Orbital Period Decay Research Articles

Ticking away: The long-term X-ray timing and spectral evolution of eRO-QPE2

Quasi-periodic eruptions (QPEs) are repeated X-ray flares from galactic nuclei that recur every few hours to days, depending on the source. Despite some diversity in the recurrence and amplitude of eruptions, their striking regularity has motivated theorists to associate QPEs with orbital systems. Among the known QPE sources, eRO-QPE2 has shown the most regular flare timing and luminosity since its discovery. We report here on its long-term evolution over 3.3 yr from discovery and find that: i) the average QPE recurrence time per epoch has decreased over time, albeit not at a uniform rate; ii) the distinct alternation between consecutive long and short recurrence times found at discovery has not been significant since; iii) the spectral properties, namely flux and temperature of both eruptions and quiescence components, have remained remarkably consistent within uncertainties. We attempted to interpret these results as orbital period and eccentricity decay coupled with orbital and disk precession. However, since gaps between observations are too long, we are not able to distinguish between an evolution dominated by just a decreasing trend, or by large modulations (e.g. due to the precession frequencies at play). In the former case, the observed period decrease is roughly consistent with that of a star losing orbital energy due to hydrodynamic gas drag from disk collisions, although the related eccentricity decay is too fast and additional modulations have to contribute too. In the latter case, no conclusive remarks are possible on the orbital evolution and the nature of the orbiter due to the many effects at play. However, these two cases come with distinctive predictions for future X-ray data: in the case of a decreasing trend, we expect all future observations to show a shorter recurrence time than the latest epoch, while in the case of large-amplitude modulations we expect some future observations to be found with a larger recurrence, hence an apparent temporary period increase.

Listening to dark sirens from gravitational waves : Combined effects of fifth force, ultralight particle radiation, and eccentricity

We analyse the orbital period decay in compact binary systems influenced by a fifth force and ultralight particle radiation, considering a general eccentric Keplerian orbit. The analysis provides constraints on the axion decay constant when orbital period decay involves axionic fifth force and axion radiation. The bound on axion coupling improves by an order of magnitude for high eccentricity binaries like the Hulse–Taylor binary. These bounds become stronger when considering both axion mediation and radiation. We also derive constraints on the strengths of the fifth force and radiation from GW170817 by measuring the Chirp mass, which depends on initial eccentricity. The coalescence time increases with higher initial eccentricity compared to the gravity-only scenario, highlighting the importance of accurately selecting initial eccentricity for setting bounds on fifth force searches in precision gravitational wave detection. Additionally, we provide model-independent estimates for dark matter capture by a binary system. The derived constraints can be further strengthened with the use of second and third generation gravitational wave detectors.

TESS Giants Transiting Giants. VI. Newly Discovered Hot Jupiters Provide Evidence for Efficient Obliquity Damping after the Main Sequence

The degree of alignment between a star’s spin axis and the orbital plane of its planets (the stellar obliquity) is related to interesting and poorly understood processes that occur during planet formation and evolution. Hot Jupiters orbiting hot stars (≳6250 K) display a wide range of obliquities, while similar planets orbiting cool stars are preferentially aligned. Tidal dissipation is expected to be more rapid in stars with thick convective envelopes, potentially explaining this trend. Evolved stars provide an opportunity to test the damping hypothesis, particularly stars that were hot on the main sequence and have since cooled and developed deep convective envelopes. We present the first systematic study of the obliquities of hot Jupiters orbiting subgiants that recently developed convective envelopes using Rossiter–McLaughlin observations. Our sample includes two newly discovered systems in the Giants Transiting Giants survey (TOI-6029 b, TOI-4379 b). We find that the orbits of hot Jupiters orbiting subgiants that have cooled below ∼6250 K are aligned or nearly aligned with the spin axis of their host stars, indicating rapid tidal realignment after the emergence of a stellar convective envelope. We place an upper limit for the timescale of realignment for hot Jupiters orbiting subgiants at ∼500 Myr. Comparison with a simplified tidal evolution model shows that obliquity damping needs to be ∼4 orders of magnitude more efficient than orbital period decay to damp the obliquity without destroying the planet, which is consistent with recent predictions for tidal dissipation from inertial waves excited by hot Jupiters on misaligned orbits.

