Don't Be Deceived: There Is No Such Thing As A Photo Of A "Black Hole"

The much circulated image above - purported to be of a black hole in the center of the galaxy M87- is nothing of the sort.

As usual, the mainstream media - in an effort to grab clicks or reads- has misrepresented the recently circulated image claimed to be of a "black hole" in the Virgo galaxy M87.   Of course, this is impossible. One cannot get a photo or other image of a black hole itself.  That is invisible - or better "un-seeable" - at any wavelength, including radio..   What one has in the image, is not the black hole per se, but its event horizon which is somewhat different.

TO fix ideas, the image in question was captured by a global network of 8 radio telescopes, appropriately called the "Event Horizon Telescope" or  EHT.  The effective aperture essentially formed one giant radio telescope "dish" stretching from Spain in the north to Antarctica in the south.  The mass associated with the M87 black hole  is the equivalent of 6.5 billion Suns.  That implies its event horizon would have quite a significant scale.

What is this event horizon? It is basically an "infinite redshift" surface from which no signal, no light or radiation of any kind, can escape. The key cut off occurs at what's called the Schwarzschild radius or:

R(s) = 2GM/c²

where G is the Newtonian gravitational constant, c is the speed of light in vacuo, and M is the gravitating mass.   In this case - and for a "Schwarzschild solution" all observers will agree that the surface r = R(s) is an "event horizon".  It defines the boundary or edge at which all outgoing signals are cut off so they cannot have any external manifestation - whether as radio waves or optical ones.  

A good algebraic way to show how signals are cut off  at the r = R(s) Schwarzschild event horizon has been given by Ohanian and Ruffini ('Gravitation & Spacetime', p. 445).  Thus, one considers a radio signal propagating in the radial or r direction. Then the velocity of this signal, say with respect to r, t (radius, time) coordinates can be expressed:

dr/ dt =  + {1  -   r/ R(s)}

Now note what happens when the signal approaches the critical boundary, i.e. r = R(s).  Then we see:

dr/ dt =   + {1  -   r/ R(s)}   =   + {1  -   R(s) / R(s)} =  1 - 1   =  0

The graph shown in the same text (op. cit, p. 446, Fig. 8.3) can also help to illuminate the situation vis-a-vis interior and exterior to the black hole.   We see that in the exterior of the black hole (r > R(s))  the axis of the light cones is parallel to the time (t) axis.  But in the interior of the black hole (r < R(s)) the axis of the light cones is parallel to the r- axis.  The reversal is a direct result of r being a "time-like coordinate" and t space -like.   The existence of an event horizon at r = R(s) is "obvious from the inspection of the light cones in Fig. 8.3."  as noted by the authors. (Ibid.)  Hence, any kind of signal must travel in a spacetime direction that lies within a light cone. And "since the light cones in the black hole region are oriented toward r = 0 any signal in this region is unavoidably pulled toward decreasing values of r."

Thus, all such signals can never leave the black hole, hence we cannot obtain them from outside . This is no matter how many radio telescopes we assemble in a global network, as in the case of the EHT.

Bottom line, the EHT captured exactly what its title designated: the event horizon of a monster black hole in galaxy M87.  But not the black hole itself! Think of what we are seeing as an impenetrable 'cosmic curtain' impeding our accessing the actual black hole.

Black Holes - Where There Is No Space

It seems incomprehensible, and more than a few people are unable to get their heads around it, but there are astronomical objects where space does not exist. Let me rephrase that by saying the space is not that which is conformal space-time that can support the laws of physics. Since the space  literally occupies a one-dimensional point at the hole's singularity, and an infinitely small point is occupied by a collapsed, stellar scale mass, then the laws of physics (which incorporate causality) do not apply.

