The Geonomy Scientific Committee of the Hungarian Academy of Sciences held a one-day session on on 12th April, 2001, about supernova (SN) events. The reason for such a session was the claimed geological importance for SN events. It seems that (apart from the SN event having triggered the contraction of the protosolar nebula) mainly two SN events are believed to make terrestrial impact: 1) the hypothetic SN claimed to have caused the Permo-Triassic extinction (see some lectures of Cs. H. Detre) and 2) the Vela SN believed to be behind the Younger Dryassic transient re-glaciation (see some works of G. R. Brakenridge). I wanted to comment both claims, so I had a lecture "The Physics behind SN Events and Almost Historic SN's". However the present text is not simply my lecture on 12th April, 2001, but a synthesis of that and another lecture on 10th June, 1998 in Tsukuba about the end-Permian crisis; plus some reflections to new developments.

The April session was planned at least half a year in advance, so it was not triggered by the February paper of Luann Becker. For example, for me it was obvious for years that SN is not an explanation for the P/T events. Maybe other colleagues also felt likewise; but no heated argumentation happened at the session. This study is also not a heated argumentation: one cannot make heated argumentations about purely physical processes, astronomical probabilities and such.

B. Lukács

CRIP RMKI, Dept. of Theoretical Physics, H-1525 Bp. 114. Pf. 49., Budapest, Hungary

lukacs@rmki.kfki.hu

Quantitative consequences of 3 possible scenarios, SN, asteroid impact and immersion into galactic dust/cloud for the Permo-Triassic crisis are compared. The SN scenario seems highly improbable. Among the 3 mechanisms the galactic cloud seems to meet most quantitative constraints. However, obviously, we do not yet sufficiently understand what have happened at the P/T boundary.

I think the opinion of the leader of IGCP 384 "Impact and Extraterrestrial Spherules: New Tools for Global Correlation" is authentically presented by the Internet material referred here as [0]. However, being its language Hungarian, I am afraid, that the Japanese, Chinese and other colleagues within and outside IGCP 384 (Impact and Extraterrestrial Spherules: New Tools for Global Correlation) would have some difficulties to interpret it. (Of course, Europeans & Americans, maybe simply yojin for the other half of IGCP 384 "Impact and Extraterrestrial Spherules: New Tools for Global Correlation", can read it without any problem but I do not think they understand the content.)

I cannot help this. For any case, Ref. [0] narrates a terrifying scenario with a nearby supernova. Briefly: a really nearby SN (at cca. 10 pc distance) killed a lot of the biomass, either directly, or via atmospheric nitrogenoxides, or by damaging the ozone shield. Then the putrifying organic matter caused superanoxy, so killing a lot more of animals. (Even skies were ghastly brown; or purple?) So the nearby SN triggered a stagnation and misery for 20 million years.

The leader of a project has more possibilities to express his opinion than a simple member; but not more rights. My opinion was never asked about the SN scenario; so now I state it. But, quite apart from the real cause of the end-Permian catastrophe: if a project has the title "Impact and Extraterrestrial Spherules: New Tools for Global Correlation", then spherules should get more weight in it than UV, g or the acidic rains and the ghastly dark brown or magenta sky (from NO). But of course the project leader is the only person to determine the main path of the research.

Originally there were stellae (stars; fixed stars; eternal stars in the Aristotelian sense [1]), and stellae novae (which appeared ex nihilo and after some months vanished again; something, if above Moon, hardly interpretable in the Aristotelian context). Sometimes at the end of the XIXth century it turned out that the class of novae is inhomogeneous: the vast majority are "ordinary" novae but there are some super novae too. The absolute brightness of supernovae is much higher than that of novae, up to -19 magnitudo in peak.

Later it turned out that the class divides into 2-5 subclasses, with a luminosity M=-19 magnitudo for Class 1 and -17 magnitudo for the others, supernovae in different galaxies are similar, moreover, even SN rates are roughly similar (Zwicky's traditional number [2] was cca. 1/300 1/(yeargalaxy)). So an SN event is local, including only one star (or maybe also the companion). Today the statistics is better; I will return to the problem in due course.

The order of the deliberated energy indicates that in some sense the star ceases to exist in the SN event. Namely the total energy output is >10⁴⁸ erg in visible. (The decay time is 1-2 months.) However the majority of energy is outside of visible wavelengths: according to observations and various simulations UV, g and radio waves carry a lot of energy, + neutrinos and kinetic energy of ejecta too. A guess is 10⁵⁰ erg. Now, gravitational binding of Sun is cca.

E(b)~0.1GM²/R ~ 10⁴⁸ erg

So the star is destroyed in SN events.

We know a few SN remnants. They will be discussed in due course. For now it is enough to tell that

1) the ejected matter is seen as a "cloud" (M1=Crab, Gum=Vela remnant, Veil=Cygnus Loop);

2) generally the remnant is active at radio frequencies;

3) in some cases a pulsar is identified (e.g. Crab, Vela), so a neutron star has been formed in the event.

Two processes were seriously suggested which can result in SN event. The first I only mention; the second will be somewhat detailed.

Consider a close enough double star. One component just have developed a H-free core; fusion goes at the outer boundary of the core. Therefore the outer shells expand and become thin ("red giant stage"). Then a close compact companion, a white dwarf, can steal from the expanded, H-rich, outer shells and with the H-rich fresh fuel fusion can restart. In some cases it may restart vehemently, resulting in an explosion.

The second process can develop for lone stars too. Assume that the star exhausted its fuel and now it consists of nuclei in the neighbourhood of Fe (at least in the central region). Then further fusion cannot deliberate energy. To get a pressure one needs temperature (or electron degeneration, but that in itself cannot support a star above cca. 1.5 solar mass [3]). But the star radiates thermal energy with a rate proportional to T⁴, so the hydrostatic balance will break down. A gravitational contraction starts.

