The Combined Effects of Two-body Relaxation Processes and the Eccentric Kozai–Lidov Mechanism on the Extreme-mass-ratio Inspirals Rate

Naoz, Smadar; Rose, Sanaea C.; Michaely, Erez; Melchor, D. A.; Ramírez-Ruiz, E.; Mockler, Brenna; Schnittman, Jeremy D.

doi:10.3847/2041-8213/ac574b

Cited by 24 publications

(19 citation statements)

References 100 publications

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“…We simulate the effects of relaxation in our code. Over each time step, we apply a small instantaneous velocity kick to the star, from which we calculate the new, slightly altered orbital parameters (see Naoz et al 2022 Rose et al 2022). Here, v orbital and P orbital are the orbital speed and period of the star in question.…”

Section: Two-body Relaxationmentioning

confidence: 99%

Stellar Collisions in the Galactic Center: Massive Stars, Collision Remnants, and Missing Red Giants

Rose,

Naoz,

Sari

et al. 2023

ApJ

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Like most galaxies, the Milky Way harbors a supermassive black hole (SMBH) at its center, surrounded by a nuclear star cluster. In this dense star cluster, direct collisions can occur between stars before they evolve off the main sequence. Using a statistical approach, we characterize the outcomes of these stellar collisions within the inner parsec of the Galactic center (GC). Close to the SMBH, where the velocity dispersion is larger than the escape speed from a Sun-like star, collisions lead to mass loss. We find that the stellar population within 0.01 pc is halved within about a billion years because of destructive collisions. Additionally, we predict a diffuse population of peculiar low-mass stars in the GC. These stars have been divested of their outer layers in the inner 0.01 pc before migrating to larger distances from the SMBH. Between 0.01 and 0.1 pc from the SMBH, collisions can result in mergers. Our results suggest that repeated collisions between lower-mass stars can produce massive (≳10 M ⊙) stars, and that there may be ∼100 of them residing in this region. We provide predictions on the number of so-called G objects, dust- and gas-enshrouded stellar objects, that may result from main-sequence stellar collisions. Lastly, we comment on uncertainties in our model and possible connections between stellar collisions and the missing red giants in the GC.

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Section: Two-body Relaxationmentioning

confidence: 99%

Stellar Collisions in the Galactic Center: Massive Stars, Collision Remnants, and Missing Red Giants

Rose,

Naoz,

Sari

et al. 2023

ApJ

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“…Relaxation can cause the orbit of an object in a GN to reach high eccentricities. If the object is a BH, it can spiral into the SMBH and form an EMRI, while a star can be tidally disrupted by the SMBH (e.g., Magorrian & Tremaine 1999;Wang & Merritt 2004;Hopman & Alexander 2005;Aharon & Perets 2016;Stone & Metzger 2016;Amaro-Seoane 2018;Sari & Fragione 2019;Naoz et al 2022). The relaxation process is therefore crucial to our study.…”

Section: Two-body Relaxation Processesmentioning

confidence: 99%

“…(see Bradnick et al 2017 for an approach to changes in the angular momentum). The new orbital parameters can be calculated following Lu & Naoz (2019), and see Naoz et al (2022) for the full set of equations.…”

Section: Two-body Relaxation Processesmentioning

confidence: 99%

The Formation of Intermediate-mass Black Holes in Galactic Nuclei

Rose

Naoz

Sari

et al. 2022

ApJL

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Most stellar evolution models predict that black holes (BHs) should not exist above approximately 50–70 M ⊙, the lower limit of the pair-instability mass gap. However, recent LIGO/Virgo detections indicate the existence of BHs with masses at and above this threshold. We suggest that massive BHs, including intermediate-mass BHs (IMBHs), can form in galactic nuclei through collisions between stellar-mass BHs and the surrounding main-sequence stars. Considering dynamical processes such as collisions, mass segregation, and relaxation, we find that this channel can be quite efficient, forming IMBHs as massive as 104 M ⊙. This upper limit assumes that (1) the BHs accrete a substantial fraction of the stellar mass captured during each collision and (2) that the rate at which new stars are introduced into the region near the SMBH is high enough to offset depletion by stellar disruptions and star–star collisions. We discuss deviations from these key assumptions in the text. Our results suggest that BHs in the pair-instability mass gap and IMBHs may be ubiquitous in galactic centers. This formation channel has implications for observations. Collisions between stars and BHs can produce electromagnetic signatures, for example, from X-ray binaries and tidal disruption events. Additionally, formed through this channel, both BHs in the mass gap and IMBHs can merge with the SMBHs at the center of a galactic nucleus through gravitational waves. These gravitational-wave events are extreme- and intermediate-mass ratio inspirals.

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“…Here we remind the reader that we generated 100,000 initial conditions per set of Monte Carlo simulations. To arrive at the "EMRIs (or any other outcome) per initial stellar binary" figure, we simply count the number of EMRIs (or any other outcome) in each set of simulations and divide this by 100,000.4 Note that these rates are about one to two orders of magnitude lower than the EMRI rate estimated via two-body relaxation processes (e.g.,Hopman & Alexander 2006), and three to four orders or magnitude lower than the estimated rate of MBH binaries(Naoz et al 2022). …”

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confidence: 86%

Binary Natal Kicks in the Galactic Center: X-ray Binaries, Hypervelocity Stars, and Gravitational Waves

Hoang,

Naoz,

Sloneker

2022

Preprint

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Theoretical and observational studies suggest that stellar binaries exist in large numbers in galactic nuclei like our own Galactic Center. Neutron stars (NSs), and debatedly, black holes (BHs) and white dwarfs (WDs), receive natal kicks at birth. In this work we study the effect of two successive natal kicks on a population of stellar binaries orbiting the massive black hole (MBH) in our Galactic Center. These natal kicks can significantly alter the binary orbit in a variety of ways, and also the orbit of the binary around the MBH. We found a variety of dynamical outcomes resulting from these kicks, including a steeper cusp of single NSs relative to the initial binary distribution. Furthermore, hypervelocity star and binary candidates, including hypervelocity X-ray binaries, are a common outcome of natal kicks. In addition, we show that the population of X-ray binaries in the Galactic Center can be used as a diagnostic for the BH natal kick distribution. Finally, we estimate the rate of gravitational wave (GW) events triggered by natal kicks, including binary mergers and EMRIs.

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The Combined Effects of Two-body Relaxation Processes and the Eccentric Kozai–Lidov Mechanism on the Extreme-mass-ratio Inspirals Rate

Cited by 24 publications

References 100 publications

Stellar Collisions in the Galactic Center: Massive Stars, Collision Remnants, and Missing Red Giants

Stellar Collisions in the Galactic Center: Massive Stars, Collision Remnants, and Missing Red Giants

The Formation of Intermediate-mass Black Holes in Galactic Nuclei

Binary Natal Kicks in the Galactic Center: X-ray Binaries, Hypervelocity Stars, and Gravitational Waves

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