Do details in LIGO’s signals distinguish ‘frozen stars’ from ‘black hole’ interpretations

R. J. Spivey argues that “Coincident down-chirps in GW150914 betray the absence of event  horizons”.  The LIGO discovery is said to confirm Einstein’s gravitation theory, yet Einstein (in 1939) gave mathematical grounds for dismissing the notion that black holes exist, points out Spivey.  His article uses secondary signals seen in both LIGO detectors (Fig. below)

Spivey Fig. 1: The gravitational wave spectrograms for the Hanford (top) and Livingston (bottom) Advanced LIGO detectors. Right column: the common secondary trace (down-chirp) deviating from the primary up-chirp suggests the ejection of mass against gravity of the merging binary system. Credit: LIGO-Virgo collaboration.

Spivey Fig. 1: The gravitational wave spectrograms over the 170ms (0.17 seconds) prior to merging for the Hanford (top) and Livingston (bottom) aLIGO detectors. Right column: the common secondary trace (down-chirp) deviating from the primary up-chirp suggests the ejection of mass against gravity of the merging binary system. Credit: LIGO-Virgo collaboration.

It’s well appreciated that close binaries of compact stellar objects (neutron stars) are strong sources of gravitational waves – the energy loss in the waves causes the orbits to spiral inwards until the objects are disrupted or merge.  The LIGO gravitational wave pulses show the predicted oscillating signal of directional beamed waves, increasing in frequency corresponding to the shrinking orbits.

The LIGO community was so taken with this ‘chirp’ of increasing frequency (curving upwards in the Fig.) and the finding that the mass associated with ‘chirp’ models is much bigger than normal stars (totals ~20 and 65 solar masses Ms in the two LIGO instances) that they failed to look at details in the spectrogram.  They largely embraced the claim that the objects must be fashionable ‘black holes’ rather than supermassive neutron stars or other extreme matter.   They’ve dismissed these as ‘exotic’ matter, whereas the ‘event horizon’ that delays mass accretion into black-holes for infinite time is the real ‘exotic’ physics.

The last stage of the LIGO signals, as the inspiralling objects touch and merge, would distinguish between models.  It’s expected that oscillations depend on a boundary or a ‘horizon’.  But this stage is lost in the signal noise, below the detection threshold.  Robin Spivey points out an earlier secondary signal – from 160ms, a ‘down-chirp’ of decreasing frequency – provides some evidence.  The spectral traces from the two detectors (at Hanford and Livingstone, Fig. above) would match ejection of a fraction of the matter with a launch radial velocity  ~ 0.04c.  (Other secondary spectral features are ‘noise’, differing in the two detectors.)

Was disruption not expected, associated with the violent inspiralling ?  Gigantic amounts of energy are emitted in gravitational waves, equivalent to 3 solar masses (3Msc2 in the larger case).  Calculations for a binary of unequal point-masses do find that the smaller mass can be expelled at high (sub-relativistic) speed.   Strong perturbations of extended bodies might well expel significant amounts of matter from their fringes.  Non-radial instabilities have been indicated in a model ‘gravastar’, implying asymmetric break-up.  On the other hand, disruption of a black-hole is inconceivable – is this why the LIGO community have overlooked the ‘down-chirp’ signal ?

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Second Gravitational Wave signal – Coalescing binary components, not Black Holes

Following the February discovery, a second signal was found by the same LIGO team in the ‘noise’, by looking for a pulse of waves of increasing frequency in the two detectors.  This pulse is longer (~55 waves compared with ~10 previously) and the frequency change (‘chirp’) indicates binary components of smaller mass (total ~20M⊙ compared with ~60M⊙).

LIGO2-wave-in-noise2 Jun'16

The modelled wave train (in black) on the two detectors’ signals (red and blue)

The new LIGO paper again asserts coalescing Black-Holes is the only explanation, saying the masses are higher than the maximum for canonical neutron stars. The last stage ‘ringdown’ signal, which could distinguish the form of the merging object, is minor and well below detection threshold.

It retains this position as originally agreed by its thousand authors, despite some critical voices eg. in Physics World of 29th April  reporting Vitor Cardoso on the gravastar interpretation “Are ‘gravastars’ mimicking…“.  That it’s vital to detect the ringdown part of the signal is stressed by a leading expert Remo Ruffini (“What we can really infer from GW150914?“).  B. Sathyaprakash of Cardiff’s LIGO team admitted (to Physics World) “Our signal is consistent with both the formation of a black hole and a horizonless object – we just can’t tell.”  ‘Horizonless’ models of super-compact objects include gravastars and do not suffer from the infinite time dilution at black-hole horizons:

The new LIGO paper shows weakness in stating the only alternative binary components are neutron stars and not admitting to excluding the ‘exotic’ alternatives – lest people point out that Black Holes are ‘exotic’. It’s weak also in not admitting that the ‘ringdown’ signal of black-hole coalescence is below their detection threshold.