Investigating the orbital evolution of the eccentric HMXB GX 301–2 using long-term X-ray light curves

ABSTRACT We report the orbital decay rate of the high-mass X-ray binary GX 301–2 from an analysis of its long-term X-ray light curves and pulsed flux histories from CGRO/BATSE, RXTE/ASM, Swift/BAT, Fermi/GBM, and MAXI by timing the pre-periastron flares over a span of almost 30 yr. The time of arrival of the pre-periastron flares exhibits an energy dependence (hard lag) and the orbital period decay was estimated after correcting for it. This method of orbital decay estimation is unaffected by the fluctuations in the spin rate of the X-ray pulsar associated with variations in the mass accretion rate. The resulting $\dot{P}_\textrm {orb}$ = −(1.98 ± 0.28) × 10−6 s s−1 indicates a rapid evolution time-scale of $|P_\textrm {orb}/\dot{P}_\textrm {orb}|\sim 0.6\times 10^{5}$ yr, making it the high mass X-ray binary with the fastest orbital decay. Our estimate of $\dot{P}$orb is off by a factor of ∼2 from the previously reported value of −(3.7 ± 0.5) × 10−6 s s−1 estimated from pulsar TOA analysis. We discuss various possible mechanisms that could drive this rapid orbital decay and also suggest that GX 301–2 is a prospective Thorne–Żytkow candidate.

Gravitational radiation from binary systems in f(R) gravity: A semi-classical approach

The rate of energy loss and orbital period decay of quasi- stable compact binary systems are derived in f(R) theory of gravity using the method of a single vertex graviton emission process from a classical source. After linearising the f(R) action written in an equivalent scalar-tensor format in the Einstein frame, we identify the appropriate interaction terms between the massless spin-2 tensor mode, massive scalar mode, and the energy momentum tensor. The definition of the scalar field is related to the f(R) models. Then using the interaction vertex we compute the rate of energy loss due to spin-2 quadrupole radiation, which comes out to be the same as the Peter-Mathews formula with a multiplication factor, and also the energy loss due to the scalar dipole radiation. The total energy loss is the sum of these two contributions. Our derivation is most general as it is applicable for both arbitrary eccentricity of the binary orbits and arbitrary mass of the scalar field. Using the derived theoretical formula for the period decay of the binary systems, we compare the predictions of f(R) gravity and general relativity for the observations of four binary systems, i.e. Hulse-Taylor Binary, PSR J1141-6545, PSR J1738+0333, and PSR J0348+0432. Thus we put bound on three well-known f(R) dark energy models, namely the Hu-Sawicki, the Starobinsky, and the Tsujikawa model. We get the best constraint on f'(R 0)-1 (where R 0 is the scalar curvature of the Universe at the present epoch) from the Tsujikawa model, i.e |f'(R 0)-1| < 2.09 × 10-4. This bound is stronger than those from most of the astrophysical observations and even some cosmological observations.

Tests of gravitational scalar polarization and constraints of chameleon f(R) gravity from comprehensive analysis of binary pulsars

Chameleon $f(R)$ gravity is equivalent to a class of scalar-tensor theories of gravity with chameleon screening mechanism allowing the theory to satisfy local tests of gravity. Within the framework of chameleon $f(R)$, we study the impact of the chameleon mechanism on the orbital evolution of binary pulsars, and calculate in detail the post-Keplerian (PK) effects (periastron advance, Einstein delay, Shapiro delay, orbital period decay and eccentricity decay) of binary orbit. The differences in PK effects between general relativity (GR) and chameleon $f(R)$ are elegantly quantified by a combination of star's compactness and theory parameter. We use the mass-radius relation to break the degeneracy between these two parameters, thus allowing us to constrain the theory. We simulate the temporal evolution of the orbital period and eccentricity of neutron star (NS) - white dwarf (WD) binaries, and the results indicate that the orbital evolution is typically faster than in GR due to the emission of dipole radiation in chameleon $f(R)$. We use the observables of PK parameters from the three NS-WD binary pulsars to place constraints on chameleon $f(R)$ and possible deviations from GR by performing Monte-Carlo simulations. We find that PSR J1738$+$0333 is the most constraining test of chameleon $f(R)$ in these systems. Our results show no solid evidence of the existence of helicity-0 or helicity-1 polarization states inducing dipole radiation, exclude significant strong-field deviations and confirm that GR is still valid for strong-field asymmetric systems.

