Antimatter comet

Antimatter comets (and antimatter meteorites) are hypothetical comets (meteorites) composed solely of antimatter instead of ordinary matter. Although never actually observed, and now believed (from experimental data) to be unlikely to exist anywhere within the Milky Way, they have been hypothesized to exist, and their existence (on the presumption that that hypothesis is correct) has been put forward as one (of usually several) possible explanations for different observed natural phenomena over the years.

Contents

Hypothesized existence

The hypothesis of comets made of anti-matter can be traced back to the 1940s, when physicist Vladimir Rojansky proposed, in his paper The Hypothesis of the Existence of Contraterrene Matter the possibility that some comets and meteorites could be made from "contraterrene" matter (i.e. antimatter).[1] Such objects, Rojanski stated, would (if they existed at all) have their origins outside the solar system.[2] He hypothesized that if there were an antimatter object in orbit in the solar system, it would exhibit the behavior of comets observed in the 1940s: As its atoms annihilated with "terrene" matter from other bodies and solar wind, it would generate volatile compounds and undergo a change of composition to elements with lower atomic masses. From this basis he propounded the hypothesis that some objects that had been identified as comets may, in fact, be contraterrene objects, suggesting, based upon calculations using the Stefan-Boltzmann law, that it would be possible to determine the existence of such objects within the solar system by observing their temperatures. A contraterrene body subjected to normal levels of meteoric bombardment (per 1940s figures), and absorbing half of the energy created by the annihilation of terrene and contraterrene matter, would have a temperature of 120 K (−153 °C) for bombardment figures calculated by Wylie or 1,200 K (930 °C) for calculations by Nininger.[3] In the 1970s, when comet Kohoutek was observed, Rojanski again suggested hypothesis of anti-matter comets in a letter in Physical Review Letters, and suggested that gamma-ray observations be made of the comet to test this hypothesis.[1][4]

Rojansky's original 1940 hypothesis was that perhaps the only bodies within the solar system that could be contraterrene were comets and meteorites, all others being almost certainly terrene.[5] Experimental evidence gathered since then has not only borne out this restriction but has made the existence of actual antimatter comets and meteorites themselves seem ever more unlikely. Gary Steigman, assistant professor of Astronomy at Yale University observed in 1976 that space probes had proven — by the fact that they were not annihilated upon impact — that bodies such as Mars, Venus, and the Moon were not contraterrene. He also noted that had any of the planets or similar bodies been contraterrene, their interaction with the terrene solar wind and the sheer strength of the gamma ray emissions that would have resulted1 would have made them readily noticeable long since.[6] He noted that not even contraterrene cosmic rays had been found, with all of the nuclei found in studies having been uniformly terrene, the experimental data in several studies made from 1961 onwards by various people excluding the presence of a fractional antimatter composition of cosmic rays any larger than 10−4 of the total. Further, the uniformly terrene nature of the cosmic ray flux indicates that nowhere in the Milky Way are there any sources of heavier contraterrene elements (such as carbon), since (although it is not proven) it is a likely assumption that they represent the overall composition of the entire galaxy. They are representative of the galaxy as a whole — goes the logic — and since they do contain terrene carbon and other atoms, but have not been observed to contain any contraterrene atoms, therefore there is no reasonable source for extrasolar contraterrene comets, meteorites, or any other large scale heavy element objects to originate from, within this galaxy.[7]

Martin Beech from the University of Western Ontario (London, Ontario, Canada) referred to the various hypotheses and experimental results that support non existence of antimatter in the Universe. He discussed the Papaelias formula about the "Velocity-height relation of antimatter meteors"[8] and argued that any contraterrene comets and meteors that exist must be (at least) extrasolar in origin because the nebular hypothesis for the formation of the solar system precludes their being solar. Any antimatter in a pre-formation nebula or planetary accretion disc has a comparatively short lifetime, astronomically speaking, before annihilation with the terrene matter that it is mixed with. This lifetime is measured in the hundreds of years, and so any solar antimatter present at the time that the system was formed will have long since been annihilated. Any antimatter comets and meteors must therefore come from another, contraterrene, solar system, and be extrasolar. Furthermore, not only must contraterrene meteors be extrasolar in origin, they must have been recently (i.e. within the past 104 ~ 105 years) captured by the solar system. Most meteoroids are broken down to sizes of 10−5g within that timeframe, because of meteoroid-upon-meteoroid collisions. Thus any contraterrene meteor must be either extrasolar in origin itself, or broken off from a contraterrene comet that is extrasolar in origin. The former are unlikely to exist from observational evidence. Any extrasolar meteoroid would have a hyperbolic orbit, but less than 1% of the observed meteoroids have such, and the process of perturbation of ordinary (terrene) solar objects, by planetary encounters, into hyperbolic trajectories accounts for all of those. Beech concluded that a continued null result, however, does not constitute a proof ('Absence of evidence is not evidence of absence', M. Rees) and a single positive detection negates the arguments presented.[9] Taking into account the work of Alfvẻn, Lehnert and Papaelias, Herbert Shaw detected a seeming necessity of antimatter structures in our vicinity of the Galaxy.[10]

