scholarly journals Gravitational burst radiation from pulsars in the Galactic centre and stellar clusters

2020 ◽  
Vol 495 (1) ◽  
pp. 600-613 ◽  
Author(s):  
Tom Kimpson ◽  
Kinwah Wu ◽  
Silvia Zane
Keyword(s):  
Gravitational Radiation ◽  
Globular Clusters ◽  
Radio Signal ◽  
Strong Field ◽  
Galactic Centre ◽  
Stellar Clusters ◽  
Mass Ratio ◽  
Pulsar Radio ◽  
Orbital Parameters ◽  
Pulsar Timing

ABSTRACT Pulsars (PSRs) orbiting intermediate or supermassive black holes at the centre of galaxies and globular clusters are known as Extreme Mass Ratio Binaries (EMRBs) and have been identified as precision probes of strong-field GR. For appropriate orbital parameters, some of these systems may also emit gravitational radiation in a ‘burst-like’ pattern. The observation of this burst radiation in conjunction with the electromagnetic radio timing signal would allow for multimessenger astronomy in strong-field gravitational regimes. In this work we investigate gravitational radiation from these PSR-EMRBs, calculating the waveforms and SNRs and explore the influence of this GW on the pulsar radio signal. We find that for typical PSR-EMRBs, gravitational burst radiation should be detectable from both the Galactic centre and the centre of stellar clusters, and that this radiation will not meaningfully affect the pulsar timing signal, allowing PSR-EMRB to remain ‘clean’ test-beds of strong-field GR.

scholarly journals CN Anomalies in the Halo System

2012 ◽  
Vol 10 (H16) ◽  
pp. 282-283
Author(s):  
Daniela Carollo
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Strong Field ◽  
Significant Source ◽  
Red Giants ◽  
Orbital Parameters ◽  
Halo Stars ◽  
Halo Population ◽  
Absorption Features ◽  
Kinematic Properties

AbstractI present an evaluation of the kinematic properties of halo red giants thought to have formed in globular clusters based on the strength of their UV/blue CN and CH absorption features. The sample has been selected from the catalog of Martell et al. (2011). The orbital parameters of CN-strong halo stars are compared to those of the inner and outer halo populations, and to the orbital parameters of globular clusters with well-studied Galactic orbits. It has been found that both the clusters and the CN-strong field stars exhibit kinematic and orbital properties similar to the inner halo population, indicating that globular clusters could be a significant source of inner halo field stars, and suggesting that both globular clusters and CN-strong stars could belong primarily to the inner halo population of the Milky Way.

scholarly journals Radio timing in a millisecond pulsar – extreme/intermediate mass ratio binary system

2020 ◽  
Vol 644 ◽  
pp. A167
Author(s):  
T. Kimpson ◽  
K. Wu ◽  
S. Zane
Keyword(s):  
Globular Clusters ◽  
Relativistic Effects ◽  
Propagation Delay ◽  
Higher Order ◽  
Galactic Centre ◽  
Millisecond Pulsar ◽  
Fundamental Physics ◽  
Timing Model ◽  
Pulsar Timing ◽  
Timing Models

Radio timing observations of a millisecond pulsar in orbit around the Galactic centre black hole (BH) or a BH at the centre of globular clusters could answer foundational questions in astrophysics and fundamental physics. Pulsar radio astronomy typically employs the post-Keplerian approximation to determine the system parameters. However, in the strong gravitational field around the central BH, higher order relativistic effects may become important. We compare the pulsar timing delays given by the post-Keplerian approximation with those given by a relativistic timing model. We find significant discrepancies between the solutions derived for the Einstein delay and the propagation delay (i.e. Roemer and Sharpiro delay) compared to the fully relativistic solutions. Correcting for these higher order relativistic effects is essential in order to construct accurate radio timing models for pulsar systems at the Galactic centre and the centre of globular clusters and informing issues related to their detection.

scholarly journals Are we observing an NSC in course of formation in the NGC 4654 galaxy?