Transit Timing Variation of XO-3b: Evidence for Tidal Evolution of Hot Jupiter with High Eccentricity

Observed transit timing variation (TTV) potentially reveals the period decay caused by star-planet tidal interaction which can explain the orbital migration of hot Jupiters. We report the TTV of XO-3b, using TESS observed timings and archival timings. We generate a photometric pipeline to produce light curves from raw TESS images and find the difference between our pipeline and TESS PDC is negligible for timing analysis. TESS timing presents a shift of 17.6 minutes (80σ), earlier than the prediction from the previous ephemeris. The best linear fit for all timings available gives a Bayesian Information Criterion (BIC) value of 439. A quadratic function is a better model with a BIC of 56. The period derivative obtained from a quadratic function is −6.2 × 10−9 ± 2.9 × 10−10 per orbit, indicating an orbital decay timescale 1.4 Myr. We find that the orbital period decay can be well explained by tidal interaction. The “modified tidal quality factor” would be 1.8 × 104 ± 8 × 102 if we assume the decay is due to the tide in the planet; whereas would be 1.5 × 105 ± 6 × 103 if tidal dissipation is predominantly in the star. The precession model is another possible origin to explain the observed TTVs. We note that the follow-up observations of occultation timing and radial velocity monitoring are needed for fully discriminating the different models.

Binary Star System Decay by Graviton Interaction

The action of gravitons in a binary star system is modelled as the locus of points on an ellipse synchronous to the elliptic orbit of the binary star. In their interaction between the masses in the system the rotational energy of the gravitons is reduced by gravitational redshift, which accounts for the decay of the binary star orbital period. This model is able to fit a broad range of eccentricities of binary pulsar orbits and orbital period decay comparable to the General Relativistic gravitational wave model.

Strong-Field Gravity Tests with the Double Pulsar

Continued observations of the Double Pulsar, PSR J0737-3039A/B, consisting of two radio pulsars (A and B) that orbit each other with a period of 2.45hr in a mildly eccentric (e=0.088) binary system, have led to large improvements in the measurement of relativistic effects in this system. With a 16-yr data span, the results enable precision tests of theories of gravity for strongly self-gravitating bodies and also reveal new relativistic effects that have been expected but are now observed for the first time. These include effects of light propagation in strong gravitational fields which are currently not testable by any other method. We observe retardation and aberrational light-bending that allow determination of the pulsar's spin direction. In total, we have detected seven post-Keplerian (PK) parameters, more than for any other binary pulsar. For some of these effects, the measurement precision is so high that for the first time we have to take higher-order contributions into account. These include contributions of A's effective mass loss (due to spin-down) to the observed orbital period decay, a relativistic deformation of the orbit, and effects of the equation of state of super-dense matter on the observed PK parameters via relativistic spin-orbit coupling. We discuss the implications of our findings, including those for the moment of inertia of neutron stars. We present the currently most precise test of general relativity's (GR's) quadrupolar description of gravitational waves, validating GR's prediction at a level of $1.3 \times 10^{-4}$ (95% conf.). We demonstrate the utility of the Double Pulsar for tests of alternative theories by focusing on two specific examples and discuss some implications for studies of the interstellar medium and models for the formation of the Double Pulsar. Finally, we provide context to other types of related experiments and prospects for the future.

