KIC8462852: Ingen svækkelse 1934-1995

Sonneberg plate photometry in two colors for KIC 8462852: No dimming between 1934 and 1995

ABSTRACT: The F3 main sequence star KIC 8462852 has raised interest because of its mysterious day-long brightness dips, and an unusual ~3% brightness decrease during the 4 years of the Kepler mission. Recently, a 0.164mag (~14%) dimming between 1890 and 1990 was claimed, based on the analysis of photographic plates, although this has been refuted. To resolve this controversy, we have gathered an independent set of historic data from Sonneberg Observatory, Germany. From these historic plates, we could extract 862 magnitudes in blue light, and 401 magnitudes in red light. The data cover the years 1934 to 1995 and are very evenly sampled between 1956 and 1995. In both colors, we find the star to be of constant brightness within 0.033mag/century (~3%). The previously claimed dimming is inconsistent with these data at the ∼5σ-level, however the recently reported modest dimming of ~3% in the Kepler data is not inconsistent with these data. We have also searched for periodicities and yearly trends in the data and find none within our limits of ~10% per year.

 

Gådefuldt ydre lag i Jordens kerne

Nyere seismiske målinger understøtter den hypotese, at den yderste del af Jordens kerne har et lagdelt område af en gådefuld oprindelse. Artiklen viser, at et gigantisk sammenstød med en mindre planet kan medføre en turbulent opblanding og dannelsen af et lagdelt område oven på kernen. Laget formodes dannet i forbindelse med Månens dannelse ved Jordens sammenstød med en mindre planet.

Core merging and stratification following giant impact

ABSTRACT: A stratified layer below the core–mantle boundary has long been suspected on the basis of geomagnetic and seismic observations. It has been suggested that the outermost core has a stratified layer about 100 km thick that could be due to the diffusion of light elements. Recent seismological evidence, however, supports a layer exceeding 300 km in thickness of enigmatic origin. Here we show from turbulent mixing experiments that merging between projectile and planetary core following a giant impact can lead to a stratified layer at the top of the core. Scaling relationships between post-impact core structure and projectile properties suggest that merging between Earth’s protocore and a projectile core that is enriched in light elements and 20 times less massive can produce the thick stratification inferred from seismic data. Our experiments favour Moon-forming impact scenarios involving a projectile smaller than the proto-Earth and suggest that entrainment of mantle silicates into the protocore led to metal–silicate equilibration under extreme pressure–temperature conditions. We conclude that the thick stratified layer detected at the top of Earth’s core can be explained as a vestige of the Moon-forming giant impact during the late stages of planetary accretion.

Transits of Proxima b ?

No Conclusive Evidence for Transits of Proxima b in MOST photometry

ABSTRACT: The analysis of Proxima Centauri’s radial velocities recently led Anglada-Escud’e et al. (2016) to claim the presence of a low mass planet orbiting the Sun’s nearest star once every 11.2 days. Although the a-priori probability that Proxima b transits its parent star is just 1.5%, the potential impact of such a discovery would be considerable. Independent of recent radial velocity efforts, we observed Proxima Centauri for 12.5 days in 2014 and 31 days in 2015 with the MOST space telescope. We report here that we cannot make a compelling case that Proxima b transits in our precise photometric time series. Imposing an informative prior on the period and phase, we do detect a candidate signal with the expected depth. However, perturbing the phase prior across 100 evenly spaced intervals reveals one strong false-positive and one weaker instance. We estimate a false-positive rate of at least a few percent and a much higher false-negative rate of 20-40%, likely caused by the very high flare rate of Proxima Centauri. Comparing our candidate signal to HATSouth ground-based photometry reveals that the signal is somewhat, but not conclusively, disfavored (1-2 sigmas) leading us to argue that the signal is most likely spurious. We expect that infrared photometric follow-up could more conclusively test the existence of this candidate signal, owing to the suppression of flare activity and the impressive infrared brightness of the parent star.