2021 ◽  
Vol 503 (1) ◽  
pp. 594-602
Author(s):  
R Schiavi ◽  
R Capuzzo-Dolcetta ◽  
I Y Georgiev ◽  
M Arca-Sedda ◽  
A Mastrobuono-Battisti
Keyword(s):  
Central Zone ◽  
Effective Radius ◽  
Host Galaxy ◽  
Galactic Centre ◽  
Future Evolution ◽  
Orbital Parameters ◽  
Relative Orbit ◽  
The Future ◽  
The Galaxy ◽  
Massive Clusters

ABSTRACT We use direct N-body simulations to explore some possible scenarios for the future evolution of two massive clusters observed towards the centre of NGC 4654, a spiral galaxy with mass similar to that of the Milky Way. Using archival HST data, we obtain the photometric masses of the two clusters, M = 3 × 105 M⊙ and M = 1.7 × 106 M⊙, their half-light radii, Reff ∼ 4 pc and Reff ∼ 6 pc, and their projected distances from the photometric centre of the galaxy (both <22 pc). The knowledge of the structure and separation of these two clusters (∼24 pc) provides a unique view for studying the dynamics of a galactic central zone hosting massive clusters. Varying some of the unknown cluster orbital parameters, we carry out several N-body simulations showing that the future evolution of these clusters will inevitably result in their merger. We find that, mainly depending on the shape of their relative orbit, they will merge into the galactic centre in less than 82 Myr. In addition to the tidal interaction, a proper consideration of the dynamical friction braking would shorten the merging times up to few Myr. We also investigate the possibility to form a massive nuclear star cluster (NSC) in the centre of the galaxy by this process. Our analysis suggests that for low-eccentricity orbits, and relatively long merger times, the final merged cluster is spherical in shape, with an effective radius of few parsecs and a mass within the effective radius of the order of $10^5\, \mathrm{M_{\odot }}$. Because the central density of such a cluster is higher than that of the host galaxy, it is likely that this merger remnant could be the likely embryo of a future NSC.

scholarly journals The ecology of the galactic centre: Nuclear stellar clusters and supermassive black holes

2019 ◽  
Vol 14 (S351) ◽  
pp. 80-83 ◽  
Author(s):  
Melvyn B. Davies ◽  
Abbas Askar ◽  
Ross P. Church
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Large Fraction ◽  
Galactic Nuclei ◽  
Supermassive Black Holes ◽  
Galactic Centre ◽  
Stellar Clusters ◽  
Stellar Cluster ◽  
Supermassive Black Hole ◽  
Multiple Clusters

AbstractSupermassive black holes are found in most galactic nuclei. A large fraction of these nuclei also contain a nuclear stellar cluster surrounding the black hole. Here we consider the idea that the nuclear stellar cluster formed first and that the supermassive black hole grew later. In particular we consider the merger of three stellar clusters to form a nuclear stellar cluster, where some of these clusters contain a single intermediate-mass black hole (IMBH). In the cases where multiple clusters contain IMBHs, we discuss whether the black holes are likely to merge and whether such mergers are likely to result in the ejection of the merged black hole from the nuclear stellar cluster. In some cases, no supermassive black hole will form as any merger product is not retained. This is a natural pathway to explain those galactic nuclei that contain a nuclear stellar cluster but apparently lack a supermassive black hole; M33 being a nearby example. Alternatively, if an IMBH merger product is retained within the nuclear stellar cluster, it may subsequently grow, e.g. via the tidal disruption of stars, to form a supermassive black hole.

Twin stars as tracers of binary evolution in the Kepler era

2021 ◽  
Author(s):  
Sara Bulut ◽  
Baris Hoyman ◽  
Ahmet Dervisoglu ◽  
Orkun Özdarcan ◽  
Ömür Cakilrli
Keyword(s):  
High Resolution ◽  
Internal Structure ◽  
Spectroscopic Analysis ◽  
Independent Method ◽  
Eclipsing Binaries ◽  
Physical Parameters ◽  
Evolutionary Status ◽  
Mass Ratio ◽  
Orbital Parameters ◽  
Binary Evolution