Very Long Baseline Astrometry of PSR J1012+5307 and its Implications on Alternative Theories of Gravity

Abstract PSR J1012+5307, a millisecond pulsar in orbit with a helium white dwarf (WD), has been timed with high precision for about 25 yr. One of the main objectives of this long-term timing is to use the large asymmetry in gravitational binding energy between the neutron star and the WD to test gravitational theories. Such tests, however, will be eventually limited by the accuracy of the distance to the pulsar. Here, we present very long baseline interferometry (VLBI) astrometry results spanning approximately 2.5 yr for PSR J1012+5307, obtained with the Very Long Baseline Array as part of the project. These provide the first proper motion and absolute position for PSR J1012+5307 measured in a quasi-inertial reference frame. From the VLBI results, we measure a distance of kpc (all the estimates presented in the abstract are at 68% confidence) for PSR J1012+5307, which is the most precise obtained to date. Using the new distance, we improve the uncertainty of measurements of the unmodeled contributions to orbital period decay, which, combined with three other pulsars, places new constraints on the coupling constant for dipole gravitational radiation and the fractional time derivative of Newton’s gravitational constant in the local universe. As the uncertainties of the observed decays of orbital period for the four leading pulsar-WD systems become negligible in ≈10 yr, the uncertainties for and κ D will be improved to ≤1.5 × 10−13 yr−1 and ≤1.0 × 10−4, respectively, predominantly limited by the distance uncertainties.

NGTS-10b: the shortest period hot Jupiter yet discovered

ABSTRACT We report the discovery of a new ultrashort period (USP) transiting hot Jupiter from the Next Generation Transit Survey (NGTS). NGTS-10b has a mass and radius of $2.162\, ^{+0.092}_{-0.107}$ MJ and $1.205\, ^{+0.117}_{-0.083}$ RJ and orbits its host star with a period of 0.7668944 ± 0.0000003 d, making it the shortest period hot Jupiter yet discovered. The host is a 10.4 ± 2.5 Gyr old K5V star (Teff = 4400 ± 100 K) of Solar metallicity ([Fe/H] = −0.02 ± 0.12 dex) showing moderate signs of stellar activity. NGTS-10b joins a short list of USP Jupiters that are prime candidates for the study of star–planet tidal interactions. NGTS-10b orbits its host at just 1.46 ± 0.18 Roche radii, and we calculate a median remaining inspiral time of 38 Myr and a potentially measurable orbital period decay of 7 s over the coming decade, assuming a stellar tidal quality factor $Q^{\prime }_{\rm s}$ =2 × 107.

Vector gauge boson radiation from compact binary systems in a gauged Lμ−Lτ scenario

The orbital period of a compact binary system decays mainly due to quadrupole gravitational radiation, which agrees with the observation to within one percent. Other types of radiation such as ultralight scalar or pseudoscalar radiation, massive vector boson radiation also contribute to the decay of orbital period as long as the mass of the emitted particle is less than the orbital frequency of the compact binary system. We obtain an expression of the energy loss due to the radiation of massive vector field from the neutron star-neutron star and neutron star-white dwarf binaries. Due to large chemical potential of the degenerate electrons, neutron stars have large muon charge. We derive the energy loss due to $U(1)_{L_\mu-L_\tau}$ gauge boson radiation from the binaries. For the radiation of vector boson, the mass is restricted by $M_{Z^\prime}<\Omega \simeq10^{-19}eV$ are the orbital frequencies of the compact star binaries. Using the formula of orbital period decay, we obtain constraints on the coupling constant of the gauge boson in the gauged $L_\mu-L_\tau$ theory for the four compact binary systems. For vector gauge boson muon coupling we find that for $M_{Z^\prime}<10^{-19}eV$, constraints on the coupling constant is $g<\mathcal{O}(10^{-20})$. We also obtain the exclusion plots of the massive vector proca field and the gauge field which can couple to muons.

Binary pulsar constraints on massless scalar–tensor theories using Bayesian statistics

Binary pulsars provide some of the tightest current constraints on modified theories of gravity and these constraints will only get tighter as radio astronomers continue timing these systems. These binary pulsars are particularly good at constraining scalar–tensor theories in which gravity is mediated by a scalar field in addition to the metric tensor. Scalar–tensor theories can predict large deviations from general relativity due to the fact that they allow for violation of the strong-equivalence principle through a phenomenon known as scalarization. This effect appears directly in the timing model for binary pulsars, and as such, it can be tightly constrained through precise timing. In this paper, we investigate these constraints for two scalar–tensor theories and a large set of realistic equations of state. We calculate the constraints that can be placed by saturating the current bounds on single post-Keplerian parameters, as well as employing Bayesian methods through Markov-chain-Monte-Carlo simulations to explore the constraints that can be achieved when one considers all measured parameters simultaneously. Our results demonstrate that both methods are able to place similar constraints and that they are both indeed dominated by the measurements of the orbital period decay. The Bayesian approach, however, allows one to simultaneously explore the posterior distributions of not only the theory parameters but of the masses as well.

