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Register a new userObserving intermediate-mass black holes and the upper--stellar-mass gap with LIGO and Virgo
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We investigate the potential of ground-based gravitational-wave detectors to probe the mass function of intermediate-mass black holes (IMBHs) wherein we also include BHs in the upper mass gap $sim 60-130~M_odot$. Using the noise spectral density of the upcoming LIGO and Virgo fourth observing (O4) run, we perform Bayesian analysis on quasi-circular non-precessing, spinning IMBH binaries (IMBHBs) with total masses $50mbox{--} 500 M_odot$, 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 $2sigma$, the source-frame mass of the heavier component of the IMBHBs can be constrained with an uncertainty of $sim 10-40%$ at a signal to noise ratio of $20$. Focusing on the stellar-mass gap, we first evolve stars with massive helium cores using the open-source MESA software instrument to establish the upper and lower edges of the mass gap. We determine that the lower edge of the mass gap is $simeq$ 59$^{+34}_{-13}$ $M_{odot}$, while the upper edge is $simeq$ 139$^{+30}_{-14}$ $M_{odot}$, where the error bars indicate the mass range that follows from the $pm 3sigma$ uncertainty in the ${}^{12}text{C}(alpha, gamma) {}^{16} text{O}$ nuclear rate. 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. In this context, we also re-analyze the GW190521 event and show that the 90$%$ confidence interval of the primary-mass measurement lies inside the mass gap. Finally, we show that the precision achieved with the O4 run (and future O5 run) could be crucial for understanding the mass function, the formation mechanism, and evolution history of IMBHs.
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The detection of an intermediate-mass black hole population ($10^2-10^6 M_odot$) will provide clues to their formation environments (e.g., disks of active galactic nuclei, globular clusters) and illuminate a potential pathway to produce supermassive black holes. Ground-based gravitational-wave detectors are sensitive to a subset of such mergers and have been used to detect one $142^{+28}_{-16} M_odot$ intermediate-mass black hole formation event. However, ground-based detector data contain numerous incoherent short duration noise transients that can mimic the gravitational-wave signals from merging intermediate-mass black holes, limiting the sensitivity of searches. Here we search for binary black hole mergers using a Bayesian-inspired ranking statistic which measures the coherence or incoherence of triggers in multiple-detector data. We use this statistic to identify candidate events with lab-frame total masses $gtrsim55 M_odot$ using data from LIGOs second observing run. Our analysis does not yield evidence for new intermediate-mass black holes. However, we find support for some stellar-mass binary black holes not reported in the first LIGO--Virgo gravitational-wave transient catalog, GWTC-1.
By probing the population of binary black hole (BBH) mergers detected by LIGO-Virgo, we can infer properties about the underlying black hole formation channels. A mechanism known as pair-instability (PI) supernova is expected to prevent the formation of black holes from stellar collapse with mass greater than $sim 40-65,M_odot$ and less than $sim 120,M_odot$. Any BBH merger detected by LIGO-Virgo with a component black hole in this gap, known as the PI mass gap, likely originated from an alternative formation channel. Here, we firmly establish GW190521 as an outlier to the stellar-mass BBH population if the PI mass gap begins at or below $65, M_{odot}$. In addition, for a PI lower boundary of $40-50, M_{odot}$, we find it unlikely that the remaining distribution of detected BBH events, excluding GW190521, is consistent with the stellar-mass population.
Gravitational wave astronomy has been firmly established with the detection of gravitational waves from the merger of ten stellar mass binary black holes and a neutron star binary. This paper reports on the all-sky search for gravitational waves from intermediate mass black hole binaries in the first and second observing runs of the Advanced LIGO and Virgo network. The search uses three independent algorithms: two based on matched filtering of the data with waveform templates of gravitational wave signals from compact binaries, and a third, model-independent algorithm that employs no signal model for the incoming signal. No intermediate mass black hole binary event was detected in this search. Consequently, we place upper limits on the merger rate density for a family of intermediate mass black hole binaries. In particular, we choose sources with total masses $M=m_1+m_2in[120,800]$M$_odot$ and mass ratios $q = m_2/m_1 in[0.1,1.0]$. For the first time, this calculation is done using numerical relativity waveforms (which include higher modes) as models of the real emitted signal. We place a most stringent upper limit of $0.20$~Gpc$^{-3}$yr$^{-1}$ (in co-moving units at the 90% confidence level) for equal-mass binaries with individual masses $m_{1,2}=100$M$_odot$ and dimensionless spins $chi_{1,2}= 0.8$ aligned with the orbital angular momentum of the binary. This improves by a factor of $sim 5$ that reported after Advanced LIGOs first observing run.
Inspirals and mergers of black hole (BHs) and/or neutron star (NSs) binaries are expected to be abundant sources for ground-based gravitational-wave (GW) detectors. We assess the capabilities of Advanced LIGO and Virgo to measure component masses using inspiral waveform models including spin-precession effects using a large ensemble of GW sources {bf randomly oriented and distributed uniformly in volume. For 1000 sources this yields signal-to-noise ratios between 7 and 200}. We make quantitative predictions for how well LIGO and Virgo will distinguish between BHs and NSs and appraise the prospect of using LIGO/Virgo observations to definitively confirm, or reject, the existence of a putative mass gap between NSs ($mleq3 M_odot$) and BHs ($mgeq 5 M_odot$). We find sources with the smaller mass component satisfying $m_2 lesssim1.5 M_odot$ to be unambiguously identified as containing at least one NS, while systems with $m_2gtrsim6 M_odot$ will be confirmed binary BHs. Binary BHs with $m_2<5 M_odot$ (i.e., in the gap) cannot generically be distinguished from NSBH binaries. High-mass NSs ($2<m<3$ $M_odot$) are often consistent with low-mass BH ($m<5 M_odot$), posing a challenge for determining the maximum NS mass from LIGO/Virgo observations alone. Individual sources will seldom be measured well enough to confirm objects in the mass gap and statistical inferences drawn from the detected population will be strongly dependent on the underlying distribution. If nature happens to provide a mass distribution with the populations relatively cleanly separated in chirp mass space, as some population synthesis models suggest, then NSs and BHs are more easily distinguishable.
This paper reports on an unmodeled, all-sky search for gravitational waves from merging intermediate mass black hole binaries (IMBHB). The search was performed on data from the second joint science run of the LIGO and Virgo detectors (July 2009 - October 2010) and was sensitive to IMBHBs with a range up to $sim 200$ Mpc, averaged over the possible sky positions and inclinations of the binaries with respect to the line of sight. No significant candidate was found. Upper limits on the coalescence-rate density of nonspinning IMBHBs with total masses between 100 and $450 mbox{M}_{odot}$ and mass ratios between $0.25$ and $1,$ were placed by combining this analysis with an analogous search performed on data from the first LIGO-Virgo joint science run (November 2005 - October 2007). The most stringent limit was set for systems consisting of two $88 mbox{M}_{odot}$ black holes and is equal to $0.12 mbox{Mpc}^{-3} mbox{Myr}^{-1}$ at the $90%$ confidence level. This paper also presents the first estimate, for the case of an unmodeled analysis, of the impact on the search range of IMBHB spin configurations: the visible volume for IMBHBs with nonspinning components is roughly doubled for a population of IMBHBs with spins aligned with the binarys orbital angular momentum and uniformly distributed in the dimensionless spin parameter up to 0.8, whereas an analogous population with antialigned spins decreases the visible volume by $sim 20%,$.
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