Planck Stars & FRBs: Rovelli's Hypothesis

[skydivephil]

Nor sure if this has already been discussed. But recently Rovelli has suggested the mysterious Fast Radio Bursts might be from Planck Stars :
https://www.gravity.physik.fau.de/events/tux3/rovelli.pdf
Any thoughts? What are the other explanation and how can resolve this?

 

[marcus]

It's an excellent unanswered questions. As far as I can tell FRBs are real astrophysical events which appear to have an extragalactic origin and for which there is so far no satisfactory explanation.

Earlier there was some confusion about terrestrial microwave signals that could be picked up (e.g. by the Parkes antenna when aimed at the right low angle).
These "fake" FRBs were called "Perytons" and seem to have been caused by someone opening a microwave oven door prematurely.

But the confusion has been sorted out. This was published August 2015 by the MNRAS:

http://arxiv.org/abs/1504.02165
Identifying the source of perytons at the Parkes radio telescope
E. Petroff, E. F. Keane, E. D. Barr, J. E. Reynolds, J. Sarkissian, P. G. Edwards, J. Stevens, C. Brem, A. Jameson, S. Burke-Spolaor, S. Johnston, N. D. R. Bhat, P. Chandra, S. Kudale, S. Bhandari
(Submitted on 9 Apr 2015)
"Perytons" are millisecond-duration transients of terrestrial origin, whose frequency-swept emission mimics the dispersion of an astrophysical pulse that has propagated through tenuous cold plasma. In fact, their similarity to FRB 010724 had previously cast a shadow over the interpretation of "fast radio bursts," which otherwise appear to be of extragalactic origin. Until now, the physical origin of the dispersion-mimicking perytons had remained a mystery. We have identified strong out-of-band emission at 2.3--2.5 GHz associated with several peryton events. Subsequent tests revealed that a peryton can be generated at 1.4 GHz when a microwave oven door is opened prematurely and the telescope is at an appropriate relative angle. Radio emission escaping from microwave ovens during the magnetron shut-down phase neatly explain all of the observed properties of the peryton signals. Now that the peryton source has been identified, we furthermore demonstrate that the microwaves on site could not have caused FRB 010724. This and other distinct observational differences show that FRBs are excellent candidates for genuine extragalactic transients.
8 pages, 7 figures, 1 table. Monthly Notices of the Royal Astronomical Society, Volume 451, Issue 4, p.3933-3940

There are links to other source material in the Wikipedia article:
https://en.wikipedia.org/wiki/Fast_radio_burst

Earlier FRBs were found by people searching through the recorded data from radio telescopes (Parkes and Arecibo) sometimes months or years after the fact. Little unexplained 5 millisecond "chirps" coming from no identified object. Recently an FRB was observed LIVE, by astronomers on the lookout for just such an event.
https://www.ras.org.uk/news-and-press/2578-cosmic-radio-burst-caught-red-handed.

Several issues would, I suppose, have to be settled before one could tie FRBs to Planck stars. One is the lifetime of Planck stars. If this is long then the only Planck stars now exploding would be PRIMORDIAL. Formed not from collapsing stars but by density fluctuations in the early universe. In that case one might plausibly conjecture that the Planck star explosions were comparatively small low energy. Then one has a problem explaining the DISPERSION of the typical FRB signal which has frequencies spread out in time, in a kind of "chirp". This seems to suggest that the FRB has been traveling for a long time in dilute plasma. (Speed of radio waves in dilute plasma is frequency dependent allowing some frequencies to get there sooner)

 

[skydivephil]

Thanks Marcus.

 

[marcus]

You are most welcome! I should thank you, Skydive, for broaching an interesting topic like this.
I think this QG conjecture is a longshot, as any proposed explanation for FRBs would be at this point. It's worth reviewing how Barrau, Rovelli, Vidotto addressed these issues a year ago, in their September 2014 paper. They already discussed some unresolved tensions in that paper and suggested possible solutions. It will be interesting to see a followup paper, hopefully before long.

In the meantime I'll point to some sections of the September 2014 paper:
http://arxiv.org/abs/1409.4031
Fast Radio Bursts and White Hole Signals
Aurélien Barrau, Carlo Rovelli, Francesca Vidotto
(Submitted on 14 Sep 2014)
We estimate the size of a primordial black hole exploding today via a white hole transition, and the power in the resulting explosion, using a simple model. We point out that Fast Radio Bursts, strong signals with millisecond duration, probably extragalactic and having unknown source, have wavelength not far from the expected size of the exploding hole. We also discuss the possible higher energy components of the signal.
5 pages, published in Physical Review D (December 2014)
http://inspirehep.net/record/1316456?ln=en
==quote from page 2==
These signals are believed to be of extragalactic origin, mostly because the observed delay of the signal arrival time with frequency agrees quite well with the dispersion due to a ionized medium, expected from a distant source. The total energy emitted in the radio by a source is estimated to be of the order 10³⁸ erg. The progenitors and physical nature of the Fast Radio Bursts are currently unknown [42].

There are three orders of magnitude between the predicted signal (5) and the observed signal (7). But the black-to-white hole transition model is still very rough. It disregards rotation, dissipative phenomena, anisotropies, and other phenomena, and these could account for the discrepancy.

In particular, astrophysical black holes rotate: one may expect the centrifugal force to lower the attraction and bring the lifetime of the hole down. In turn, this should allow larger black holes to be exploding today, and signals of larger wavelength. Furthermore, we have not taken the astrophysics of the explosion into account. (The total energy (3) available in the black hole according to the theory is largely sufficient --–9 orders of magnitude larger–-- than the total energy emitted in the radio estimated by the astronomers.)
==endquote==

The next paper (though not explicitly about FRBs) could indicate the direction that Planck star research is going---detailed modeling may significantly modify expectations about astrophysical Planck star lifetimes.
This could have an impact on the FRB question:

http://arxiv.org/abs/1412.6015
On the Effective Metric of a Planck Star
Tommaso De Lorenzo, Costantino Pacilio, Carlo Rovelli, Simone Speziale
(Submitted on 18 Dec 2014, last revised 9 Mar 2015)
Spacetime metrics describing `non-singular' black holes are commonly studied in the literature as effective modification to the Schwarzschild solution that mimic quantum gravity effects removing the central singularity. Here we point out that to be physically plausible, such metrics should also incorporate the 1-loop quantum corrections to the Newton potential and a non-trivial time delay between an observer at infinity and an observer in the regular center. We present a modification of the well-known Hayward metric that features these two properties. We discuss bounds on the maximal time delay imposed by conditions on the curvature, and the consequences for the weak energy condition, in general violated by the large transversal pressures introduced by the time delay.
10 pages, many figures. Published in General Relativity and Gravitation (March 2015)
http://inspirehep.net/record/1334933?ln=en