Research

Research interests

My publications

Publications

Rodriguez Carl L., Antonini Fabio (2018) A triple origin for the heavy and low-spin binary black holes detected by LIGO/VIRGO, The Astrophysical Journal IOP Publishing
We explore the masses, merger rates, eccentricities, and spins for field binary black holes driven to
merger by a third companion through the Lidov-Kozai mechanism. Using a population synthesis
approach, we model the creation of stellar-mass black hole triples across a range of different initial
conditions and stellar metallicities. We find that the production of triple-mediated mergers is enhanced
at low metallicities by a factor of ~ 100 due to the lower black hole natal kicks and reduced stellar mass
loss. These triples naturally yield heavy binary black holes with near-zero effective spins, consistent
with most of the mergers observed to date. This process produces a merger rate of between 2 and 25
Gpc-3yr-1 in the local universe, suggesting that the Lidov-Kozai mechanism can potentially explain
all of the low-spin, heavy black hole mergers observed by Advanced LIGO/Virgo. Finally, we show
that triples admit a unique eccentricity and spin distribution that will allow this model to be tested
in the near future.
Antonini Fabio, Rodriguez Carl L, Petrovich C, Fischer C (2018) Precessional dynamics of black hole triples: binary mergers
with near-zero effective spin,
Monthly Notices of the Royal Astronomical Society: Letters 480 (1) pp. L58-L62 Oxford University Press
The binary black hole mergers detected by Advanced LIGO/Virgo have shown no
evidence of large black hole spins. However, because LIGO/Virgo best measures the
effective combination of the two spins along the orbital angular momentum (Xeff), it is
difficult to distinguish between binaries with slowly-spinning black holes and binaries
with spins lying in the orbital plane. Here, we study the spin dynamics for binaries with
a distant black hole companion. For spins initially aligned with the orbital angular
momentum of the binary, we find that Xeff \freezes" near zero as the orbit decays
through the emission of gravitational waves. Through a population study, we show
that this process predominantly leads to merging black hole binaries with near-zero
Xeff. We conclude that if the detected black hole binaries were formed in triples, then
this would explain their low _eff without the need to invoke near-zero spins or initially
large spin-orbit angles.
Hamers Adrian S., Bar-Or Ben, Petrovich Cristobal, Antonini Fabio (2018) The impact of vector resonant relaxation on the evolution of binaries near a massive black hole: implications for gravitational wave sources, The Astrophysical Journal American Astronomical Society
Binaries within the sphere of influence of a massive black hole (MBH) in galactic nuclei are susceptible to
the Lidov-Kozai (LK) mechanism, which can drive orbits to high eccentricities and trigger strong interactions
within the binary such as the emission of gravitational waves (GWs), and mergers of compact objects. These
events are potential sources for GW detectors such as Advanced LIGO and VIRGO. The LK mechanism is
only effective if the binary is highly inclined with respect to its orbit around the MBH (within a few degrees of
90æ), implying low rates. However, close to an MBH, torques from the stellar cluster give rise to the process of
vector resonant relaxation (VRR). VRR can bring a low-inclination binary into an ?active? LK regime in which
high eccentricities and strong interactions are triggered in the binary. Here, we study the coupled LK-VRR
dynamics, with implications for LIGO and VIRGO GW sources. We carry out Monte Carlo simulations and
find that the merger fraction enhancement due to LK-VRR dynamics is up to a factor of end of assumed MBH masses (M" = 104M™), and decreases sharply with increasing M". We find that, even
in our most optimistic scenario, the baseline BH-BH merger rate is small, and the enhancement by LK-VRR
coupling is not large enough to increase the rate to well above the LIGO/VIRGO lower limit, 12Gpc?3 yr?1.
For the Galactic Center, the LK-VRR-enhanced rate is M" = 104M™, the rate barely reaches 12Gpc?3 yr?1.
Erkal Denis, Boubert Douglas, Gualandris Alessia, Evans N. Wyn, Antonini Fabio (2018) A hypervelocity star with a Magellanic origin, Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP)
Using proper motion measurements from Gaia DR2, we probe the origin of 26 previously known hypervelocity stars (HVSs) around the Milky Way. We find that a significant fraction of these stars have a high probability of originating close to the Milky Way centre, but there is one obvious outlier. HVS3 is highly likely to be coming almost from the centre of the Large Magellanic Cloud (LMC). During its closest approach, 21.1 +6.1 ?4.6 Myr ago, it had a relative velocity of 870 +69 ?66 kms ?1 with respect to the LMC. This large kick velocity is only consistent with the Hills mechanism, requiring a massive black hole at the centre of the LMC. This provides strong direct evidence that the LMC itself harbours a massive black hole of at least 4×10 3 ?10 4 M ™ .
Fragione Giacomo, Antonini Fabio, Gnedin Oleg Y. (2019) Millisecond Pulsars and the Gamma-Ray Excess in Andromeda, The Astrophysical Journal 871 (1) L8 The American Astronomical Society / IOP Publishing
The Fermi Gamma-Ray Space Telescope has provided evidence for diffuse gamma-ray emission in the central parts of the Milky Way and the Andromeda galaxy. This excess has been interpreted either as dark-matter annihilation emission or as emission from thousands of millisecond pulsars (MSPs). We have recently shown that old massive globular clusters (GCs) may move toward the center of the Galaxy by dynamical friction and carry within them enough MSPs to account for the observed gamma-ray excess. In this Letter we revisit the MSP scenario for the Andromeda galaxy by modeling the formation and disruption of its GC system. We find that our model predicts gamma-ray emission ~2?3 times larger than for the Milky Way, but still nearly an order of magnitude smaller than the observed Fermi excess in the Andromeda. Our MSP model can reproduce the observed excess only by assuming ~8 times a larger number of old clusters than inferred from galaxy scaling relations. To explain the observations we require either that Andromeda deviates significantly from the scaling relations, or that a large part of its high-energy emission comes from additional sources.