jeudi 25 août 2016

The bumpy road to the discovery of quasars and massive black holes

Invitation to a Midsummer Night's Dream Reading

My intention in this talk is to share a story in which I was very fortunate to participate almost since the beginning, but which is often ignored by the young generation of astronomers. It is the story of the discovery of Massive Black Holes (MBHs). Since everybody in this assembly knows well the subject in its present stage of development, I thought indeed that it could be interesting to show how the ideas that people take for granted presently had such difficulties to emerge and to gain credence. I think that this subject allows, better than any others, to observe that research is not “a long quiet river”, and on the contrary evolves in a non-linear and erratic way, full of mistakes and of dead ends, and that it gives rise to passionate controversies. We will see that the story of MBHs is made of fruitless researches opening on unexpected discoveries, come-backs of visionary models which were first neglected, temporary very fashionable but wrong models, strong debates involving even new physical laws, misinterpretations responsible for decades of stagnation, thousands of papers and nights of the largest telescopes. But finally it opened on a coherent physical model and on a new vision of galaxy evolution. Since it is a long story, I have selected only a few fragments...
Suzy Collin (Submitted on 27 Apr 2006 (v1), last revised 1 Sep 2006 (this version, v3))

The article is not long in fact. I reproduce below its two figures as lobby cards to advertise its reading!

Figure 1. This radio map of NGC 6251, as published by Readhead, Cohen & Blandford in 1978, shows that a small jet 5 light-years long is aligned with a larger jet of 600 000 light-years, itself aligned with the direction of the radio lobes, separated by 9 millions light-years. The fact that the two jets at the small and intermediate scales are seen only on one side, while the lobes at large scale are almost symmetrical with respect to the galaxy, proves that the side of the jet directed towards us is relativistic boosted, and therefore that the bulk velocity of the jet is very close to the velocity of light. {It was a fundamental discovery to support the cosmological distance hypothesis of quasars}
Figure 2. Cartoon produced by McCray at the Cambridge summer school in 1977 and called “Response of astrophysicists to a fashionable new idea”. I extract a few lines from his paper: “Beyond the accretion radius, r, astrophysicists are sufficiently busy to not be influenced by the fashionable new idea. But others, within r, begin a headlong plunge towards it... In their rush to be the first, they almost invariably miss the central point, and fly off on some tangent... In the vicinity of the idea, communication must finally occur, but it does so in violent collisions... Some individuals may have crossed the rationality horizon rs beyond which the fashionable idea has become an article of faith. These unfortunate souls never escape. Examples of this latter phenomenon are also familiar to all of us.”
Pour le lecteur francophone je recommande chaudement la lecture d'un autre texte de Susy Collin-Zahn lui aussi extrêmement pédagogique et informatif sur les controverses autour des quasars et plus généralement autour du modèle cosmologique standard : La théorie du Big Bang rend bien compte des décalages observés publié sur le riche site Science... et pseudo-sciences.

mercredi 24 août 2016

The seven pillars of (heuristical) wisdom

... it helps to recall the definition of an expert as a man who knows all the mistakes possible in his field*. Our whole problem is to make the mistakes as fast as possible- my part- and recognize them** -your part! Can a unifying concept in one field be applied in another? Let me call on a septet of sibyls to say yes if they will.
Sayings of the seven sibyls
(1) The Unknown is Knowable
(2) Advance by Trial and Error 
(3) Measurement and Theory are Inseparable
(4) Analogy Gives Insight
(5) New Truth Connects with Old Truth
(6) Complementarity Guards against Contradiction
(7) Great Consequences Spring from Lowly Sources
 John Archibald Wheeler

* Approximate quote possibly attributable to Niels Bohr, the real one being "An expert is a person who has found out by his own painful experience all the mistakes that one can make in a very narrow field" according to Edward Teller.

Addendum on August 25, 2016:
Fluctuat [et,nec] mergitur
This post is dedicated to the whole community of physicists at LHC and is also a continuation of my comment on the blog Resonaance about the huge amount of research articles devoted to the now notorious excess of events at invariant mass around 750 GeV in pp → γγ collisions, first reported [1a, 1b] in the preliminary 2015 LHC data collected at 13 TeV and later fading away in the new 2016 LHC data [2a, 2b].