Now, for cold matter ("final state") the equilibrium configurations can be calculated [3]. Without repulsive nuclear interactions the M(R) function has a second, stable peak (after the white dwarf state), slightly above nuclear density ("neutron stars") but the total mass does not exceed cca. 2/3 solar mass. Later peaks are unstable [3]. Repulsive interactions do exist [4], and they increase the possible neutron star masses, but not without limit. Namely, strong repulsion causes high energy, that is source of gravity, so it tries to pull together the matter in spite of the repulsion. According to numerous calculations one can guess that there is no equilibrium configuration above cca. 2 solar mass.

But then a burnt-out star M>2M(Sol) starts an inevitable gravitational contraction. The final fate is a matter of detailed calculations, but there is only one alternative. Either all the matter collapses, or one part collapses, and the other, smaller, part is ejected.

If all matter collapses, the far observer does not see too much. At transient high densities explosions may occur; and when the matter goes through nuclear densities, g-radiation appears. Neutrinos can be produced too. The final state, for the external observer, is the story of gravitational collapse, the matter asymptotically approaches the horizon and radiations become more and more redshifted. (To be sure, radiation means mass loss and so the horizon shrinks too, and then in strict sense it is not horizon anymore, but the more complicated scenario belongs to quasar physics, not to SN.)

In vehement contraction at high densities one may expect high rate of energy and momentum output, however. This may eject shells. Such a process would give transient luminosity increases. We do see the ejected shells with an initial velocity ~0.1c in SN events. There is luminosity increase because of the expansion, until the cooling is not extensive. Then the cooling shells start to dim.

While there is energy enough for ejection, more and more inward momentum is being built up in the collapse. So for SN event an agent is needed to carry momentum outwards, and transport it to the outer shells, otherwise the initially inward momenta will not be turned back even at the periphery. It turns out that neutrinos can do it [5], but not for every mass.

Anybody who is not familiar with SN simulations should read Ref. [5]. Today the details of calculations would differ and the scenario of Ref. [5] as anything told up to now is strictly spherical; still, the paper is easy to follow and then the reader gets an insight into an unfamiliar topics. For the Permo-Triassic extinction it is enough.

Vital statistics of stars [6] show that here something is missing. Again neglecting the details, Sun is an average star and its lifetime is cca. 10 billion years. Then in each year some 10 stars of the galaxy would burn out, but we see only one SN in 300 years per galaxy [2]. Although here we substituted average of ratio with ratio of averages, and obviously there is a threshold at 1.5-2 solar mass, still it is true [7], [8] that we do not see the majority of stellar deaths even above threshold. One process is automatically got to explain this. Conserved angular momentum causes an angular velocity ~1/R². Therefore during contraction at the equator "gravitational force" goes as 1/R², but "centrifugal force" does as J²/R³. Substituting observed data one gets that an average massive star (massive enough not to stop as white dwarf) will arrive a very nonspherical state well before the neutrino emission in Ref. [5]. It is simplest to tell that such a star will continuously lose mass on its equator, without vehement processes. Luminosity will go up, but not tremendously, so no SN event is seen. Another important feature is that high mass would prevent shell ejection. So there is only a narrow range of mass for sources and then it is not surprising that the luminosities are fairly the same in the same class.

More details are unnecessary because 1) Permo-Triassic extinction studies do not need the details; and 2) details continuously change with the changes of particle physical theories. However now we can be sure that indeed

1) an SN is so luminous as we see;

2) the luminosity is accompanied with large UV radiation (there is high temperature at the beginning);

3) at the stage when the core approaches nuclear density, extensive g- and neutrino radiation starts;

4) the formed neutron star emits more g-radiation, plus radio waves via the compressed magnetic field (pulsar activity); if neutron star is formed at all;

5) the remnant activity can last for long enough and moderately old remnants (at least up to 100,000 y) can be detected by optical and radio astronomy; and

6) physics completely prescribe the characteristics of SN events, and physics + galactic stellar statistics completely determine the rates of SN.

Astronomy indeed gives us a list of SN remnants when either a cloud is seen or a pulsar or at least some characteristic radio activity is detected. An incomplete list reads as

The list is compiled from several lists, so I do not give here references. There was one more SN observed with naked eye, the SN1987A in a Magellanic Cloud. At this event neutrino telescopes detected several dozen neutrino events, so the theoretical predictions for large neutrino fluxes are now corroborated.

SN’s 1-4 of the list are proven or at least the probability is high for them. SN 5-9 occurred in Chinese records as "guest stars" and sometimes modern astronomers are not sure if they were supernovae, novae or comets. Some authors suggest further historic SN’s, but there are serious doubts. Some authors include one or more of the 3 unnamed SN’s, some exclude all 3. I will return to this problem in a later Chapter.

Pulsars are not seen at the three newest galactic SN's. Maybe neutron stars have not survived, but maybe simply the equatorial plane does not contain Earth at any possible tilt. However M1 has a quite excellent pulsar, and so does Vela X too. Both period times are below 0.1 s, showing that they are quite fresh. The age of Vela SN is estimated partly from its period time.

The details of the Chinese SN's (5-9) of the list are not very well known and until Tycho Brahe European astronomers were not too interested. Aristotelian physics had the theory that the real sky (above Moon) is eternal, so transient events were regarded as meteorology (as meteors, lightnings &c.) and astronomers considered them rubbish. The turning point was SN 3 of this list; via parallax Tycho proved it superlunar.

But SN 10 & 11 need more discussion. They are before historic times, but humans were already present.

The time -12,000 for the Vela SN is only a guess, mainly from remnant explosion, although probably good within a factor 2. It is almost sure that it happened before -3500, because up to now it did not turn up in any written text, although it must have been very bright. At peak it must have been only marginally dimmer than full Moon; and if Cha & al. [9] are right and the distance should be halved, then it was even brighter; and point-like.

