiter (already more starlike than planet-like) with minimal mass,
low surface temperature, methane-rich atmosphere, and initial radiation
in the far infra-red in the far infrared in the 1-300 mm wavelength range;
they progress right along the main sequence with increasing mass, increasing
temperature, and increasing luminosity to the hot blue and ultraviolet
stage, as illustrated by the typical sequence of Table 1.
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During its progression along the main sequence (that is, as its mass increases) the star reaches thresholds where the behaviour suddenly changes. I suggest the following as some of the thresholds encountered by a star as it progresses along the main sequence:
With the onset of spontaneous fusion of H to He, at about 0.08 times mass of Sun the body becomes a brown dwarf M8. Even Neptune, one ten-thousandth of the mass of the Sun, is a net radiator of 117 watts and Saturn is a net radiator of more than 80% of what it receives from Sun. Jupiter at present radiates energy at the rate of 1018 watts at radio and infrared frequencies and emits electrons in the 1-20 MeV range.
What is the source of this heat? No adequate theory has been given. Compare this with the boiling of water, which only occurs at 373oK at standard pressure. Should we therefore conclude that dewdrops on the grass must remain indefinitely unless boiling temperature is reached? Of course not! The gaussian distribution of temperature of individual water molecules, allows an occasional molecule to jump the inter-molecular cohesion energy barrier until in due course every molecule has made it, and the grass is dry.
Is it not probable that a similar situation prevails with fusion processes? Violent fusion, corresponding to water boiling, occurs at fusion temperatures, but could not slow atom-by-atom fusion occur spontaneously at very much lower mean temperatures, declining to zero at absolute zero. Certainly the rate might be extremely slow (so is the radioactive breakdown of uranium-238 with a half life of 4.5 billion years - 1016 seconds), but geologic time is adequate for the slowest process to yield real results.
Every step in the nucleosynthesis from hydrogen all the way to iron drops to a lower energy state, since iron has the lowest energy per nucleon of all elements. However, "cold" nuclear fusion, although probably real, could not become a source of useful power, any more than the evaporation of water below its boiling point could drive a steam engine.
The whole of the original helium would have been lost in the beginning, and helium now escapes from the atmosphere at the rate of its radiogenic production. Helium seeps in deep mines in Precambrian crystalline rocks (as at Broken Hill, N.S.W.), and the helium in deep drilling, along; with methane, must be radiogenic. N.C. Craig reported that the excess He in the Pacific Ocean indicates that the degassing of the Earth is still going on. Jones, et al. (1989) attributed the presence of 3He in the Earth to cold fusion at 10-44 fusions per deuterium atom per second. Jupiter radiates at 1018 watts, which could be due to 10-19 fusions of deuterium atoms per second. Sivaram and de Salbata (1989) estimate that a brown dwarf 20 times the mass of Jupiter would radiate 16x1022 watts.
In my model, random creation of matter and spontaneous nuclear fusion have been proceeding within the Earth from the beginning, at an increasing rate, with rising pressure and temperature, with increasing yield of iron in the core.
In due course, as the temperature approaches fusion temperature, a Jupiter stage will be reached with the hydrogen production outstripping the slow fusion down the iron ladder, and shortly Jupiter, already more like a star than planet, will reach fusion temperature and commence "boiling" - hydrogen fusion to become a true star, a brown dwarf.
However, Eddington, in his benchmark book The internal constitution of the stars, reasoned from the gas laws that a star should not commence to glow until bigger than Jupiter and about one-tenth of the mass of the Sun.
The natural radioactivity in the Earth was not conceived or detected until 1896 when the mysterious fogging of Henri Bequerel's photographic plates led to its discovery. If natural spontaneous fusion were also proceeding deep within the Earth, no particles would be released at the surface, but there would be release of heat.
Certainly heat is continuously flowing out of the Earth. Before 1905, this was universally regarded as primal heat, mainly derived from the initiate accretion of the planet. Now it is regarded as the result of natural radioactive decay. Schubert et al. show that the Earth cannot be in a steady state with radioactive heat production, but rather must also have a secular cooling component that could account for about one-third of the present-day heat flux.