The statement in mid-May by Ruffini and colleagues thus remains unchallenged:

“… the signal around 150 Hz occurs just at the limit of the sensitivity of LIGO… not sufficient to determine the astrophysical nature of GW 150914, nor to assess that it was produced by a binary black-hole merger leading to a newly formed black-hole.”

NOTE  The topic ‘mentors’ of physicsforums didn’t like me questioning the Black-Hole interpretation. They first stopped an informative exchange on grounds of unpublished ‘personal speculation’. When I showed Cardoso (and others) had already published, they allowed the new thread, citing Physics World and Ruffini’s new paper on arXiv, but then blocked me from continuing the discussion.  It smells of a conspiracy to give LIGO prizes for discovering black-holes, when there’s no such ‘discovery’ – LIGO’s gravitational pulse indicated the spin-down and merging of two compact bodies in a binary system. Unexpectedly massive bodies indeed, at 10-30 times the Sun’s mass M⊙, something for theorists to explain.

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Gruber Prize for LIGO team’s gravitational waves

The 2016 Gruber Cosmology Prize of $500 000 award citation reads:

The Gruber Foundation proudly presents the 2016 Cosmology Prize to Rainer Weiss, Kip Thorne, Ronald Drever, and the entire LIGO team for pursuing a vision to observe the universe in gravitational waves, leading to a first detection that emanated from the collision of two black holes. 

This remarkable event provided the first glimpse into the stronggravity regime of Einstein’s theory of general relativity that governs the dynamics of black holes, giving direct evidence for their existence, and demonstrating that their nature is consistent with the predictions of general relativity.

The first detection of gravitational waves was a major technical achievement, but it’s the identification as from a collision of a pair of black-holes that’s given by Gruber as its cosmological significance.  If not black-holes, then would theoretician Kip Thorne still merit the prize?  The “first glimpse” into Einstein’s general relativity was of course gained from “pulsars”, rapidly-pulsing radio wave emitters which were quickly identified with neutron stars of highly compact neutron matter.  The collision of two such objects has long been predicted to give a mega-burst of gravitational radiation.

Science normally demands an observation is reproducible – waiting for further detections or even a spectrum  of wave sizes and periods would normally be required.  Moreover, a study back in 2002 established that the late-stage part of the wave pulse (‘ring-down’ modes) would be needed to provide strong evidence for black-holes [Abramowicz et al., Astron & Astrophys.] – the LIGO signal was not strong enough for this.  So the LIGO team fell back on saying neutron stars cannot be as big as 30 times the sun’s mass and ignoring possibilities of other condensed-matter astrophysical objects of similar size.

The cosmological significance of the LIGO detection was thus the first detection of compact objects of around 30 times the sun’s mass, spiralling in to touch each other and then coalescing in the way predicted by Landau and Lifshitz in the 1960s.  But condensed-matter objects generally, whether the ‘horizonless’ variety or exotic black-holes.  The analysis and computational methods (‘post Newtonian’ expansions) have been advanced since then, but as leading theorists have just shown (Ruffini et al.), the results are close to the Landau-Lifshitz modelling.   As long as the nature of the binary compact objects remains uncertain, there’s no living theoretician to share the prize with Weiss, Drever and the LIGO team.

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LIGO scientists row back on claim to detect black-holes from their gravitational signal

It is gradually coming out that LIGO’s main gravitational wave pulse could indicate various types of binary astrophysical systems, as we said on this blog in February. Cardoso et al 2016 point out (Phys Rev Lett. to come) there are compact objects that are not black holes, including gravastars of similar dimensions (~30 solar masses) which produce a similar main signal. The late part of the signal was below detection threshold, and that is needed to distinguish between astrophysical objects. In discussing this, Physics World quotes Prof Sathyaprakash from Cardiff’s LIGO team saying that “Our signal is consistent with both the formation of a black hole and a horizonless object – we just can’t tell.” Rather different from him in the Guardian of 11 Feb. “The fusion of two black holes created this event”. Now, Remo Ruffini (of the Rees-Ruffini-Wheeler textbook) co-authors an preprint (16 May 2016) saying: unfortunately the signal of the merging “occurs just at the limit of the sensitivity of LIGO (so is) not sufficient to determine the astrophysical nature of GW 150914, nor to assess that it was produced by a binary black-hole merger leading to a newly formed black-hole.”

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Gravitational wave event at last – success for Einstein, not black-holes

Detecting gravitational waves after decades of searching and developing more sensitive techniques is a great achievement, in technology as well as the accompanying analysis.

