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
NASA, ESA / Tepletz+ 2014
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
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
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
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)
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)
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)
NASA, ESA / Tepletz+ 2014
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)
NASA, ESA / Tepletz+ 2014
Milky Way Analog M66 / NASA, ESA, Hubble Heritage team, and S. Van Dyk+
M66 / NASA, ESA, Hubble Heritage team, and S. Van Dyk+
Milky Way Analog M66 / NASA, ESA, Hubble Heritage team, and S. Van Dyk+
Milky Way Analog M66 / NASA, ESA, Hubble Heritage team, and S. Van Dyk+
European Southern Observatory
Event Horizon Telescope
ALMA array, Chile
South Pole Telescope
Event Horizon Telescope courtesy L. Vertatschitsch
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.
What will Event Horizon Telescope see?
What will Event Horizon Telescope see? build computer model of hot, infalling, magnetized gas write, solve model PDEs Blue Waters Supercomputer University of Illinois
H. Shiokawa
Dolence+ 2012
Andrew Hamilton
Dolence+ 2012
Ring angular radius, according to Einstein: (27) 1/2 GM/(c 2 D) Dolence+ 2012
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.
Galactic Center Overview GM/c 2 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10 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
Jones et al. 2012
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
Simulated EHT Images of Sgr A* Fish et al. 2014
hot disk, cold jet λ = 13mm λ = 7mm λ = 1.3mm cold disk, hot jet Mościbrodzka+ 2014
Chandra+, in prep
M106 [NGC4258] / NASA, ESA, Hubble Heritage team, and R. Gendler
M87 / Biretta+, Hubble Heritage, NASA