Who can assert that natural nucleosynthesis does not fill this shortfall? There has long been the anomaly that the heat flux through the oceanic regions is about the same as the heat flux through the continents, although the latter have ten times as much radioactive matter.
According to my model, the spontaneous fusion process is logarithmically dependent on temperature and pressure, so although nucleosynthesis may be a real process even at the surface, its activity there would be below the threshold of detection, even after thousands of millions of years. But the rate would be faster with increase of pressure and temperature to a maximum in the inner core. Neutrons released by such fusion in the core could not be detected at the surface, and gamma radiation would degenerate to heat, so the only surface effect, apart from Earth expansion, would be a contribution to heat flux, and perhaps a minute seepage of 3He.
Astronomers have been debating whether to call Van Briesbroek 8B a planet or a star. VB8B is about the same size as Jupiter but at least ten times more massive, with a surface temperature of about 2,OOOoK, radiating in the infrared. It orbits about VB 8 with a radius of 8.5 astronomic units (compare Jupiter 5:2 about the Sun). VB8B must be on the threshold of nuclear ignition.
The current paradigm begins with a primordial gas cloud, which spawned the solar system. But should we not now consider in general the origin of such planetary systems. Considering only stars in a similar evolutionary stage, there are at least ten billion sun-like stars in our own galaxy. Surely some of them have planetary systems?
A few of the nearest stars have been proved to possess satellites, not by directly observing them (which is quite impossible in the intense light of their primary, itself reduced by distance to a mere point) but the star's velocity relative to us has minuscule oscillation as the orbiting satellite pulls the star towards us and away from us, thus causing microscopic oscillation of the red-shift of spectral lines much too small for individual determination, but which do show up statistically in thousands of passes.
Our Sun oscillates in an orbit with a diameter of four times the sun's radius which would be an ellipse in phase with Jupiter, if Jupiter were the only satellite but each planet makes its contribution, so the orbit is less perfect (Jose, 1965).
One general process which could develop a primordial plasma cloud in the normal evolution of a star is a nova explosion.
During stellar evolution, condensation driven by gravity is opposed by radiation pressure. Energy generated in the core is transmitted out by various mechanisms (such as conduction, convection, radiation, and neutrino flux.) so that with progressively increasing mass and hence of energy to be excreted, the contraction-expansion balance may trigger explosive expansion. Such nova expansion probably occurs at several stages of a star's evolution along the main sequence. Approaching half the present mass of the Sun in the red star range M5, I suggest that a nova explosion occurs and the star becomes a red giant.
I suggest that the early Sun entered this threshold some 5x109 years ago and became a red giant like Betelgeuse and Antares, with half the mass of present day Sun, a radius 500 times that of Sun, a surface temperature of about 3,000oK, and a mean density (5x10-7 g/cm3), one-thousandth of that of air.
Thus came into being the "primordial gas cloud" of orthodox theory from which the present solar system evolved. Betelguese or Antares now (each with a mass about half of the present Sun and mean density 10-8 of the present Sun) is the paradigm of Sun then, with a diameter equal to the present orbit of Mars and a tenuous envelope extending 1015 m further.
The re-condensation of this tenuous red-giant proto-Sun to the present-day planets, their satellites, asteroids, and meteorites reset the radioactive clocks of the solar system.
Such a beginning would yield a significantly different evolutionary sequence leading to the formation of the planets because:
(b) at all stages there would be a functioning central star,
(c) the angular momentum distribution would differ because of the probable associated binary star.
Alpha Centauri, Sun's nearest large companion star is a possible candidate. A recession velocity of about 100 km/s since the birth of the solar system would take it to its present distance. (100 km/s is well within the range of velocities relative to Sun of the observed proper motions of Sun's nearest twenty stars)
I suggest that the red giant resulting from the nova explosion of the the proto-Sun condensed to a group consisting of the precursors of the Sun, a-Centauri with its close binary partner, and Proxima Centauri, which now forms a stable ternary with a close binary. Such a quadruple group could be gravitationally unstable, which could account for the ejection of the Sun from the system, and perhaps for the fact that a-Centauri is now at least 35o south of the ecliptic.
