Active Galactic Centers – do they house a Burning Disk (BD)?

Among the foremost unsolved astrophysical problems of these decades are the structures, and working schemes of the central regions of galaxies, called “CEs” (:= Central Engines), “AGNs” (:= Active Galactic Nuclei), “UMOs” (:= Unidentified Massive Objects), or more recently “SMBHs” (:= Supermassive Black Holes).

In the (nearest) case of our own Galaxy, the CE is agreed to be the unresolved broadband point source Sgr A*, at the rotation center of the Milky Way disk, whose mass has been determined as ≳106.4 M (from the Keplerian periods of several orbiting S-stars), and whose emission is variable on all timescales down to an hour or even much shorter, down to 0.1 min, and ranges in frequency from GHz up to PeV energies. In my understanding, Sgr A* is the innermost part of our Galactic disk, a “Burning Disk”(=: BD), a flat star, of stellar mass density, stellar height (= some 1012 cm), and of radius some 1014 cm, as likewise calculated by Endrik Krügel & A.Tutukov in A&A 158, 367 (1986), and by Ian Roxburgh in MNRAS 264, 636 (1993). It is this innermost part of our Galactic disk in which its growing mass density – for inspiralling matter – reaches stellar values, and therefore starts nuclear burning – like stars – feeding our Galaxy’s BLR, and NLR, with its stormy outflow (of 10-2.5 M/yr, at 103 km/s), and launching our (feeble) Galactic twin jet, (which has been mapped out to large halo distances).

None of these central structures of our Galaxy is unstable to BH formation, or has been unstable to such in the surveyable past, hence no hint at a SMBH anywhere near Sgr A*, or anywhere else in our Galaxy. Above-mentioned outflow requires a steadily blowing powerhouse – unlike what BHs could do, if such existed – as well as above-mentioned twin jet, whose source should be a heavy, magnetised rotator, like for all the other well-understood jet sources, and as well as the hard Fermi Bubbles, see Fig.1. All these facts, and reasonings, have been discussed, and documented in my books edited in 1996, 2005, and 2014, whereby my present understanding of the functioning of jet sources is first presented in Kundt & Krishna (2004). In my most recent writeup on Sgr A*, I hold 28 independent reasons against a SMBH in the core of our Milky Way.

Fermi Bubbles of the Milky Way

Fig.1: Buoyant CR-bubbles in the halo of our Galaxy mapped at 408 MHz, centered on SgrA*. (Credit: Fermi/NASA GSFC)

An extreme case of an AGN has just been reported in NATURE 543, 83 (2017) by M.L. Parker et al, the Narrow Line Seyfert 1 galaxy IRAS 13224-3809, at redshift z = 0.0658, whose outflows are even relativistic, of speed ≲0.24c, and whose absorption redshifts signal nuclear burning, up to Fe XXV, or even Fe XXVI. Again, the core of this active galaxy appears to be powered by a nuclear stove, a BD, keeping its fountain-like, transrelativistic motions active throughout Myrs, or longer. A SMBH, even if such had not been ruled out in recent investigations (Kundt, 2015), would fail for many reasons. Even worse: it would have grown spectacularly via accretion,  and swallowed our solar system, already a long time ago. Similar well-studied galaxy-scale fountain motions have been recently encountered in the nearby massive, active galaxies NGC 3842, 4859, and 1600, as well as in Mrk 1018, and in the brightest cluster galaxy in Abell 2597. Swallowing BHs would have prevented their steady powering.

Another strong (statistical) argument against the presence of SMBHs in the centers of active galaxies is the monotonic decline of their masses with cosmic evolution, from an initial ≲1010 M, near z = 4, to a present ≲107 M, as shown by the SDSS plot, in Fig.2; SMBH masses should have grown, not shrunken with time.

