Oka, Tomoharu

写真a

Affiliation

Faculty of Science and Technology, Department of Physics (Yagami)

Position

Professor

E-mail Address

E-mail address

Related Websites

External Links

Career 【 Display / hide

  • 1993.04
    -
    1996.03

    日本学術振興会特別研究員

  • 1996.04
    -
    1999.03

    理化学研究所基礎科学特別研究員

  • 1998.04
    -
    1999.03

    玉川大学非常勤講師(兼任) 集中講義「宇宙科学」担当

  • 1999.04
    -
    2007.03

    東京大学大学院理学系研究科物理学専攻,助手

  • 2005.04
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    2006.03

    京都大学大学院理学系研究科非常勤講師(兼任) 集中講義「星間分子雲の物理・化学過程およびその電波観測」担当

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Academic Background 【 Display / hide

  • 1996.03

    The University of Tokyo, Graduate School, Division of Science, Department of Astronomy

    Graduate School, Completed, Doctoral course

Academic Degrees 【 Display / hide

  • Doctor of Science, Ph.D., The University of Tokyo, 1996.03

 

Research Areas 【 Display / hide

  • Astronomy

Research Themes 【 Display / hide

  • Formation Process of Supermassive Black Holes in Galactic Nuclei, 

    2006
    -
    Present

  • Observational Study of Interstellar Matter in the Galactic Center Region, 

    1996
    -
    Present

 

Books 【 Display / hide

Papers 【 Display / hide

  • Indication of Another Intermediate-mass Black Hole in the Galactic Center

    Takekawa S., Oka T., Iwata Y., Tsujimoto S., Nomura M.

    Astrophysical Journal Letters (Astrophysical Journal Letters)  871 ( 1 )  2019.01

    ISSN  20418205

     View Summary

    © 2019. The American Astronomical Society. We report the discovery of molecular gas streams orbiting around an invisible massive object in the central region of our Galaxy, based on the high-resolution molecular line observations with the Atacama Large Millimeter/submillimeter Array. The morphology and kinematics of these streams can be reproduced well through two Keplerian orbits around a single point mass of (3.2 ± 0.6) ×10 4 M o . We also found ionized gas toward the inner part of the orbiting gas, indicating dissociative shock and/or photoionization. Our results provide new circumstantial evidences for a wandering intermediate-mass black hole in the Galactic center, suggesting also that high-velocity compact clouds can be probes of quiescent black holes that abound in our Galaxy.

  • Magnetohydrodynamic Simulations of a Plunging Black Hole into a Molecular Cloud

    Nomura M., Oka T., Yamada M., Takekawa S., Ohsuga K., Takahashi H., Asahina Y.

    Astrophysical Journal (Astrophysical Journal)  859 ( 1 )  2018.05

    ISSN  0004637X

     View Summary

    © 2018. The American Astronomical Society. All rights reserved.. Using two-dimensional magnetohydrodynamic simulations, we investigated the gas dynamics around a black hole (BH) plunging into a molecular cloud. In these calculations, we assumed a parallel-magnetic-field layer in the cloud. The size of the accelerated region is far larger than the Bondi-Hoyle-Lyttleton radius, being approximately inversely proportional to the Alfvén Mach number for the plunging BH. Our results successfully reproduce the "Y" shape in position-velocity maps of the "Bullet" in the W44 molecular cloud. The size of the Bullet is also reproduced within an order of magnitude using a reasonable parameter set. This consistency supports the shooting model of the Bullet, according to which an isolated BH plunged into a molecular cloud to form a compact broad-velocity-width feature.