But in any case, the observed proper motions of nearby stars are of the right order to produce the present separation of Sun and the (Centauri group in five billion years. Of these four stars, the Sun and a-Centauri are twins in mass, luminosity, and temperature. Alpha Centauri's binary partner, separated from it by only 10,000 astronomic units (about the distance of Pluto from the Sun) is only a tenth of the mass of its primary. Proxima Centauri, the nearest to us of the three, has about 30 times the mass of Jupiter and one-tenth of the mass of Sun.
The red-giant stage must be rather brief, because stars in that stage are so luminous that all are visible out to great distance, so we would see many more of them if the red-giant stage lasted long. Heat loss from the immense surface area allows gravity condensation to surpass radiation pressure so they soon drop back to the main sequence.
Sun's Betelguese-Antares stage may have lasted less than a million years. Recently (Monthly Notices Royal Astronomic Society, 202: 61, p. 64, 1991) another possible member has been added to the group, BRI 0021-0214, one-tenth of the mass of Sun, at a distance of 8 light-years. It is a faint brown dwarf, 10,000 times fainter than Sun, with a surface temperature of 2,259oK.
Application to the solar system of the continuous creation of matter and perhaps the change of the gravitational constant with time implies changes in the planetary orbits as well as variation in the luminosity of the Sun, which should show up in the geologic record. Certainly there was marine sedimentation back to three billion years ago, and several epochs of glaciation. Chin and Stothers (1975) have investigated this question in the case of multiplicative creation (that is where mass grows in proportion to its own concentration) and they found the rather surprising result that are nearly the same as the final model based on standard theory! This occurs in spite of the widely disparate initial masses, occasioned by the full range of choices for T0. The reason for this similarity is that the effect of a larger G in the past is to increase the luminosity, while lower stellar mass decreases it.
They go on to investigate the effect on the orbits, and conclude that the deduced temperatures at the surface of Earth do not conflict with paleogeographical evidence.
At a little more than Sun's mass, the star becomes unstable as a radially pulsating variable, first of the RR Lyrae type, pulsating with a period from one to ten hours (the shortest pulsation period known is the 89 minutes of CY Aquarii), with a surface temperature of 6,500o to 7,000o K; then as a d Scutae variable at about two solar masses and surface temperature 7,000o K pulsating at 10 to 24 hours, then from three times the mass of Sun as a d Cephei type variable, pulsating at 1 to 70 days.
Compare the cepheid pulsation with regular eruptions of a geyser, where steady flow of heat to the base of the water column raises the temperature there until the boiling point is reached for the local pressure. The onset of boiling reduces the load of overlying water, and the whole column flashes into steam as an explosive eruption, to settle back to commence the next heating cycle.
The majority of stars are variables because of geyser-like instabilities. The first regular variable known to astronomy was Mira (o Ceti), which was discovered by Fabricius in 1596 and called Mira "the wonderful". Mira is a red giant of spectral type M5 to M9, with a period of 332 ± 9 days. It has a binary companion, Mira B, also a variable with its maximum luminosity at Mira's minimum.
Mira is the prototype of a class of stars which are red giants with a mass about equal to that of Sun, radius about 100 times Sun's, luminosity about 1000 times, and periods between 100 and 2,000 days. Some have suggested that Sun will undergo a Mira type explosion about 5,000 million years hence. Perhaps the normal evolution of stars along the HR sequence involves several nova episodes such as RR Lyrae, Mira, Cepheids, FG Sagittae, planetary nebulae, and perhaps others, in their course to ultimate supernova explosions.
The most thoroughly studied of all pulsating stars are d Cephei siblings which have yielded an empirical period-luminosity-color relationship which correlates period with intrinsic luminosity. The ratio of apparent luminosity to intrinsic luminosity gives the distance from Earth. The identification of cepheids in the Small Magellanic Cloud, and then in M31, the great galaxy in Andromeda, began the mensuration of the Universe.
In my cosmology, Sun will eventually pass through the pulsation sequence as it progresses along the Hertzsprung-Russell sequence, volatilizing Earth and our civilization.