Now, Brakenridge suggested -8,700 for the event, on the grounds that Younger Dryas happened then [10], [11]. Let us accept this tentatively; there is no evidence against. Brakenridge mentions a string of terrestrial consequences, of which I discuss 3:

1) Meteorology: transient cooling back to pleniglacial temperatures for 700 years. Afterwards final changes to neothermal climate.

2) C14 anomaly.

3) Extinction of megaherbivores in the Americas.

Now let us see them item by item, with possible mechanisms and my comments.

1) I think, nobody really knows how meteorology is regulated. It is possible that some extraterrestrial agent caused Younger Dryas; but then what caused Oldest and Older Dryas? The transition from paleothermal (glacial) to neothermal happened through 3 oscillations; the Dryases were stadials, and Sausacá, Bölling and Alleröd were the respective interstadials. Surely there were no 3 nearby SN's in 4000 years.

2) Brakenridge suggests g -induced spallation of atmospheric N14, so generally a secondary cosmic radiation caused by the Vela radiation. Indeed, there seems to have been a C14 anomaly in that time [12]. However the case is somewhat obscure, because independent dating, either dendrochronology or varve chronology are near to the edge of possibilities and thermoluminiscence chronology is not accurate enough. It is difficult to transmit the Vela radiation to terrestrial C14. C14 is produced from atmospheric N14 via nuclear reactions. Neutrons could do it, but they decay while coming. I would rather not discuss SN neutrinos. UV and g photons can arrive but nuclear reactions via these photons are rather rare. As I told, it seems as if a C14 anomaly were to have existed then, but the matter is obscure.

3) Megaherbivores of the Americas indeed died out around Younger Dryas, for example mastodons and gigantic sloths. The same time is without bigger extinctions, however, in the Old World, except mammoths, which nobody exactly knows when died out in Siberia, and woolly rhino, adapted to cold. And do not forget, Homo sapiens starts to populate the Americas about -10,000. One cannot yet exclude the trivial explanation that incoming Man killed out the American megaherbivores during Younger Dryas.

Anyway, the Vela X source is well known. Its pulsar has a very short period time about 85 msec, the characteristic time P/(dP/dt) is cca. 1 order of magnitude higher than that of the Crab pulsar, and the main source of age estimation is this characteristic time. The X-ray luminosity of the pulsar is cca. 0.1 total solar luminosity, and the surface temperature is cca. million degree. The pulsar mass is between 1.5 and 2 solar mass [13]. If we apply the simplest model of braking of pulsar rotation [14], it gives cca. 15,000 y for the Vela X pulsar. We can almost be sure about the general features of the Vela SN event, we can reconstruct what was seen by the end-glacial observers.

The Vela SN was visible from Central and Southern Africa, Southernmost India, Indonesia, Australia and South America. But South America was still thinly populated and there may have been later migrations elsewhere except in Australia. Eva Papp, of AGSO, Australia, told to consider the possibility to collect dreamtime data of the Vela SN from aborigines, but still I have not heard anything new. Summarizing: Vela SN may have caused something detectable on Earth, but nothing has been proven beyond doubt.

The last SN of the list is now seen as the Cygnus Loop or Veil. Dating is rather hard, I saw a lot of ages between 30,000 and 100,000. No pulsar is detected. Perhaps in some years gravitational wave detectors will reach the necessary sensitivity [15] for rotating neutron star with "improper" equatorial plane in the Veil; but now we cannot say anything definite. However the Veil SN surely caused disturbances in the ozone layer of the northern hemisphere [16], [17]. In spite of this, no terrestrial trace of the event is seen now.

Almost any kind of terrestrial influence of supernovae can be imagined, but from the ways of astrology we know that not everything happens what can be imagined. It is better to restrict ourselves to effects observed (or not) at the historic and near-historic supernovae.

A supernova leaves optical impressions for some months. OK, this is the way candidates are listed. They gave enhanced UV radiation too. This radiation can cause biological effects, mostly destructive, but they cannot be verified at the supernovae of our list. Also, the ionizing UV can cause chemical reactions in the atmosphere, see next paragraphs.

The situation is similar with g-radiation. That radiation may have left traces in the rocks, but they are not found. Also, they may cause death, enhanced mutation rate &c, not verified. True, there is an idea of Ross [18] that Vela SN caused increase of cosmic radiation at Earth (true) therefore human life span was reduced from 900+ years to 100- and this is reported in Old Testament. However our closest living relatives have cca. our lifespans, so we cannot depend too much in old longevity. True, the Sumerian King List [19] is another source (and older); but while in Old Testament mentions the Flood as the border of longevity, in the Sumerian King List some post-Flood dynasties are still quite long-living, although in continuously decreasing degree [19], [20]. In northern Kish the division line is cca. Kish III, in Uruk the last long-living king is Gilgamesh, in southern Ur all kings seem "normal". If we accept the Sumerian King List in face value, then Vela SN erupted somewhere just before the Sumerian Flood (as we know, cosmic radiation diffuses with a square root of t law, so the desctructive effects are gradua), and the respective SN remnant is then would rather be Geminga, not Vela X; but it is better not too depend on theology & history; anyway, the data of the Sumerian King List have other explanations too [20]. But ionizing radiation can cause something in the atmosphere too.

This point may be important, so let us go into some details. The atmosphere of Earth is practically a mixture of N2, O2 and Ar. Since Ar is noble gas, we can forget about. The molecular ratio of N2 to O2 is roughly 4 to 1, so according to classic valence chemistry the present atmosphere is impossible: one would expect massive formation of nitrogenoxides and free O2 could vanish. However this does not happen.

The problem would deserve some attention. But, from sheer empiry, N2 is surprisingly inert. Agricultural fertiliser industry uses some ionising radiation or electric discharges or such to produce the oxides. But then an SN event with its ionising radiation may be a candidate for the cause of anoxy.