Black Hole Masses

Fig.2: SDSS plot of unresolved CE-masses of 14584 galaxies, as functions of their ages, as measured by their redshifts z (in the range {0.2, 4.5}); red squares denote mass averages for fixed z. (Credit: SDSS DR3, Vestergaard et al. 2008, ApJ 674, L1)

In summary: I feel like the little boy in the fairytale of the emperor’s new dresses: I see BDs, where most other people (have learned to) see SMBHs. In my view, the cores of galactic disks burn even faster, and even more intensely than their surroundings, like BDs. They re-expand the infalling matter.


  • Kundt, W., 1996, ed.: Jets from Stars and Galactic Nuclei, Lecture Notes in Physics 471, Springer, 1-290.
  • Kundt, W., 2005: Astrophysics, A New Approach, Springer, 1-223.
  • Kundt, W., Krishna, Gopal, 2004: The Physics of ExB-drifting Jets, J. Astrophys. Astr. 25, 115-127.
  • Kundt, W., 2013: Our Galactic Center – the nearest Burning Disk, Vulcano Workshop 2012, ACTA POLYTECHNICA 53, Supplement 2013, pp. 506-512.
  • Kundt, W., Marggraf, Ole, 2014: Physikalische Mythen auf dem Prüfstand, Springer, 1-445.
  • Kundt, W., 2015: A brief Observational History of the Black-Hole Spacetimes, Advances in Mathematical Physics, doi:10.1155/2015/617128.
  • Kundt, W., 2017: Sgr A*, the best-sampled of all AGN, PoS(MULTIF17)050, 1-12 (2017).
  • Kundt, W., 2018: Gravitational Astrophysics, PoS(MULTIF18)016.

Gravitational Waves from a coalescing Neutron-Star Binary ?



On 14 September 2015, the first gravitational-wave signal ever was detected, by the two ‘Advanced LIGO’ antennae in North America, 100 years after Einstein’s prediction, and published (in Phys. Rev. Letters) on 11 February 2016 by a team of more than 1000 authors, interpreted as the coalescence of two stellar-mass Black Holes not far from the edge of the observable Universe. How has this interpretation been reached?

A simulation shows gravitational waves coming from two black holes as they spiral in together.

A simulation shows gravitational waves coming from two black holes as they spiral in together. [S. Ossokine, A.Buonanno (MPI für Gravitationsphysik), W.Benger (Airborne Hydro Mapping)]

In the summer of 1971,”Black Holes” (BHs) were baptised by Princeton’s John A. Wheeler, backed up by his young guest Remo Ruffini (from Rome) as well as by their mental father Stephen Hawking (from Cambridge, England) and his supervisor Roger Penrose, and a handful of other pioneers around the world. The BHs were believed to be the final outcome of gravitational collapses of massive bodies under gravity – more massive than some 3 solar masses – because General Relativity teaches that such a collapse cannot be halted by (even extreme) pressures, pressure being heavy, hence eventually counteracting itself. But this belief has turned out to be erroneous: Try to drop a solar mass quasistatically onto a neutron star, you fail. You will ‘recycle´ the neutron star, i.e. spin it up towards higher rates – flattening it towards a compact disk – because the `dropped´ matter reaches it at almost the speed of light, and at extreme angular momentum. No BH will form; we all overlooked this possibility.

Over the years, a large number of BH candidates have been proposed, such as the massive X-ray binary Cyg X-1, the supermassive center Sgr A* of our Galaxy, and others, but have all been invalidated because of (respectively) their ability to blow jets, their various powerful outputs, and their emission of the (hot) He II line 4686 Å, characteristic of a neutron star; see Kundt & Fischer (1989), and Kundt (1996, 2014, 2015). We should not be worried, though, because there are many hurdles to a complete gravitational collapse, in particular in a young cosmic environment like ours, containing abundant nuclear fuel, like hydrogen, helium, and other light nuclei (whose detonations can help at re-expanding matter condensations), and because of angular momentum.

