The document summarizes information presented by Dr. Christina Lacey about imaging the supermassive black hole at the center of galaxy M87. It provides evidence for the existence of black holes through observations of stars orbiting Sagittarius A* at the center of the Milky Way and discusses images taken of M87 and its jet by the Hubble Space Telescope and Event Horizon Telescope. It describes properties of the M87 black hole revealed by the EHT such as its mass of 6.5 billion solar masses and size of 40 billion km in diameter.

1. Imaging the Monster
at the Center of M87
Dr. Christina Lacey
Department of Physics and Astronomy

2. What is a black hole?
— A black hole is a region of space where light and
matter must travel faster than the speed of light to
escape
11 October 2019Galaxy Forum,, Scarsdale High School
Artist's concept illustrates a supermassive black hole with millions to
billions times the mass of our sun. Credit: NASA/JPL-Caltech -
http://www.nasa.gov/mission_pages/nustar/multimedia/pia16695.html

3. Center of the Milky Way
11 October 2019Galaxy Forum,, Scarsdale High School
A view of the night sky near Sagittarius, enhanced to show better contrast
and detail in the dust lanes. The principal stars in Sagittarius are indicated
in red. Credit: https://en.wikipedia.org/wiki/Galactic_Center User:
Moondigger CC-By-SA-2.5

4. Galactic Center: Sag A*
— Zooming in on the center of
the Milky Way
— Image taken by ISAAC, the
Very Large Telescope’s (VLT’s)
near- and mid-infrared
spectrometer and camera
(ISAAC)
— False color image that shows
the infrared light
— VLT is located in Chile’s
Atacama Desert
— Credit: ESO/R. Schoedel -
http://www.eso.org/public/ima
ges/potw1047a/ CC BY 4.0
11 October 2019Galaxy Forum, Scarsdale High School

5. Evidence for the Existence of
a Black Hole
—
11 October 2019Galaxy Forum, Scarsdale High School
Infrared image of Sgr
A* - the Galactic
Center
Some of these stars
have been identified
and tracked over
decades.
Credit:
http://www.astro.ucl
a.edu/~ghezgroup/g
c/blackhole.html

6. Galactic Center: Sgr A*
— The center of the Milky Way,
as imaged by 64 radio
telescopes in the South
African wilderness (via
MeerKAT array).
— Radio image – false color.
white represents area of
most intense radio
emission, orange
represents weaker radio
emission
— Credit: MeerKAT Public
release photo -
https://gizmodo.com/new-
south-african-telescope-
releases-epic-image-of-the-
1827572028
11 October 2019Galaxy Forum, Scarsdale High School

7. Evidence for the Existence of
a Black Hole
11 October 2019Galaxy Forum, Scarsdale High School
Infrared image of Sgr A* - the
Galactic Center
- Stars follow Newtonian
(Keplerian) orbits
Credit Keck.UCLA Galactic center
Group,
http://www.astro.ucla.edu/~ghezgr
oup/gc/blackhole.html

8. Evidence for the Existence of
a Black Hole
11 October 2019Galaxy Forum, Scarsdale High School
http://www.astro.ucla.edu/~ghezgroup/gc/blackhole.html

9. Virgo Cluster
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The Virgo cluster
with M87
indicated in the
white circle.
The dark spots
indicate where
bright foreground
stars were
removed from the
image.
Credit: Chris
Mihos/ESO -
http://www.eso.o
rg/public/images
/eso0919a/

10. M87
— NASA Hubble Space
Telescope image
— Optical and infrared
light composite image
— M87 is 55 million
light-years from Earth
— Notice jet feature on
right.
— Credit: NASA/HST
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11. M87 => Virgo A
— The jet from the
black hole shows
that the black
hole's spin axis is
inclined at an
angle of 17°
relative to the
observer's line of
sight.
— EHT concluded
the black hole
spins clockwise,
as seen from
Earth.
11 October 2019Galaxy Forum, Scarsdale High School
Credit: NASA, ESA, and Z. Levay (STScI) Science: Radio: NRAO/AUI/NSF/W. Cotton;X-ray: NASA/CXC/CfA/W. Forman et
al.; Optical: NASA, ESA, and the Hubble Heritage Team (STScI/AURA), and R. Gendler