The reasoning is correct; the only question is the quantity. E. g. Burgess & Zuber claim that they found supernovae Kepler, Tycho & Crab, together with a mysterious SN1320, in nitrates in Antarctic ice [21]. Now, the curves show that 1) under normal circumstances the nitrate concentration in ice is 2*10^-5, and the 3 newest supernovae increased this for a short time to cca the double, not more. (Also, the hypothethical SN1320 did not cause more although very close, cca. 0.2 kpc.) So the presence of ionising radiation does not ignite a prairie fire of oxidising atmospheric nitrogen; for the historic supernovae nitrogenoxides still were rarities. Similarly, the Vela SN, albeit nearby, does not seem to have produced too much nitrates. Anyway, the 3 SN nitrate peaks in [21] are needle peaks. The duration of nitrate excess is rather short. So Tycho’s SN from 3.5 kpc did not double the NO concentration in waters; maybe it doubled it in one or few rain/snowfalls. But these details rather belong to a later Chapter; here it is enough to conclude that nitrates are terrestrial traces of supernovae, but these traces are not too expressed and it is doubtful how old SN nitrates can be preserved.

As for g-rays, they may cause atmospheric C14 excess, but in two steps. To get C14 from N14 formally one has to change one p in the nucleus to n. The process is energetically dispreferred, but can go at places of high energy concentration, so e.g. in collisions. However nuclear reactions are much easier to initiate with neutrons than with photons. So probably g photons lead to C14 as follows. First any atmospheric gas can interact with photons via the giant resonance; the resonance curve is wide, centered around 15-20 MeV, the total cross section cca. 0.1 barn, quite high [22]. Something is then emitted, in a significant part of the reactions a neutron. Then in the second step this neutron can be taken by an N14, with proton emission and the final result indeed is C14. As told, there are slight indications that Vela SN caused C14 excess. However C14 decays fastly on geologic timescale.

In principle the lithosphere may preserve also traces of SN influence. However nobody saw such.

Now, an SN emits corpuscular radiation too. The cosmic distance means that all unstable particles decay while travelling. Nuclei can arrive but they would be hardly distinguishable from terrestrial nuclei [23]. Spherules may be specific, but SN theory has not yet be applied to spherule formation to predict the unambiguous SN signal spherules. And empiry is little help here. No spherule could yet arrive Earth from a historical SN, because the hydrodinamical velocities are less than c by more than one order of magnitude. Very probably the same is true for the Vela SN; I do not know the situation about Veil SN, but never saw any suggestion for Veil spherules. Therefore we do not know what type of spherules would be characteristic signals of nearby supernovae.

Henceforth I want to restrict myself to nearby supernovae, say, not much farther than 10 ly = cca. 3 pc. Now what would we detect from a 10 ly SN without modern apparatuses?

Optically at peak the apparent brightness would be cca. -22 magnitudo. While definitely less than the daytime luminosity (almost -27 magnitudo), it would be brighter in night than anything, so it would disturb night life; for some months.

UV radiation would probably exceed the solar component. So skin cancer &c. would be frequent in one generation. Also, nitrogenoxides would be formed in the atmosphere, but model calculations would be needed to see how much. Note that they are formed only in trace quantities even under UV lamps.

Now we must turn to the forefather of the idea of Permo-Triassic killer SN: the paper of Schramm and Ellis [24]. I doubt their SN rate statistics, but that can wait until Chap. 11. On the other hand, they did perform quantitative analyses, for example for nitrogenoxides and for the fate of the ozone shield.

Since they believed in an SN at 10 pc, let us take that scenario. Then the neutral ionizing radiation would go up cca. one order of magnitude for cca. one year, while the particle flux becomes cca. doubled for cca. 300 years. This seems rather harmful.

Still similar is the increase of nitrates. Schramm & Ellis estimates a 30-fold increase from a 10 pc SN for 300 years. This means that molecular concentration of NO goes up to cca. 10^-7. While it is chemically measurable and makes the rain acidic, after some time the oceans take the nitrates and their molecule number dominates the atmosphere almost thousandfold, so the very thin salpetre acid becomes even much more diluted. Maybe some environmental damage is present but not an overkill to 97 %. Also, a 10^-7 concentration of NO is not an anoxy.

However Ellis & Schramm emphasize that nitrogenoxides catalise the decay of the ozone shield. They guess that an SN at 10 pc would diminish the ozone concentration to 1-2 % of the present (for 300 ys), and then the solar UV can make the damage. For this I would return in Chapter 12.

Hard radiation, mostly g, would increase tremendously, albeit maybe only for hours at most; later radionuclide decay produces secondary g's for some months, but less.

Solid droplets might arrive too, later. However they would be very much dispersed. It is difficult to tell, what elements would be expected (but see [23]): one could argue for Fe and nearby elements in the periodic table. Surely no compounds would come.

The primary meteorologic effect would be small, because insolation would increase by cca. 1 %. However shortrange disturbances surely would occur.

If anybody expects more effects, definite calculations are needed.

It seems that, apart from damages in the ozone shield, really serious effects could be experienced from an SN nearer than 1 ly. Then the optical brightness would still be below that of the Sun, but marginally comparable for months, UV much higher for months, g tremendous for hours, climate much warmer for months and unpredictable for say one year. And still no anoxy via NO formation.

The P/T boundary is possibly the second largest extinction in Earth's biosphere; the first was between Vendian and Cambrian, killing all Vendobionta and a lot of Radiata. Some authors go up to 97% of the extinct species. The extinction was more thorough in the seas than on land.

During the Permian there was a glacial period with many advances and retreats of glaciers. It seems that the southern hemisphere was more ice-covered, just as now. Such repeated glacials did not happen between Permian and Quaternary.

Many authors report severe anoxia from the seas at end-Permian. The atmospheric conditions are less known, but many Siberian volcanoes started to work "simultaneously", so polluting air. For Permian and Triassic temperatures and atmospheric conditions see [25].

In the Plant Kingdom the Mesozoic composition is characteristic from Middle Permian (gymnosperms instead of lycopods). During Permian the dominant land animals are the synapsids; first one sees adaptation to cold climate, then, at P/T boundary their sizes shrink. Obviously some environmental conditions were bad at P/T. But otherwise the evolution of synapsids continued. See Ref. [26].