The threshold for making this cut is given by the well known Schwarzschild radius or:

R(s) = 2GM/c²

where G is the Newtonian gravitational constant, c is the speed of light in vacuo, and M is the gravitating mass. Once a stellar remnant collapses within this radius, light cannot escape and the object is no longer visible, hence effectively "air tight" to use the words of the article. It is a characteristic radius associated with every mass of macroscopic scale

Such is the case with the stellar- collapsed black hole., but we need to explore the specific conditions for the zero space singularity in more detail. It depends really on a spherically symmetric solution    (Kurt Schwarzschild's  solution)  of Einstein's general relativity field equations, viz.

ds² = -(1- 2M/r)dt²    + dr² / (1 - 2M/r)  + r²  (dq² + sin²  q dφ² )   

Where r, q,  φ  are spherical coordinates, for this conventional Schwarzschild metric..

As noted by Ciufolini and Wheeler ('Gravitation and Inertia', Princeton University Press, p. 69), for the above defined Schwarzschild metric the r = 2M region is a "mere coordinate singularity".  However, they note that the r = 0 region (where g₀₀   = - g₁₁  referring to the Einstein field potentials). is "a true geometrical singularity". In other words, expressing a region of no causality-based space time that we recognize. Of course, there are many different solutions, among which we find those well -behaved. The authors point out a specific example on p. 67 where "it is possible to extend analytically the Schwarzschild  solution to cover the whole Schwarzschild  geometry."

To fix ideas, reference is then made to a diagram on p. 66 showing an "Einstein -Rosen Bridge" or "wormhole connecting two regions in one Euclidean space."   It is emphasized that the sequence of diagrams (Fig. 2,9a, 2.9b, 2.9 c) denote "alternative interpretations of the three-dimensional maximally extended metric of Kruskal at time t' = 0"  For those interested, this referenced metric is given as (p. 67):

ds² =   (32 M³  / r) [exp (-r/ 2M)] (- dt'²  + dx'²  )  + r²  (t', x') (dq² +  sin²  q dφ² )

This is after transformation of the original Schwarzschild metric using the Kruskal -Szekeres coordinates given at the top of page 67.

The point is that a suitable mathematical approach can be used where one avoids a "spaceless" (e.g. true singularity) outcome, and instead engenders one with a space-time "escape hatch" - the Einstein-Rosen Bridge.

Obviously, in this post, many details are being left out including for the wide array of divergent black hole conditions (e.g. for angular momentum, rotation - rotating or not) and geometry, e.g. for Kerr black holes, see e.g.

http://www.daviddarling.info/encyclopedia/K/Kerr_black_hole.html

I only touch the bare surface here to encourage readers to investigate many more aspects on their own.

Granted, no one has ever seen a black hole but we know how to recognize the physical evidence for its existence: very powerful and periodic bursts of x-rays, registered on sensitive satellite detectors. Mathematically, the very brief periods of less than a millisecond betray an extremely compact volume. The x-rays indicate accretion to a large mass. Together, these can be matched to predictions given in the Einstein general relativity equations and Voila! the black hole emerges as an object consistent with the observations.

In general black hole identification is predicated upon observing its effects as a member of a binary (double) star system. Thereby, the black hole presence is inferred from x-rays given off when the companion star’s gaseous layers are sucked into it. As those accreting gaseous layers are pulled through the hole's event horizon, they are condensed and the impacting plasma leads to intense heating and x-rays.

The most convincing recent find which puts the question of black holes existence to rest once and for all has been via the Laser Interferometer Gravitational Wave Observatory (LIGO). e.g.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102


The recent LIGO detection provides the first direct evidence for gravitational waves but also opens the door to using them to study the powerful cosmic events that create them, in this case two colliding black holes. Based on the paper cited in the above link, the two black holes are  each roughly 30 times the mass of the Sun. They evidently merged some 1.3 billion light years from Earth. The  gravitational waves themselves were generated in the final moments before the black holes merged. The signal was brief but definitive and we on Earth have now received it.

It is in fact the most direct observation for black holes ever made.

