Astrometric satellite Gaia published Gaia Data Release 3 in 2022. From Gaia Data Release 3, we found a candidate of a binary system with black hole and red-giant star (hereafter, black hole binary). Its astrometric and spectroscopic mass functions have similar values, and the values are about 7 solar mass. Thus, the binary system is likely to be a black hole binary. The candidate has a bianry period of 1300 days. The binary period is 10 times longer than those of black hole binaryes previously discovered.

Such a black hole binary can be formed through dynamical interactions in open clusters rather than through isolated binary evolution.

• Tanikawa, Cary S., Shikauchi M., Wang L., Fujii M. S. 2024, MNRAS, 527, 4031

• Shikauchi M., Tsuna D., Tanikawa, Kawanaka N. 2023, ApJ, 953, 52

• Tanikawa et al. 2023, ApJ, 946, 79

• Shikauchi M., Tanikawa, Kawanaka N. 2022, ApJ, 928, 13

• Shikauchi M., Kumamoto J., Tanikawa, Fujii M. S. 2020, PASJ, 72, 45

Binary black holes as gravitational wave sources

Recently, many binary black hole mergers have been discovered by gravitational wave observations. Their origin is still an open question. We investigated isolated binary evolution, considering all the stellar metallicities from zero metallicity to the solar metallicity. We showed that isolated binaries can form all the binary black hole mergers observed so far.

• Tanikawa 2024, RMPP, 8, 13

• Tanikawa et al. 2022, PASJ, 74, 512

• Tanikawa et al. 2022, ApJ, 926, 83

• Tanikawa et al. 2021, MNRAS, 505, 2170

• Hijikawa, Tanikawa et al. 2021, MNRAS letters, 505, 69

• Tanikawa et al. 2021, ApJ, 910, 30

• Tanikawa et al. 2020, MNRAS, 495, 4170

Double white dwarfs as type Ia supernova progenitors

One of the two popular scenarios for type Ia supernovae is the double degenerate scenario. We investigated the violent merger and D6 models along with the double degenerate scenario. We found that both of them can cause stellar explosions, however that their features may be different from those of type Ia supernovae.

• Kinugawa, Takeda, Tanikawa, Yamaguchi 2022, ApJ, 938, 52

• Ferrand, Tanikawa et al. 2022, ApJ, 930, 92

• Tanikawa et al. 2019, ApJ, 885, 103

• Tanikawa et al. 2018, ApJ, 868, 90

• Sato, Nakasato, Tanikawa et al. 2016, ApJ, 821, 67

• Sato, Nakasato, Tanikawa et al. 2015, ApJ, 807, 105

• Tanikawa et al. 2015, ApJ, 807, 40

Tidal disruption events of white dwarfs

We investigated tidal disruption events of white dwarfs by means of numerical simulations. This events can generate astronomical transients similar to type Ia supernovae. Because only intermediate mass black holes can disrupt white dwarfs, this events can be a probe to search for intermedial mass black holes.

• Tanikawa et al. 2022, MNRAS, 515, 4038

• Kawana, et al., Tanikawa 2020, ApJL, 890, 26

• Kawana, Tanikawa et al. 2018, MNRAS, 477, 3449

• Tanikawa 2018, ApJ, 858, 26

• Tanikawa 2017, MNRAS Letters, 475, 67

• Tanikawa et al. 2017, ApJ, 839, 81

Particle simulators

We developed highly optimized particle simulation codes: Phantom-GRAPE (a numerical library for gravitational N-body simulation to utilize SIMD units on x86 architecture) and FDPS (a framework to support development of arbitrary particle simulation codes). The above figures are snapshots generated by particle simulation codes with FDPS.

• Yoshikawa, Tanikawa 2018, RNAAS, 2, 4

• Namekata et al. Tanikawa et al. 2018, PASJ, 70, 70

• Iwasawa, Tanikawa et al. 2016, PASJ, 68, 54

• Tanikawa et al. 2013, NewA, 19, 74

• Tanikawa et al. 2012, NewA, 17, 82