The crisis was long; some authors see a 10-20 My period of "bad times". Now, if it was so long, then the 97% extinction at species level is an artefact. Namely the human/chimpanzee split was only 5 My ago, and donkey/horse split 2 My ago; so if we wait 20 My, almost all species extant at beginning will be extinct at the end even without specific extinctions. However I do not doubt P/T extinction: it happened at family and order levels too. Only I am not sure that the "97 %" is not an exaggeration.

While there is no major impact crater from the P/T boundary, spherules do exist. Miono collects them from Japanese and Chinese layers. In the Sasayama layers (near Osaka) he found iron nuggets (not spherical) at P/T [27], but he reports them from Cretaceous and Jurassic layers too. The composition is mainly iron, sometimes with Cr and Ni as major components, and K, Ca, Ti and Mn as minor ones; as if the matter were primary product of terminal stellar fusion. From some layers he could collect really spherical objects too, and at least at one place the peak of spherule occurrence significantly coincided with the P/T boundary [28]. So called Miono spherules (spherical, mainly Fe) are reported from Hungary too, from Upper Permian layers of the Bükk Mnt. [29]. (One can see Japanese and Hungarian Miono spherules in [0].) Spherules are considered necessary conditions to identify an impact. The problem is that there is no crater, and the overwhelming majority of spherule matter (~97%) is generally the ejected terrestrial matter, but the Fe+near-iron composition is not that of terrestrial crust.

In February 2001 Luann Becker and coworkers found He3 in P/T fullerenes [30]; and from compositions they concluded that a 9 km carbonaceous asteroid made an impact. Then the Siberian volcanism started and this led to a rapid catastrophe. An alternative suggestion is a cometary impactor. Japanese, Chinese and Hungarian layers contained the He3-bearing fullerenes, and Hungarian samples contained the lest fullerenes. (The Hungarian samples come from the locality Bálvány, just from the neighbourhood of the highest peak of Bükk Mtn. But Becker doubts if they are from the exact P/T border; I do not know the opinion of Hungarian geologists.)

Now, I doubt if this was the last word about the P/T event: e.g. carbonaceous chondrite meteorites contain low (C3) or no (C1, C2) metallic iron [31], and then Miono's Fe nuggets remain unexplained. However the kinship of Japanese, Chinese and Hungarian P/T layers was a commonplace in Japanese, Chinese and Hungarian geology at least from 1997, and IGCP 384 (led by Cs. H. Detre and Y. Miura) started to look for these similarities. (I belonged to the collaboration until its untimely stop on the Hungarian side.) I emphasize the fact that the few tentatively Miono-type Hungarian spherules [29] were collected (as far as I know, due to strange information exchange at the Hungarian side of IGCP 384) also from the Bükk Mnt. P/T layers. Anyway, Luann Becker's results strongly prefer impact at P/T boundary, either asteroidal, or cometary.

The next Chapter compares the SN, impact and cloud scenarios. Note that the original text is from 1998 [32].

This Chapter is an edited transcription of a lecture in Tsukuba, 1998 at TISS 2, a spherule conference [32], with very brief comments here and there, marked with C.

Although data are accumulating about the biggest biologic catastrophe of the Phanerozoic, the huge extinction at the P/T boundary, and there are good hopes to establish a global spherule horizon with iron-oxide spherules, we still do not know what was the mechanism. Even of extraterrestrial influence at least 3 mechanisms are possible: a nearby SN, encounter with an interstellar cloud and an impact of an asteroid. We collect here quantitative predictions for 4 effects: spherule surface density, anoxy (in the atmosphere), thermal changes in the atmosphere and mutagenic radiation. The size of the present paper does not permit full derivations; a more substantial paper is planned. [Still planned; C.] The way of presentation goes as follows. In each of the mechanisms first obvious order of magnitude data are chosen, and then further quantitative number constants, defined in due course, are denoted by small Greek letters.

The mechanisms are defined as follows. 1) is a nearby SN at a*10 ly, ejecting b*1 solar mass in g*0.1 mm grains with d*7.8 g/cm³ density. 2) is an interstellar cloud of atomic iron, with atomic density e*100 1/cm³ and l*1 ly diameter; Earth passes with the 20 km/s relative speed to neighbours. 3) is an iron asteroid of m*1 km radius. From astronomical observations a<<1 is improbable, b~1, e~1 for bright clouds and ~10 for dark ones, and l<100 for bright ones, and <1 for dark ones; m>10 is improbable. See e.g. [33].

Now the results are as follow:

Surface density of incoming iron droplets from a nearby SN is definitely smaller than

(9.A1) S(SN) = 0.0545(b/a²g³d) 1/cm²

since the majority of ejecta is H and He. For a cloud

(9.B1) S(cl) = 2.70*10²(el/g³d) 1/cm²

while for asteroid impact the effect is probably not global, but for a formal surface density we get

(9.C1) S(im) = 75.2(m³/g³) 1/cm².

For atmospheric anoxy we need first the present oxygen content. For the mass of present atmosphere the 510 million km² surface, 8 km equivalent height, cca. 29 molar mass and the Avogadro number gives

M_atm = 4.93*10²¹ g

Now the present O concentration is 21 %, so we take z*0.21*M_atm for end-Permian, z~1 [34]. We imagine the anoxy via consummation of some free O as FeO and similar with the positive elements of the incoming matter. [Ellis and Schramm have shown that NO formation does not lead to anoxy [24]; C.] Then for the relative anoxy

(9.A2) -DO₂/O₂(SN) = 6.29*10^-10 (b/a²z)

(9.B2) -DO₂/O₂(cl) = 3.10*10^-6 (el/z)

(9.C2) -DO₂/O₂(im) = 3.46*10^-6 (m³/z).