The first true candidate for eventual gravitational collapse – in about 108.5 yr from now – has been the Hulse-Taylor Binary Pulsar B1913+16, discovered in 1974 to lose orbital angular momentum due to the emission of gravitational waves. And we now know several more of these fusing binary neutron stars in our Galaxy, all candidates for eventual gravitational collapse, and candidates for the eventual emission of strong gravitational signals. Has the 14-September event been one of them? My answer reads “yes”, quite likely so.

But hasn’t the careful evaluation of GW150914 yielded masses of order 30 M for the two coalescing objects, much larger than those of a neutron star? I am not convinced, for two independent reasons. The first reason is that BHs have meanwhile been proven to be of measure zero within the class of all collapse solutions, (by several independent authors): During collapse, it is infinitely unlikely that all higher multipole moments (beyond the dipole) are radiated to infinity. This insight was published in Scientific American in February 2009, by Pankaj Joshi, and literally reprinted four years later, in May 2013. Moreover, on 22 January 2014, Stephen Hawking expressed on the internet: “BHs do not exist”.  Even worse: ancient BHs would have grown via accretion, and swallowed large parts of the Universe by now, including our solar system. All this is my first reason, (to no longer believe in the availability of BH binaries).

My second reason for not trusting the “30 M” of the (> 103) authors of B.P. Abbott et al (PRL 116, 061102 (2016)) is that they have been derived from the “chirp mass”

M(f, f) = (c3/G) [(5/96) π-8/3 f-11/3 f]3/5 ,

a first-order approximation obtained from Landau & Lifschiz II §102 (1963) for two point masses m1, m2 orbiting around each other on circular Kepler orbits at not too high velocities, and not too large mass densities, by differentiating their (doubled) orbital frequency f(t), and re-expressing it as a function of the involved masses. This appealing first-order approximation has stood its observational test for wide binaries like the (present) Hulse-Taylor binary pulsar, but is unlikely to equally apply to its (final) coalescence phase, during which the two (magnetized) stars are no longer pointlike, and during which tidal forces are expected to strongly modify the functional dependence of both f and f on the two masses. My estimate holds for such a coalescing neutron-star binary, at a (mass-controlled) distance of <~ 30 Mpc, whilst revolving around each other a few times with a shrinking orbital radius r <~ 107 cm, at a growing orbital velocity v >~ 10-1 c. It will have ended up as a heavy neutron star inside a cloud of ejected splinters, formed from r-process elements.


References in the text:

Tunguska (1908) – Impact or Outburst ?

When at 7 o’clock in the morning of 30 June 1908, hell broke loose near the townlet Vanavara – located on the Siberian river ‘Stoney Tunguska’ – both eyewitnesses and scientists believed in an impact from outer space, even though at second thought, at least 30 facts speak against. Already the duration of the crash – more like an hour than a few seconds – argued against an impact. And so do the large size of the destroyed area – comparable to the German province ‘Saarland’ – and the zero net momentum of its (quasi-radial) treefall pattern, which follows the ridges and the valleys of the mountainous ambient area, issuing from its center. Conspicuous was likewise a central area of ‘telegraph posts’, viz. tall trees that had lost all their branches, reminding us of certain trees in Hiroshima that were similarly crippled by the supersonic storm blown by the first dropped nuclear bomb.

(partially burnt) root stumps

One of the many (partially burnt) root stumps which were thrown into the surroundings of the big gas ejection, in the morning of 30 June 1908, still lying there when photographed, after 93 years (Photo: W. Kundt)

Quite generally, impacts of meteorites – comets or asteroids – are at least 20 times rarer than volcanic outbursts of the same destruction energy: Here on Earth, we live in a rather sheltered region of the Universe. Clear evidence against an impact were not only the size and the structured morphology of its treefall pattern, but also the facts that a) the sounds – barisal guns – and pressure waves – overthrowing people and horses – reached Vanavara and its environs earlier than did the lights in the sky; similarly behaved b) the recorded seismic and atmospheric waves between the site and Irkutsk, whereby a strong shock wave raced once around our planet during one day, known before only from the first hydrogen-bomb test in air. c) Root stumps of trees were thrown through large distances from where they had grown, after having been broken loose from their trees. d) One of the stumps was later detected by Leonid Kulik, at the bottom of a conical lake (called “Suslov Hole”), rather undistorted, unlike objects inside impact craters, and e) “John’s stone”, weighing 10 tons, had landed on the slope of Mt. Stoikewich, at sonic speed. Moreover, f) the 3.5 accompanying bright nights of the holocaust – between Asia and Europe – asked for large methane ejections towards and up into the ionosphere.