In spectral type 0, above ten solar masses, a supernova explosion occurs, blasting off the outer envelope and leaving a small hot core. b Centauri and Spica are approaching this stage, and Sandaleuk 69o 202 (the star in the Greater Magellanic Cloud, 169,000 ± 9,000 light-years from Sun, which exploded to form Supernova 1987A) had been a very hot blue star at the end of the main sequence, about 13 times as massive as Sun and with a surface temperature of about 35,000o K.
Our Galaxy is littered with many Supernova remnants, which is what we should expect if such was the end point of normal stellar evolution. Like the Crab Nebula and h Carinae supernova remnants, Sandaleuk 1987A is now surrounded by a ring of hot gas. Other supernova remnants are the Veil Nebula in Cygnus (also called the Network Nebula, NGC433), and the Ring Nebula (M37 or NGC6720) in Lyra, and many of the so-called planetary nebulae (not in any way related to planets), such as the Helix nebula NGC7293.
Indeed, supernova remnants abound in the Milky Way galaxy, in the Magellanic Clouds, and in the Triangulum spiral (M33), without trace of any original star. Pulsars have been observed so far in only three supernova remnants - Crab, Vela SN pulsar (26th magnitude, 0.089 sec), and Sandaleuk. More remote pulsars are mostly too faint to be detected, but some are not too distant, which suggests that the central stars may disappear as black holes.
Five supernova explosions have been witnessed in our galaxy: one in 1300 B.C. near Antares; another in 185 A.D. The one on 4 July 1053 in Tauius, 6000 light-years away was seen and recorded by oriental astronomers and left behind the Crab nebula. Yang Wei Te, the Chinese "chief calendrical computer", reported to the emperor that a "guest star" had appeared, which faded after a few months; another supernova was seen in 1572, and the 1604 Cassiopeia A supernova was studied by Kepler and is now surrounded by a gas ring emitting strong X-rays. On average, supernovae occur in our galaxy every fifty years, each releasing ~1050 joules.
It is interesting to speculate on possible future supernovae. Another star in the Large Magellanic Cloud, h Carinae, said to be 300 times as massive as the Sun, in the far southern hemisphere, has been suggested as a pending supernova, but its 1843 explosion from +6 (about as bright as Sirius) to 1 magnitude, plus its gas ring similar to the Crab nebula, suggest that it was then a supernova.
Sally Heap, of NASA, reported that Selnick 42, a W class star in the Large Magellanic Cloud that is is 106 more luminous than the Sun, 100 times more massive, and with stellar winds blowing up to 2900 km/s) is expected to explode as a supernova.
Perhaps the most likely other candidates are the Wolf Rayet stars, which are more than ten times as massive as the Sun: very hot blue stars of spectral class O, with temperatures of some 40 kilokelvin, radiating energy at 1035 watts (10,000 times the Sun's output) and with very strong stellar winds.
Not far behind them is Centauri, the southern pointer, the tenth brightest star in the sky although 490 light-years away, spectral type B0.5, temperature 21 kilokelvin, and nine times as massive as the Sun.
The dense heavy stellar core left behind by a supernova collapses under the inward pull of gravity and the force of the explosion above it, crushing together the protons and electrons of its atoms to form neutrons. The object becomes a neutron star with a density of about 107 kg/cm3. A neutron star contains the mass of two or three suns compacted into a 20 km sphere. A thimble full of neutron star material would weigh over a billion tons.
The existence of neutron stars was predicted by theorists long ago, but astronomers realized that they would be almost impossible to see because of their tiny size and consequent faintness. But in 1967, Jocelyn Bell and Antony Hewish, radio astronomers at Cambridge, England, picked up radio pulses coming from several directions in space. The pulses came as regularly as the ticks of the most accurate clocks, at intervals of a second or so. These flashing radio objects were termed pulsars.
Thomas Gold, of Cornell, proposed a lighthouse model because only a rapidly rotating star seemed able to account for the regularity and frequency of the pulses. The only stars small enough to spin once a second or less were neutron stars. Astronomers now accept that pulsars and neutron stars are the same thing. The neutron star gives out a flash of radiation from its magnetic poles in our direction each time it turns, like a celestial lighthouse.
