Fig 12 - uploaded by Edward J Colbert
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— Velocity structure in the core of the Galactic globular cluster M15. Top left: random component of the line of sight velocity as a function of angular distance from the center of the cluster. Top right: systematic rotational velocity as a function of angular distance from the center. Note that v rot /σ ≈ 1 near the core, indicative of significant net rotation. Bottom left: position angle of the rotation, as a function of angular distance from the center. The position angle varies significantly, suggesting that the cluster as a whole does not have a constant direction of rotation. Bottom right: total velocity dispersion, including both random and rotational components. Reprinted with permission from Gerssen et al. (2002).
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The mathematical simplicity of black holes, combined with their links to some of the most energetic events in the universe, means that black holes are key objects for fundamental physics and astrophysics. Until recently, it was generally believed that black holes in nature appear in two broad mass ranges: stellar-mass (M~3–20 M⊙), which are produce...
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... models of globulars without massive compact objects predict essentially no rotation in the cores of clusters (see, e.g., Figure 3 of Baumgardt et al. 2003b, which shows the expected rapid decrease of ellipticity inside of ∼1 pc). However, Gebhardt et al. (2000b) and Gerssen et al. (2002) find that in the center of M15 the rotational speed is comparable to the velocity dispersion, v rot /σ ≈ 1 (see Figure 12, from Gerssen et al. 2002), with a correspondingly high ellipticity of isophotes (K. Gebhardt, personal communication). ...
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Context. Located within the central region of the Galaxy, the Arches cluster appears to be one of the youngest, densest, and most massive stellar aggregates within the Milky Way. As such, it has the potential to be uniquely instructive laboratory for the study of star formation in extreme environments and the physics of very massive stars.
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... Hyper-luminous X-ray sources (HLXs) are intrinsically luminous X-ray sources (L X 10 41 erg s −1 ) located in offnuclear regions of galaxies (e.g., Gao et al. 2003). In contrast to the population of ultra-luminous X-ray sources (ULXs; L X 10 39-41 erg s −1 ; see Kaaret et al. 2017 and references therein) that are typically associated with X-ray binaries (XRBs; e.g., Remillard & McClintock 2006), the higher luminosities of HLXs suggest they are most likely powered by accretion onto compact objects more massive than stars (e.g., Miller & Colbert 2004;King & Dehnen 2005). This distinction is further suggested by a break in the X-ray point source luminosity function at L X ∼ 1-2 × 10 40 erg s −1 (e.g., Swartz et al. 2011;Mineo et al. 2012;Tranin et al. 2024). ...
Hyper-luminous X-ray sources (HLXs) are extragalactic off-nuclear X-ray sources with luminosities exceeding the theoretical limit for accretion onto stellar-mass compact objects. Many HLXs may represent intermediate-mass black holes (IMBHs) deposited in galaxy halos through mergers, and the properties of the stellar cores surrounding HLXs provide powerful constraints on this scenario. Therefore, we have systematically built the largest sample of HLX candidates with archival Hubble Space Telescope (HST) imaging (24) for the first uniform population study of HLX stellar cores down to low masses. Based on their host galaxy redshifts, at least 21 (88%) have stellar core masses ≥ 10 ⁷ M ⊙ and hence are consistent with accretion onto massive black holes from external galaxies. In 50% of the sample, the HST imaging reveals features connecting the HLXs with their host galaxies, strongly suggesting against the background/foreground contaminant possibility in these cases. Assuming a mass scaling relation for active galactic nuclei and accounting for an estimated contamination fraction of 29%, up to ∼60% of our sample may be associated with IMBHs. Similar to previously known HLXs, the X-ray luminosities are systematically elevated relative to their stellar core masses, possibly from merger-driven accretion rate enhancements. The least massive stellar cores are preferentially found at larger nuclear offsets and are more likely to remain wandering in their host galaxy halos. The HLX galaxy occupation fraction is ∼ 10 ⁻² and has a strong inverse mass dependence. Up to three of the HLX candidates (12%) are potentially consistent with formation within globular clusters or with exceptionally luminous X-ray binaries.
