The Webb telescope unlocks secrets of primeval galaxy
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This image
from Webb’s NIRCam (Near-Infrared Camera) instrument shows a portion of the
GOODS-North field of galaxies. At the lower right, a pullout highlights the
galaxy GN-z11, which is seen at a time just 430 million years after the Big
Bang. The image reveals an extended component, tracing the GN-z11 host galaxy,
and a central, compact source whose colours are consistent with those of an
accretion disc surrounding a black hole. Credit: NASA, ESA, CSA, B. Robertson
(UC Santa Cruz), B. Johnson (CfA), S. Tacchella (Cambridge), M. Rieke
(University of Arizona), D. Eisenstein (CfA), CC BY 4.0 INT or ESA Standard
Licence.
Looking deep into space and time, two teams using the NASA/ESA/CSA James Webb Space Telescope have studied the exceptionally luminous galaxy GN-z11, which existed when our 13.8 billion-year-old universe was only about 430 million years old.
Delivering on its promise to transform our
understanding of the early universe, the James Webb Space Telescope is probing
galaxies near the dawn of time. One of these is the exceptionally luminous
galaxy GN-z11, which existed when the universe was just a tiny fraction of its
current age. Initially detected with the NASA/ESA Hubble Space Telescope, it is
one of the youngest and most distant galaxies ever observed, and it is also one
of the most enigmatic. Why is it so bright? Webb appears to have found the
answer.
A team studying GN-z11 with Webb found the
first clear evidence that the galaxy is hosting a central, supermassive black
hole that is rapidly accreting matter. Their finding makes this the most
distant active supermassive black hole spotted to date.
"We found extremely dense gas that is
common in the vicinity of supermassive black holes accreting gas,"
explained principal investigator Roberto Maiolino of the Cavendish Laboratory
and the Kavli Institute of Cosmology at the University of Cambridge in the United
Kingdom. "These were the first clear signatures that GN-z11 is hosting a
black hole that is gobbling matter."
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This two-part
graphic shows evidence of a gaseous clump of helium in the halo surrounding the
galaxy GN-z11. In the top portion, at the far right, a small box identifies
GN-z11 in a field of galaxies. The middle box shows a zoomed-in image of the
galaxy. The box at the far left displays a map of the helium gas in the halo of
GN-z11, including a clump that does not appear in the infrared colors shown in
the middle panel. In the lower half of the graphic, a spectrum shows the
distinct 'fingerprint' of helium in the halo. The full spectrum shows no
evidence of other elements and so suggests that the helium clump must be fairly
pristine, made almost entirely of hydrogen and helium gas left over from the
Big Bang, without much contamination from heavier elements produced by stars.
Theory and simulations in the vicinity of particularly massive galaxies from
these epochs predict that there should be pockets of pristine gas surviving in
the halo, and these may collapse and form Population III star clusters. Credit:
NASA, ESA, CSA, Ralf Crawford (STScI), CC BY 4.0 INT or ESA Standard Licence. |
Using Webb, the team also found indications of
ionized chemical elements typically observed near accreting supermassive black
holes. Additionally, they discovered that the galaxy is expelling a very
powerful wind. Such high-velocity winds are typically driven by processes
associated with vigorously accreting supermassive black holes.
"Webb's NIRCam (Near-Infrared Camera) has
revealed an extended component, tracing the host galaxy, and a central, compact
source whose colors are consistent with those of an accretion disk surrounding
a black hole," said investigator Hannah Übler, also of the Cavendish
Laboratory and the Kavli Institute.
Together, this evidence shows that GN-z11 hosts
a two-million-solar-mass, supermassive black hole in a very active phase of
consuming matter, which is why it's so luminous.
A second team, also led by Maiolino, used Webb's NIRSpec (Near-Infrared Spectrograph) to find a gaseous clump of helium in the halo surrounding GN-z11.
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This image of
the GOODS-North field, captured by Webb's Near-Infrared Camera (NIRCam), shows
compass arrows, a scale bar, and a color key for reference. The north and east
compass arrows show the orientation of the image on the sky. Note that the
relationship between north and east on the sky (as seen from below) is flipped
relative to direction arrows on a map of the ground (as seen from above). The
scale bar is labelled in angular distance on the sky, where one arcsecond is
one 3600th of a degree. The scale bar is 60 arcseconds long. This image shows
invisible near-infrared wavelengths of light that have been translated into
visible-light colors. The color key shows which NIRCam filters were used when
collecting the light. The color of each filter name is the visible light color
used to represent the infrared light that passes through that filter. Credit:
NASA, ESA, CSA, B. Robertson (UC Santa Cruz), B. Johnson (CfA), S. Tacchella
(Cambridge), M. Rieke (University of Arizona), D. Eisenstein (CfA), CC BY 4.0
INT or ESA Standard Licence.
"The fact that we don't see anything else
beyond helium suggests that this clump must be fairly pristine," said
Roberto. "This is something that was expected by theory and simulations in
the vicinity of particularly massive galaxies from these epochs—that there
should be pockets of pristine gas surviving in the halo, and these may collapse
and form Population III star clusters."
Finding the so far unseen Population III
stars—the first generation of stars formed almost entirely from hydrogen and
helium—is one of the most important goals of modern astrophysics. These stars
are expected to be very massive, very luminous, and very hot. Their signature
would be the presence of ionized helium and the absence of chemical elements
heavier than helium.
The formation of the first stars and galaxies
marks a fundamental shift in cosmic history, during which the universe evolved
from a dark and relatively simple state into the highly structured and complex
environment we see today.
In future Webb observations, Roberto, Hannah,
and their team will explore GN-z11 in greater depth, and they hope to
strengthen the case for the Population III stars that may be forming in its
halo.
Theresearch on the pristine gas clump in GN-z11's halo has been accepted for
publication in Astronomy & Astrophysics and is currently available on the
arXiv preprint server. The results of the study of GN-z11's black hole were
published in the journal Nature on 17 January 2024.
Source: European Space Agency
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