Sky & Telescope - May 2024 - 22

Early Black Holes
Lighthouses in the Distant Darkness
Black holes, counterintuitively, are some of the brightest
objects in the cosmos. A supermassive black hole frantically
accreting matter will radiate large amounts of light - not
from itself but from the extremely hot gas that it's trying
to swallow from the surrounding environment. Typically,
astrophysicists use the name quasar to refer to a supermassive
black hole that's accreting so much gas that it becomes bright
enough to outshine its host galaxy. Although there is no
clear-cut definition of a quasar, they are very massive - generally
more than a billion times the mass of the Sun.
These cosmic lighthouses had their heyday about 2 to 3
billion years after the universe's birth, but we've seen them
much earlier than that. The most distant quasars observed
were already shining when the universe was only several
hundred million years old, an infant compared to today's age
of 13.8 billion years. The rays of light originating from those
quasars have traveled billions and billions of years to reach
our telescopes. Along the way, their wavelengths stretched
due to cosmic expansion, and the light became much redder,
in the well-known redshift phenomenon. Astronomers use
how much a source's light is redshifted to estimate how much
the universe has expanded since those photons were emitted
and, consequently, how long the light has been traveling: the
higher the redshift, the older and more distant the source.
Before JWST, the black hole horizon, defined as the farthest
black hole we could observe with our telescopes, stood at a
redshift of 7.6, or 690 million years after the Big Bang. With
JWST, astronomers have (so far) pushed 250 million years
earlier, detecting a supermassive black hole in a faraway
galaxy at a redshift of 10.6, or just 440 million years after the
Big Bang. The host galaxy is named GN-z11.
This remote galaxy, which appears to the sight of our
mightiest telescopes as an unremarkable red blob, has a marGN-Z11
This unassuming blob is the host galaxy of the current record holder for the farthest supermassive black hole detected, seen as it was
nearly 13.4 billion years in the past, just 440 million years after the Big Bang. Bright, young, blue stars suffuse the galaxy, but its light has been
stretched to redder wavelengths by the universe's expansion. The field image is from the Hubble Space Telescope Great Observatories Origins Deep
Survey (GOODS), which contains tens of thousands of galaxies stretching far back into time.
22 MAY 2024 * SKY & TELESCOPE
NASA / ESA / P. OESCH (YALE UNIVERSITY), G. BRAMMER (STSCI), P. VAN DOKKUM (YALE
UNIVERSITY), AND G. ILLINGWORTH (UNIVERSITY OF CALIFORNIA, SANTA CRUZ)

Sky & Telescope - May 2024

Table of Contents for the Digital Edition of Sky & Telescope - May 2024

Contents
Sky & Telescope - May 2024 - Cover1
Sky & Telescope - May 2024 - Cover2
Sky & Telescope - May 2024 - 1
Sky & Telescope - May 2024 - Contents
Sky & Telescope - May 2024 - 3
Sky & Telescope - May 2024 - 4
Sky & Telescope - May 2024 - 5
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Sky & Telescope - May 2024 - Cover4
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