Monster in the Middle The Milky Way s Central Black Hole

Transcription

1 Monster in the Middle The Milky Way s Central Black Hole Charles F. Gammie University of Illinois at Urbana-Champaign Department of Astronomy and Department of Physics OLLI, 12 Oct 2017

2 NASA, ESA / Tepletz+ 2014

3 Black Holes: Introduction Notion of escape speed: v 2 esc = 2 G M/R G Newton s constant M mass R radius If v > vesc an object can coast freely to large distance Examples: Earth: 11.2 km/s (about 25,000 mph) Jupiter: 59.5 km/s Sun: 618 km/s

4 Black Holes: Introduction What if vesc = c = speed of light (300,000 km/s)? v 2 esc = 2 G M/R = c 2 Then R = Rs = 2GM/c 2 ( Schwarzschild radius ) Light cannot escape! Examples: Earth: Rs = 0.89 cm Jupiter: Rs = 2.8m Sun: Rs = 3.0 km

5 Black Holes: Introduction What if vesc = c = speed of light (300,000 km/s)? v 2 esc = 2 G M/R = c 2 Then R = Rs = 2GM/c 2 ( Schwarzschild radius ) Light cannot escape! Examples: Earth: Rs = 0.89 cm Jupiter: Rs = 2.8m Sun: Rs = 3.0 km

6 Brief History of Black Holes Rømer (1676): finite speed of light (Jupiter s moon Io) Newton (1687): law of gravitation, escape speed Michell (1784): vesc > c; dark star Einstein (Nov. 25,1915): relativistic theory of gravity Schwarzschild (Jan. 13, 1916): exact solution (spherical) Kerr (1963): black holes with spin (axisymmetric solution)

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8 Brief History of Black Holes Rømer (1676): finite speed of light (Jupiter s moon Io) Newton (1687): law of gravitation, escape speed Michell (1784): vesc > c; dark star Einstein (Nov. 25,1915): relativistic theory of gravity Schwarzschild (Jan. 13, 1916): exact solution (spherical) Kerr (1963): black holes with spin (axisymmetric solution)

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10 Brief History of Black Holes Rømer (1676): finite speed of light (Jupiter s moon Io) Newton (1687): law of gravitation, escape speed Michell (1784): vesc > c; dark star Einstein (Nov. 25,1915): relativistic theory of gravity Schwarzschild (Jan. 13, 1916): exact solution (spherical) Kerr (1963): black holes with spin (axisymmetric solution)

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12 NASA, ESA / Tepletz+ 2014

13 Black Hole Demographics Two types of black hole candidates: Stellar mass Supermassive M ~ 10M M > 10 6 M M mass of the sun Stellar mass black holes: Endpoint of life for heaviest stars ~10 8 in our galaxy Only see ~20 well-fed black holes Supermassive black holes: made by BH coalescence or gas accretion 1 (or maybe 2 or 3!) in the middle of every large galaxy ~1% of galaxy stellar mass (Magorrian) few percent are active (accreting)

14 NASA, ESA / Tepletz+ 2014

15 Milky Way Analog M66 / NASA, ESA, Hubble Heritage team, and S. Van Dyk+

16 M66 / NASA, ESA, Hubble Heritage team, and S. Van Dyk+

17 Milky Way Analog M66 / NASA, ESA, Hubble Heritage team, and S. Van Dyk+

18 Milky Way Analog M66 / NASA, ESA, Hubble Heritage team, and S. Van Dyk+

19 European Southern Observatory

20 Event Horizon Telescope

21 ALMA array, Chile

22 South Pole Telescope

23 Event Horizon Telescope courtesy L. Vertatschitsch

24 Event Horizon Telescope Status Large collaboration (140 people, > 14 countries) First data taken in April 2017 (when Sgr A*, M87 are up) Detections between all pairs of antennas Data now under analysis Results expected in Spring 2018.

25 What will Event Horizon Telescope see?

26 What will Event Horizon Telescope see? build computer model of hot, infalling, magnetized gas write, solve model PDEs Blue Waters Supercomputer University of Illinois

27 H. Shiokawa

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29 Dolence+ 2012

30 Andrew Hamilton

31 Dolence+ 2012

32 Ring angular radius, according to Einstein: (27) 1/2 GM/(c 2 D) Dolence+ 2012

33 Event Horizon Telescope Status Large collaboration (140 people, > 14 countries) Data taken in April 2017 (when Sgr A*, M87 are up) Detections between all pairs of antennas Data now being analyzed Announcement expected in Spring 2018.

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35 Galactic Center Overview GM/c GM/c 2 GRMHD models 5µas 1mas 1as 1deg 6x10 11 cm 1AU 1pc SO-2 Bondi radius minispiral Central Molecular Zone EHT resolution PSR J1745 circumnuclear disk

36 Jones et al. 2012

37 The Galactic Centre Observations (Genzel, Ghez) measure for each star: v: line of sight velocity θ: angular size of orbit P: orbital period Kepler s laws (mass M, distance D, R = Dθ) give: v 2 ~ GM / (Dθ) P 2 ~ (Dθ) 3 / (GM) 2 eqtns, 2 unknowns: M,D angular size of hole

38 Simulated EHT Images of Sgr A* Fish et al. 2014

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40 hot disk, cold jet λ = 13mm λ = 7mm λ = 1.3mm cold disk, hot jet Mościbrodzka+ 2014

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42 Chandra+, in prep

43 M106 [NGC4258] / NASA, ESA, Hubble Heritage team, and R. Gendler

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45 M87 / Biretta+, Hubble Heritage, NASA