... Non-nuclear X-ray point sources exibiting isotropic luminosity ≥ 10 39 erg s −1 in the (0.1 -10.0) keV energy range are usually termed as Ultraluminous X-ray Sources (ULXs) [1]. Essentially, ULXs are accreting sources with X-ray luminosities surpassing the Eddington limit of a 10M ⊙ black hole (BH) [2,3]. The inferred high luminosity of ULXs have been modelled as due to -sub-Eddington accretion on to the Intermediate Mass Black Holes (IMBHs) [4,5,6]. ...
This report presents a comprehensive analysis of the spectral and temporal characteristics of a highly significant Ultraluminous X-ray Source (ULX) designated as CXOUJ122956.7+075728 (ULX-1) situated in the elliptical galaxy NGC 4472 within the Virgo cluster. ULX-1 exhibits a soft spectral state, featuring a cool accretion disk component with kTin ∼ 0.15 keV, accompanied by a power-law tail displaying a steep power-law photon index, Γ ∼ 2.8. The spectral findings strongly support an estimated black hole mass of approximately 3.30 × 10^3 M⊙ under an isotropic emission model, and around 1.47 × 10^3 M⊙ in an extreme beaming scenario. Temporally, ULX-1 displays significant variability on time scales of 0.5, 1, and 2 ks, suggesting the possibility of instabilities within the accretion disk contributing to this behavior. However, despite this temporal variability, the power spectra analysis of this soft ULX reveals no signatures of pulsations, distinguishing it from certain pulsating ULXs (PULXs) typically associated with neutron stars. This absence of pulsations in ULX-1 further underscores its unique spectral and temporal characteristics within the broader context of ULX phenomena.
... In particular, bounds from microlensing and accretion show 10-10 3 M ⊙ PBHs can constitute a fraction or all of dark matter [13,15]. Unfortunately, the mechanism for forming IMBHs, either from massive stars or primordial black holes, is not well understood (see [16] for a review). ...
We examine the flux density ratio anomaly in the quadruply imaged strong gravitational lens, B1422+231, and consider the contribution of 10–103M⊙ primordial black holes (PBHs) as a potential dark matter constituent. We describe the first flux density ratio measurement of B1422+231 in the millimeter-wave band using the Atacama Large Millimeter Array (ALMA). The flux density of the quasar at 233 GHz is dominated by synchrotron emission and the source size is estimated to be less than 66.9 pc. The observed flux density ratios at 233 GHz are similar to those measured in other wave bands, which cannot be explained by a simple smooth mass model of the lens galaxy. We examine the probability of the flux density ratio anomaly arising from PBH microlensing using ray tracing simulations. The simulations consider the cases where 10% and 50% of dark matter are 10–103M⊙ PBHs with a power law mass function. The simulated scenarios are consistent with the ALMA observations, so PBH dark matter cannot be ruled out as a cause of flux density ratio anomalies. Our analysis shows that the anomalous flux density ratio for B1422+231 can be explained by a lens model with a significant fraction of dark matter being PBHs. This study demonstrates the potential for new constraints on PBH dark matter using ALMA observations of multiply imaged strong gravitational lenses.
... Their analysis suggest that HLX-1 harbour black hole with mass, M, 3000 M ⊙ < M < 10 5 M ⊙ which is the range of IMBHs. The review of Miller & Colbert (2004) [26] and Miller (2005) [27] discussed various arguements regarding the evidence for IMBHs in ULXs. Many other bright ULXs such as M82 X-1 [28,29], M51 ULX-7 [30] and NGC 2276-3c [31] also give evidence for ULXs harboring IMBHs. ...
... Their analysis suggest that HLX-1 harbour black hole with mass, M, 3000 M ⊙ < M < 10 5 M ⊙ which is the range of IMBHs. The review of Miller & Colbert (2004) [26] and Miller (2005) [27] discussed various arguements regarding the evidence for IMBHs in ULXs. Many other bright ULXs such as M82 X-1 [28,29], M51 ULX-7 [30] and NGC 2276-3c [31] also give evidence for ULXs harboring IMBHs. ...