Meanwhile, the total current assay of black holes may be dramatically underestimated. This is a result of difficulty of detection, as is the case with all forms of dark matter. Despite that, the research thrust goes on, along with black hole identifications in a variety of formats and scenarios.

Those who want to investigate more, can consult any or all of this sampling of research papers, from The Astrophysical Journal, on the American Astronomical Society website:

1) On the Correlations of Massive Black Holes with Their Host Galaxies

http://iopscience.iop.org/0004-637X/637/1/96/fulltext

2) The Jet Power, Radio Loudness, and Black Hole Mass in Radio-loud Active Galactic Nucleihttp://iopscience.iop.org/0004-637X/637/2/669/fulltext

3) Binary Mergers and Growth of Black Holes in Dense Star Clusters
http://iopscience.iop.org/0004-637X/637/2/937/fulltext

4) Black Hole Advective Accretion Disks with Optical Depth Transition

http://iopscience.iop.org/0004-637X/637/2/968/fulltext

5) Black Hole Masses and Eddington Ratios at 0.3 less than z less than 4http://iopscience.iop.org/0004-637X/648/1/128/fulltext

Dozens and dozens of other papers are also available, which show in concert that the black hole is no mere macguffin created by some math genius fantasizing in his parents' basement, but a valid object of inquiry worthy of serious scientific investigation.

New Model For Black Hole Accretion: Beautiful - But Is It Real?

Though a certain minority of physicists-astrophysicists (such as Lawrence Krauss) continues to believe black holes are some kind of myth or abstract confection with no grounding in reality, most of us don't buy that. Indeed, if it were true, we'd never see the frequency of papers on black holes published in reputable journals including the Astrophysical Journal, Nature, and Science.

Over the years the dynamics of the black hole as part of a binary system have been especially well investigated given that such pairing is the only way we can detect their presence. Usually, this is by the x-radiation give off in the process of "accretion" or layers of the companion star being pulled off and into the black hole with the friction unleashing the x-rays.

The Schwarzschild radius  provides the theoretical basis for the formation of most supermassive black holes and is given by:

R(s) = 2GM/ c ²


Where c is the speed of light, M is the gravitating or collapsed mass, and G the Newtonian gravitational constant. Thus, the value R(s) denotes the radius of the putative black hole given the mass M as the source. By way of insight, for the Sun R(s) would be about 3 km, but of course this is purely a theoretical limit given our star is simply not massive enough to collapse down to that size!  Not so for truly massive supergiants in the 10- 20 solar mass range, and further the super black hole at the center of our galaxy with 9.7 billion times the mass of the Sun.


Fig :Showing 3 different numerical  modelings-simulations.

In a recent numerical simulation study published in Science, (Vol. 345, p. 1330), the authors consider a scenario (depicted in Fig. 1) in which a low mass Population III remnant black hole (BH) remains embedded in a nuclear star cluster fed by cold gas flows and under the right conditions has the potential to grow rapidly. The simulation, model is beautiful and self-consistent but the question remains whether it is real, that is, has a correspondent system in physical reality. (I am writing not just about the black hole but the aggregate system).

In the model, the stars and the gas are "virialized" in the cluster potential - see e.g.

http://brane-space.blogspot.com/2010/11/basic-problems-in-astrophysics-4.html


So that basically the binding energy of the star cluster (E(s):

E(s) =  K  + W  = W/2 = -K

Thus, the total energy of the  star cluster E(S) is equal to half the gravitational potential energy (e.g. W/2)

The black hole is initially a "test particle" in equipartition with the stars. Then gas within the accretion (capture) radius of the BH

_{r a}   = [2 c ² /  c' ²  +   v ²  ] _{r g}

is dynamically bound to it. (Note: the gravitational radius  _{r g}  =  2 R(s) the Schwarzschild radius)  Note also that c' is the gas sound speed, i.e. in the cold flow far from the BH - and is a measure of the star cluster's gravitational potential.  Meanwhile, v is the BH velocity relative to the gas.  The authors point out that "prompt accretion requires gas to flow from r a   into the black hole on a specific trajectory with low angular momentum j =  4   _r g c.  and through the innermost stable periapse distance  r p, "    They note it is this angular momentum barrier not the Eddington limit (for which outward gas pressure balances gravity) that is the main obstacle to super-exponential growth.