Mørkt stof som skalart felt

Partiklen med den skalare bølgefunktion har i dette her tilfælde en masse, som er 1022 gange lettere end den partikel, som jeg omtalte i forbindelse med superflydende mørkt stof. Den superlette bosons bølgefunktion har en udstrækning svarende til en galakses størrelse, hvorimod udstrækningen af bosonen i det superflydende kondensat svarer til middelafstanden mellem bosonerne.

Scalar Field Dark Matter in Clusters of Galaxies

ABSTRACT: One alternative to the CDM paradigm is the Scalar Field Dark Matter (SFDM) model, which assumes dark matter is a spin-0 ultra-light scalar field with a typical mass m∼10-22eV/c2 and positive self-interactions. Due to the ultra-light boson mass, the SFDM could form Bose-Einstein condensates in the very early universe, which are interpreted as the dark matter haloes. Although cosmologically the model behaves as CDM, they differ at small scales: SFDM naturally predicts fewer satellite haloes, cores in dwarf galaxies and the formation of massive galaxies at high redshifts. The ground state (or BEC) solution at zero temperature suffices to describe low-mass galaxies but fails for larger systems. A possible solution is adding finite-temperature corrections to the SF potential which allows combinations of excited states. In this work we test the finite-temperature multistate SFDM solution at galaxy cluster scales and compare our results with the NFW and BEC profiles. We achieve this by fitting the mass distribution of 13 Chandra X-ray clusters of galaxies, excluding the brightest galaxy central region. We show that the SFDM model accurately describes the clusters’ DM mass distributions offering an equivalent or better agreement than the NFW profile. The complete disagreement of the BEC model with the data is also shown. We conclude that the theoretically motivated multistate SFDM profile is an interesting alternative to empirical profiles and ad hoc fitting-functions that attempt to couple the asymptotic NFW decline with the core SFDM model.

Dannede P9 den indre Oort-sky?

Vi må endnu nøjes med teoretiske spekulationer om betydningen af Planet9 for Oort-skyens dannelse. Der er endnu intet nyt om P9. Artiklen anvender betegnelsen TAUS, som jeg mener står for Thousand AU Structure.

Shaping of the inner Oort cloud by Planet Nine

ABSTRACT: We present a numerical calculation of the dynamical interaction between the proposed Planet Nine and an initially thin circular debris disk around the Sun for 4Gyr, accounting the secular perturbation of the four giant planets. We show that Planet Nine governs the dynamics in between 1000-5000AU and forms spherical structure in the inner part (~1000AU) surrounded by an inclined disk aligned to its orbital plane. This structure is the outcome of mean motion resonances and secular interaction with Planet Nine. We compare the morphology of this structure with the outcome from a fly-by encounter of a star with the debris disk and show distinct differences between the two scenarios. We predict that this structure serves as a source of comets and calculate the resulting comet production rate to be detectable.

Elon Musks marsraket

Jeg vil benytte lejligheden til at vise udvalgte figurer fra Elon Musks præsentation af en interplanetar raket.

Raketdesign.
Raketdesign. Den drives af flydende metan og ilt.
Raptor-raketmotor.
Raptor-raketmotor.
Rumskibet, som skal lande på Mars.
Rumskibet, som skal lande på Mars.
Ærodynamisk opbremsning ved ankomsten til Mars.
Ærodynamisk opbremsning ved ankomsten til Mars.
Brændstofproduktion på Mars.
Brændstofproduktion på Mars.

 

Superflydende mørkt stof

Einstein-Bose kondensater af kolde atomer bliver rutinemæssigt produceret i laboratoriet. Det er derfor naturligt at spørge, om de mørke haloer omkring galakserne kunne være superflydende kondensater. Artiklen foreslår, at lydkvanter (fononer) i det superflydende kondensat kan vekselvirke med baryoner (protoner og neutroner) og danne en langtrækkende kraft, som kan forklare de flade rotationskurver for skivegalakser. Jeg er ikke specialist på området og artiklen er for lang og teknisk til, at jeg tidligere har kommenteret den. Men nu er emnet jo blevet bragt ud i offentlighedens søgelys.

