Are merger remnants of binary white dwarfs observable by spaceborne gravitational-wave detectors?

• Project/Area Number: 18K03641
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 15010:Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics
• Research Institution: The University of Tokyo
• Principal Investigator: Shin'ichirou Yoshida 東京大学, 大学院総合文化研究科, 助教 (40568284)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Project Status: Completed (Fiscal Year 2020)
• Budget Amount: ¥2,080,000 (Direct Cost: ¥1,600,000、Indirect Cost: ¥480,000); Fiscal Year 2020: ¥260,000 (Direct Cost: ¥200,000、Indirect Cost: ¥60,000); Fiscal Year 2019: ¥650,000 (Direct Cost: ¥500,000、Indirect Cost: ¥150,000); Fiscal Year 2018: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
• Keywords: 白色矮星 / 連星 / 重力波 / 恒星振動 / Ia型超新星 / 連星合体 / 高速自転 / 有限温度 / 平衡モデル / 宇宙物理（理論） / 連星白色矮星 / 高速回転星

Outline of Final Research Achievements

A close binary composed of two white dwarfs emits gravitational wave and finally merges to form a single remnant. In this research
I studied characteristic oscillations of rapidly rotating remnants. The oscillations modes of interest here are in the frequency range of 0.1 Hz (decihertz). The frequency range is in the observable window of such planned space-borne gravitational wave observatories as DECIGO (DECI-hertz Gravitational Observatory) and BBO (Big Bang Observer). Here I numerically constructed the remnant models of the mergers and computed the unstable eigenmode oscillations of them. I also computed the amplitude of gravitational waves from the oscillations. By this study it is shown that the remnant's oscillations are observable with the planned space-borne gravitational wave observatory.

Academic Significance and Societal Importance of the Research Achievements

近接する白色矮星連星の合体は，熱核融合型（Ia型）超新星爆発の前駆天体として，また質量の大きな，あるいは磁場の強い白色矮星を作る過程として興味深い現象である．今回の研究では，これまで議論されていなかった，合体直後に残された残存天体からの重力波放射について，全く新たな可能性を提案できた．周波数0.1Hz帯での重力波観測において，これは新たなターゲット天体となるだろう．また，Ia型超新星爆発が合体に引き続き起きるならば，一連の過程において重力波と電磁波によるマルチメッセンジャー観測も期待できることを示唆できた．

Research Products

• [Journal Article] Decihertz Gravitational Waves from Double White Dwarf Merger Remnants (2021)
  • Author(s): Yoshida Shin’ichirou
  • Journal Title: The Astrophysical Journal Volume: 906 Issue: 1 Pages: 29-29
  • DOI: 10.3847/1538-4357/abc7bd
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] On the Central Engine of the Fastest-declining Type I Supernova SN2019bkc (2019)
  • Author(s): Shin'ichirou Yoshida
  • Journal Title: Research Notes of the American Astronomical Society Volume: 3 Issue: 7 Pages: 112-112
  • DOI: 10.3847/2515-5172/ab35de
• [Presentation] Near-Chandrasekhar Mass Type Ia Supernovae from the Double-Degenerate Channel (2021)
  • Author(s): S. Neopane, R. Fisher, K. Bhargava, N. Roy, S. Yoshida, S. Toonen
  • Organizer: 237th American Astronomical Society Meeting
  • Int'l Joint Research
• [Presentation] 連星白色矮星合体レムナントからの deciHz 帯重力波放射 (2020)
  • Author(s): 吉田慎一郎
  • Organizer: 日本物理学会秋季年会
• [Presentation] Double white dwarf merger remnants as low frequency gravitational wave sources (2019)
  • Author(s): Shin;ichirou Yoshida
  • Organizer: The Beginning and Ends of Double White Dwarfs
  • Int'l Joint Research
• [Presentation] 自転する星の超大質量ブラックホールによる潮汐破壊 (2018)
  • Author(s): 吉田慎一郎
  • Organizer: 日本物理学会2018年秋季大会
• [Presentation] Rotating merger remnant models of white dwarf binaries (2018)
  • Author(s): 吉田慎一郎
  • Organizer: The 28th Workshop on General Relativity and Gravitation in Japan
  • Int'l Joint Research