Other points noted:

- The BH is more massive than a cluster star so that  v ²  <  c' ²  (The accretion flow is quasi-spherical)

- In the idealized case (flow radial and adiabatic) the Bondi solution is assumed such that:

_MB   = [ π  / Ö2 ]  ( r a ² )  r c'

(With adiabatic index   g  = 4/3  assumed)

- The stronger than linear dependence of the accretion rate on the BH mass leads to a solution that diverges supra-exponentially.

Focusing now on Fig. 1, the graphic shows dense cold gas (green) flowing to the center (X) of the stellar cluster (light blue region) of total mass:

_M o  = N_{o   M o}  +  Mg

And radius  R c  which contains  Ns  stars (yellow circles) of mass M  with velocity v, and gas of mass   Mg.

The gas is nearly pressure supported and close to the virial temperature, which from the previous link to my post on the virial theorem would be found from:  E(S) = - 3/2 [ g  - 1] U  where the internal energy U = f(T). A stellar black hole (BH) which is accreting from its capture radius (dark blue circle) is initially in a dissipation equilibrium with the stars and is scattered by them (black dashed line) over the distance: D (red circle).

Figure 2 summarizes the results of three different numerical simulations including a Monte Carlo run. Note that the vertical axis gives the angular momentum ratio   j a  / j iso    ie. in terms of gas captured by the BH, as a function (abscissa) of the BH mass and the corresponding time ratio t/ t' for Bondi accretion.   The authors note that the initial stages of BH growth is computed in the "ballistic wind accretion limit:  using an angular momentum capture efficiency of  h = 1/3 (red line).validated against results from a Monte Carlo integration over the exact capture cross section (tiny blue circles along the analytic  h = 1/3 red graph.

Note that  j a  falls to zero at _M o  = 20 solar masses (where the density and velocity gradients cancel each other). The vertical line displayed at _{M eq}  = 25 solar masses marks the transition to a dynamical regime where two -body relaxation can no longer establish equipartition of energy between the BH and stars.

Comments:

Examining the authors' model and their inputs as well as the model parameters (Table,  p. 1331) it appears they have a brilliant simulation for a rapidly growing black hole in a star cluster with particular dynamical properties in relation to it. I also, in 1977, believed I had a brilliant model for Epsilon Aurigae - to account for its binary eclipse phase-  until actual observations revealed I was wrong.  But this is the problem inherent in all numerical models. You carefully design them and they can entertain and inform...only up to the point that actual observations can confirm them.

I have no issues with the authors' modeling and simulations but I would like to see some kind of validation - preferably using a 'real world' system that displays similar properties to what the authors show in their Table.

Einstein 'Stole' Relativity From Others? Irredeemable Codswallop!

Every so often a question comes out of 'left field' and appears  at ‘All Experts’ (Astrophysics forum) that confounds  and also piques curiosity. In this most recent case the person wrote:

"Up till now I have read that Einstein definitely stole much of his work from others, simply plagiarising them. What interests me now is that a current scientist is claiming , re a recent study,

http://www.dailymail.co.uk/sciencetech/article-2769156/Black-holes-NOT-exist-Big-Bang-Theory-wrong-claims-scientist-maths-prove-it.html

 that Einstein was wrong and that black holes cannot exist.

Is this correct, that, with no black holes in the Universe, Einstein has a gaping flaw in his theories?"