  • Detection of Another Molecular Bubble in the Galactic Center

    Shiho Tsujimoto, (/)-RTomoharu Oka, Takekawa Shunya, Masaya Yamada, Sekito Tokuyama, Yuhei Iwata, Justin A. Roll

    The Astrophysical Journal (Astrophysical Journal)  856 ( 2 ) 91 - 95 2018.03

    Research paper (scientific journal), Joint Work, Accepted,  ISSN  0004637X

     View Summary

    The l=-1buildrel{circ}over{.} 2 region in the Galactic center has a high CO J = 3–2/J = 1–0 intensity ratio and extremely broad velocity width. This paper reports the detection of five expanding shells in the l=-1buildrel{circ}over{.} 2 region based on the CO J = 1–0, 13CO J = 1–0, CO J = 3–2, and SiO J = 8–7 line data sets obtained with the Nobeyama Radio Observatory 45 m telescope and James Clerk Maxwell Telescope. The kinetic energy and expansion time of the expanding shells are estimated to be {10}48.3{--50.8} erg and {10}4.7{--5.0} yr, respectively. The origin of these expanding shells is discussed. The total kinetic energy of 1051 erg and the typical expansion time of ∼105 yr correspond to multiple supernova explosions at a rate of 10‑5–10‑4 yr‑1. This indicates that the l=-1buildrel{circ}over{.} 2 region may be a molecular bubble associated with an embedded massive star cluster, although the absence of an infrared counterpart makes this interpretation somewhat controversial. The expansion time of the shells increases as the Galactic longitude decreases, suggesting that the massive star cluster is moving from Galactic west to east with respect to the interacting molecular gas. We propose a model wherein the cluster is moving along the innermost x 1 orbit and the interacting gas collides with it from the Galactic eastern side.

  • Millimetre-wave emission from an intermediate-mass black hole candidate in the Milky Way

    (/)-RTomoharu Oka, Shiho Tsujimoto, Yuhei Iwata, Mariko Nomura, Shunya Takekawa

    Nature Astronomy 1 ( 1 ) 709 - 712 2017.09

    Research paper (scientific journal), Joint Work, Accepted

     View Summary

    It is widely accepted that black holes with masses greater than a million solar masses (M⊙) lurk at the centres of massive galaxies. The origins of such ‘supermassive’ black holes (SMBHs) remain unknown1, although those of stellar-mass black holes are well understood. One possible scenario is that intermediate-mass black holes (IMBHs), which are formed by the runaway coalescence of stars in young compact star clusters2, merge at the centre of a galaxy to form a SMBH3. Although many candidates for IMBHs have been proposed, none is accepted as definitive. Recently, we discovered a peculiar molecular cloud, CO–0.40–0.22, with an extremely broad velocity width, near the centre of our Milky Way galaxy. Based on the careful analysis of gas kinematics, we concluded that a compact object with a mass of about 105M⊙ is lurking in this cloud4. Here we report the detection of a point-like continuum source as well as a compact gas clump near the centre of CO–0.40–0.22. This point-like continuum source (CO–0.40–0.22*) has a wide-band spectrum consistent with 1/500 of the Galactic SMBH (Sgr A*) in luminosity. Numerical simulations around a point-like massive object reproduce the kinematics of dense molecular gas well, which suggests that CO–0.40–0.22* is one of the most promising candidates for an intermediate-mass black hole.

  • Discovery of Two Small High-velocity Compact Clouds in the Central 10 pc of Our Galaxy

    Takekawa Shunya, (/)-RTomoharu Oka, Iwata Yuhei, Tokuyama Sekito, Nomura Mariko

    The Astrophysical Journal Letters 843 ( 1 ) L11 - L15 2017.06

    Research paper (scientific journal), Joint Work, Accepted

     View Summary

    We discovered two small high-velocity compact clouds (HVCCs) in the HCN J = 4-3 and J = 3-2 maps of the central 20 pc of our Galaxy. Both HVCCs have broad velocity widths ({{Δ }}V≳ 40 km s-1) and compact sizes (d˜ 1 {pc}), and originate from the dense molecular clouds in the position-velocity space. One of them has a faint counterpart in a Paschen-α image. Their spatial structure, kinematics, and absence of luminous stellar object are compatible with the notion that each of the small HVCCs is driven by the plunge of an invisible compact object into a molecular cloud. Such objects are most likely inactive, isolated black holes.