During the >≈ 100 years after the event, a lot of further evidence against an impact has been collected, in the form of g) dispersed diamonds, h) a complete absence of detected extraterrestrial matter (<≈ 10-10), i) outgassing of radon from the near Lake Cheko, and j) via the preferred location of the site, adjacent to the (Kulikovsky) paleovolcanic crater, near the crossing point of several tectonic fault lines which, at the same time, marks a
center of Asian heat flow, and of geomagnetic activity. Finally, k) during the year of the catastrophe, the recorded local earthquake activity grew steadily until the day of the eruption, when it culminated.


The Circulation of Water inside Plants, pumped by their Hearts

Just like animals (and people), plants must permanently perform work in order to grow and survive, only at much slower speeds. For instance, grown-up palm trees lift a ton of water per day into their crowns.


Plants suck in soil water through their roots, and pump it up towards their leaves, branches, stems, fruits, and also back to their roots, for supply with photosynthesis products. The upward transport happens through their xylem tubes, the downward transport through their phloem tubes. In all these cases, tube water flows downhill w.r.t. the water potential ψ, the latter being defined as the (weighted) sum of all pressures: gravitational, pressurized, osmotic, and imbibition:

ψ = ρ g z + p – π – τ ;

whereby osmotic suctions are most important in (not too small) plants as they can be easily controlled – e.g. by converting starch into sugar – and as they are strong enough even to lift the water up to the crowns of the tallest trees, of height <≈ 140 m, and also force nutrients down into the ground through their long, penetrating roots, at pressures reaching up to 15 bar and more [Kundt (1998), Kundt & Gruber (2006)].

Such a transport of solutes by water has a number of important properties, which are guaranteed by suitable (densities of) membrane valves, in particular inside two or more membranes in series (in the endodermis plus sometimes exodermis) containing (a huge number of) pumping ‘hearts’ which propel clean water, just like the hearts in animals pump their blood through their bodies.

Quite likely, these pumps act like heat pumps [Kundt & Robnik (1998)]. This transport realises a steady supply of nutrients at roughly constant pressure inside the tubes, from the ground to the leaves – supported by a sequence of inclined, transverse ‘valves’ – and at the same time establishes the familiar (strong) root pressure that guarantees a steady penetration into the ground of their (growing) roots.

And where does the circulating water supply end? In the leaves, and in the fruits? By evaporation, during respiring? Not enough: A natural end of this circulation is ‘guttation’, the squeezing out of (almost pure) water by, or near the consuming leaves. Guttation discharges excess water from what has been supplied by the sucking roots. It helps establishing the osmotic gradient in the vertical water columns.

Historically, the above interpretation was first given by Acharya J.C. Bose, see: Collected Scientific Papers 1895-1918, Bose Institute, Calcutta, 1996, (22 + 592) pages, in particular pp. XVIII & XIX.


References in the text:

The Extragalactic Gamma-Ray Bursts ?

Our planet Earth emits one very short gamma-ray burst (GRB) per day on average, (<≈ 5 ms), and receives ≈ three GRBs per day from all directions, usually with durations Δt of 10-2 s <≈ Δt <≈ 30s . But even frequent precursors, and postcursors to these bursts have been recorded, and recently even long, and ‘ultra-long’ bursts, with durations <≈ 105.5 s, and with comparable inferred energies ∫ L dt <≈ 1038 erg (d/0.3 kpc)22 (for estimated distances d, and for measured Lorentz factors γ <≈ 5 ). Their energy spectra
range from 10 KeV up to 10 MeV, occasionally even up to 10 GeV, or even 10 TeV, with peak values near 1 MeV.  Their distances (<≈ kpc) are restricted by fundamental constraints, based on the bursts’ spectral hardness. And they are all followed by waning, broad-band, years-long ‘afterglows’ of all photon energies <≈ 10 GeV. Where do they come from?