Den observerede rotationskurve for NGC 1560 (blå punkter). MOND-kurven (grøn) giver et meget bedre fit end ΛCDM-kurven (rød).
Den observerede rotationskurve for NGC 1560 (blå punkter). MOND-kurven (grøn) giver et meget bedre fit end ΛCDM-kurven (rød).

Der er to partikeltyper: a) Bosoner med heltalligt spin og b) Fermioner med halvtalligt spin. Der kan forekomme mange bosoner i samme kvantetilstand, hvorimod der kun kan forekomme 1 fermion i en bestemt kvantetilstand. Elektronen er en fermion med halvtalligt spin. Fermionegenskaben sikrer, at elektronerne i et atom ikke alle befinder sig i grundtilstanden. Fotonen er en boson med heltalligt spin (polarisation). Bosonegenskaben tillader laserens eksistens. Man formoder, at de mørke partikler er bosoner med spin 0.

En partikel er i kvantemekanisk forstand en bølgepakke med en rumlig udstrækning σx og en impulsudstrækning σp, hvor impulsen for en ikke-relativistisk partikel er givet ved p = m⋅v (v er partiklens hastighed). Heisenbergs berømte usikkerhedsprincip siger at σxσp ≥ ℏ/2. Princippet kan også udtrykkes ved hastighedsspredningen (σv): σx ≥ ℏ/(2mσv). Jeg teldeler nu hver partikel rumfanget af en terning med sidelængden l. Hvis massefylden af det mørke stof er ρ, gælder l3ρ = m. Betingelsen for at der kan dannes et Bose-Einstein-kondensat (BEC) er σx > l, som kan omskrives til m4σv3/ρ ≤ (ℏ/2)3. Figuren viser den øvre grænse for partikelmassen m (udtrykt i eV) som funktion af haloens totale masse M udtrykt i solmasser.

Det skraverede område svarer til haloer med massen M, hvori de mørke partikler med massen m bliver superflydende (Bose-Einstein-kondensat). For en given værdi af partikelmassen m overgår stoffet kun til den superflydende tilstand for tilstrækkeligt små halomasser M, hvor det mørke stofs temperatur er under en kritisk værdi.
Det skraverede område svarer til haloer med massen M, hvori de mørke partikler med massen m bliver superflydende (Bose-Einstein-kondensat). For en given værdi af partikelmassen m overgår stoffet kun til den superflydende tilstand for tilstrækkeligt små halomasser M, hvor det mørke stofs temperatur er under en kritisk værdi.

Man kan under antagelse hydrostatisk ligevægt og sfærisk symmetri beregne tæthedsprofilen for den superflydende kerne af det mørke stof. Det viser sig, at trykket er proportionalt med ρ3. Dette er en polytrop tilstandsligning med index n = 1/2.

Hydrostatisk ligevægt kondensatet findes ved at løse Lane-Emden ligningen for en polytrop. Den vertikale retning angiver kvadratet på tætheden. Den horisontale retning angiver afstanden fra centrum. Den superflydende tilstand har en veldefineret overflade.
Den hydrostatiske ligevægt for kondensatet findes ved at løse Lane-Emden-ligningen for en polytrop. Den vertikale retning angiver kvadratet på tætheden, den horisontale retning afstanden fra centrum. Den superflydende tilstand har en veldefineret overflade.

