Sky & Telescope - September 2022 - 8

NEWS NOTES
M87* image; S&T: Sept. 2019, p. 18).
The new image shows Sgr A* in
silhouette, a dark center encircled by a
fuzzy ring of light. That light is radio
emission that comes from electrons in
the gas swirling around the black hole;
the dark center is where light plunges
past the event horizon, leaving a
" shadow " where the black hole is.
The ring caused the imaging team
members grief. Unlike initial reconstructions
of M87*, those of Sgr A*
didn't agree - many showed a ring, but
not all. Team members doubted their
results until they created mock data to
test how their algorithms reacted to different
situations, ultimately convincing
themselves that the ring was real.
The ring is about 50 microarcseconds
wide on the sky, exactly as Einstein's
theory of gravity predicts given the
black hole's mass and distance.
What the reconstructed images still
don't agree on is the bright knots that
dot the ring. The knots move depending
on the reconstruction used, and
they tend to line up along directions
observed with more telescopes, warns
SUPERMASSIVE BLACK HOLES
Astronomers Unveil Image of the Milky Way's
Central Black Hole
SCIENTISTS WITH THE Event Horizon
Telescope project have unveiled the first
image of the black hole at the heart of
our galaxy.
Sagittarius A* (Sgr A*) packs the
mass of about 4 million Suns into a
region smaller than Mercury's orbit.
It's a " gentle giant " among black holes,
grazing on a thin trickle of gas and putting
out only about 100 times as much
energy as the Sun does. At 26,000 lightyears
away, Sgr A* is also the closest
pThis is the first image of Sgr A*, the supermassive
black hole at the center of our galaxy.
supermassive black hole to Earth and
thus an irresistible target.
More than 300 people, working at
80 institutions in various countries,
helped make the new image a reality.
It's a painstaking reconstruction from
data taken in April 2017 by eight radio
telescopes that operated together as
a single, planet-size virtual telescope.
(The same observing run brought us the
Feryal Özel (University of Arizona).
" We don't trust the knots that much, "
she says.
Gas whips around Sgr A* in only
a few minutes, so its image is constantly
changing - much faster than
the hours-long observing sessions
undertaken. Yet over five nights of EHT
observations, the gas flow remained surprisingly
calm. " To my mind, that is one
of the most interesting things that we
learned, " says theorist Dimitrios Psaltis
(University of Arizona). " We predicted
the storm, and we got a beautiful sunny
day. " The magnetic fields in the gas
might not be as tangled as expected,
he speculated, although whether this
condition is temporary is unclear.
A second notable result is that the
pComputational methods resulted in thousands of images that all accurately fit the data. These
images cluster into four groups; the bar graphs show how many images belong to each cluster.
8
SEPTEMBER 2022 * SKY & TELESCOPE
team determined we're essentially looking
down on Sgr A*'s head - the angle
between our line of sight and the black
hole's rotation axis is less than 30°.
¢CAMILLE M. CARLISLE
Read the full story at https://is.gd/
EHTSgrA. A deeper analysis of the
image will appear in a future issue.
EHT COLLABORATION (2)
https://www.is.gd/EHTSgrA https://www.is.gd/EHTSgrA

Sky & Telescope - September 2022

Table of Contents for the Digital Edition of Sky & Telescope - September 2022

Contents
Sky & Telescope - September 2022 - Cover1
Sky & Telescope - September 2022 - Cover2
Sky & Telescope - September 2022 - 1
Sky & Telescope - September 2022 - Contents
Sky & Telescope - September 2022 - 3
Sky & Telescope - September 2022 - 4
Sky & Telescope - September 2022 - 5
Sky & Telescope - September 2022 - 6
Sky & Telescope - September 2022 - 7
Sky & Telescope - September 2022 - 8
Sky & Telescope - September 2022 - 9
Sky & Telescope - September 2022 - 10
Sky & Telescope - September 2022 - 11
Sky & Telescope - September 2022 - 12
Sky & Telescope - September 2022 - 13
Sky & Telescope - September 2022 - 14
Sky & Telescope - September 2022 - 15
Sky & Telescope - September 2022 - 16
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Sky & Telescope - September 2022 - 18
Sky & Telescope - September 2022 - 19
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Sky & Telescope - September 2022 - 28
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Sky & Telescope - September 2022 - 33
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Sky & Telescope - September 2022 - 84
Sky & Telescope - September 2022 - Cover3
Sky & Telescope - September 2022 - Cover4
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