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巨大ブラックホール ジェットの形成機構の謎
紀 基樹 (KASI: 韓国天文宇宙科学研究院)
今日のお話
巨大ブラックホールジェットの形成機構の謎 “加速•収束機構, 粒子加速、相対論効果、磁場の働き” (from 嶺重さんからのリクエスト) の研究の現状をレヴューする。 “Blandford-‐Znajek機構のテスト?!” についての現状をレビューする。 最後に、残された謎にVLBI (EHT, KaVA, VLBA etc) でどこまで迫れるか? について簡単に話します。
Blandford-‐Znajek mechanism
Blandford and Znajek 1977, MNRAS
Blandford-‐Znajek (BZ) 1977 proposed “electromagneMc extracMon of energy from Kerr black holes”.
For a~O(1), the extracted PoynMng power can be comparable to observaMonal requirement.
Assuming “Split monopole B-‐field”
Force-‐Free magnetosphere in staMonary Kerr space-‐Mme. expansion in powers of a i.e., “slow rotaMon (a<<1)
approximaMon”.
Cascade producMon of e+e-‐ pair (<= current carrier) via vacuum breakdown due to “spark-‐gap (non-‐zero E•B)”
類似： 誘導モーター： 磁石を回転 ⇒ 誘導電流 ⇒ =>j×B force (但し、BZはpoyn6ng flx)
BZ77, split monopole
Black holes the membrane paradigm
BH= badery (平行電波) ~粒子加速 電池に導線をつなぎ、 電流が流れ、電流回路 が閉じて初めてBZ機構 がBH回転エネルギーの 抽出機構として機能する。
Beyond split-‐monopole B-‐field
• Steady Force-‐Free: BZ77 (split-‐monopole)
• Steady Vacuum: Pederson+74, 75=> ring-‐current at the equatorial plane of Schwarzschild and Kerr metric; Ghosh00 => vector potenMal of vacuum B-‐field mulMpole expansion in Schwarzschild metric; Tomimatsu & Takahashi 01 => magnetosphere around BH and thin-‐disk
• GRMHD code: Time-‐dependent FF by McKinney & Gammie 04; Stability analysis of BZ by Komissarov 01, 04; large scale simularion by McKinney 06
McKinney (2006) MNRAS Beyond split-‐monopole B-‐field
a=0.9375 t=1.4*10^4 t_g -‐iniMal condiMon plasma donut with plasma beta=100 pure-‐poloidal field
McKinney (2006) MNRAS
Light cylinder
ergosphere
ingoing-‐Alfven (see Takahashi 90)
outgoing-‐fast
Beyond a<<1 approximaMon
• PerturbaMve approach: Including a^4 term (Tanabe & Nagataki 08).
• GRMHD code (HARM) approach: Tchekhovskoy+10 (TNM10 hereaser). TNM10 analyMcally derive the formula of P by expanding P upto Ω_H^6 and it is applicable up to a~1 and confirm its validity by HARM.
Tchekhovskoy+ 10
α=1.38 β= -‐ 9.2 this minus sign do a good job for reproducing the fladening at a>0.95
GRMHD数値実験を良く再現する解析解（灰色）
Comparison with observaMons
• Observed correlaMons between accreMon and jet powers, radio-‐loud/quiet dichotomy, FR I/II dichotomy etc can be explained in the framework of “BH spin paradigm” (e.g., Allen+06; Sikora+07; Baum+95, Volonteri+ and many others).
• Happy end w/ “BH spin paradigm”! True?
For me, there are elephants in the room…
Is BZ-‐mechanism really at work? Below are criMcal quesMons (my personal view). • Force-‐Free (FF) is realized? • Measurement of BH-‐spin? • Is “spark-‐gap” realized? （original BZ77ではvacuum=>FFのために必須だった。モダンBZでは、accreMng plasmaを用いてFFを実現できているため(?) E// は必須ではなくなった? しかしながらfloor modelが, spark-‐gapでのpair creaMonの不整合な代用になってないか？が心配。Komissarov04でE// は維持されると主張。stagnaMonの重要性 by Broderick+15） • How to produce non-‐thermal e-‐e+
at the FF region? （最新鋭のVLBIによるM87観測は、すでにBadery領域の空間スケールに到達している。この電波放射を起こす非熱的電子の生成は、極端なlow-‐plasma-‐beta領域においては自明ではない。リコネクションの可能性?)
• Return current in accreMon flow? (そもそも観測が至難の技。バッテリー部分の形状、構造の鍵。)
• How to convert PoynMng power to
kineMc one? (いわゆるσ問題。TNM10はfast surfaceまで追ってない？ McKinney06のequiparMMon では道半ば。) • Velocity field is consistent? (vはσと共に本質的な物理量. field profileのBH スピンaへの依存性は未調査。観測的にもvelocity field計測は、不十分。KaVA AGNのキーサイエンス。)
Badery (BH + FF B-‐field)
Load/Current
ResisMve Badery?
Load/Current
There is a hope
VLBI is an earth-‐sized (baseline: D_max~10000km) radio telescope with ultra high spaMal resoluMon <1mas with VLBI, we can indeed explore in the vicinity of SMBHs.
KaVA (KVN and VERA) VLBA EHT (Event Horizon Telescope)
Hada, MK, Doi et al. (2013), ApJ, 775, 70
Our strategy: Focusing on M87
-‐ Rs = 2GM/c2 = 1.9×1015 cm -‐ θs = 7 μas
radio core
M87 at 43GHz
Upstream-‐end of SSA-‐thick radio core is located!