Abstract We present results of the combined photometric and spectroscopic analysis of four systems, which are eclipsing binaries with a twin–component (mass ratio q ≃ 1). These are exceptional tools to provide information for probing the internal structure of stars. None of the systems were previously recognized as twin binaries. We used a number of high–resolution optical spectra to calculate the radial velocities and later combined them with photometry to derive orbital parameters. Temperatures and metallicities of systems were estimated from high-resolution spectra. For each binary, we obtained a full set of orbital and physical parameters, reaching precision below 3 per cent in masses and radii for whole pairs. By comparing our results with PARSEC and MIST isochrones, we assess the distance, age and evolutionary status of the researched objects. The primary and/or secondary stars of EPIC 216075815 and EPIC 202843107 are one of the cases where asteroseismic parameters of δ Sct and γ Dor pulsators were confirmed by an independent method and rare examples of the twin–eclipsing binaries, therefore the following analyses and results concern the pulsating nature of the components.

scholarly journals UV-Observations of Young Populous Clusters in the Large Magellanic Cloud

1984 ◽  
Vol 108 ◽  
pp. 55-56
Author(s):  
Edward H. Geyer ◽  
Angelo Cassatella
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Large Magellanic Cloud ◽  
Time Interval ◽  
Sequence Evolution ◽  
Stellar Clusters ◽  
T Tauri ◽  
Red Supergiants ◽  
Evolution Phase ◽  
Massive Clusters

The young populous star clusters give evidence for the ‘explosive’ star formation in the Magellanic Clouds which took place in the time interval 5·106 yrs to < 108 yrs agoe. They are also key objects for the understanding of the formation of massive stellar clusters, because they are still situated close to their ‘birthplace’ in the parent galaxy and are dynamically not relaxed (Geyer et al. 1979). Their HRD-morphology shows most of the member stars in the upper Main Sequence range with only a few massive yellow and red supergiants. The lower massive stars are still in the pre-main-sequence evolution phase (‘T-Tauri state’), which cannot be observed at the MC's distances. Thus in the uv-spectral range the blue stars with (B-V) < 0.1 on the upper MS contribute to the uv-fluxes. In the optical spectral regions the bright ‘blue’ globular clusters seem not be embedded in remanent interstellar matter, though neighbouring loose stellar aggregates of similar age are in many cases surrounded by dense HII-regions. This rises the questions wether the starformation process in such massive clusters was so efficient that no remanent matter was left over, or was this material blown away by the uv-radiation of the numerous OB-member stars?

scholarly journals Orbits of Galactic Globular Clusters from Schmidt Plate Astrometry

1994 ◽  
Vol 161 ◽  
pp. 453-459 ◽  
Author(s):  
M. Odenkirchen ◽  
R.-D. Scholz ◽  
M.J. Irwin
Keyword(s):  
Globular Clusters ◽  
Proper Motions ◽  
Mass Model ◽  
Orbital Parameters ◽  
The Galaxy ◽  
Galactic Globular Clusters

We present results from orbit integrations for the globular clusters M 3 and M 92. Absolute proper motions recently measured from Tautenburg Schmidt plates and a three-component mass model for the Galaxy have been used to derive the galactic orbits of these clusters. Orbital parameters and the influence of observational uncertainties on the determination of the orbits are discussed.

A Study of the Orbital and Intrinsic Variability of the Double-Lined Spectroscopic Binary β Centauri

2002 ◽  
Vol 185 ◽  
pp. 86-87
Author(s):  
M. Ausseloos ◽  
C. Aerts ◽  
K. Uytterhoeven
Keyword(s):  
High Resolution ◽  
Orbital Motion ◽  
High Signal ◽  
Mass Ratio ◽  
Eccentric Orbit ◽  
Intrinsic Variability ◽  
Signal To Noise ◽  
Orbital Parameters ◽  
Spectroscopic Binary ◽  
First Time

AbstractWe introduce our observational study of the orbital motion of β Cen. Using 463 high signal-to-noise, high-resolution spectra obtained over a timespan of 12 years it is shown that the radial velocity of β Cen varies with an orbital period of 357.0 days. We derive for the first time the orbital parameters of β Cen and find a very eccentric orbit (e = 0.81) and similar component masses with a mass ratio M1/M2 = 1.02. Both the primary and the secondary exhibit periodic line-profile variations.

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