The present work aims to study the previously unstudied Ultraluminous X-ray sources (ULXs) in the galaxy NGC 3585 at its various epochs of Chandra observation. We report here the detection of two new ULXs viz. CXOUJ111306.0-264825 (X-1) and CXOUJ111325.3-264732 (X-2) with their bolometric luminosity > 1039erg s−1 in its various Chandra observations. X-1 was found to be a spectrally hard ULX in both the epochs where it was detected. However in the ULX, X-2, a slight hardening of the spectra was observed within a period of 17 years. Assuming isotropic emission and explained by disk blackbody model, the spectrally softer epoch of X-2 with an inner disk temperature, kTin ∼ 0.79 keV and bolometric luminosity ∼ 2.51 × 1039erg s−1 implies for X-2 to be powered by a compact object, necessarily a black hole of mass, MBH ∼ 44.85+82.11−25.92M⊙ accreting at ∼ 0.42 times the Eddington limit. The Lightcurve of X-1 and X-2 binned at 500s, 1ks, 2ks and 4ks has shown no signature of short-term variability in both the ULXs in kilo-seconds time scales. Overall, both the detected ULXs seem to be almost static sources both in long-term (years) as well as short-term (kilo-seconds) time scales with the presently available Chandra Observations.
... merger waves from CBCs comprised of black holes and/or neutron stars. Types of CBC signals include binary systems with circular orbits [10][11][12][13][14], eccentric orbits [15][16][17][18][19][20][21], head-on collisions [22,23], extreme mass-ratio binaries [24], primordial black holes [25][26][27][28], and hyperbolic encounters [29][30][31]. Gravitational waves may also be generated in the post-merger phase of the binary neutron star systems [32,33]. ...
This paper presents a search for generic short-duration gravitational-wave (GW) transients (or GW bursts) in the data from the third observing run of Advanced LIGO and Advanced Virgo. We use coherent WaveBurst (cWB) pipeline enhanced with a decision-tree classification algorithm for more efficient separation of GW signals from noise transients. The machine-learning (ML) algorithm is trained on a representative set of the noise events and a set of simulated stochastic signals that are not correlated with any known signal model. This training procedure preserves the model-independent nature of the search. We demonstrate that the ML-enhanced cWB pipeline can detect GW signals at a larger distance than the previous model-independent searches, and the sensitivity improvements are achieved across a broad spectrum of simulated signals used in the analysis. At a false-alarm rate of one event per century, the detectable signal amplitudes are reduced up to almost an order of magnitude, most notably for cosmic strings. By testing the pipeline for the detection of compact binaries, we verified that it detects more systems in a wide range of masses from stellar mass to intermediate-mass black-holes, both with circular and elliptical orbits. After excluding previously detected compact binaries, no new gravitational-wave signals are observed for the two-fold Hanford-Livingston and the three-fold Hanford-Livingston-Virgo detector networks. With the improved sensitivity of the all-sky search, we obtain the most stringent constraints on the isotropic emission of gravitational-wave energy from the short-duration burst sources.
... Primary source targets of LISA include the coalescence of black hole binaries (BHBs) with primary masses 10 6 -10 8 M , which are called supermassive BHs (SMBHs), as well as inspirals of BHBs with secondary-to-primary mass ratio q = 10 −6 -10 −3 , termed extreme or intermediate mass-ratio inspirals (E/IMRIs; Babak et al. 2017;Amaro-Seoane 2018). Another important source for LISA will be intermediate-mass BHBs (IMBHBs), wherein both companions' masses are in the range 10 2 -10 5 M (Miller & Colbert 2004). ...