There are two literal howlers that emerge in the question, and it's well to  consider each in turn:

1)     The belief that Einstein somehow plagiarized all the previous work of others, in particular Lorentz and Poincare, and

2)     The belief  that Einstein was responsible for the black hole concept. (A subsidiary howler is that black holes "cannot exist" which I will consider in conjunction with the claim Einstein was the creator of the black hole concept)

Let’s take (2) first, which is the more straightforward to deal with. As I pointed out in my response:

First of all, Einstein never claimed that black holes existed. What Einstein actually showed was a kind of precursor to the idea in one of his papers (‘On the Influence of Gravitation on the Propagation of Light’). Therein he described  how light could bend in a gravitational field. He found this angle of deflection of starlight - say from a distant star passing near the Sun during a total eclipse, was:

a   = 2k M/ c² R

In truth, though Einstein provided a quantitative method to estimate gravitational bending of light, he himself never believed a celestial body could collapse in on itself such that its own light rays would never escape.

That didn't emerge until Karl Schwarzschild showed the Einstein field equations could be used to show such collapse. A simplified threshold for making this cut is given by the well known Schwarzschild radius or:

R(s) = 2GM/c²

where G is the Newtonian gravitational constant, c is the speed of light in vacuo, and M is the gravitating mass. Once a stellar remnant collapses within this radius, light cannot escape and the object is no longer visible.  R(s) then is a characteristic radius associated with every mass of macroscopic scale.   It is this that (technically) gave rise to the black hole concept.

(Incidentally, the term "black hole" never existed until 1964 when it appeared in a science article written by journalist Ann Ewing.)

I added:

This is another thing, IF black holes were fictitious objects then a heck of a lot of astrophysicists are wasting their time on them in their research. What good reason would there be to do so? And more importantly, why would esteemed journals like the Astrophysical Journal publish such fictitious, "fantasy" work? It makes no sense so the onus is on those who claim they don't exist to explain and explain in full!

Some recent titles of papers on black holes appearing in recent issues of the Ap. J.:


'Illuminating Massive Black Holes with White Dwarfs: Orbital Dynamics and High-energy Transients from Tidal Interactions'


'Single-epoch Black Hole Mass Estimators for Broad-line Active Galactic Nuclei: Recalibrating Hβ with a New Approach'

'Roche-lobe Overflow Systems Powered by Black Holes in Young Star Clusters: The Importance of Dynamical Exchanges'

All of these appeared in Ap. J.,  Vol. 794,  No. 1, Oct. 10. 2014

E.g.

http://iopscience.iop.org/0004-637X/794/1

Again, and not being facetious, if black holes don't exist why all the papers on them?

 The point emphasized is that if black holes genuinely were an impossible fiction, they’d never be granted the space they have in a peer-reviewed journal like the Ap. J.

 

Then there is the nonsense about Einstein "plagiarizing" earlier work. As I pointed out:

As for the claim that "Einstein definitely stole much of his work from others, simply plagiarising them" - all I can say is: ‘Bollocks’! What evidence is there for this? WHO made the claim and where? In what peer-reviewed paper or source? If it is just sappy opinion blabbed in some rag of a newspaper the claim isn't worth anything. There has to be substance to it. This again reinforces the cautionary note that what must be careful about what one reads and always do very careful cross-checking. Don't believe the first thing you see even if it might resonate at some level.

Also, if Einstein did plagiarize previous work, how come no other serious physicists have come to this conclusion?

Look, the world is full of iconoclasts all trying to make a name for themselves (like that astronomer who claimed to 'prove black holes don't exist' cited in the Daily Mail) and some do - for a time. But it never lasts, because ultimately it is usually found they were too quick on the draw and overlooked key facts - as you did in merely putting this question forward- presuming that Einstein himself had anything to do with black holes.

 The questioner clearly couldn’t accept this response and wrote in a further comment after giving his ratings:

"Look up "Relativity priority dispute" on wikipedia to see that it isn't just fringe people who have evidence that Einstein ripped off other scientists' ideas. Roger Schlafly now has a book out "How Einstein ruined physics", which goes into detail on this issue.”