For temperature changes an SN causes them by extra insolation. SN simulations are manifold, for the classical work see [5]. Here we estimate it as converting 1 solar mass H into Fe (binding energy is then 0.008) and radiating with decay time 1 month; all other factor in h.

L(SN) = 5.55*10⁴⁵ h erg/s.

The present solar luminosity is 4.3*10³³ erg/s and the end-Permian value was smaller at most by percents [35]. So

(9.A3) DL/L(SN) = 3.26 h/a³

In the cloud and impact scenarios the entering mass is only some 6 orders of magnitude less than M_atm, so large cooling may have happened by "nuclear winter" mechanisms.

For mutagenic radiation the present global cosmic radiation is estimated as 10¹⁹ erg/s. Then

(9.A4) DCR/CR(SN) = 6.34*10⁵ hk/a²

where k~1 is the part in hard radiation. [For a more elaborated estimation see [24]; C.] In the other 2 mechanisms there is practically no enhanced mutageny.

Consequently, as seen, SN would cause cca. 4 orders of magnitude less spherule density than the others. For anoxy, SN influence seems nil [as formulae of [24] have demonstrated; C], at the cloud the transition time is 1.50*10⁴ l y. If we explain the > million y duration of anoxy [36] with transition, then l~100 (permitted) and with e~1000 (high?) the anoxy will be large. If the asteroid triggered the Siberian lava flow [37] as the dinosaur killer did the Deccan one, then the anoxy could be almost anything.

For temperatures SN would increase for months, the cloud would cause indefinite decrease for million years and the impact a very serious decrease for ~ 1 y. The mid-Permian glaciation is fact [34], but it is possible that we see the previous Fowler cycle [38]. Since the dominant land animals were mammal-like synapsids [39] on the way of homeothermy, fur, double circulation and lactation, they could easily survive temperature changes, as they did indeed.

The mutageny from SN is serious, from the other 2 effects nil. My opinion is that we do not see mass extinction & speciation by induced mutation; e.g. Dicynodontia lived from the first half of Late Permian till later Upper Triassic, while land plants performed the great extinctions in Early Permian. Cf. too [26].

In Chapter 3 I gave a list of 9 historical and 2 almost historical SN’s. However I told that it is only one list of the possible ones. So now let us revise the list once more, from two viewpoints: maybe not all the 9 historical items of the list were supernovae, and, in the same time, others may have existed. Since the list is important mainly for statistics, we do not go beyond AD 1. In that time there was already some astronomy in China and in the Mediterranean.

A galactic SN should be visible for naked eye: the maximal distance is some 20 kpc, which would mean at most 17 magnitudo difference to absolute brightness, so even a Type II SN would be at least first order star for weeks. (Indeed, even the Magellanic SN1987A was third order star in peak.) Of course, absorption may hide some SN’s, but that is maybe an exception.

Now, let us go backward in time. SN’s 1-4 are without doubt even if SN 1 was not observed. SN 5 from 1006 is also generally accepted, although it was slightly faint. The next two supernovae are rather doubtful and many lists omit them. They are known from Chinese sources as "guest stars". Surely something was seen in the neighbourhood of the celestial position indicated in my list (the coordinates are guesses from the old Chinese report + the radio source, not necessarily the same phenomenon), but for example they may have been novae as well. SN 8 is doubtful too: some lists give AD 396, some 393 or 386, and there is no consensus about the remnant. Finally, SN 9 from AD 185 is widely discussed.

Thorsett [40] claimed in 1992 that he had found its remnant, including a pulsar, PSR1509-58. In the same time Manchester [41] expressed his doubts on the ground that the pulsar seemed too old. Then came Chin & Huang and told that for everybody understanding Chinese well it must be clear that the "guest star" was a comet [42]. Clearly it is pointless to continue here the argumentation.

On the other hand, there are new SN candidates. Since anybody can suggest a past supernova, here we mention only two serious suggestion.

Source 3C58 (G 130.7 +3.1) is a 9’x5’ source at RA 02h05m41s D 64°49’. Recently it is frequently considered as the remnant of SN1181, which was reported as a "guest star" by Chinese, and also by Japanese. The maximal apparent brightness of the guest star seems to have been m=-1 magn., so the SN seems to have been far enough.

Source RXJ 0852.0-0462 (G 266.2 -1.2) was suggested to be an SN remnant from cca. AD 1320. Namely, the remnant seemed to be young [43]. It was estimated at 200 pc with an age cca 680+/-100 y [44]. In Antarctic ice cores nitrate deposits were found at cca. 1320 which, then, was considered as the trace of a nearby SN [45], [46], although not stronger than much farther SN 1604, 1572 and 1181. However recently Slane & al. put much farther, to 1-2 kpc, RXJ 0852.0 -1.2 [47], and Mereghetti [48] suggests a neutron star as remnant with age few times 10,000 y.

These two cases show the difficulties of identifying historical supernovae; but also they demonstrate that it is not at all sure that all suggested SN’s were indeed SN’s of historical ages. So it is not impossible that the number of galactic SN’s were cca. 9 in the last 2000 years.

From the above list one would get one galactic SN in 220 years, however with some error, hard to estimate. However now all detailed estimates give higher galactic SN rate; no surprise, maybe galactic absorption has hidden some SN’s in historical times. While Zwicky’s classical rate (for extragalaxies) was cca. 1/300y, it seems that in the present years the two extrema of estimations at least applicable to our Galaxy too are Chai & van der Bergh [49] which is 1/100 y, and Tammann [50] which was 1/(26+/-10 y), but later the author himself corrected it to 1/(40+/-10) y [51].

The new guesses are somewhere near to 1/50 y. I will take for definiteness’ sake the very detailed [52], which is

4 SN Ia, 2 SN Ib, 12 SN II in 1000 y

so 1/55 y.

Ellis and Schramm argue for an even higher SN rate 1/10 y [24]. Their main argument is the very existence of Geminga. However their rate goes against all extragalactic experience.