We study the effect of torques on circular inspirals of intermediate-mass black hole binaries (IMBHBs) embedded in gas discs, wherein both BH masses are in the range $10^2$-$10^5~\rm{M}_\odot$, up to redshift $z = 10$. We focus on how torques impact the detected gravitational wave (GW) waveform in the frequency band of the Laser Interferometer Space Antenna (LISA) when the binary separation is within a few hundred Schwarzschild radii. For a sub-Eddington accretion disc with a viscosity coefficient $\alpha=0.01$, surface density $\Sigma\approx10^5$ g cm$^{-2}$, and Mach number $\mathcal{M}_{\rm a}\approx80$, a gap, or a cavity, opens when the binary is in the LISA band. Depending on the torque's strength, LISA will observe dephasing in the IMBHB's GW signal up to either $z\sim5$ for high mass ratios ($q\approx0.1$) or to $z\sim7$ for $q\approx10^{-3}$. We study the dependence of the measurable dephasing on variations of BH masses, redshift, and accretion rates. Our results suggest that phase shift is detectable even in high-redshift ($z = 10$) binaries, provided that they experience super-Eddington accretion episodes. We investigate if the disc-driven torques can result in an observable `time-dependent' chirp mass with a simplified Fisher formalism, finding that, at the expected signal-to-noise ratio, the gas-induced variation of the chirp mass is too small to be detected. This work shows how perturbations of vacuum waveforms induced by gas should be strong enough to be detected by LISA for the IMBHB in the early inspiral phase. These perturbations encode precious information on the astrophysics of accretion discs and galactic nuclei. High-accuracy waveform models which incorporate these effects will be needed to extract such information.
... The evidence for the existence of intermediate-mass black holes (IMBHs) in the 10 2 -10 4 M mass range is still inconclusive at present. Attempts to look for electromagnetic signatures are hampered by the small dynamical footprint of low-mass IMBHs and the difficulty of associating phenomena such as ultraluminous x-ray sources specifically with IMBHs [83]. On the other hand, a handful of promising sources have been observed [84], and multiple formation scenarios have been proposed-though none without problems [85]. ...
The next generation of gravitational-wave observatories can explore a wide range of fundamental physics phenomena throughout the history of the universe. These phenomena include access to the universe's binary black hole population throughout cosmic time, to the universe's expansion history independent of the cosmic distance ladders, to stochastic gravitational-waves from early-universe phase transitions, to warped space-time in the strong-field and high-velocity limit, to the equation of state of nuclear matter at neutron star and post-merger densities, and to dark matter candidates through their interaction in extreme astrophysical environments or their interaction with the detector itself. We present the gravitational-wave detector concepts than can drive the future of gravitational-wave astrophysics. We summarize the status of the necessary technology, and the research needed to be able to build these observatories in the 2030s.
... However, the prevalence of IMBHs remains highly uncertain despite a variety of approaches to their detection (e.g., Pasham et al. 2014;Paynter et al. 2021). The challenges associated with observing IMBHs are discussed by Miller and Colbert (2004) and Greene et al. (2020). Given the many orders of magnitude uncertainties, we resist the temptation to review the merger rates of binaries involving IMBHs. ...
Gravitational-wave detections are enabling measurements of the rate of coalescences of binaries composed of two compact objects—neutron stars and/or black holes. The coalescence rate of binaries containing neutron stars is further constrained by electromagnetic observations, including Galactic radio binary pulsars and short gamma-ray bursts. Meanwhile, increasingly sophisticated models of compact objects merging through a variety of evolutionary channels produce a range of theoretically predicted rates. Rapid improvements in instrument sensitivity, along with plans for new and improved surveys, make this an opportune time to summarise the existing observational and theoretical knowledge of compact-binary coalescence rates.
... Indeed, there is no definitive electromagnetic evidence for their existence. Thus, their formation channels and mass function are highly uncertain (Miller & Colbert 2004;Amaro-Seoane et al. 2007;Gair et al. 2011;Belczynski et al. 2014). GW observations have the potential to solve these mysteries, by providing accurate measurements of their properties, such as their masses, spins, and location. ...