Crucial for a reliable answer to this (highly controversial) question is a correct determination of their distances d, derived from the relativistic red-shifts of their (rare, faint) spectral lines, from the (controversial) visibility of their ‘host galaxies’, from the small, though systematic anisotropy of their infall directions, but also from a convincing model of their sources. Clearly, their energies at formation would be gigantic for distances d of cosmological size, compared to local Galactic distances – of order 0.3 kpc – even if they were emitted in a highly beamed manner. My own conviction, which can be found in [Kundt 2014] and [Kundt & Marggraf 2014], interprets them as an accretion phenomenon by middle-aged Galactic neutron stars, often called ‘magnetars’.

scetch signal ellipses

Geometry of a light echo: The observer in the right focal point receives all those light rays at the same time which have been reflected or re-emitted at the same ellipsoid by suitable scattering material.

In greater detail: I interpret the GRBs as the upper end (in mass) of accretion by elderly Galactic neutron stars, the rare infall of heavy chunks onto the surface of a suffocated pulsar from its surrounding low-mass disk. Such a catastrophic infall creates instantaneous temperatures of T <≈ 1012 K, and (large) column heights kT/mg ≈ 106 cm, comparable to the neutron star’s radius, such that the accreted plasma is seized by its corotating magnetosphere, and centrifugally re-ejected at relativistic speeds, with Lorentz factors γ <≈ 5, mimicking cosmic redshifts of z = γ(1+β)-1 <≈ 9. When the relativistic ejecta crash into a burst’s CSM, they cause its (structured) afterglow emission, and seeming host galaxy’s light, all of a similar redshift; see above figure, which sketches the light-echo phenomenon.


Supernova Explosions

Novae are ‘new’ stars in the sky, or rather ‘suddenly brightening’ stars which had been previously too dark to be considered at their (large) distances, and ‘supernovae’ are yet more intensely brightening stars. The increases in brightness correspond to factors of <≈{106, 1010} respectively, in the two cases, due to increases of <≈ {103, 105} in the radii of their photospheres (for only moderate increases of their temperatures). Apparently, we deal with gigantic explosions in our cosmic surroundings, which involve either white dwarfs, or neutron stars, of radii ≈ {104, 10}km respectively. Why do they explode, and how?

One generic cause for energetic cosmic processes is the conversion of gravitational energy during the collapse of a cosmic cloud, successively into a hot star, of radius >≈ that of our Sun – some 1011 cm – then to a white dwarf, of radius >≈ 109 cm, and eventually to a neutron star, of radius >≈ 10 km. Yet further collapse – so we have learned from Pankaj Joshi [Scientific American, Feb. 2009] – would lead to a naked singularity, i.e, to an object that can no longer be described by Einstein’s GRT; but no such event has so far been detected. Even worse: Quasistatic collapse of a neutron star to a BH may even be prevented by the dynamic hurdle.

A lot of heat is created when a star collapses towards the (small) size of a white dwarf, and/or when ambient matter falls onto its surface; such processes are of nova type. But even much more heat is created when a white dwarf collapses through another factor of 103 in radius, to the tiny size of a neutron star. We then expect a supernova to be launched. But are we sure? With this question, we enter more than 50 years of controversial answers, following Shklovskii’s (1964) seminal paper.