**For why it can be difficult to admit mistakes some psychologists have explained with the theory of cognitive dissonance.  

lundi 4 juillet 2016

Neutrino physics cold[ol] case{s}

The 20th century (story of the) neutrino
In the recent past, two Nobel Prizes were given to Neutrino Physics. In 2002 Ray Davis of USA and Matoshi Koshiba of Japan got the Nobel Prize for Physics while last year (2015) Arthur McDonald of Canada and Takaaki Kajita of Japan got the Nobel Prize. To understand the importance of neutrino research it is necessary to go through the story of the neutrino in some detail. 
Starting with Pauli and Fermi, the early history of the neutrino is described culminating in its experimental detection by Cowan and Reines. Because of its historical importance the genesis of the solar neutrino problem and its solution in terms of neutrino oscillation are described in greater detail. In particular, we trace the story of the 90-year-old thermonuclear hypothesis which states that the Sun and the stars are powered by thermonuclear fusion reactions and the attempts to prove this hypothesis experimentally. We go through Davis’s pioneering experiments to detect the neutrinos emitted from these reactions in the Sun and describe how the Sudbury Neutrino Observatory in Canada was finally able to give a direct experimental proof of this hypothesis in 2002 and how, in the process, a fundamental discovery i.e. the discovery of neutrino oscillation and neutrino mass was made. 
We next describe the parallel story of cosmic-ray-produced neutrinos and how their study by SuperKamioka experiment in Japan won the race by discovering neutrino oscillations in 1998. 
Many other important issues are briefly discussed at the end...
Milestones in the neutrino story

  • 1930 Birth of Neutrino: Pauli 
  • 1932 Theory of beta decay, ”Neutrino” named: Fermi
  • 1954 First detection of neutrino: Cowan and Reines 
  • 1964 Discovery of muneutrino: Lederman, Schwartz and Steinberger 
  • 1965 Detection of atmospheric neutrino: KGF 1970 Start of the solar neutrino experiment: Davis 
  • 1987 Detection of neutrinos from supernova: SuperKamioka 
  • 1998 Discovery of neutrino oscillation and mass: SuperKamioka
  • 2001 Discovery of tauneutrino: DONUT 
  • 2002 Solution of the solar neutrino puzzle: SNO 
  • 2005 Detection of geoneutrinos: KamLAND 
  • 2013 Detection of ultra high energy neutrinos from space: Ice Cube 

G Rajasekaran (Institute of Mathematical Sciences, Chennai & Chennai Mathematical Institute) (Submitted on 22 Jun 2016)

A potential 21st century counterpart...
What exactly is Dark Matter? New theories for what really constitutes Dark Matter appear to make the news headlines every week. At a slower pace, these theories are slowly being eliminated. We revisit this scientific thriller and make the case that condensed neutrino matter is a leading suspect. We provide a forensic discussion of some subtle evidence and show that independent experimental results due out in 2019 from the KATRIN experiment [1] will either be the definitive result or eliminate condensed neutrinos as a Dark Matter candidate... The ... experiment ... will have the sensitivity to determine the mass of the electron antineutrino down to 0.35 eV/c2 ... This mass range for the electron antineutrino is in direct contradiction to the upper bound claimed by the Planck satellite consortium. If KATRIN discovers a neutrino mass in this range, we contend that the cosmological blackbody radiation raw data analysis must be revisited and that it would be a major finding endorsing condensed neutrinos as the so-called Dark Matter, which everyone has been looking for.
(Submitted on 27 Jun 2016)
... and another speculative (rival?) one here

jeudi 16 juin 2016

Gravitational wave astronomy stays pitch-black (up to now)

No electromagnetic counterparts from optical wavelengths...
We present a search for an electromagnetic counterpart of the gravitational wave source GW151226. Using the Pan-STARRS1 telescope we mapped out 290 square degrees in the optical i_ps filter over a period starting 11.45hr after the LIGO information release (49.48hr after the GW trigger) and lasting for a further 28 days. We typically reached sensitivity limits of i_ps=20.3-20.8 and covered 26.5% of the LIGO probability skymap. We supplemented this with ATLAS survey data, reaching 31% of the probability region to shallower depths of m~19. We found 49 extragalactic transients (that are not obviously AGN), including a faint transient in a galaxy at 7Mpc (a luminous blue variable outburst) plus a rapidly decaying M-dwarf flare. Spectral classification of 20 other transient events showed them all to be supernovae. We found an unusual transient, PS15dpn, with an explosion date temporally coincident with GW151226 which evolved into a type Ibn supernova. The redshift of the transient is secure at z=0.1747 +/- 0.0001 and we find it unlikely to be linked, since the luminosity distance has a negligible probability of being consistent with that of GW151226. In the 290 square degrees surveyed we therefore do not find a likely counterpart. However we show that our survey strategy would be sensitive to Neutron Star-Nentron Star mergers producing kilonovae at D < 100 Mpc, which is promising for future LIGO/Virgo searches.
S. J. Smartt et al, (Submitted on 15 Jun 2016)