The Physics that governs an antimatter meteor fall is published by Philip M. Papaelias (assistant professor at the National University of Athens, Greece) who derived a set of formulae that explains how its cosmic velocity and original mass are decreasing and for how long its remaining mass may survive.[8][11][12][13][14][15]This framework of Physics helped Ken Bullough from Sheffield (UK), to realize that a small group of comets he was studying were in fact made of antimatter, since they were showing unusual characteristics to distinguishing them from the other ones. This study was radar observations at 73MHz made in June 1953 at Jodrell Bank as part of the meteor/radio-aurora observational programme. Publication of these data was suppressed because, at that time, no interpretation was possible within the then existing framework of physics and, in addition, the radar echoes were not detected on nominally similar equipment operating at 72MHz. Decades later, when he was aware about the physics of antimatter meteors and comets, he returned at the Jodrell Bank Observatory (Manchester) to search for the list of those comets. Forty two years after the first observations he published the results which include the short period (6.37 year) 7P/Pons–Winnecke and the 29P/Schwassmann-Wachmann in a group of few dozens of antimatter comets. In this new study, Bullough also analyzed extensively the Tunguska event and concluded that the explosion was generated by the annihilation of an antimatter meteor in the atmosphere.[16]

Hypothesized explanations for observed phenomena

Tektites

In 1947, Mohammad Abdur Rahman Khan, professor at Osmania University and research associate at the Institute of Meteoretics in the University of New Mexico, put forward the hypothesis that antimatter comets or meteorites were responsible for tektites (Khan 1947). However, this explanation, out of the many proposed explanations for tektites, is considered to be one of the more improbable.[17][18]

Tunguska event of 1908

By the 1950s, speculating about contraterrene comets and meteorites was a commonplace exercise for astrophysicists. One such, Philip J. Wyatt of Florida State University, suggested that the Tunguska event may have been a meteorite made of antimatter (Wyatt 1958).[19] Willard Libby and Clyde Cowan took Wyatt's idea further (Cowan, Atluri & Libby 1965), having studied worldwide levels of carbon-14 in tree rings and noticing unusually high levels for the year 1909. However, even in 1958 the theoretical flaws in the hypothesis were observed, aside from the evidence that was coming in at the same time from the first gamma ray measurement satellites. For one, the hypothesis did not explain how a contraterrene meteor could have managed to survive that low into the Earth's atmosphere, without being annihilated as soon as it encountered terrene matter at the upper levels.[19][20]Nevertheless, Papaelias suggested a number of mechanisms that may prevent an antimatter meteor of being evaporated[11]. This helps the object to escape complete annihilation during its infall flight and therefore to reach the ground level. Such a mechanism exists also for ordinary matter meteors which can escape complete evaporation by forming an air cap in front of them and in many cases they can be collected from the ground.

Ball lightning

In 1971, fragments of antimatter comets or meteorites were hypothesized, by David E. T. F. Ashby of Culham Laboratory and Colin Whitehead of the U.K. Atomic Energy Research Establishment, as a possible cause for ball lightning (Ashby & Whitehead 1971). They monitored the sky with gamma-ray detection apparatus, and reported unusually high numbers at 511 keV (kilo-electron volts) which is the characteristic gamma ray frequency of a collision between an electron and a positron. There were natural explanations for such readings. In particular positrons can be produced indirectly by the action of a thunderstorm, as it creates the unstable isotopes nitrogen-13 and oxygen-15. However, Ashby and Whitehead noted that there were no thunderstorms present at the times that the gamma-ray readings were observed. They instead presented the hypothesis of antimatter meteorites as an interesting one that did explain all of what their observations had recorded, and suggested that it merited further investigation.[21][22]

Ashby and Whitehead's hypothesis, which Dr. Neil Charman (lecturer at the University of Manchester Institute of Science and Technology) in his 1972 roundup of the several hypothetical explanations of ball lightning characterized as one of the more bizarre explanations, was based upon the (unproven) supposition that there was a potential barrier between contraterrene and terrene matter. This barrier allowed micrometeorites and meteorid fragments that entered the Earth's atmosphere from space to survive for comparatively lengthy periods, because the terrene atmospheric molecules would not always possess enough energy to overcome the barrier and annihilate the antimatter fragments. Contraterrene atoms in micrometeorites would instead become negatively charged antimatter ions, as a result of positrons being stripped from them by the photoelectric effect (and also as a result of secondary effects from annihilation of matter around them). These negatively charged antimatter ions would be electrically attracted to the ground in stormy weather, and, gaining enough kinetic energy to finally overcome the (supposed) repulsive barrier would finally annihilate with terrene matter to form what is observed as ball lightning.[22][23]To explain the survival of an antimatter meteor during its infall flight, Papaelias introduced the formula σannihilation=σelastic Π fi, where 0<fi≤1[11]. All mechanisms that may reduce the annihilation cross section σ are involved in the factors fi of the product Π, including the repulsive potential described above. Several studies, by using various methods to determine a possible barrier between ordinary matter and antimatter resulted into controversial discussions, since the decade of 60s.