Authenticating the Presence of a Relativistic Massive Black Hole Binary in OJ 287 Using Its General Relativity Centenary Flare: Improved Orbital Parameters

Abstract Results from regular monitoring of relativistic compact binaries like PSR 1913+16 are consistent with the dominant (quadrupole) order emission of gravitational waves (GWs). We show that observations associated with the binary black hole (BBH) central engine of blazar OJ 287 demand the inclusion of gravitational radiation reaction effects beyond the quadrupolar order. It turns out that even the effects of certain hereditary contributions to GW emission are required to predict impact flare timings of OJ 287. We develop an approach that incorporates this effect into the BBH model for OJ 287. This allows us to demonstrate an excellent agreement between the observed impact flare timings and those predicted from ten orbital cycles of the BBH central engine model. The deduced rate of orbital period decay is nine orders of magnitude higher than the observed rate in PSR 1913+16, demonstrating again the relativistic nature of OJ 287's central engine. Finally, we argue that precise timing of the predicted 2019 impact flare should allow a test of the celebrated black hole “no-hair theorem” at the 10% level.

Constraining f(R) gravity in solar system, cosmology and binary pulsar systems

The f(R) gravity can be cast into the form of a scalar–tensor theory, and scalar degree of freedom can be suppressed in high-density regions by the chameleon mechanism. In this article, for the general f(R) gravity, using a scalar–tensor representation with the chameleon mechanism, we calculate the parametrized post-Newtonian parameters γ and β, the effective gravitational constant Geff, and the effective cosmological constant Λeff. In addition, for the general f(R) gravity, we also calculate the rate of orbital period decay of the binary system due to gravitational radiation. Then we apply these results to specific f(R) models (Hu–Sawicki model, Tsujikawa model and Starobinsky model) and derive the constraints on the model parameters by combining the observations in solar system, cosmological scales and the binary systems.

Wind-accelerated orbital evolution in binary systems with giant stars

Using 3D radiation-hydrodynamic simulations and analytic theory, we study the orbital evolution of asymptotic-giant-branch (AGB) binary systems for various initial orbital separations and mass ratios, and thus different initial accretion modes. The time evolution of binary separations and orbital periods are calculated directly from the averaged mass loss rate, accretion rate and angular momentum loss rate. We separately consider spin-orbit synchronized and zero spin AGB cases. We find that the the angular momentum carried away by the mass loss together with the mass transfer can effectively shrink the orbit when accretion occurs via wind-Roche-lobe overflow. In contrast, the larger fraction of mass lost in Bondi-Hoyle-Lyttleton accreting systems acts to enlarge the orbit. Synchronized binaries tend to experience stronger orbital period decay in close binaries. We also find that orbital period decay is faster when we account for the nonlinear evolution of the accretion mode as the binary starts to tighten. This can increase the fraction of binaries that result in common envelope, luminous red novae, Type Ia supernovae and planetary nebulae with tight central binaries. The results also imply that planets in the the habitable zone around white dwarfs are unlikely to be found.

Dark matter dynamical friction versus gravitational wave emission in the evolution of compact-star binaries

