"Seeing a Black Hole" The First Image of a Black Hole from the Event

Horizon Telescope

Matthew NewbyTemple University

Department of PhysicsMay 1, 2019

Matthew Newby, Temple University, May 1, 2019 2

● Black Holes – a Background● Techniques to observe M87*● Implications

"Seeing a Black Hole" The First Image of a Black Hole from the Event

Horizon Telescope

Matthew Newby, Temple University, May 1, 2019 3

"Seeing a Black Hole"

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What is a black hole?

Let vesc

→ c, and the escape velocity is greater than the speed of light → “Black”

Classical escape velocity:

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Einstein (and Hilbert) Field Equation

In General Relativity

Ricci curvature tensor

Metric tensor

Scalar curvature

Stress-energy tensor

“Solution”(“source” term)

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Constant rs Schwarzschild Radius:

Schwarzschild Metric

Spherically symmetric, isolated, vacuum solution:

Looks like classical escape velocity!

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Space-Time Interval

● τ is proper time● t is time measured at infinity (τ

∞)

● r, θ, φ, are Schwarzschild spherical coordinates

(i.e., coordinates as viewed at infinity)

● ds is a path element in spacetime

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General Relativistic Time Dilation

Allow a photon emitted at r to travel to infinity; in that photon’s rest frame:

Since the frequency of a photon is a proper time interval, this implies that the photon’s frequency (and energy) are lower as it travels away from a spherical mass.

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The Event Horizon

rs is the “Surface of infinite redshift” or event horizon

https://arxiv.org/abs/1511.06025

The event horizon is the “surface” of a black hole.

(Image simulated using Schwarzschild metric and ray tracing)

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Some Schwarzschild Radii

Object Mass rs

Proton 1.67 x10-27 kg 2.5 x10-54 m

Football 0.5 kg 7.4 x10-28 m

Earth 6.0 x1024 kg 8.8 x10-3 m

Sun 2.0 x1030 kg 3.0 km

Sgr A* 4.3 x 106 M☉ 17 R☉

M87* 6.5 x109 M☉ 127 AU

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Space

Time

rs

Light Cones are Warped

“One way” inside of Schwarzschild radius

All paths lead to the singularity

Possible Futures

Possible Futures

Possible Futures

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Simulation of lensing effect near an event horizon. (Click image for animation)

https://arxiv.org/abs/1511.06025

Warped Space Modifies Trajectories

https://upload.wikimedia.org/wikipedia/commons/2/23/Newton_versus_Schwarzschild_trajectories.gif

Gravitationally lensed Einstein Ring (actual image)

ESA/Hubble/NASA

See also: precession of orbits:

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Rotating Black Hole: Kerr Metric

Rotating black holes involve two event horizons and an “ergosphere.”

Drags space along with its rotation (“frame dragging”)

Wikimedia commons

“Gargantua,” from the movie Interstellar. Based on rotating black hole simulations.

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Information and Evaporation

Thermodynamic Considerations imply that Black Holes should be able to radiate.

- Frozen Stars: Redshifted imprint of original collapse- Unruh Effect: Relativistic temperatures- Hawking Radiation: pair creation/annihilation

No-Hair Theorem: Black holes destroy all infalling information except for:

- Mass/Energy- Angular Momentum- Electric Charge

Solutions to some of these considerations involve “fuzzy” event horizons, or create incompatibilities between particle physics and general relativity.

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Laboratories for Extreme Physics

Very importantly:

The event horizon of a black hole is not only a test of General Relativity, but also of how General Relativity, Quantum Physics, and Thermodynamics come together in an extreme situation.

New physics may reveal itself here.

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Known Black Holes

Black Holes have been detected through:

- X-ray Binaries (Cygnus X-1)- Companion Orbits (Sgr A*)- Active Galactic Nuclei (M87*)- Gravity Wave Detections (LIGO/VIRGO)- Direct Radio Imaging (EHT)

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Stellar-mass BHs:3-15 M☉

Form from exploding high-mass stars.

Supermassive BHs:105+ M☉

Form alongside galaxy formation.

Intermediate-mass BHs:Formation unknown!

Primordial BHs:Formed with Big Bang, maybe intermediate-mass?

Black Hole Masses

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The Event Horizon Telescope

Wavelength 1.3 mm (microwave)

Angular Resolution 35 micro arcseconds

Mass of M87* 6.5 x109 M☉

Distance to M87* 53.5 Mly

Gas accretion rate of M87* 90 Earth masses/day

Apparent velocity of relativistic jet

4 to 6 c

Quick Facts:

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Interferometry

Very Long Baseline Interferometry (VLBI) [Credit: EHT]

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Very Long Baseline

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Big Data

Statistical reconstruction of wave data (Image: Katie Bouman, EHT)

Petabytes of data – too much for the internet!

(https://www.nsf.gov/news/special_reports/blackholes/downloads/data_infographic.jpg)

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Target: M87*

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M87*

Accretion Disk

“Shadow”

Relativistic Brightening

Relativistic Dimming

Rotation Direction

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M87* Time Series

Shows changes with time.

More importantly, shows image is from a stable source (and not random noise)

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Summary: Science Products

● Test of Schwarzschild metric

● Test of General Relativity

● Test of interplay between quantum mechanics and relativity

● High energy gas physics (accretion disk dynamics)

● Jet creation

● Details of active galactic nuclei action