University:
Boston University
Course:
CAS AS 311 | Planetary Physics
Academic year:

2021
Views:

241

Pages:

11
Author:

Akira Velez

The Jet in the Quasar-Like Galaxy M87 • Hubble Space Telescope observations of motions of stars in nucleus: Black hole of 3x109 solar masses at center Goal: Probe jets as close to black hole as possible Questions we want to answer: How are jets accelerated to near the speed of light & focused? - Test theory that twisted magnetic fields propel the jets Where do the outbursts of light occur? Our study of AGN BL Lacertae Late 2005: Double optical/X-ray flare, radio outburst starts during 2nd flare X-ray gamma-ray X-ray Strong gamma-ray detection during 1st flare visible visible light X-ray visible Microwave visible Polarization angle of visible light rotates smoothly during 1st flare BL Lacertae (cont.) New moving bright spot (“blob”) appears after 1st flare, 2nd flare occurs as blob passes through the “core” X-ray visible Moving bright spot (“blob”) coincident with core Physical Picture of BL Lac: Exactly as Expected BL Lac: Physical Picture Theoretically* *N. Vlahakis (2006) Moving bright spot follows spiral path Passes through coiled magnetic field pattern where jet accelerates & focuses Moving bright spot Coiled magnetic field Stationary bright spot site of 1st flare site of 2nd flare Our Picture of a Quasar • Complex but we have confirmed reality of most of the components • Can test this further + continue to explore inner jet with comprehensive observations of all forms of light, including gamma-rays now that Fermi is in orbit Early Fermi/Optical Observations: The Quasar 3C 454.3 Sept. 4, 2008 Gamma-ray - optical - infrared varied simultaneously Role of Optical Monitoring Observations 1. Optical light curves of selected blazars known to be strong gamma-ray emitters 2. Compare optical light curves (filled in with data from other telescopes) with gamma-ray light curves (Fermi) & X-ray light curves (RXTE, Swift) 3. Link flares with new superluminal “blobs” seen in VLBA images 4. Figure out where flares occur relative to the “core” on VLBA images & what this means for models of the jet Join the fun! Magnitudes of blazars vs. time needed for Global Telescope Network; visit website http://gtn.sonoma.edu/resources/observing_program.php Superluminal Blazar [original song by A. Marscher] 1. Attracted by strong gravity, the mass is so compact, Pulling me inward, prepare for close contact No strength to resist, spinning out of control, Falling toward the abyss, approaching the black hole 2. Full of twisting magnetism, feeling hot inside, Bursting forth with energy, ready for a high-speed ride Acceleration growing, focusing my beam, The jet starts flowing, plasma shoots downstream Drawing closer . . . faster . . . closer . . . faster . . . closer . . . faster . . . Poloidal field! . . . Magnetic spring! . . . PROPULSION!!! Chorus: I'm a superluminal blazar, emission beamed into the night Check out my relativistic jet, it seems faster than the speed of light I'm beaming as a blazar into your line of sight Watch as my relativistic jet goes faster than the speed of light! 3. Don't mind the illusions, it's just relativity, Pardon the intrusions into the naked singularity Enjoy the time dilation, relax and take it slow, Beam the radiation, make the central engine glow 4. I shine as a quasar, with brilliant intensity, Powered by the black hole’s ultra-strong gravity I get energized with a shock wave, I get turbulent inside, The magnetic propulsion just can't be denied Drawing closer . . . faster . . . closer . . . faster . . . [chorus] The Quasar-Like Galaxy 3C 111 (z=0.0485) Clear example of one-sided jet structure with faster-than-light apparent motion at 5c (1.5 milliarcsec/yr) Jet propagates through galaxy and into intergalactic space, where it feeds giant twin radio “lobes” Scale: 1 mas = 0.92 pc = 3.0 lt-yr (Ho=70) Stationary core Observations made at 43 GHz with the Very Large Array (VLBA) of the National Radio Astronomy Observatory Faster-than-light (Superluminal) Motion (An Illusion) to observer θ βc Velocity transverse to line of sight: βc sin θ; Γ = (1-β2)-½ But, in observer’s frame, source of radio waves keeps getting closer, so arrival times of radio waves are compressed Time required for source to move distance Δr is t´=(Δr/Γ)/(βc) in source frame (length contraction) → Δr = Γβct´ Transformation to observer’s frame: t = t´[Γ(1-β cos θ)] (Doppler effect) So, βappc= (Δr sin θ)/t = Γβc(t´/t) sin θ = (βc sin θ)/(1-β cos θ) → Maximum value: βapp= Γβ [occurs at angle θ = sin-1(1/Γ)]

Jets from Black Holes in Quasars Chapter 2

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