What the study found
Repeated tidal perturbations from a massive black hole can, in some cases, drive a binary star system into a close binary rather than immediately breaking it apart. When the inner orbit becomes highly eccentric and the stars pass within a few stellar radii, stellar oscillation modes can grow chaotically and rapidly harden the binary to a very small separation.
Why the authors say this matters
The authors conclude that this provides a new channel for producing the fastest hyper-velocity stars, which are stars ejected at very high speed. The study also says these tidally hardened binaries are connected to nuclear transients such as repeating partial tidal disruption events and quasi-periodic eruptions.
What the researchers tested
The researchers developed a physical model of a massive black hole-binary system. Their model includes outer orbital relaxation, tidal perturbations from the massive black hole, and dynamical tides, which are tidal interactions between the stars that involve stellar oscillations.
What worked and what didn't
The model shows that when the inner orbit reaches very high eccentricity, chaotic tidal growth can rapidly shrink the binary to semi-major axes of about 10 stellar radii or less. The study finds that up to 50% of initially wide binaries in the empty loss-cone regime do not undergo Hills breakup as wide binaries; instead, they experience chaotic tidal growth and become close binaries.
What to keep in mind
The abstract describes the result for initially wide binaries in the empty loss-cone regime, so the stated fraction applies to that setting. The available summary does not give additional limitations beyond that scope.
Key points
- A massive black hole can perturb a binary star long enough for the inner orbit to become highly eccentric.
- At very small pericenter distances, stellar oscillation modes can grow chaotically and harden the binary.
- The study reports that up to 50% of initially wide binaries in the empty loss-cone regime may become close binaries instead of undergoing Hills breakup as wide binaries.
- These hardened binaries may provide a new channel for producing the fastest hyper-velocity stars.
- The authors connect the outcome to repeating partial tidal disruption events and quasi-periodic eruptions.
Disclosure
- Research title:
- Massive black holes can turn wide binaries into close binaries
- Image credit:
- Photo by NASA Hubble Space Telescope on Unsplash
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