There may be a way to reconcile the contradiction. E.g. they argue that SN1987A would have been unseen if in a farther galaxy; so there may be dim SN’s not seen in extragalactic observations. And indeed, majority of gravitational collapse precursors have too high angular momentum for a "classical" SN process [7], [8], as told in Chap. 2. Some of them may produce a very dim SN.

Or not at all. A supercritically rotating sufficiently big star will start its gravitational collapse. Probably the majority of its matter will go into a Kerr black hole. However some part may escape on the equator [7]. And no collapse calculation exists for a genuine nonspherical situation. So nobody has ever shown that the majority of collapse precursors would produce UV and g flash, n bursts, charged particle bursts &c; that such a collapse would lead to ("true") SN event. Maybe yes, maybe not; and we have not identified such "mild" processes. We definitely do not see SN in each decade (we did not see since 1604…), and anyway "very mild SN’s" would not cause mass extinctions. It is better to remain at Cappellaro & al. [52].

We can be fairly certain that we do not lose too much supernovae from near extragalaxies. If there the inclination is high, absorption is not too much. The estimations of this Chapter have combined galactic and extragalactic methods.

I admit that the comparative list of Chapter 9 is not complete. For example, from amongst oxygen-eating mechanisms I calculated only oxidation of the incoming matter. However I methodically compared 3 mechanisms; if one find this insufficient, he may do what is thought necessary. From the incomplete work I would prefer the galactic cloud. From lectures on TISS 1 conference, Tokyo, 1997 it seems that S. Miono took this as the most probable mechanism behind the Paleozoic iron nuggets, at least in 1997 [53], [54]. And indeed, clouds can at least relatively easily explain the long duration of the crisis, and not too absurd for the anoxy.

I think, the meteorite impact cannot explain meteorology. It is a single event, which, with "nuclear winter" mechanisms, can cause anomal weather for some years at most. To be sure, we may find some moderate crater in Upper Permian; they are not very rare. Asteroid impacts may have contributed to the crisis. But my feeling is that an impact alone could not explain the P/T extinctions, while it seems proper to K/T.

And now the SN Overkill. One SN cannot act for 20 My. Its UV radiation lasts for weeks. Its primary g radiation lasts for hours, the secondary (from the decay of radioisotopes) for months. The expanding shells far from the SN can collide with the interstellar gas and then (only once) some X-rays can be generated. From the boundary of the Solar System we can guess that this happens ~10 y after; and then the bad effects stop; except, of course, solar UV with damaged ozone shield. Spherules may be formed and may reach us, but in small numbers.

A really close SN, however, can kill. Also, in the atmosphere its UV and maybe g-rays can initiate NO-formation; and even Sun can kill without the ozone shield. Then, as the SN scenario claims, the dead biomass will putrify, the atmosphere will be heavily polluted and altered, and that causes the long crisis.

Personally I doubt this scenario. The 20 My crisisis too short and too long. OK; the SN damaged the ozone shield for 300 years. Then there are two possibilities. One is that the mortality simply (!) tremendously goes up, therefore some taxa die out; for 300 years. Afterwards the crisis is over. Or simple biochemical processes kill almost everything. Ref. [0] prefers this; but let us calculate.

For simplicity let us start with the scenario now. We saw that the mass of atmospheric oxygen is cca. 10²¹ g. The mass of humanity is well below 10¹⁵ g, and humanity is a non-negligible part of the mass in Regnum Animalia. So now all animal organic matter would be insufficient to use up half of the oxygen. Of course putrefying matter can infect, poison, &c. But if the circumstances are so deadly, maybe everything will go back to microbiology. And they did not. Or were we (our direct ancestors, the synapsids) so strong as the scenerio suggests? That during the global death and putrefaction our ancestors proudly walked erect (albeit dwarved), not in posture, true, but at least for hindlimbs (parasagittal, if one likes better), which was something sure for Permian)? Because paleozoology proves that end-Permian environment was not deadly for us, synapsids, although not optimal either. And the atmospheric O2 level was already decreasing since the C/P boundary [25]; this process is not Upper Permian. Briefly, it seems that paleontology does not support too much the scenario.

If somebody still likes this scenario, he has the possibility to prove it. For any case it has not been proven up to now. Even probability considerations are heavily against it. Let me repeat. Zwicky observed one SN per one galaxy in 300 years. Our table shows 9 in the Milky Way Galaxy in the last two millenia, so one in 220 years. Finally according to the Cappellaro guess [52], which is higher, I take a rate as 4 SN’s in 220 My per 100,000 stars. In our well researched 17 ly neighbourhood we find 60 stars including very faint red dwarfs. Then between us and end-Permian the expected distance of the nearest SN would be some 125 ly; a nearer SN is of course possible accidentally but not expected. A 125 ly SN will not make overkill and definitely will not turn seas into dilute salpetre acid. To see the SN scenario everybody can calculate the formulae in Chap. 9 with a=12.5. Unfortunately we do not know such nearby SN for comparison, but anyway, Vela SN, maybe only from 1000 ly, did not kill us even via deteriorating the ozone layer, not even in Australia.

It is possible that Earth was very unlucky with an accidental SN very near 240 My ago; but then some evidence should be found in the layers for that SN. It is not the orthodox way to explain a catastrophe with a very improbable event not seen by anybody.

I think the SN scenario relies on something I would call saurian principle, (albeit, maybe, drakonic would be more direct analogy to anthropic). Let us see. Anthropic principle works in the way: something (e.g. an initial condition; a fluctuation) seems to have been improbable. However all others would (would have? did?) lead to a story without us. Now, the correct statement is: we have measured quantity X and found value x, which means that the initial condition was x. But with sufficiently different x’ initial conditions (values x’) we would not exist. Therefore it is impossible that we measure x’. Then what is the meaning of probability?

Although this way of thinking may be dangerous, it is formally correct (and in an Everett-type Quantum Mechanics, popularly known as Parallel Worlds it is even meaningful). However now we are confronted with a concurrent principle.