What a pity the research teams have sullied the discovery by conflating the detection of a very clear gravitational wave signal with their particular interpretation.  Doubtless the big signal over milliseconds implies very large condensed masses interacting cataclysmically, inferred to be over 25 solar masses. The event had to be relatively close to us in space to give a signal well above numerous extragalactic ones.  The teams apply their model for two ‘black holes’ merging, as if it’s the sole contending explanation. The model merging scale is the Schwarzschild radius MG/c2, not of point-like black holes. Megamassive condensed stars (largely of neutrons) are of this scale too.  The rapid merging two of them would generate a similar signal, if with differences in detail.  This was dismissed simply on the basis of the out-dated belief that neutron stars can be no bigger than 2 solar masses (Ms).

Einstein himself did not believe in Black Holes; physicists should at least accord him respect in allowing that this first clear gravitational wave event implies the sudden rebalancing of large condensed masses, probably a merging binary – to give his quadrapole emissions – and opens up a way to investigate such structures.  The big majority of the gravitational energy pulse comes out from the mutually orbiting stars (rapid, up to ~0.5c) as they become increasing close in last second before becoming one.  Open-minds are especially required when black-hole modelling uses a faulty metric, having a non-physical region beyond a ‘surface of separation’, which requires dodgy computational treatments.

The discovery kills off the notion that gravitational energy is non-localised. The observed pulse was tightly constrained in time, ~10ms scale.  The pulse moves through space with the speed of light, akin to electromagnetic waves, not through “space-time” as is confusingly said.  Both electromagnetic and gravitational equations have wave solutions to small perturbations – travelling waves that carry energy – as Einstein first predicted, though not dipole but of quadrupole order for gravitational waves.

The inference of large compact masses – neutron stars of tens of solar masses – is an indirect discovery of an unrecognised population of mega-stars that are indeed predicted from the Hilbert-Einstein equations of General Relativity.  These can be neutron stars above the so-called TOV size limit of 2.0Ms given by Cameron (1959); our modelling given at the recent Moscow PIRT conference (link here) finds higher mass ‘gravastar’ structures, ie. shell-stars of compact matter with centres dominated by hypergravitational fields.

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Einstein not to blame for the Flow-of-Time deviation

comment on Saving time: Physics killed it. Do we need it back?  

New Scientist feature 01 November 2013 by Michael Slezak

It’s unfair to blame Einstein for the ‘fatal blow’ to the ‘flow of time’, which some physicists still find problematic.  Lee Smolin argued recently (26 April 2013) that the blows were never fatal.

The source of the trouble is the time-reversible formulations of ‘laws’ of physics, such as Newton’s laws. Einstein’s special relativity showed clock-timing is not unique, but did retain the time-sequence that is essential for causality – a principle that Einstein stoutly defended.

Einstein also advocated the Faraday-Maxwell concept of space-filling fields, and extended the differential equations for their field-borne light waves to apply to field-borne gravity waves.

However, these time-reversible formulations are not the whole story. Light-rays reach us only from the past, not the future. The time-explicit formulation of light waves uses (Liénard-Wiechert) retarded potentials to form an integral over waves reaching each point from earlier times. This integral satisfies both Maxwell’s time-reversible equations and the Penrose criterion that a truly fundamental law of physics is irreversible.

Thus the difficulty of standard physics with the ‘flow of time’ arises because it tries to dispense with fields of force, presuming they can be represented by particles (‘photons’, ‘gravitons’) governed by reversible interactions. Physics has to return to fields, carrying waves at the speed of light (following Einstein’s special relativity) to recover common sense over passage of time.

Einstein’s much quoted phrase “the distinction between past, present, and future is only a stubbornly persistent illusion” was written 3 weeks before his death and months after he’d expressed doubts about his whole life’s work including gravitation “based on the field principle”.  Evidently, the Einstein in 1955 was failing fast, had lost confidence and influence as a physicist, and his weak blow to the flow of time has proved non-fatal.

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Why Space has Three Dimensions

Why Space has Three Dimensions   – see Matthew Chalmers, New Sci 28 Sept 2013

That space is 3-D follows from electromagnetic and gravitational theory, both being experimentally validated and both free of quantum theory’s offence to views of reality (Chalmers, NS 28 Sept, p.34).

The reasons are surely much deeper than the inverse square ‘law’ (argument in the Box).

First, accelerated charges emit synchrotron radiation in a beam relative to the inertial reference frame of special relativity, of 3-space plus time.

Second, Einstein’s general relativity gives slightly different answers for light travel times (eg. Earth to Venus) for different accelerated frames – a unique answer comes by specializing to the inertial frame.

Einstein’s strong form of the “equivalence principle” led him astray, in that it took accelerated frames as equally valid, rejecting a unique space frame. His followers like Fock, Weinberg and Logunov have found good reasons for the inertial frame and thus for 3-space being real.

Seeing 3-space as real and higher dimension spaces as mathematical models, thus implies a weak form of the equivalence principle, applying locally, eg. in Einstein’s lift, but not in rotating planetary systems.

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