 

Relativity priority dispute? Who would have ever thought? I'd never before heard of such a thing, since in all the monographs and peer-reviewed papers I've read - such as in Physical Review D- all the papers citing Einstein or his work never ONCE referred to "plagiarism" or not giving enough credit to predecessors. So where did this odious meme or claim come from? What nest of vipers hatched it and spread it in assorted books and all over the net?

 As I responded to the questioner:

I did look up the so called "relativity priority issue" and the consensus appears to be Einstein was still original in his particular development. Yes, Poincare, Lorentz et al had seminal ideas predating the special theory but it was still left to Einstein to put them together and it was Einstein who first applied the tensor calculus to put them in that setting - paving the way for general relativity. Alas, much of the "plagiarism" nonsense originated as Nazi propaganda. See also:

http://research.calvin.edu/german-propaganda-archive/einstein.htm

 

As noted therein:

"Since Einstein was Jewish, the Nazis had to argue that he was no scientific genius, but rather a typical Jew of limited abilities. This 1939 article comes from the Mitteilungen über die Judenfrage, a newsletter published by the Institut zum Studium der Judenfrage, the most prestigious of the Nazi research institutes on the “Jewish Question.”

 

It is typical of much Nazi propaganda directed against Einstein. It makes, among other things, the interesting claims that there is nothing new about the Theory of Relativity, and even if there were, Einstein plagiarized it."

The Nazis just couldn't stomach that a Jew could develop ground breaking theories of physics, because - of course - they held Jews in such contempt and even consigned them to a "final solution".

The other fact above all, cited by more than one source, is that if Einstein had indeed plagiarized previous work he'd never have been published in journals like 'Zeitschrift fur Physik'. The nonsense that the referees were too dumb to learn of it because Einstein provided few references is just plain balderdash.

 

Then there is the guy he cites, Roger Schlafly. At first the name didn't ring a bell but then the surname jibed and I instantly related it to an extremist right winger, Phyllis Schlafly, who's  always been dedicated to an American nativist imperium and dominion. Then Roger had to be related to her in some way and it turns out he's her son. That the 'apple' never falls far from the tree was evident from this Rational Wiki synopsis of this character:


"Roger Schlafly writes two blogs. At Dark Buzz, a science-focused blog, he conveys "ideas and information that are essential to understanding our world...ignored by the mainstream media".^[ There, he engages in quite a bit of Einstein-bashing and frequently labels him a plagiarist and fraud. He frequently writes about Henri Poincare, a French physicist who he believes is a victim of under-appreciation because of Einstein, despite that everyone seems to know the name

 He writes from (as you'd expect) the perspective of a right-wing, white male heterosexual American Christian with libertarian leanings, and has cited the white nationalist website VDARE”

Like Larry Schweikart with his false liberal history nonsense, Schlafly turns out to be another putz who wants to turn scientific iconoclast. But why would anyone take the scribblings of  a white nationalist sympathizer and the son of Phyllis Schlafly seriously? Besides, his specialty isn’t even physics but electrical engineering and math. While true, physics is  needed in electrical engineering and math is used in physics, neither Schlafly specialty is as concentrated as one expects in graduate specialist  Physics courses.   Fair question: Could he pass a  Ph.D. comprehensive exam in mechanics, thermodynamics, general relativity or quantum mechanics? I seriously doubt it. (I will post one of these soon, to see if he can.)

 I mean, as  one of the (negative) reviewers of Schlafly’s book also noted (correctly):

"Lorentz himself said in 1927:

'Only the true time existed for me. I regarded the transformation of time merely as a heuristic working hypothesis. Thus, the theory of relativity is, in fact, exclusively Einstein's product.' "

So if even  Hendrik Lorentz acknowledged Einstein’s priority in special relativity – why not Roger Schlafly or the person who asked the Einstein question at All Experts? Well, not Schlafly because as a white nationalist sympathizer  it would not be his wont to be fair to a Jew – who white nationalists and earlier Reich propagandizers  never regarded as equal to "Aryans". Hence who'd try to diminish Einstein’s accomplishments.  As for the naïve questioner, well, all I can say is that he was misled by Schlafly’s apparent academic creds into buying into this hogswill and that he really had a case – he didn’t.

