Disrupted globular clusters and the gamma-ray excess in the Galactic Centre

Compact object mergers eject neutron-rich matter in a number of ways: by the dynamical ejection mediated by gravitational torques, as neutrino-driven winds, and probably also a good fraction of the resulting accretion disc finally becomes unbound by a combination of viscous and nuclear processes. If compact binary mergers indeed produce gamma-ray bursts, there should also be an interaction region where an ultra-relativistic outflow interacts with the neutrino-driven wind and produces moderately relativistic ejecta. Each type of ejecta has different physical properties, and therefore plays a different role for nucleosynthesis and for the electromagnetic (EM) transients that go along with compact object encounters. Here, we focus on the dynamic ejecta and present results for over 30 hydrodynamical simulations of both gravitational wave-driven mergers and parabolic encounters as they may occur in globular clusters. We find that mergers eject approximately 1 per cent of a Solar mass of extremely neutron-rich material. The exact amount, as well as the ejection velocity, depends on the involved masses with asymmetric systems ejecting more material at higher velocities. This material undergoes a robust r-process and both ejecta amount and abundance pattern are consistent with neutron star mergers being a major source of the ‘heavy’ ( A >130) r-process isotopes. Parabolic collisions, especially those between neutron stars and black holes, eject substantially larger amounts of mass, and therefore cannot occur frequently without overproducing gala- ctic r-process matter. We also discuss the EM transients that are powered by radioactive decays within the ejecta (‘macronovae’), and the radio flares that emerge when the ejecta dissipate their large kinetic energies in the ambient medium.

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Is the Galactic Centre gamma-ray source 1E1740.7 – 2942 accreting from a molecular cloud?

Nature ◽

10.1038/353234a0 ◽

1991 ◽

Vol 353 (6341) ◽

pp. 234-237 ◽

Cited By ~ 44

Author(s):

John Bally ◽

Marvin Leventhal

Keyword(s):

Molecular Cloud ◽

Gamma Ray ◽

Galactic Centre

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An Upper Limit to the Mass Loss from the Centre of the Galaxy

Symposium - International Astronomical Union ◽

10.1017/s0074180900235948 ◽

1974 ◽

Vol 64 ◽

pp. 36-36

Author(s):

Arcadio Poveda ◽

Christine Allen

Keyword(s):

Mass Loss ◽

Gravitational Waves ◽

Mass Distribution ◽

Globular Clusters ◽

Loss Rate ◽

Galactic Centre ◽

Isotropic Source ◽

The Past ◽

Upper Limit ◽

The Galaxy

A mass loss of 200 M⊙ per year, as conservatively suggested if Weber is detecting gravitational waves from an isotropic source at the galactic centre, is shown to be incompatible with the existence of (a) globular clusters, (b) old wide binaries, if this loss rate has been constant over the past 1010 yr.From the orbit of ω Centauri in the galactic field and its observed mass distribution and tidal radius an upper limit to the mass loss from the galactic centre is found to be 1 M⊙ yr-1 over the past 1010 yr.

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Statistical analysis of Galactic globular cluster type properties

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa901 ◽

2020 ◽

Vol 495 (4) ◽

pp. 3981-3989

Author(s):

M Simioni ◽

A Aparicio ◽

G Piotto

Keyword(s):

Globular Clusters ◽

Principal Component ◽

Slow Neutron ◽

Galactic Centre ◽

Type I ◽

Type Ii ◽

Relative Age ◽

Average Complexity ◽

Chromosome Maps ◽

Cluster Type

ABSTRACT The analysis of pseudo-colour diagrams, the so-called chromosome maps, of Galactic globular clusters (GCs) permits to classify them into type I and type II clusters. Type II GCs are characterized by an above-the-average complexity of their chromosome maps and some of them are known to display star-to-star variations of slow neutron-capture reaction elements including iron. This is at the basis of the hypothesis that type II GCs may have an extragalactic origin and were subsequently accreted by the Milky Way. We performed a principal component analysis to explore possible correlations among various GCs parameters in the light of this new classification. The analysis revealed that cluster type correlates mainly with relative age. The cause of this relation was further investigated finding that more metal-rich type II clusters, also appear to be younger and more distant from the Galactic centre. A depletion of type II clusters for positive values of Galactic coordinate Z was also observed, with no type II clusters detected above Z ∼ 2 kpc. Type II cluster orbits also have larger eccentricities than type I ones.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1259 ◽

2020 ◽

Vol 495 (1) ◽

pp. 600-613 ◽

Cited By ~ 2

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.

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Constraints on the Distribution of Gas and Young Stars in the Galactic Centre in the Context of Interpreting Gamma Ray Emission Features

Galaxies ◽

10.3390/galaxies6020055 ◽

2018 ◽

Vol 6 (2) ◽

pp. 55 ◽

Cited By ~ 2

Author(s):

Steven Longmore ◽

J. Kruijssen

Keyword(s):

Gamma Ray ◽

Young Stars ◽

Galactic Centre ◽

Gamma Ray Emission

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Gamma-ray emission from globular clusters 2MS-GC01, IC 1257, FSR 1735, NGC 5904 and 6656

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stv185 ◽

2015 ◽

Vol 448 (4) ◽

pp. 3215-3220 ◽

Cited By ~ 4

Author(s):

J. N. Zhou ◽

P. F. Zhang ◽

X. Y. Huang ◽

X. Li ◽

Y. F. Liang ◽

...

Keyword(s):

Globular Clusters ◽

Gamma Ray ◽

Gamma Ray Emission

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Globular clusters as gamma ray sources

Journal of Astrophysics and Astronomy ◽

10.1007/bf02702266 ◽

1992 ◽

Vol 13 (4) ◽

pp. 287-291 ◽

Cited By ~ 2

Author(s):

V. B. Bhatia ◽

S. Mishra ◽

N. Panchapakesan

Keyword(s):

Globular Clusters ◽

Gamma Ray

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The Future of X-Ray Time-Domain Surveys

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312000609 ◽

2011 ◽

Vol 7 (S285) ◽

pp. 199-206

Author(s):

Daryl Haggard ◽

Gregory R. Sivakoff

Keyword(s):

Time Domain ◽

Gamma Ray ◽

High Energy ◽

Galactic Centre ◽

Time Resolved ◽

X Ray ◽

Stellar Flares ◽

Time Domain Data ◽

Deep Fields ◽

Energy Dependent

AbstractModern X-ray observatories yield unique insight into the astrophysical time domain. Each X-ray photon can be assigned an arrival time, an energy and a sky position, yielding sensitive, energy-dependent light curves and enabling time-resolved spectra down to millisecond time-scales. Combining those with multiple views of the same patch of sky (e.g., in the Chandra and XMM-Newton deep fields) so as to extend variability studies over longer baselines, the spectral timing capacity of X-ray observatories then stretch over 10 orders of magnitude at spatial resolutions of arcseconds, and 13 orders of magnitude at spatial resolutions of a degree. A wealth of high-energy time-domain data already exists, and indicates variability on timescales ranging from microseconds to years in a wide variety of objects, including numerous classes of AGN, high-energy phenomena at the Galactic centre, Galactic and extra-Galactic X-ray binaries, supernovæ, gamma-ray bursts, stellar flares, tidal disruption flares, and as-yet unknown X-ray variables. This workshop explored the potential of strategic X-ray surveys to probe a broad range of astrophysical sources and phenomena. Here we present the highlights, with an emphasis on the science topics and mission designs that will drive future discovery in the X-ray time domain.

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