But with the discovery of sub millisecond pulsars this model is no longer tenable, because even ultra dense nuclear matter with a field of 1011 gauss, spinning at such rates should rapidly disintegrate. The rate of rotation at 2000 Hz is beyond the limit of known equations of state. Moreover, surely we should question the probability that the spin axes of so many pulsars being so oriented that their polar beam would be directed our way.
So we should abandon the cosmic searchlight model and seek a different explanation. Indeed, Wang and Mazzoli (1992) have already suggested that the pulsation derives from a vibrational mode, and not rotation.
Over 400 radio pulsars have been detected, flashing from every 4 seconds to more than 600 times per second. The nearest recorded pulsar is 80 parsecs away, the most distant 50,000 parsecs. Some pulsars have also been detected at X-ray and y-ray wavelengths.
Because of the small surface area to radiate, pulsars are extremely faint optically, notwithstanding the intense energy output (1029 watts). But in 1969 the Crab pulsar was observed flashing optically at the same rate as the radio pulses. Only one other pulsar, that in the constellation Vela, has been observed optically. The others are too faint.
Few pulsars have proper names, but are named according to their place in the sky. Thus the Crab pulsar is known as PSR 0521+21o, meaning a pulsar found at right ascension 5 hr and 2I minutes and a declination of 21.0o north.
At first the
pulsation is extremely rapid, but the period declines slowly with time.
Periods of other pulsars (in milliseconds) are:
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The Magellanic Cloud pulsar is the most distant so far recorded. It is a supernova remnant, and is surrounded by a nebula like the Crab pulsar The next dozen pulsars have periods less than 100 ms. The pulsar with the longest period so far observed is PSR 1845-19 with a period of 4.3 seconds.
Note that three of the pulsars listed above are at 19 hr right ascension. Indeed one-fifth of the recorded pulsars are on this celestial latitude. This is an artefact because the most prolific observer of pulsars is the giant fixed radio-telescope at Arecibo Puerto Rico, which points in this celestial direction as the Earth rotates. This implies that many more pulsars remain to be recorded on other celestial latitudes.
In 1974 Hulse and Taylor, of Amherst, systematically studied Arecibo pulsars and found that the period of PSR 1913 (above) varied daily by up to 80 microseconds on a 7 hour 45 minute cycle. After eliminating several "impossible" alternatives, they concluded that the regular variation implied, not a pulsar, but a binary pulsar couple 1.8 million km apart. This raised the problem why the first supernova explosion did not destroy the gravitational coupling between them even if the second supernova explosion did not. Random capture of one neutron star by another was excluded by Narayan's estimate that there must be 30,000 neutron star binaries in our galaxy alone. A neutron star heavier than two solar masses must theoretically collapse into a black hole, so there must be many such.
The periods of all pulsars are observed to be slowing, and it is suggested below that pulsars evolve into quasars and then into X-ray stars, as they decline in period with increasing mass. The pulsation periods of quasars vary from a few hours to several years. Many X-ray stars fluctuate so regularly that they have been interpreted as spectral binaries although in a single such star the oscillation period is several times shorter in the hard X-ray bands (10-30 keV) then in the softer X-ray bands (10-1 keV), and longer still in the optical spectrum.
Recently many pulsars (perhaps most) have been observed to suffer "glitches" - sudden impulsive discontinuities in their rotation rates. The Vela pulsar is a conspicuous example, with large glitches recurring at intervals of about three years, but the period and patterns are not regular. The Crab pulsar glitches more frequently but with less amplitude.
Glitches were interpreted as "star-quakes" that impulsively reduce the oblateness thus causing a sudden increase in angular velocity. Alternatively the glitches might be caused by "core-quakes" causing increase in angular velocity. McKenna and Lyne attribute the glitches to "discontinuous transfer of angular momentum from the star's fluid interior to the more slowly rotating crust".
None of these are really plausible and give further reason for abandoning the pulsar "lighthouse" model on which they are based. Several other puzzling pulse variations occur. There is much variation in pulse shape, and pulses often fail to appear, even for as long as 1000 pulses. Small sub pulses appear at one edge of a pulse envelope and creep progressively across the envelope through successive pulses.