Orion Molecular Cloud Outflows

Wide-field image showing the OMC1 outflow in H2 (orange) and [Fe II] (cyan) [Bally et al., 2015, A&A 579, A130]

So, how does a supernova (SN) function? How can ejected matter reach escape velocity from the vicinity of a neutron star without recollapsing, like a fountain? This condition cannot be fulfilled by a nuclear explosion – as is often assumed – it requires a relativistic ‘piston’, i.e. a pushing plasma whose particles have relativistic velocities. (Stellar core collapses reach only non-relativistic temperatures, of order T <≈ 1011 K, which cool as r-2 during radial expansion, whereas relativistic pistons cool only as r-1). In [Kundt 1988 & 2008], I have shown quantitatively that all the known types of SN – including those of type Ia – can be understood as caused by the collapse of a white dwarf to a neutron star, whose growing spin energy enhances the strength of its anchored magnetic field to <≈ 1017 G, which subsequently decays into an extremely relativistic cavity, with particle energies reaching <≈ 1020 eV.

In other words: During a SN explosion, the envelope of an exploding star is ejected by a combination of its core’s superstrong magnetic coil plus the coil’s decay product, a dense plasma of cosmic rays. Strong Rayleigh-Taylor instabilities guarantee an extreme splinter geometry of the ejecta, as shown in the figure.

References in the text:

Jets in the Universe


Our nearest radio-cD galaxy M87, complete as well as in five successive enlargements, seen at radio frequencies [from: NRAO/AUI and F.Owen, J.Biretta, J.Eilek 2012]

Jet sources are arguably the most sophisticated machines of the inorganic Universe. Without a building plan, or a constructor, they are formed by all types of stars – from young brown dwarfs up to the brightest (young, ordinary) stars, through white dwarfs and neutron stars – as well as by the cores of galactic disks, (often misleadingly called SMBHs). They blow low-weight channels across distances of up to several million light years, through which electrons and positrons propagate almost loss-free at almost the speed of light, for up to a billion years, eventually emitting photons anisotropically of up to and beyond 102 TeV (= 1014 eV) energy. How do they do that?

A quantitative answer to this question has been given by Gopal Krishna and me in 2004, in the Indian journal J. Astrophys. Astron. 25, 115-127. Required is a fast-rotating, heavy magnet whose corotating magnetosphere is permanently strained and stretched, via friction on a surrounding accretion disk, and subsequently creates relativistic e± pair plasma, via reconnections. In active galactic nuclei, the role of the corotating magnetosphere is taken by the disk’s coronal magnetic fields. The almost weightless, newly formed pairs rise by buoyancy, away from the massive core, parallel to the local spin axis, are post-accelerated by outgoing low-frequency magnetic waves, and are focussed by ambient heavy matter into two antipodal (twin-) jets, at right angles to the local accretion disk.

In this way, there forms a quasi-steady, trans-relativistic, mono-energetic flow of freshly created pair plasma, whose charges (E x B)-drift in self-supplied toroidal magnetic and transverse (axi-symmetric) electric fields, in strict equipartition between kinetic and electromagnetic energy density. The complete class of exact flow solutions has been described, and shown to be stable, with uniform, transrelativistic, loss-free particle velocities – apart from mild inverse-Compton scatterings – out to a distant obstacle that terminates the flow, observed as a ‘head’ of the elongated ‘lobe’ into which the stream is eventually dumped.

These almost loss-free, leptonic cosmic jet sources are stabilised by their low inertia. Their strongest radiation is emitted right at the beginning, during focussing, inside their deLaval nozzles, as well as near occasional obstacles, seen as ‘knots’, and at their termination points (heads), where the beams are stalled. Moreover, jets can drag along ionic channel-wall material – in the shape of structured skins – which can emit spectral lines at optical and X-ray frequencies,  as it does in the exotic neutron-star binary SS 433, and in the ultraluminous supersoft X-ray source ULS-1 in M81.


  • Kundt, Wolfgang: A Uniform Description of All the Astrophysical Jets, Mondello 2014, PoS(FRAPWS2014)025, 1-9 (2015)
  • Kundt, Wolfgang: The Astrophysical Jets (again): as the most complicated inorganic machines known to us, Talk presented at Mondello on 16 June 2017, PoS(MULTIF17)075, 1-8 (2017)