In a series of papers, Philip M. Papaelias described how an antimatter meteor can produce the ball lightning phenomena.[24][25][26] He also suggested that an antimatter meteor is continually heated when the annihilation products are passing through it. Depending on the dimensions of it, those particles depose part or all of their energy, increasing in that way its temperature. As a result, the residual mass of the antimatter meteor would reach its melting point and consequently liquid drops would start to escape from the parental object. Papaelias calculated the energy absorbed and studied melting processes for 10, 100 or 1000 individual drops, each one glowing separately.[27][28] Twenty two years later, a ball lightning of about 10-15 m in diameter appeared over Alexanderplatz, a central location of Berlin, Germany. This bright object, which was hovering for about 10 minutes at a height which was estimated between 400 and 250 m slowly evolved into a luminous sphere of about 1 m in diameter and was emitting intense light, maybe equivalent to 10-25 kW of sodium street lighting lamps. The phenomenon was captured by two web cameras and is showing the ball lightning slowly changing shape and color. It was observed by Wilfried Heil and Noemi Zudor, shortly before a thunderstorm on July 29th, 2006 at 3:10 AM. The luminus object was gradually divided into 100 independently glowing smaller objects that were seen as escaping from the central one.[29]

Gamma-ray bursts

Antimatter comets thought to exist in the Oort cloud were in the 1990s hypothesized as one possible explanation for gamma ray bursts.[30] These bursts can be explained by the annihilation of matter and antimatter microcomets. The explosion would create powerful gamma ray bursts and accelerate matter to near light speeds.[30] These antimatter microcomets are thought to reside at distances of more than 1000 AU.[30] Calculations have shown that comets of around 1 km in radius would shrink by 100 cm if they passed the sun with a perihelion of 1 AU. Microcomets, due to the stresses of solar heating, shatter and burn up much more quickly because the forces are more concentrated within their small masses. Antimatter microcomets would burn up even more rapidly because the annihilation of solar wind with the surface of the microcomet would produce additional heat.[30] As more gamma-ray bursts were detected in subsequent years, this theory failed to explain the observed distribution of gamma-ray bursts about host galaxies and detections of x-ray lines associated with gamma-ray bursts. The discovery of a supernova associated with a gamma-ray burst in 2002 provided compelling evidence that massive stars are the origin of gamma-ray bursts.[31] Since 2002, more supernovae have been observed to be associated with gamma-ray bursts, and massive stars as the origin of gamma-ray bursts has been firmly established.

Footnotes

References

  1. ^ a b NS 1974a, pp. 55
  2. ^ Rojansky 1940, pp. 258
  3. ^ Rojansky 1940, pp. 259–260
  4. ^ Rojansky 1973, pp. 1591
  5. ^ Rojansky 1940, pp. 257
  6. ^ Steigman 1976, pp. 342
  7. ^ Steigman 1976, pp. 342–344
  8. ^ a b Papaelias 1987, pp. 13
  9. ^ Beech 1988, pp. 215
  10. ^ Shaw 1995, p. 436
  11. ^ a b c Papaelias 1990, pp. 1-13
  12. ^ Papaelias 1991a, pp. 105-111
  13. ^ Papaelias 1991b, pp. 215-222
  14. ^ Papaelias 1993, pp. 41-46
  15. ^ Papaelias 1994, pp. 71-77
  16. ^ Bullough 1995, pp. 1533-1551
  17. ^ Bagnall 1991, pp. 124
  18. ^ Vand 1965, pp. 57
  19. ^ a b TIME 1958a
  20. ^ Steel 2008
  21. ^ NS 1971a, pp. 661
  22. ^ a b Charman 1972, pp. 634
  23. ^ Stenhoff 1999, pp. 219–220
  24. ^ Papaelias 2006
  25. ^ Papaelias 2006
  26. ^ Papaelias 2006
  27. ^ Papaelias 1984
  28. ^ Papaelias 2010
  29. ^ Heil 2006
  30. ^ a b c d Dermer 1996
  31. ^ Bloom et al. 2002, pp. L45
  32. ^ Steigman 1976, pp. 355

Bibliography

Further reading

Original publications of the various hypotheses

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