Partial Tidal Disruptions of Main-sequence Stars by Intermediate-mass Black Holes

Abstract

We study close encounters of a 1 M ⊙ middle-age main-sequence star (modeled using MESA) with massive black holes through hydrodynamic simulations, and explore in particular the dependence of the outcomes on the black hole mass. We consider here black holes in the intermediate-mass range, M BH = 100–104 M ⊙. Possible outcomes vary from a small tidal perturbation for weak encounters all the way to partial or full disruption for stronger encounters. We find that stronger encounters lead to increased mass loss at the first pericenter passage, in many cases ejecting the partially disrupted star on an unbound orbit. For encounters that initially produce a bound system, with only partial stripping of the star, the fraction of mass stripped from the star increases with each subsequent pericenter passage and a stellar remnant of finite mass is ultimately ejected in all cases. The critical penetration depth that separates bound and unbound remnants has a dependence on the black hole mass when M BH ≲ 103 M ⊙. We also find that the number of successive close passages before ejection decreases as we go from the stellar-mass black hole to the intermediate-mass black hole regime. For instance, after an initial encounter right at the classical tidal disruption limit, a 1 M ⊙ star undergoes 16 (5) pericenter passages before ejection from a 10 M ⊙ (100 M ⊙) black hole. Observations of periodic flares from these repeated close passages could in principle indicate signatures of a partial tidal disruption event.

Fallback Rates in Partial Tidal Disruptions of White Dwarfs by Intermediate-mass Black Holes

“…In our case, we find that the kick velocity is highest, ∼1.58 × 10 4 km s −1 , for the minimum mass of the remnant core (0.2 M e ). This can be contrasted with the findings in Table 1 of Kıroğlu et al (2023), where for the same black hole mass of 10 3 M e , the minimum remnant mass (0.027 M e ) corresponds to a kick velocity of 9.38 × 10 2 km s −1 . Additionally, we can also compare the kick velocities for the same remnant mass.…”

“…It is important to contrast our results with those of Kıroğlu et al (2023), who have recently studied partial tidal disruptions of main-sequence stars by IMBHs. They choose a stellar mass of 1 M e (with radius 0.9 R e ) and vary the black hole mass from 10 to 10 4 M e .…”

“…To compare with their results, we focus on the kick velocity v kick on the surviving core, which results from the mass difference of the two asymmetric tidal tails, for impact parameters below the critical value of β = β c , above which the disruption becomes total. (While we have mentioned that β c ∼ 0.85 in our case, its value is found to be ∼3.3 for mainsequence stars considered in Kıroğlu et al (2023).) In our case, we find that the kick velocity is highest, ∼1.58 × 10 4 km s −1 , for the minimum mass of the remnant core (0.2 M e ).…”

“Tidal Peeling Events”: Low-eccentricity Tidal Disruption of a Star by a Stellar-mass Black Hole

“…Another important comparison should be made between TPEs and tidal disruptions of a solar-like star by an IMBH. Recent work by Kıroğlu et al (2022) find, using hydrodynamics simulations, that in all cases where a 1 M e star is disrupted by an IMBH, the stellar remnant is eventually ejected to be unbound, either after the first pericenter or after many pericenter passages. In our TPE simulations, all stars remain in a binary with the BH, or are eventually completely disrupted by the BH.…”

Binary Black Hole Mergers and Intermediate-mass Black Holes in Dense Star Clusters with Collisional Runaways

“…However, there are some caveats that we leave to future work. For example, we have not included in our treatment the interaction of the IMBH with ordinary stars, which could lead to interesting phenomena, such as tidal disruption events (e.g., Liu et al 2009;Fragione et al 2021;Angus et al 2022;Kıroğlu et al 2023). We have also fixed some of the distributions that describe the birth properties of star clusters, consistent with observed properties in the local universe (Portegies Zwart et al 2010), but these are poorly constrained elsewhere.…”