2GHz
5
8 24
15
43
Hada, Doi, MK+ (2011) Nature, 477, 185
Force-‐Free (Ue/UB<<1) is realised?
Hada, Doi, Kino et al. 2011, Nature, 477, 185 Hada, Kino, Doi et al. 2013, ApJ, 775, id.70 Doeleman, Fish, Schenck et al. 2012, Science, 338, 355 Kino, Takahara, Hada, Doi, ApJ, 2014, 786, 5 Kino, Takahara, Hada, Akiyama, Nagai & Sohn, 2015, ApJ, 803, 30
Breakthrough
l The detecMon of radio-‐core’s posiMon shis (core-‐shis, hereaser) at the jet base of M87 （Hada et al. 2011, Nature) means that the radio core is SSA-‐thick ν_ssa = ν_obs up to 43 GHz and also the core-‐shis is verified at 86GHz by Rioha et al. 2011).
l The 230GHz emission region size at the jet base of M87 has been measured by Event Horizon Telescope (EHT) (Doeleman et al. 2012, Science). The derived FWHM angular size is θ=40 μas.
l Using these accurate ν_ssa and θ, then we can uniquely determine B (field strength) and Ke (electron content)!
Simple but robust! We can uniquely determine B and Ke
Let’s apply this general formula to EHT data@230GHz.
Kino+ 14, 15
radio core
Single-‐zone (θFWHM=40μas, 1Jy) esMmate leads to Btot~ 300 gauss i.e., too large L_poy.
θ_FWHM * 1.8 =72 µas The 1.8 factor by Marscher (1983)
If the field strength is,
then the Poynting power below exceeds L_jet, max ~ 5*1044 erg/s
?
SSA-‐ thick
SSA-‐thin
SoluMon: ParMally SSA-‐thick (two-‐zone) EHT region
• The idea of parMal-‐SSA-‐thick region can avoid too-‐large-‐L_poy problem because B ∝ νssa ^5.
• BH-‐shadow may be hidden by SSA-‐thick region.
EsMmate of SSA-‐thick region size and flux
SSA-‐thick 21μas, 0.27Jy
With phased-‐ALMA & USA staMons, S_thick is testable！
Kino+ 15
Allowed log (U±/UB), Btot , γ ±,min in the SSA-‐thick region
We find “U±<<UB(i.e., FF)”.
Kino+ 15
Summary: “FF is realized?”
Only using the standard physics synchrotron-‐self absorpMon (SSA) and the 230GHz emission region size measured by EHT, we find that “FF is realized unless the EHT region is fully SSA-‐ thin@230GHz and relaMvisMc proton dominated”.
Kino et al. 2015, ApJ, 803, 30
残された謎にVLBIでどこまで迫れるか？
Hada, Kino, Doi et al. 2015, ApJ, submided KaVA AGN sub-‐WG’s challenge East Asia VLBI Network’s challenge
Is BZ-‐mechanism really at work? Below are criMcal quesMons (my personal view). • Force-‐Free (FF) is realized? • Measurement of BH-‐spin? • Is “spark-‐gap” realized? （original BZ77ではvacuum=>FFのために必須だった。モダンBZでは、accreMng plasmaを用いてFFを実現できているため(?) E// は必須ではなくなった? しかしながらfloor modelが, spark-‐gapでのpair creaMonの不整合な代用になってないか？が心配。ちなみにKomissarov04でE// は維持されると主張。） • How to produce non-‐thermal e-‐e+
at the FF region? （最新鋭のVLBIによるM87観測は、すでにBadery領域の空間スケールに到達している。この電波放射を起こす非熱的電子の生成は、極端なlow-‐plasma-‐beta領域においては自明ではない。リコネクションの可能性?)
• Return current by accreMon flow? (そもそも観測が至難の技。バッテリー部分の形状、構造の鍵。)
• How & where to convert PoynMng
power to kineMc one? (いわゆるσ問題。 McKinney06のequiparMMon では道半ば.) • Velocity field is consistent? (vはσと対になる本質的な物理量. field profileのBH スピンaへの依存性は未調査。観測的にもvelocity field計測は、不十分。KaVA AGNのキーサイエンス。)
Badery
Load/Current
ResisMve Badery?
Load/Current
Can we see any imprint of accre6on flow with VLBI?
VLBA@86GHz, possessing highest resoluMon imaging capability, can explore this spaMal scale.
Stay tuned to next Hada-‐san’s talk!
McKinney (2006)
low β (FF)
β=1
β=3
unbound
bound
10 102 1 103 104
Lorentz factor
Specific Matter energy flux
KaVA’s dense monitoring will clarify velocity field
Distance from black-hole (Rg unit)
McKinney (2006)
“Key-Zone” @1~10mas
Niinuma-‐san will talk about this in details!
Summary
• Using ultra high resoluMon VLBI data and standard physics, we indeed can test BZ-‐mechanism at M87.
• We find that “FF is realized unless the EHT region is fully SSA-‐thin@230GHz and relaMvisMc proton dominated”. (Kino+15)
• KaVA array’s intensive monitoring of “Key-‐zone@M87” is essenMal for Poyn6ng-‐to-‐kine6c conversion process.
• mm/sub-‐mm VLBI is essenMal for tesMng BH-‐mechanism at M87. NRO baselines are important for discriminate BH-‐shadow model.