Others who may dispute this - for whatever reason, even if they genuinely question Einstein's honesty - are invited to look up and read his most seminal paper on special relativity: 'Does the Inertia of a Body Depend On Its Energy Content?' (Annalen Der Physik, Vol. 17, 1905). Therein the doubters will see first hand how Einstein ingeniously used the Lorentzian  radical :

[1 - (v/c)²)]^1/2

Einstein deftly uses this to arrive at his most famous equation:  

  E  = Mc²   

To quote the reviewer again:

“In summary, if nothing of what we think Einstein did was actually his original work, how in the world can we say that Einstein ruined physics? Assuming that Physics is ruined, and assuming Dr. Schlafly's thesis is correct regarding Einstein's dishonesty, I would rationally tend to blame those who `really' developed Modern Physics, those of us who were so naïve as to allow ourselves to be deceived by Einstein for over 100 years, or both.... But not Einstein, whose only crime was -apparently- to be a thief!!!”


Points well taken!

And further advice to those who jump on claims that seek to take down a genuine genius of physics: Look at the source! Find out all you can about him or her before jumping the gun and conferring validity on his assertions!

Is General Relativity Vindicated Again? Maybe!

Top: Line-of-sight components of the orbital velocities of the radio pulsar J0348 and its white-dwarf companion, measured, respectively, by radio-pulse timing and spectral Doppler shift.  Bottom:  All binary radio pulsars with measured masses and no significant tidal or mass losses are plotted by mass (with corresponding gravitational binding energy) and orbital-velocity parameter β.


Amazingly, in many scientific circles general relativity or GR remains as controversial as the Darwinian theory of evolution in biology. This despite the fact that for all intents, at least within the confines of our own solar system, GR has been vindicated. For example, it very well predicts the annual advance in perihelion of the planet Mercury, and fairly well predicts the deviation of starlight as it passes near to the Sun in our line of sight. Recall here that the closest thing to a strong field object in the solar system is the Sun whose radius is more than 100,000 times its Schwarzschild radius of 3 km. (The  Schwarzschild radius R(s) = 2GM/c²,  where G is the Newtonian gravitational constant, c is the speed of light in vacuo, and M is the gravitating mass. Once a stellar remnant collapses within this radius, light cannot escape and the object is no longer visible .)

The situation is dramatically different for neutron stars, which comprise the components of what we call "extreme binary pulsars."  The neutron star is an ultradense stellar remnant of a  core-collapsed supernovae. A one solar-mass (1 M_⊙) neutron star has a radius of order 10 km, only a few times its R_s. And whereas the gravitational binding energy of an ordinary star is a negligible fraction of its mass, the binding energy of a neutron star can reduce the total mass of its unassembled constituents by as much as 20%.

Thus, the binary pair, labeled J0348+0432, in which the most massive component is a neutron star closely orbited every 2.46 hours by a much lighter white-dwarf star, has attracted astrophysical attention. Though 7000 light-years away, J0348 is quite observer friendly. The white dwarf’s unusually bright hydrogen spectrum yields high-resolution Doppler-shift data and much information about its intrinsic properties. And the neutron star is a radio pulsar whose lighthouse-like radio beam, sweeping Earth every 39 milliseconds, provides an excellent long-term timing reference.

This is the very type of object that would be useful in vindicating GR in an extra-solar context. But why does GR remain so suspect? First, it has problems with quantization, so hasn't yet been reconciled to the other powerful theory of modern physics: the quantum theory. It also has problems with spacetime infinities (i.e. the singularities at the center of black holes), and has difficulty incorporating cosmic inflation (because of superluminal rates of expansion associated with it) and finally GR can't quite cope with the unification of fundamental forces (gravitation, electromagnetism, the strong and weak nuclear forces).