12. M87 Jet
— Credit: NASA, National Radio Astronomy
Observatory/National Science Foundation, John Biretta
(STScI/JHU), and Associated Universities, Inc. -
http://hubblesite.org/newscenter/newsdesk/archive/re
leases/1999/43/
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13. Event Horizon Telescope
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200 members, 60 institutions, across
20 countries and regions. Credit:
https://eventhorizontelescope.org

14. M87’s Black Hole Image
— The image shows the the shadow
cast by the black hole as the
bright accretion disk material is
bent around the event horizon.
— The bottom part of the ring is
brighter due to general relativistic
effects (doppler beaming)
— Credit: Event Horizon Telescope -
https://www.eso.org/public/imag
es/eso1907a/ CC by 4.0
11 October 2019Galaxy Forum, Scarsdale High School

15. Size of the M87 Black Hole
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Comparing our
Solar System to the
Black Hole
Credit:
https://imgs.xkcd.co
m/comics/m87_bla
ck_hole_size_compa
rison.png

16. Properties of the Black Hole
— "Overall, the observed image is consistent
with expectations for the shadow of
a spinning Kerr black hole as predicted by
general relativity." Paul T.P. Ho, EHT Board
member
— Mass: 6.5±0.7 billion times the mass of our
Sun
— Diameter of event horizon: ~40 billion
kilometers (270 AU; 0.0013 pc; 0.0042 ly)
— Diameter of black hole is roughly 2.5 times
smaller than the shadow that it casts
— Accretion disk is roughly seen edge on
11 October 2019Galaxy Forum, Scarsdale High School

17. Simulation of a Black Hole
— Predicted view from outside the horizon of a Schwarzschild black hole lit by a thin accretion disc.
— NASA’s Goddard Space Flight Center/Jeremy Schnittman -
https://www.nasa.gov/feature/goddard/2019/nasa-visualization-shows-a-black-hole-s-warped-
world CC BY-SA 4.0 Created: 27 September 2019
11 October 2019Galaxy Forum, Scarsdale High School

18. Simulation of a Black Hole
— Predicted view from
outside the horizon of
a Schwarzschild black
hole lit by a thin
accretion disc.
— NASA’s Goddard
Space Flight
Center/Jeremy
Schnittman -
https://www.nasa.gov/
feature/goddard/2019
/nasa-visualization-
shows-a-black-hole-s-
warped-world CC BY-
SA 4.0 Created: 27
September 2019
11 October 2019Galaxy Forum, Scarsdale High School

19. Data
— Observations were made at a wavelength of 1.3 mm and with a
theoretical resolution of 25 micro arcseconds
— Resolution enough to read a newspaper in New York from a café in
Paris!
— Observations were taken over 10 days in April 2017
— Each telescope of the EHT produced enormous amounts of data –
roughly 350 terabytes per day
— Each telescope recorded data using an atomic clock (hydrogen masers)
so the observations could be synchronized their
— Data was stored on high-performance helium-filled hard drives.
— The observations were combined using specialized supercomputers —
known as correlators — at the Max Planck Institute for Radio Astronomy
and MIT Haystack Observatory and an image was produced
— Source: http://news.mit.edu/2019/eht-astronomers-direct-image-black-
hole-0410
11 October 2019Galaxy Forum, Scarsdale High School

20. Computation (Imaging)
— Four teams of astronomers made images, in which
the main features agreed
— Katherine Bouman developed a self-calibrating
algorithm (CHIRP)
— CLEAN imaging algorithm (Jan Hogbom)
— Regularized Maximum Likelihood (RML) Algorithm
— Source: https://en.wikipedia.org/wiki/Event_Horizon_Telescope
11 October 2019Galaxy Forum, Scarsdale High School