Quasars are a by-product of radio astronomy, which developed out of the intense radar developments of World War II. Radio telescopes are blunt instruments, so most radio sources covered too much sky for precise identification with optical images. The radio emission does not come from the central source but from two considerably distant lobes symmetrically displaced on either side of the source.
The width of the lobes diminishes with distance, so a young radio astronomer, Tom Matthews, selected ten of the smallest known radio sources and sought the help of Allan Sandage, the master of the 200 inch Palomar telescope to identify them optically. The smallest radio source, 3C48 in Triangulum coincided with a sixteenth magnitude star. The spectrum of this star showed unusually intense radiation in the ultraviolet and blue, and the spectrum differed from any previously seen, with a pattern of lines not matching any known elements.
Moreover, the brightness varied significantly over several days, which implied that it was too small to be a galaxy, and had to be only a star. More of Matthews' sources turned out to be equally peculiar, and were dubbed "quasi-stellar objects", which was contracted to "quasars".
But through the next three years, the strange spectral lines remained a mystery. Until in 1962, when the Moon was due to pass across another of Matthews' radio sources, 3C278. That enabled Australian radio astronomers to fix precisely the time of the eclipse of the radio signal, and hence record precisely its position.
It was a 13th magnitude blue star, and its spectrum again had the strange lines. But this time Martin Schmidt at Palomar recognized them as hydrogen lines redshifted 16%, which implied a recession velocity of 47,000 km/s and a distance of 1.5 billion light years. With the new understanding, the spectral lines of quasar 3C48 were found to be red-shifted 37% !
Since their 1962 discovery by Martin Schmidt, more than 500 "ordinary" looking blue stars have been reclassified as quasars because of their very large redshifts (z up to 5.53), and systematic search has increased the count to 3,000 and still rising.
If their large redshifts indicate distance (up to 1010 light-years) it implies enormous speed of recession at great distance, and hence masses 108 times the mass of the Sun, and extremely high intrinsic luminosity in excess of 1040 watts, across the radio, infrared, optical, X-ray, and y-ray spectrum - more than a hundred times the output of the whole Milky Way galaxy (!) corresponding to thousands of super-nova explosions per year. But they could not be larger than a tenth of an arc-second (or telescopes would resolve them), and their rapid fluctuations imply a source smaller than the solar system.
Their spectra place quasars at the extreme of the Hertzsprung-Russell sequence, blue stars with strong ultra-violet, X-ray, and radio emission. In quasars the prominent Lyman-a line at far ultraviolet wavelength of 122 vm is redshifted into the blue, and accompanied by a veritable forest of hundreds of Lyman-a lines redshifted to a spread between 350 and 450 vm, indicating a wide spread of velocities of the sources.
Quite apart from the incredible energy implied by their luminosity when combined with the Hubble distance derived from the redshift - there are other anomalies. No satisfactory explanation of energy outputs up to 1045 W has been proposed. Whereas galaxies generally give a satisfactory correlation of redshift with distance, quasars do not.
According to big bang models. such extremely distant bodies should be very old with no elements much beyond hydrogen and helium, the heavier elements only being generated after successive cycles of stars and supernova explosions. Yet some quasar spectra show elements as heavy as iron.
There are cases where two quasars with very different redshifts are seen closer together than would be expected by chance if they were not physically related. Many, perhaps all, quasars are embedded in galaxies, commonly but not exclusively spirals. The elemental abundance's are essentially similar to solar abundance's, which, according to standard theory, is anomalous for such early bodies.
John Kierin states that some quasars (3C23, 3C279, A00 23S+16) exhibit components separating at very high angular rates, which would imply velocities ten times the velocity of light (if red shift indicated distance). Such apparently superluminal velocities have been recorded in 30 sources and suspected in others. These measurements are angular rates, and the breach of relativistic physics only appears when the red-shifts are assumed to mean Hubble distances.
Some quasars appear to be spacially related to bodies of much smaller redshift. On the other hand the red-shift of some quasars is consistent with the redshift of normal galaxies grouped with them. Quasars appear to increase in abundance with distance, but this may only mean that the distances are spurious.