Using ground-based gravitational-wave detectors, we probe the mass function of intermediate-mass black holes (IMBHs) wherein we also include BHs in the upper mass gap at ∼60–130 M ⊙ . Employing the projected sensitivity of the upcoming LIGO and Virgo fourth observing run (O4), we perform Bayesian analysis on quasi-circular nonprecessing, spinning IMBH binaries (IMBHBs) with total masses 50–500 M ⊙ , mass ratios 1.25, 4, and 10, and dimensionless spins up to 0.95, and estimate the precision with which the source-frame parameters can be measured. We find that, at 2 σ , the mass of the heavier component of IMBHBs can be constrained with an uncertainty of ∼10%–40% at a signal-to-noise ratio of 20. Focusing on the stellar-mass gap with new tabulations of the ¹² C( α , γ ) ¹⁶ O reaction rate and its uncertainties, we evolve massive helium core stars using MESA to establish the lower and upper edges of the mass gap as ≃ 59 − 13 + 34 M ⊙ and ≃ 139 − 14 + 30 M ⊙ respectively, where the error bars give the mass range that follows from the ±3 σ uncertainty in the ¹² C( α , γ ) ¹⁶ O nuclear reaction rate. We find that high resolution of the tabulated reaction rate and fine temporal resolution are necessary to resolve the peak of the BH mass spectrum. We then study IMBHBs with components lying in the mass gap and show that the O4 run will be able to robustly identify most such systems. Finally, we reanalyze GW190521 with a state-of-the-art aligned-spin waveform model, finding that the primary mass lies in the mass gap with 90% credibility.
... Two plausible scenarios have been offered to explain their super-Eddington luminosities: (i) Many of the more luminous sources with L X > 10 40 erg s −1 must be powered by sub-critical accretion on to an intermediate-mass black hole (IMBH) E-mail: rsgill.rg@gmail.com with M BH ∼ (10 2 − 10 4 )M (e.g., Colbert & Mushotzky 1999;Makishima et al. 2000;Miller & Colbert 2004;Farrell et al. 2009), which can accommodate super-Eddington luminosities, and (ii) lower luminosity, but still super-Eddington, sources can be explained with super-critical accretion (e.g. Begelman 2002;Poutanen et al. 2007;Dotan & Shaviv 2011) on to a stellar-mass BH with M BH ∼ (10 − 10 2 ) M , in which a strong outflow can further boost the isotropic-equivalent luminosity by relativistic beaming (Ohsuga & Mineshige 2011). ...
The origin of the variable X-ray emission in the $(0.3-30)\,$keV energy range of ultraluminous X-ray sources (ULXs) remains unclear, making it difficult to constrain the mass of the central compact object. X-ray luminosities of bright ULXs can be explained with sub-critical accretion ($L<L_{\rm Edd}$) on to an intermediate-mass BH, with the alternative being super-critical accretion on to a stellar-mass BH. Broadband X-ray emission in the former scenario can be explained using the canonical disk plus Comptonizing corona model, whereas in the latter scenario radiation pressure driven massive winds lead to complex spectra that are inclination angle dependent. Here we fit the broadband (optical/UV to X-ray) spectrum of the persistently bright ULX Holmberg IX X-1 with the disk-corona plus irradiated outer disk model in an effort to constrain the BH mass. We use a one-zone time-dependent numerical code to exactly solve for the steady-state properties of the optically thick coronal photon-electron-positron plasma. Our modelling suggests that Holmberg IX X-1 hosts a stellar mass BH, with mass $4\lesssim(\hat M_{\rm BH}\equiv\alpha M_{\rm BH}/M_\odot)\lesssim10$ where $1/6\leq\alpha<1$ for a spinning (Kerr) BH, undergoing super-critical accretion ($L_{\rm Bol}/L_{\rm Edd}\sim20\alpha$). In our model, the X-ray spectrum below $10\,$keV is explained with an absorbed multi-colour disk spectrum having inner disk temperature $k_BT_{\rm in}\sim(2.2-2.9)\,$keV. An additional cooler thermal spectral component, as found in many works and not included in our modeling, is required. The hard excess above $10\,$keV, as seen by NuSTAR, arises in a photon-rich optically-thick Comptonizing spherical corona with optical depth $\tau_T\sim3.5$ and particle temperature $k_BT_e\sim14\,$keV.