Dark Matter Superfluidity

ABSTRACT: In this talk I summarize a novel framework that unifies the stunning success of MOND on galactic scales with the triumph of the ΛCDM model on cosmological scales. This is achieved through the rich and well-studied physics of superfluidity. The dark matter and MOND components have a common origin, representing different phases of a single underlying substance. In galaxies, dark matter thermalizes and condenses to form a superfluid phase. The superfluid phonons couple to baryonic matter particles and mediate a MOND-like force. This framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not): dark matter has a higher temperature in clusters, and hence is in a mixture of superfluid and normal phase. The rich and well-studied physics of superfluidity leads to a number of striking observational signatures, which we briefly discuss. Remarkably the critical temperature and equation of state of the dark matter superfluid are similar to those of known cold atom systems. Identifying a precise cold atom analogue would give important insights on the microphysical interactions underlying DM superfluidity. Tantalizingly, it might open the possibility of simulating the properties and dynamics of galaxies in laboratory experiments.

Justin Khoury har en anden artikel, som foreslår en anden vej mod MOND-fænomenet i superflydende mørkt stof:

Another Path for the Emergence of Modified Galactic Dynamics from Dark Matter Superfluidity

ABSTRACT: In recent work we proposed a novel theory of dark matter (DM) superfluidity that matches the successes of the LambdaCDM model on cosmological scales while simultaneously reproducing MOdified Newtonian Dynamics (MOND) phenomenology on galactic scales. The agents responsible for mediating the MONDian force law are superfluid phonons that couple to ordinary (baryonic) matter. In this paper we propose an alternative way for the MOND phenomenon to emerge from DM superfluidity. The central idea is to use higher-gradient corrections in the superfluid effective theory. These next-to-leading order terms involve gradients of the gravitational potential, and therefore effectively modify the gravitational force law. In the process we discover a novel mechanism for generating the non-relativistic MOND action, starting from a theory that is fully analytic in all field variables. The idea, inspired by the symmetron mechanism, uses the spontaneous breaking of a discrete symmetry. For large acceleration, the symmetry is unbroken and the action reduces to Einstein gravity. For small acceleration, the symmetry is spontaneously broken and the action reduces to MONDian gravity. Cosmologically, however, the universe is always in the Einstein-gravity, symmetry-restoring phase. The expansion history and linear growth of density perturbations are therefore indistinguishable from LambdaCDM cosmology.

 

En universel rotationskurve

Salucci og samarbejdspartnere har i de seneste 20 år arbejdet på, at tilpasse en universel rotationskurve til målte rotationshastigheder V(R) for normale skivegalakser. Den såkaldte universelle rotationskurve (URC) fremkommer ved en dobbelt normalisering: V(R/Ropt)/V(Ropt). Den optiske radius Ropt er defineret som den radius, der omslutter 83% af galaksens totale luminositet. Karukes & Salucci har nu fortsat arbejdet ved at bestemme den universelle rotationskurve (ddURC) for dværg-diskgalakser. I disse galakser dominerer det mørke stof over det baryoniske stof (stjerner+gas) for alle radiale værdier. Den følgende figur viser de individuelle rotationskurver normeret til Ropt og Vopt = V(Ropt):

Individuelle normaliserede rotationskurver. De sorte stjerner viser den syntetiske rotationskurve, som er fremkommet ved at tage middelværdier for alle punkter mellem de lodrette stiplede linier.
Individuelle normaliserede rotationskurver. De sorte stjerner viser den syntetiske rotationskurve, som er fremkommet ved at tage middelværdier for alle punkter mellem de lodrette stiplede linier.

Den næste figur viser den syntetiske RC (fyldte cirkler med usikkerheder) og den tilpassede URC med dens tilhørende mørke og baryoniske bidrag:

Den målte rotationskurve med de tilpassede mørke og lysende bidrag. Stjerneskiven: rød, gas: blå, mørk halo: brun, sum af alle: pink.
Den målte rotationskurve med de tilpassede mørke og lysende bidrag. Stjerneskiven: rød, gas: blå, mørk halo: brun, sum af alle: pink.