The brightest known radio source, Cygnus A, has, centrally between two strong radio lobes, a very bright star heavily dimmed by dust in the line of sight that is penetrated by the radio waves. If this is a quasar, as many believe, it must be relatively close.
For such reasons, many astrophysicists have questioned the validity of the Hubble-distance interpretation of quasar redshifts. No intrinsic relationship between quasar apparent luminosity and red-shift distance. Arp (1994) is emphatic that we must abandon the assumption that redshifts are due to recession velocity:
the empirical evidence on this point was already overwhelming and the new observation in high energy x-rays and y-rays now render the evidence completely inescapable.
Lacertids are called after the "variable star", BL Lacertae, regarded as a variable star until its high redshift indicated that it was a quasar. Lacertids have no spectral emission lines like some other quasars.
Seyferts are spiral galaxies with very bright very turbulent cores, believed to be black holes, emitting ten thousand times more energy than normal galaxies, with broadened spectral lines indicating large differential velocities at the source. A continuous progression has been reported between Seyfert galaxies and some quasars. This raises the question whether there are two categories of quasars, stellar and galactic, or alternatively that Seyferts are nearer and stellar.
The Final evidence that quasar redshifts do not correlate with Hubble recession velocities, comes from plotting the apparent luminosities of thousands of quasars against their redshifts. Instead of the linear plot given by thousands of galaxies, the quasars yield a random scatter, proving that quasar redshifts are not Hubble recession velocities.
Perhaps quasar redshifts are indeed Doppler, recording the velocity of matter streaming into a black hole at the center of the quasar, which would appear as a recession velocity from whatever direction it is viewed. Beyond the quasar, the inrushing matter would appear to be blue-shifted, but this should be obscured by the near side radiation.
These quasar spectra thus show broad emission lines of ionized gas spread enough to indicate differential velocities up to 105 km/s, which is approaching the velocity of light. In contrast, the absorption lines are quite narrow, which is consistent with a model of emission from highly accelerated plasma streaming toward a black hole, radiating through an envelope of gas with internal velocities of about 10 km/s.
The redshifts of the absorption lines are typically less than the redshifts of the emission lines, sometimes indicating velocity difference of several thousand kilometers per second. The absorption spectra would indicate the true distance of the quasar, not the emission spectra. The path of the in-rushing gas would presumably be spiral, but the transverse velocity would be insignificant compared with the inward velocity, and in any case would not register as doppler shift.
With CCDs (charge-coupled devices, using a silicon chip to increase the sensitivity by up to one hundred times the sensitivity of photographic emulsions), a faint fuzz of luminosity has been found around some twenty or so quasars (such as 3C48), reminiscent of the haloes of the nearer Crab and Vela supernova remnants. The "fuzz" was found to have the same absorption redshifts as the parent quasar, and a few others with small (presumably valid) redshifts are surrounded by a faint distribution of stars.
Nevertheless, some galaxy-quasar associations fit very closely the interpretation of a near galaxy gravitationally lensing a distant quasar, and producing multiple images which match in all spectral details, and even flux fluctuations (as with MG1654+1346, Q2237+0305, and Q50957).
It is generally accepted that the the active cores of quasars are black holes. If the remnant neutron star following a supernova explosion exceeds three solar masses, no force is known to prevent gravitational collapse to a black hole. Quasars commonly pulsate with periods ranging from several years at all wavelengths, down to some pulsating with periods of a few hours (BL-Lacertae objects, or so-called "blazars").
Quasars seem to be "long-period pulsars" with periods ranging from hours to years, taking their place in the evolutionary sequence of supernova, neutron star pulsar, Seyfert, Xray star, and quasar (with black hole), as their mass and luminosity continue to increase and pulsing period increases from (less than a millisecond to seconds, minutes, hours, days, and years.
This suggested grouping of Seyferts, quasars, BL Lacertae, and blazars, may be too simple, because many quasars have long jets extending out hundreds of kiloparsecs, with distinct bright nodes, which are not yet understood (for example, 3C75, 3C449 and 0800+608 and +187). They might be approached through plasma physics.
