Black hole tidal disruption events
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Tidal Disruption Events: Black Hole Types and Environments
Tidal disruption events (TDEs) occur when a star gets too close to a black hole and is torn apart by its gravity. These events can happen around different types of black holes, including supermassive black holes (SMBHs), intermediate-mass black holes (IMBHs), and stellar-mass black holes. TDEs are important because they help astronomers detect and study black holes that might otherwise be invisible, and they provide insights into black hole properties and galaxy evolution 59.
TDEs by Supermassive Black Holes and Black Hole Binaries
Most TDEs are observed in the centers of galaxies, where SMBHs reside. When a star is disrupted by an SMBH, the resulting flare can be seen across the electromagnetic spectrum. In galaxies with supermassive black hole binaries (SMBHBs), the presence of two black holes can significantly change the rate and nature of TDEs. The probability of a full tidal disruption event (FTDE) can be increased by up to 40–50 times or decreased by up to 10 times compared to a single black hole, depending on the binary’s properties such as mass ratio, separation, and eccentricity 110.
The lighter black hole in a binary can also have its TDE rate boosted, mainly due to the eccentric Kozai–Lidov mechanism, which perturbs stellar orbits and increases the chance of disruption. This can lead to TDEs with properties that do not match the expected mass of the main SMBH, helping to identify hidden black hole companions . The presence of a binary companion can also affect the light curve and debris fallback, creating unique observational signatures .
Partial and Repeating Tidal Disruption Events
Not all TDEs result in the complete destruction of a star. Partial tidal disruption events (PTDEs) are common, especially in systems with IMBHs or SMBH-IMBH binaries. In these cases, a star may lose some mass during each close encounter, potentially leading to multiple flares or repeating TDEs. These partial disruptions can spin up the star, change its orbit, and affect the overall TDE rate and light curve shape 17. Some observed quasi-periodic eruptions in galactic centers may be explained by repeating PTDEs in binary black hole systems .
TDEs by Intermediate-mass and Stellar-mass Black Holes
IMBHs, which are thought to be the building blocks of SMBHs, can also cause TDEs. These events are especially important for studying the properties and growth of IMBHs, which are otherwise difficult to detect. X-ray observations of TDEs can provide strong constraints on the mass and spin of IMBHs and help understand their role in galaxy evolution 89.
Stellar-mass black holes in dense star clusters can also disrupt stars, leading to fast optical transients. These TDEs are expected to have rapid rise times (about a day), high X-ray luminosities, and bright optical emission due to reprocessing by disk winds. They may explain some of the fast blue optical transients observed in the universe 26. Surveys like the Vera Rubin Observatory and ULTRASAT are expected to detect many such events in the future .
Observational Signatures and Rates
TDEs produce flares that can be observed in X-ray, ultraviolet, and optical wavelengths. The light curves and spectra of these events can be used to estimate the mass of the black hole and the properties of the disrupted star. Most observed TDEs are associated with black holes in the mass range of 10^6–10^8 solar masses, and there is a preference for disrupting low-mass stars, which are more common .
TDE rates depend on the environment. In young star clusters and globular clusters, TDEs by stellar-mass black holes and IMBHs can be as frequent as or even more common than those in galactic nuclei. Many TDEs may occur far from the centers of galaxies, especially in old globular clusters hosting IMBHs .
Conclusion
Tidal disruption events are powerful tools for discovering and studying black holes of all sizes, from stellar-mass to supermassive. The rates and properties of TDEs are strongly influenced by the type of black hole, the presence of binary companions, and the environment. Ongoing and future observations across the electromagnetic spectrum, as well as gravitational wave and neutrino detections, will continue to expand our understanding of these dramatic cosmic events .
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Most relevant research papers on this topic
Fast Optical Transients from Stellar-mass Black Hole Tidal Disruption Events in Young Star Clusters
Stellar-mass black hole tidal disruption events in young star clusters occur at a rate of up to 200 Gpc3 yr1 and share common features with Fast Blue Optical Transients.
Uncovering Hidden Massive Black Hole Companions with Tidal Disruption Events
Lighter black holes in supermassive black hole binaries can experience a dramatic increase in tidal disruption events due to perturbations from a more massive companion, potentially revealing hidden massive black hole candidates.
Wind-Reprocessed Transients from Stellar-mass Black Hole Tidal Disruption Events
Wind-reprocessed transients are expected in dense star clusters when radiation from central engines powered by accretion onto black holes is reprocessed by the optically-thick disk wind.
DOI
Partial Tidal Disruption Events by Intermediate-mass Black Holes in Supermassive and Intermediate-mass Black Hole Binaries
Partial tidal disruption events (PTDEs) are the majority of tidal disruption events in supermassive and intermediate-mass black hole binaries, with a significant number of stars experiencing partial disruption ultimately getting captured by the intermediate-mass black hole.
DOI
Probing Intermediate-mass Black Holes Using Tidal Disruption Events
Tidal disruption events provide a unique opportunity to measure the mass and spin of intermediate-mass black holes, contributing to a better understanding of their mass distribution and formation channels.
DOI