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Papers, etc., Registered in KOARA 【 Display / hide

Reviews, Commentaries, etc. 【 Display / hide

  • 銀河系中心のもう一つのブラックホール

    OKA Tomoharu

    パリティ (Maureen Publishing Co., Ltd.)  32 ( 1 ) 58 - 60 2016.12

    Introduction and explanation (commerce magazine), Single Work

  • Atomic Carbon in the Galaxy

    OKA Tomoharu

    The Astronomical Herald 99 ( 4 ) 190 - 196 2006.03

    Introduction and explanation (scientific journal), Single Work

  • 超新星残骸と相互作用する星間分子雲

    岡 朋治、瀬田益道

    原子核研究「超高エネルギー天体 (I)」 42 ( 5 ) 141 - 148 1998

    Introduction and explanation (scientific journal)

  • Galactic Center Me¥molecular Clouds -- Micro-scale Structure and Physical Conditions --

    OKA Tomoharu

    天文月報 88 ( 12 ) 506 - 511 1995.11

    Introduction and explanation (scientific journal)

Presentations 【 Display / hide

  • ブラックホールとは何か

    岡 朋治

    10MTV オピニオン「大人のための教養講座」, 2019.03, Media report,etc., イマジニア株式会社

  • 銀河系中心で発見された高速度雲の起源

    岡 朋治

    ブラックホール地平面勉強会 <銀河系中心とJASMINE> (慶應義塾大学日吉キャンパス) , 2018.12, Oral Presentation(guest/special)

  • ALMAによる小型高速度コンパクト雲の詳細観測

    竹川俊也, 岡 朋治, 岩田悠平, 辻本志保, 野村真理子

    日本天文学会2018年秋季年会 (千葉大学) , 2018.09, Oral Presentation(general)

  • 高速度コンパクト雲CO 0.02-0.02の3 mm帯ラインサーベイ観測

    岩田悠平, 岡 朋治, Justin A. Roll, 辻本志保, 竹川俊也

    日本天文学会2018年秋季年会 (千葉大学) , 2018.09, Oral Presentation(general)

  • 高速度コンパクト雲 CO–0.40–0.22 中に発見された点状電波源の観測的研究

    岩田悠平, 岡 朋治, 杉本知穂, 竹川俊也, 田邊恭介, 三好真

    日本天文学会2018年春季年会 (千葉大学) , 2018.03, Oral Presentation(general)

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Research Projects of Competitive Funds, etc. 【 Display / hide

  • Search for Intermediate-mass Black Holes in the Galactic Center Based on Molecular Line Observations

    2015.04
    -
    2018.03

    MEXT,JSPS, Grant-in-Aid for Scientific Research, 岡 朋治, Grant-in-Aid for Scientific Research (B), Principal Investigator

 

Courses Taught 【 Display / hide

  • PHYSICS SEMINAR 3

    2019

  • PHYSICS LABORATORIES 2

    2019

  • PHYSICS LABORATORIES 1

    2019

  • LITERATURE OF PHYSICS

    2019

  • LABORATORIES IN SCIENCE AND TECHNOLOGY

    2019

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Social Activities 【 Display / hide

  • 国立天文台電波専門員会 NROワーキング・グループ

    2015.01
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    2016.06
  • 国立天文台電波専門委員会

    2012.07
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    2014.06
  • 日本学術会議 電気電子工学委員URSI分科会 電波天文学小委員会

    2009.06
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    2011.09
  • 国立天文台電波専門員会 ALMA小委員会

    2008.12
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    2020.07
  • 国立天文台電波専門員会 電波天文周波数小委員会

    2006.08
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    2016.07

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Memberships in Academic Societies 【 Display / hide

  • Astronomical Society of Japan, 

    1991.04
    -
    Present
  • International Astronomical Union

     

Committee Experiences 【 Display / hide

  • 2012.07
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    2014.06

    Committee Member, 国立天文台電波専門委員会

  • 2009.06
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    2011.09

    Committee Member, 日本学術会議 電気電子工学委員URSI分科会 電波天文学小委員会

  • 2008.12
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    2018.03

    Committee Member, 国立天文台電波専門員会 ALMA小委員会

  • 2006.08
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    2014.07

    Committee Member, 国立天文台電波専門員会 電波天文周波数小委員会

  • 2005.04
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    2009.03

    Committee Member, 国立天文台 年会プログラム編成小委員会