De øvrige kurver skulle vise 3 forskellige modeller for det mørke stof. Figuren er uheldigvis overlæsset med kurver. Den første er en analytisk model, som Burkert har foreslået (der er ingen fysik bag modellen). Den anden er baseret på kosmologiske simuleringer med rent mørkt stof. Den passer dårligt med observationerne, idet tæthedsfordelingen har en spids i centret. Den sidste kurve er baseret på nogle hydrodynamiske simuleringer med feedback fra stjernedannelsesområder i skiven. Den første og den sidste model passer fint med observationerne, idet begge har en flad massefordeling nær centret af galaksen. Den sidste figur viser, at der er en tæt relation mellem kernens (for det mørke stof) radius og stjerneskivens skalalængde.

De røde cirkler repræsenterer værdier for normale spiralgalakser. Den grønne cirkel repræsenterer den universelle rotationskurve for alle dværg-skivegalakser.
De røde cirkler repræsenterer værdier for normale spiralgalakser. Den grønne cirkel repræsenterer den universelle rotationskurve for alle dværg-skivegalakser.

Der er helt klart en tæt relation mellem kernens størrelse for det mørke stof og stjerneskivens størrelse. Jeg er blevet opmærksom på artiklen:
A mass-dependent density profile for dark matter haloes including the influence of galaxy formation

The universal rotation curve of dwarf disk galaxies

ABSTRACT: We use the concept of the spiral rotation curves universality (see Parsic et al. 1996) to investigate the luminous and dark matter properties of the dwarf disk galaxies in the local volume (size 11 Mpc). Our sample includes 36 objects with rotation curves carefully selected from the literature. We find that, despite the large variations of our sample in luminosities ( 2 of dex), the rotation curves in specifically normalized units, look all alike and lead to the lower-mass version of the universal rotation curve of spiral galaxies found in Parsic et al. 1996.
We mass model V(R/Ropt)/Vopt, the double normalized universal rotation curve of dwarf disk galaxies: the results show that these systems are totally dominated by dark matter whose density shows a core size between 2 and 3 stellar disk scale lengths. Similar to galaxies of different Hubble types and luminosities, the core radius r0 and the central density ρ0 of the dark matter halo of these objects are related by ρ0r0100Mpc-2.
The structural properties of the dark and luminous matter emerge very well correlated. In addition, to describe these relations, we need to introduce a new parameter, measuring the compactness of light distribution of a (dwarf) disk galaxy. These structural properties also indicate that there is no evidence of abrupt decline at the faint end of the baryonic to halo mass relation. Finally, we find that the distributions of the stellar disk and its dark matter halo are closely related.

 

Mordehai Milgroms MOND

McGaugh, Lelli og Schomberts artikel har bragt Mordehai Milgrom helt op i det røde felt for ikke tydeligt at understrege, at deres relation er intet andet end Milgroms MOND-teori fra 1983 anvendt på galakserne.

MOND impact of the recently updated mass-discrepancy-acceleration relation

ABSTRACT: McGaugh et al. (2016) have used their extensive SPARC sample to update the well-known mass-discrepancy-acceleration relation (MDAR), which is one of the major predicted “MOND laws”. This is not a newly discovered relation. Rather, it improves on the many previous studies of it, with more and better data. Like its precedents, it bears crucial ramifications for the observed dynamical anomalies in disc galaxies, and, in particular, on their resolution by the MOND paradigm. Their result, indeed, constitute a triumph for MOND. However, unlike previous analyses of the MDAR, McGaugh et al. have chosen to obfuscate the MOND roots of their analysis, and its connection with, and implications for, this paradigm. For example, the fitting formula they use, seemingly as a result of some unexplained inspiration, follows in its salient properties from the basic tenets of MOND, and has already been used in the past in several MOND analyses. No other possible origin for such a function is known. Given that this formula had already been shown to reproduce correctly the observed rotation curves from the baryon distribution (as a MOND effect), it must have been clear, a priory, that it should describe correctly the MDAR, which is but a summary of rotation curves. The present paper corrects these oversights — bringing to light the deep connections with MOND, suppressed by McGaugh et al. It also gives due credit to previous works, and discusses some new, important, but less known, aspects of this MOND relation.