Beware: the P/T events were against us. Without it synapsids would have flourished from Triassic upwards, not hiding in the shadows of diapsid saurians from Jurassic (see also [55]). Mammal intelligence was delayed by the P/T events for 100 My, while saurian intelligence did not appear even in this extra time. The Permian catastrophe then was not necessary even in the sense of anthropic principle; it simply happened. And saurian principle is not strong enough against probability; if we want to know what happened, we must clarify it according to the orthodox although boring ways of physics, mathematics, astronomy, paleontology and so on.

As for the almost historical SN scenario of Vela X (in Dryassic, not in Triassic), it happened in a very important time and it would be important for history to know the details of the event.

The topic of this Chapter does not influence the final picture. It is rather only to be written to show that: look, I am so circumspect that I am thinking about all possible counterarguments; but even then I am right. (In fact, I have to think instead of my opponents too, because they do not discuss the question with me.) So: there is a situation when the SN rate goes up. It is just about entering a spiral arm.

The structure of the Milky Way Galaxy seems to be the following. The original (?) axial symmetry of the rotating matter is spontaneously broken now, and there are cca. standing waves of spiral arms of deeper gravitational potential [56]. Then, secondarily, matter is also denser here (see the Vlasov equation), but only moderately. However at the boundary of such a spiral trench the potential gradient helps the creation of new stars. Because of massive young stars, bright, but not living long, the spiral structures stand out optically.

The spiral potential trenches rotate rigidly, but generally the orbital velocity of matter is different. Now, consider a past time when the Solar System was just entering a spiral. SN rate is generally low because most of neighbours are long-living stars below solar mass which cannot give SN's. But the situation is different when just entering a spiral and lot of young massive stars are around.

Of course I cannot give this higher rate. And while it is quite possible that the Solar System entered a spiral just during Permian, nobody has yet proven this. It could be; both the orbital and the corotation velocities can be measured at Sun's galactic position, only (?) the second is not easy and even moderate errors will grow up in 250 My. But if somebody likes an SN scenario, he is expected to explore this possibility.

As I told, I am not overly interested in the SN rate. Imagine that a lot of supernovae made fireworks around us at end-Permian. Then according to Ref. [24] each damaged the ozone shield, repeatedly. But, as I think I showed in the last Chapter, the resulting history is not our history. Without ozone shield everything would have died on land and in shallow waters (down to 10 m?), and after some Mys the lands would have been colonised second time by some Crossopterygians. From the putrefying lands of deaths no proud (albeit small) synapsids could have walked out with erect posture (of hindlimbs). Please, reconsider arguments about synapsids able to go to shadows at UV radiation and such. One cannot be continuously in shadows or holes even for the 300 year of one ozone shield damage [24]. The end-Permian catastrophe was relatively mild to land animals and did not appear in the replacement of Palaeophytic taxa (for plants the replacement happened in Lower Permian.

Briefly: for my opinion the problem of P/T boundary is not the problem, how to kill many species. For that various scenarios can be suggested, e.g. the SN one. The problem is to kill those who have been killed and to spare those who have been spared. And we cannot lazily refer to anthropic principle; I would suggest great caution even if referring to Providence. We, synapsids, did survive the P/T catastrophe, proudly, with erect gait. But in this process of survival from the position of continental lords of Ancient Earth we fell back to weak seconds. The Medieval Ages of Earth became the age of diapsids, and for 100 My we were tiny shrews under the feet of dinosaurs. To explain such a story I think general putrefaction, brown skies and salpetre acid oceans are not properly pointed.

And: are Miono spherules explained by 5 subsequent supernovae? I do not think so.

My opinion is that Project IGCP 384 "Impact and Extraterrestrial Spherules: New Tools for Global Correlation" has not proven the SN origin of the P/T catastrophe. Of course, this was not its task either. The original goal was to study worldwide spherule types, with an emphasis on P/T spherules.

It seems that we know two such types. The first is the Miono type, the second is the 1 (one!) spherule mentioned by A. Azmi on the PIECE’99 conference in Yamaguchi (Sept. 1999) from Kashmir.

Maybe Dr. Azmi will get more P/T spherules; maybe he already has. Then their composition can be studied. But we (?) have Miono spherules anyway.

If they are characteristic to P/T boundary (and, I think, Dr. Miono has proven it at least for one site [28]), then they are good tools to see what happened at P/T. Chemical investigations would be useful, they indeed happened, but I do not get clear information because the leadership of the Hungarian side of IGCP 384 ceased to work. However I list the possibilities and the investigations which, for my opinion, were still necessary.

Without answering these questions or at least a substantial part of them I think it is difficult to see what happened at the P/T boundary. Of course it is possible that it was not the purpose of IGCP 384. For any case, I cannot prove that there was not a nearby SN event during the 20 My of the end-Permian crisis. According to Vela X and Geminga, very probably there was one; maybe even at 10 pc, damaging the ozone shield. I only state that for my personal opinion the assumption of such a supernova cannot substitute the answering of questions 1-8).

Partly supported by OTKA T/026660. Illuminating discussions with Drs. Y. Miura and Sh. Miono, and in general with the Japanese half of the IGCP 384 are acknowledged. Also I acknowledge the role of my tutor, A. Frenkel, in my SN work for Ph.D. degree at the beginning of 70's.

***

My goal and purpose with this material was primarily to produce something at least resembling a resume if (as I am informed; maybe incorrectly) the Hungarian side of IGCP 384 stopped its activity. Fortunately, discussion of impacts belongs to the activity of OTKA T/026660 "Thermodynamics of Meteorites and Asteroids". If the end-Permian catastrophe was caused by an impacting asteroid (which I do not believe but Luann Becker does) then spherules of special compositions should be found; the composition of the impactor can be known from meteoritics, and the transformation into spherules is a complicated thermodynamic process.

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July 17, 2001

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