 ... to gamma ray ones
We present the Fermi Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) observations of the LIGO binary black hole merger event GW151226 and candi- date LVT151012. No candidate electromagnetic counterparts were detected by either the GBM or LAT. We present a detailed analysis of the GBM and LAT data over a range of timescales from seconds to years, using automated pipelines and new techniques for char- acterizing the upper limits across a large area of the sky. Due to the partial GBM and LAT coverage of the large LIGO localization regions at the trigger times for both events, differences in source distances and masses, as well as the uncertain degree to which emission from these sources could be beamed, these non-detections cannot be used to constrain the variety of theoretical models recently applied to explain the candidate GBM counterpart to GW150914.
J. L. Racusin et al, (Submitted on 15 Jun 2016)

mercredi 15 juin 2016

GW151226 : Second direct detection (first replication) of a gravitational wave detection !

Live : !

The first available animation !

The Paper !
We report the observation of a gravitational-wave signal produced by the coalescence of two stellar-mass black holes. The signal, GW151226, was observed by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) on December 26, 2015 at 03:38:53 UTC. The signal was initially identified within 70 s by an online matched-filter search targeting binary coalescences. Subsequent off-line analyses recovered GW151226 with a network signal-to-noise ratio of 13 and a significance greater than 5σ. The signal persisted in the LIGO frequency band for approximately 1 s, increasing in frequency and amplitude over about 55 cycles from 35 to 450 Hz, and reached a peak gravitational strain of 3.4±0.7±0.9×10-22. The inferred source-frame initial black hole masses are 14.2±8.3±3.7M and 7.5±2.3±2.3M, and the final black hole mass is 20.8±6.1±1.7M. We find that at least one of the component black holes has spin greater than 0.2. This source is located at a luminosity distance of 440±180±190 Mpc corresponding to a redshift of 0.09±0.03 ±0.04 . All uncertainties define a 90% credible interval. This second gravitational-wave observation provides improved constraints on stellar populations and on deviations from general relativity
GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence B. P. Abbott et al.* (LIGO Scientific Collaboration and Virgo Collaboration) (Received 31 May 2016; published 15 June 2016) 

mercredi 8 juin 2016

Higgs times seven (minus one) / sept moins une fois le boson de Higgs

750 GeV = 6×125 GeV!

The first LHC data about pp collisions at √ s = 13 TeV agree with the Standard Model (SM), except for a hint of an excess in pp → γγ peaked at invariant mass around 750 GeV [1]. We denote the new resonance with the symbol {digamma}, used in archaic greek as the digamma letter and later as the number 6 ≈ Mz/Mh, but disappeared twice... unlike many other anomalies that disappeared, the γγ excess cannot be caused by a systematic issue, neither experimental nor theoretical. Theoretically, the SM background is dominated by tree-level q→ γγ scatterings, which cannot make a γγ resonance [See {below} for a attempt of finding a Standard Model interpretation.] Experimentally, one just needs to identify two photons and measure their energy and direction. The γγ excess is either the biggest statistical fluctuation since decades, or the main discovery.
(Submitted on 30 May 2016)

750 GeV scalar boson = (6 top quarks + 6 antitop quarks) bound state?
We shall here explore the possibility that the diphoton excess in the inclusive γγ spectrum, recently found by the ATLAS and CMS collaborations [1, 2], with a mass of 750 GeV can be a bound state of particles already present in the Standard Model, namely a bound state of 6 top + 6 antitop quarks. Thus we would need no new fundamental particles, interactions or free parameters beyond the Standard Model to explain this peak, which otherwise looks like “new physics”!  
For several years we have worked on the somewhat controversial idea [3, 4, 5, 6, 7, 8] that the exchange of Higgses and gluons between 6 top and 6 antitop quarks provides sufficiently strong attraction between these quarks for a very light (compared to the mass of 12 top quarks) bound state S to be formed. The 6 tops + 6 antitops are all supposed to be in the 1s state in the atomic physics notation and, because of there being just 3 colors and 2 spin states for a top-quark, this is the maximum number allowed in the 1s shell. 
Further speculations around this bound state were mostly built up under the assumption of a hoped for new principle – the multiple point principle [9, 10, 11] – from which we actually predicted the mass of the Higgs boson long before it was found [12]. This principle says that there shall be several phases of space (i.e. several vacua) with the same energy density. One of these should have a condensate of the bound states S. It was even speculated then that such a condensate – or new vacuum – could form the interior of balls, containing highly compressed ordinary matter, which make up the dark matter [13, 14, 15]. Thus the discovery, if confirmed, of the bound state S could support a theory, in which dark matter could be incorporated into a pure Standard Model theory, only adding the multiple point principle, which predicts the values of coupling constants but otherwise without new physics.
(Submitted on 12 May 2016)

mardi 12 avril 2016

Riding on a laser beam ...