Radial acceleration i skivegalakser

Det har i 40 år været kendt, at rotationskurver V(R) for rotationsunderstøttede galakser ikke har den form, som man skulle forvente ud fra massen i stjerner og gas (den baryoniske masse). Den konventionelle forklaring er, at galaksens stjerner og gas befinder sig i en halo af koldt mørkt stof. McGaugh, Lelli & Schombert rapporterer, at der findes en universel relation mellem den radiale acceleration, gobs, beregnet ud fra den observerede rotationskurve og den forudsagte acceleration, gbar, beregnet ud fra den observerede fordeling af baryoner. 2693 radiale punkter i 153 galakser med meget forskellige morfologier, masser, størrelser og relative gasindhold falder langs den samme universelle relation. Selv for galakser, hvor det mørke stof dominerer, følger de radiale punkter den samme relation. Dette betyder, at accelerationen fra det mørke stof er fuldt bestemt ved accelerationen fra baryonerne. Den observerede spredning om relationen er lille og for det meste domineret af observationsmæssige usikkerheder. Accelerationsrelationen er ensbetydende med eksistensen af en naturlov for rotationsunderstøttede galakser.

Den følgende figur viser eksempler på massemodeller og rotationskurver for tre individuelle galakser:

Punkterne med fejlsøjler i det øverste panel viser de målte rotationskurver V(R).
Punkterne med fejlsøjler i det øverste panel viser de målte rotationskurver V(R). De baryoniske komponenter: …… er gas, _  _  _ er stjerneskiven,  _ . _ . _. er den centrale bule. Summen af de baryoniske komponenter er den blå kurve. De nederste paneler viser den observerede acceleration som funktion af  den baryoniske acceleration.

Den næste figurs øverste panel viser den observerede radiale acceleration beregnet som gobs = V2(R)/R plottet mod den forudsagte acceleration, gbar=|∂Φbar/∂R|, ud fra den målte fordeling af baryoner. Næsten 2700 individuelle datapunkter for 153 galakser er inkluderet:

xxx
De store røde firkanter er middelværdier for de binnede data.

Forfatterne finder en meget tæt relation mellem den observerede radiale acceleration og den radiale acceleration fra de observerede baryoner. Relationen er fuldstændigt empirisk. De har ikke forudsat nogen speciel halomodel for det mørke stof. Fordelingen af det mørke stof er en direkte følge af relationen, idet den radiale acceleration fra det mørke stof kan skrives som

gDM = gobs – gbar = gbar/[exp(√(gbar/g0))-1], hvor g0 = 1.2 ±0.02(tilfældig) ±0.24(systematisk) x 10-10 m/s2 er en accelerationsskala.

Forfatterne nævner 3 mulige fortolkninger af relationen

  1. Den repræsenterer det afsluttede produkt af galaksedannelsen.
  2. Den repræsenterer en ny fysik i den mørke sektor.
  3. Den er et resultat af nye dynamiske love i stedet for mørkt stof.

Relationen synes at være en naturlov, en slags Keplers lov for roterende galakser. Hvis man antager, at der kræves en ny dynamisk lov, som afviger fra den newtonske gravitationslov ved accelerationer mindre end g0, vil Keplers 3. lov for solsystemet bryde sammen for afstande omkring 104 AU, som igen svarer til omløbstider på ca. 106 år.

The Radial Acceleration Relation in Rotationally Supported Galaxies

ABSTRACT: We report a correlation between the radial acceleration traced by rotation curves and that predicted by the observed distribution of baryons. The same relation is followed by 2693 points in 153 galaxies with very different morphologies, masses, sizes, and gas fractions. The correlation persists even when dark matter dominates. Consequently, the dark matter contribution is fully specified by that of the baryons. The observed scatter is small and largely dominated by observational uncertainties. This radial acceleration relation is tantamount to a natural law for rotating galaxies.