The measured orbital period decay of compact-star binaries, with characteristic orbital periods $\sim 0.1$~days, is explained with very high precision by the gravitational wave (GW) emission of an inspiraling binary in vacuum. However, the binary gravitational binding energy is also affected by an usually neglected phenomenon, namely the dark matter dynamical friction (DMDF) produced by the interaction of the binary components with their respective DM gravitational wakes. The entity of this effect depends on the orbital period and on the local value of the DM density, hence on the position of the binary in the Galaxy. We evaluate the DMDF produced by three different DM profiles: the Navarro-Frenk-White (NFW), the non-singular-isothermal-sphere (NSIS) and the Ruffini-Arg\"uelles-Rueda (RAR) profile based on self-gravitating keV fermions. We first show that indeed, due to their Galactic position, the GW emission dominates over the DMDF in the NS-NS, NS-WD and WD-WD binaries for which measurements of the orbital decay exist. Then, we evaluate the conditions under which the effect of DMDF on the binary evolution becomes comparable to, or overcomes, the one of the GW emission. We find that, for instance for $1.3$--$0.2$ $M_\odot$ NS-WD, $1.3$--$1.3$~$M_\odot$ NS-NS, and $0.25$--$0.50$~$M_\odot$ WD-WD, located at 0.1~kpc, this occurs at orbital periods around 20--30 days in a NFW profile while, in a RAR profile, it occurs at about 100 days. For closer distances to the Galactic center, the DMDF effect increases and the above critical orbital periods become interestingly shorter. Finally, we also analyze the system parameters for which DMDF leads to an orbital widening instead of orbital decay. All the above imply that a direct/indirect observational verification of this effect in compact-star binaries might put strong constraints on the nature of DM and its Galactic distribution.

Indication of a massive circumbinary planet orbiting the low-mass X-ray binary MXB 1658−298

Abstract We present an X-ray timing analysis of the transient X-ray binary MXB 1658−298, using data obtained from the RXTE and XMM–Newton observatories. We have made 27 new mid-eclipse time measurements from observations made during the two outbursts of the source. These new measurements have been combined with the previously known values to study long-term changes in orbital period of the binary system. We have found that the mid-eclipse timing record of MXB 1658−298 is quite unusual. The long-term evolution of mid-eclipse times indicates an overall orbital period decay with a time-scale of –6.5(7) × 107 yr. Over and above this orbital period decay, the O−C residual curve also shows a periodic residual on shorter time-scales. This sinusoidal variation has an amplitude of ∼9 lt-s and a period of ∼760 d. This is indicative of the presence of a third body around the compact X-ray binary. The mass and orbital radius of the third body are estimated to lie in the ranges 20.5–26.9 Jupiter mass and 750–860 lt-s, respectively. If true, then it will be the most massive circumbinary planet and also the smallest period binary known to host a planet.

Extremely fast orbital decay of the black hole X-ray binary Nova Muscae 1991

Abstract We present new medium-resolution spectroscopic observations of the black hole X-ray binary Nova Muscae 1991 taken with X-Shooter spectrograph installed at the 8.2-m VLT telescope. These observations allow us to measure the time of inferior conjunction of the secondary star with the black hole in this system that, together with previous measurements, yield an orbital period decay of $\skew4\dot{P}=-20.7\pm 12.7$ ms yr−1 (−24.5 ± 15.1 μs per orbital cycle). This is significantly faster than those previously measured in the other black hole X-ray binaries A0620-00 and XTE J1118+480. No standard black hole X-ray binary evolutionary model is able to explain this extremely fast orbital decay. At this rate, the secondary star would reach the event horizon (as given by the Schwarzschild radius of about 32 km) in roughly 2.7 Myr. This result has dramatic implications on the evolution and lifetime of black hole X-ray binaries.

Orbital evolution and search for eccentricity and apsidal motion in the eclipsing HMXB 4U 1700−37

In the absence of detectable pulsations in the eclipsing High Mass X-ray binary 4U 1700-37, the orbital period decay is necessarily determined from the eclipse timing measurements. We have used the earlier reported mid-eclipse time measurements of 4U 1700-37 together with the new measurements from long term light curves obtained with the all sky monitors RXTE-ASM, Swift-BAT and MAXI-GSC, as well as observations with RXTE-PCA, to measure the long term orbital evolution of the binary. The orbital period decay rate of the system is estimated to be ${\dot{P}}/P = -(4.7 \pm 1.9) \times 10^{-7}$ yr$^{-1}$, smaller compared to its previous estimates. We have also used the mid-eclipse times and the eclipse duration measurements obtained from 10 years long X-ray light-curve with Swift-BAT to separately put constraints on the eccentricity of the binary system and attempted to measure any apsidal motion. For an apsidal motion rate greater than 5 degrees per year, the eccentricity is found to be less than 0.008, which limits our ability to determine the apsidal motion rate from the current data. We discuss the discrepancy of the current limit of eccentricity with the earlier reported values from radial velocity measurements of the companion star.