Most active galaxies are too distant for detailed study but some are nearer: NGC3079 (3x103 light years) M82 (106 light years) and NGC1068 (5x106 light years away). Each has symptoms of active black holes, and evidence of the generation of many new stars (star bursts). Knowledge of the Universe is still in its infancy.
Along the main sequence, mass and luminosity increase logarithmically to the supernova discontinuity where much mass is lost to the neutron star stage. Thence mass increases again through the pulsar X-ray star stage, through the Eddington critical luminosity (where the outward radiation force balances gravity) to the black-hole discontinuity to become a quasar, in which rate of mass increase is eventually overtaken by mass-energy annihilation on the path to the white-dwarf stage (hot blue stars with less than three times the mass of Sun).
No white dwarf is known with more than twice the mass of the Sun. There are many white dwarfs within 12 light-years from the Sun. Presumably they continue to be abundant at greater distances but are too faint to be detected.
The properties of black holes can be exactly specified in terms of just two parameters: mass and spin. The black holes of nature are the most perfect macroscopic objects in the Universe: the only elements in their construction are our concepts of space and time. And since the general theory of relativity provides only a single family of solutions for their descriptions, they are the simplest objects as well (Chandrasekhar).
The diameter of a black hole is similar to that of the solar system. Some argue that black holes must continue to contract to a vanishing point singularity. But this assumes the validity of Newton's law to zero distance, without empirical evidence.
But black holes are theoretical objects. No black hole or accretion disc has been observed. There is a fair consensus that the central "prime mover" in active galaxies involves a spinning black hole as massive as a hundred million suns, fuelled by capturing gas or even entire stars.
The captured debris swirls downward into the hole, carrying magnetic fields with it and moving nearly at the speed of light. The destruction of single stars is compatible with the short term fluctuation of light emission. At least 10% of the rest-mass energy of the in-falling material can be radiated; further energy can be extracted from the hole's spin.
Perhaps quasars are the visible black holes, their intense radiation being synchrotron radiation of matter spiralling down the black hole vortex with velocities approaching the velocity of light. The relativistic mass added to the accelerating matter swirling down the 'black hole equals the radiated energy of the black hole.
Radio evidence suggests a core object at the very center of our galaxy with a mass of five million solar masses, probably a black hole. The Andromeda galaxy has been studied accurately enough to infer that the stars nearest its center are orbiting around a dark compact mass which answers the description of a black hole of many million solar masses.
Such an object could be quiescent, but not quite. Now and again a star would pass so close to this hole that tidal forces would shred it apart. And we might then see a flare for just as long as it takes for the debris to be swallowed or expelled from the hole's vicinity.
We may speculate whether, at the central singularity, where spiralling velocity equals the velocity of light, matter and energy mutually annihilate-back to the universal null, thereby completing a stellar cycle in a steady-state cosmos?
The ultimate fate of a black hole could be the threshold initiating mass-energy mutual annihilation. When matter is spontaneously created from zero, the potential energy created is precisely equal and opposite to inertial mass. The mass-energy sum is zero, and would remain zero on mutual annihilation in the black hole. Unless some such process exists, there should now be billions of black holes in the infinite cosmos.
The threshold from planets to stars is determined by the core pressure-temperature reaching the threshold of rapid nucleosynthesis. As stars increase in mass and progress along the Hertzsprung-Russell main sequence, they pass instability thresholds, including a nova threshold at half the mass of the Sun to a red giant which condenses rapidly to a planetary system. Next, a cepheid threshold at about twice the mass of the Sun, and a supernova threshold at about fifteen times the mass of the Sun to a neutron-star pulsar Then mass continues to increase, to quasar and black hole, then mass-energy annihilation completes the cycle.
The limiting size of galaxies is determined by the Newton-Hubble null, the limiting size of a Universe is determined by the velocity of light (itself determined by the pervasive mean density), while the cosmos is infinite and unbounded. Through it all, the total mass-energy of stars, galaxies, Universes, and cosmos remains zero, and the Perfect Cosmological Principle remains true.