Enter the extreme binary pulsar J0348+0432. The findings so far conform with it being included in a class called  “clean, relativistic” binaries—those with relativistic velocities and negligible losses due to tidal dissipation or mass transfer, hence they lose energy primarily by gravitational radiation. In GR, the lowest-order gravity-wave production by an extended dynamical source is called quadrupole radiation. But many variations on GR predict that dipole radiation will, under the right circumstances, sap a binary’s orbital energy much faster than the quadruple radiation

The report of a team at Max Planck Institute in Bonn, Germany now appears to have supported that this is the case for J0348+0432. (The new binary pulsar was first spotted by team member Ryan Lynch (McGill University) in accumulated data from a 2007 radio-telescope survey).

Figure 1 shows the 2.46-hour oscillation of the line-of-sight velocity components of the white dwarf and the pulsar as measured, respectively, by spectral Doppler shifts and pulsar timing. The ratio of their oscillatory amplitudes measures the ratio q ≡ M_p/M_wd of their masses to be 11.7 ± 0.1. The pulsar mass M_p = qM_wd was determined to be a record (2.01 ± 0.04) M_⊙. The two masses plus the orbit’s period and its line-of-sight velocity components yield a detailed description of the binary orbit: Its plane is inclined 40° from the plane of the sky, and the white dwarf’s orbital velocity is about 0.2% of the speed of light. Its separation from the pulsar is about half the diameter of the Sun.

Figure 2 compares J0348 with other binary pulsar systems, with regard to pulsar mass, orbital velocity, and gravitational binding energy. The figure shows another 2-M_⊙ pulsar orbited by a white dwarf. But that binary’s orbital velocity is much slower (see Physics Today, January 2011, page 12). On the other hand, the plot shows a unique double pulsar—two pulsars orbiting their center of mass with a relative velocity slightly faster than that of J0348.

Given the new binary’s measured parameters, GR predicts that its present 2.46-hour orbital period P_b should be decreasing by about 8 µs per year as the orbit shrinks due to energy loss by gravitational radiation. To test that prediction, Lynch and Paulo Freire began continual pulsar timing with Puerto Rico’s Arecibo radio telescope in April 2011. Now, based on two years of timing data, the orbital period’s measured time derivative is 1.05 ± 0.18 times the GR prediction. So thus far there’s no evidence of new physics.  Fig. 3 (below)



shows the constraints imposed on the masses of the binary pulsar J0348 by measurements of the white-dwarf mass M_wd, the mass ratio q, and the time derivative of the orbital period. In each case, the triplet of lines indicates one standard deviation.

The yellow segment is the 1-standard-deviation confinement imposed on the binary’s mass plane by the measurement, assuming that GR is the correct theory. The fact that the intersection of the measured q and M_wd lines, which involve no assumptions about GR, falls nicely in the middle of the calculated swath indicates that GR has thus far passed the team’s radiative test. With increased observing time t over the next few years, the uncertainty on should shrink rather rapidly—like t^−5/2.

Will it satisfy all critics? Hardly!  For example, one group at Boston University has objected based on Augur electron simulations - that challenge the claim that the high energy spectral peak is produced by Augur electrons. Thus, they claim there is "no correlation between electron energies and any information about the intrinsic properties of the pulsar." (The GR proponents have tried to tie the electronic behavior of the instrumental detection LEDs to electrons tunneling out of a quantum well to form peaks in the spectrum observed.)

In any case, as with all good physics we shall have to await confirmation, or at least wait another few years to see if indeed the uncertainty on   shrinks.  For another GR-related blog post, see:

http://brane-space.blogspot.com/2012/11/solar-oblateness-may-be-constant-over.html