...  to chase the Starshot interstellar flight dream?

In the nearly 60 years of spaceflight we have accomplished wonderful feats of exploration that have shown the incredible spirit of the human drive to explore and understand our universe. Yet in those 60 years we have barely left our solar system with the Voyager 1 spacecraft launched in 1977 finally leaving the solar system after 37 years of flight at a speed of 17 km/s or less than 0.006% the speed of light. As remarkable as this is we will never reach even the nearest stars with our current propulsion technology in even 10 millennium. We have to radically rethink our strategy or give up our dreams of reaching the stars, or wait for technology that does not currently exist. While we all dream of human spaceflight to the stars in a way romanticized in books and movies, it is not within our power to do so, nor it is clear that this is the path we should choose. We posit a technological path forward, that while not simple, it is within our technological reach. We propose a roadmap to a program that will lead to sending relativistic probes to the nearest stars and will open up a vast array of possibilities of flight both within our solar system and far beyond. Spacecraft from gram level complete spacecraft on a wafer ("wafersats") that reach more than 1/4 c and reach the nearest star in 20 years to spacecraft with masses more than 10^5 kg (100 tons) that can reach speeds of greater than 1000 km/s. These systems can be propelled to speeds currently unimaginable with existing propulsion technologies. To do so requires a fundamental change in our thinking of both propulsion and in many cases what a spacecraft is. In addition to larger spacecraft, some capable of transporting humans, we consider functional spacecraft on a wafer, including integrated optical communications, imaging systems, photon thrusters, power and sensors combined with directed energy propulsion.

...Directed energy systems are ubiquitous, used throughout science and industry to melt or vaporize solid objects, such as for laser welding & cutting, as well as in defense. Recent advances in photonics now allow for a 2D array of phase locked laser amplifiers fed by a common low power seed laser that have already achieved near 50% wall plug conversion efficiency. It is known as a MOPA (Master Oscillator Power Amplifier) design. 
Schematic design of phased array laser driver. Wavefront sensing from both local and extended systems combined with the system metrology are critical to forming the final beam.

The technology is proceeding on a "Moore's Law" like pace with power per mass at 5 kg/kW with the size of a 1 kW amplifier not much larger than a textbook. There is already a roadmap to reduce this to 1 kg/kW in the next 5 years and discussions for advancing key aspects of the technology to higher TRL are beginning. These devices are revolutionizing directed energy applications and have the potential to revolutionize many related applications. Due to the phased array technology the system can simultaneous send out multiple beams and thus is inherently capable of simultaneous multitasking as well as multi modal.  
The laser system can be built and tested at any level from desktop to extremely large platforms. This is radically different than the older "use a huge laser" approach to photon propulsion. This is the equivalent to modern parallel processing vs an older single processor supercomputer

Parameters for full class 4 [a 10 km array] system with 1 g wafer SC and 1 m sail. Craft achieves 0.2 c in about 10 min (assuming an extended illumination) and takes about 20 years to get to Alpha Centauri. Communications rate assumes class 4 drive array is also used for reception with a 1 watt short burst from a 100 mm wafer SC. Here we use the 1 meter drive reflector as the transmit and receive optical system on the spacecraft. We also assume a photon/bit ratio near unity. In this case we get a data rate at Andromeda of about 65 kb/s. In the previous figure for the same wafer scale spacecraft the only optical system on the spacecraft was the 100 mm wafer. The data rate received at the Earth from Alpha Centauri is about 0.65 kbs during the burst assuming we can use the DE-STAR 4 driver as the receiver and only the wafer itself for the transmission optic. The plot above shows a much more conservative photon/bit ratio of 40 while unity has been achieved but never over the extremely long distances discussed here.
(Submitted on 5 Apr 2016 (v1), last revised 7 Apr 2016 (this version, v2))

//added on April 13, 2016: I guess some of the advances in photonics are spin-off applications of the late Strategic Defense Initiative but it is fascinating that they could be the backbone of the new Yuri Milner scientific/speculative breakthrough initiative publicized yesterday.
Anyway the future of large phased-array lasers in Earth orbit could definitely be in Directed Energy System for Targeting of Asteroids and exploRation at a time when nuclear ballistic missiles are likely not the most pressing threat anymore...