Initially, at left, the Universe is filled with neutral, light-blocking matter back before any stars have formed. When stars begin to form, however, they create ionizing ultraviolet photons, which lead to pockets that behave as though they’re transparent to visible light, as shown in red. Over time, as we move to the right, more and more of the Universe becomes reionized, until reionization completes around 550 million years after the Big Bang. (Credit: Thesan Collaboration)
JWST has puzzled astronomers by revealing large, bright, massive early galaxies. But the littlest ones pack the greatest cosmic punch.
This image shows the full imaging field of the JWST UNCOVER Treasury Survey, which takes up about 0.007 square degrees in the sky. In this tiny patch of space, some ~50,000 objects are revealed, with the majority of them not associated with the imaged cluster, Abell 2744, at all, but rather as background galaxies that are affected by the gravity of the cluster itself. No signs of matter-antimatter annihilation are seen here, indicating that all stars and galaxies shown are made of matter, not antimatter. However, many gravitationally lensed background galaxies are among the most distant ever discovered. (Credit: R. Bezanson et al., ApJ submitted, JWST UNCOVER Treasury Survey, 2023)
At early times (left), photons scatter off of electrons and are high-enough in energy to knock any atoms back into an ionized state. Once the Universe cools enough, and is devoid of such high-energy photons (right), they cannot interact with the neutral atoms, and instead simply free-stream, since they have the wrong wavelength to excite these atoms to a higher energy level. (Credit: E. Siegel/Beyond the Galaxy)
The overdense regions that the Universe was born with grow and grow over time, but are limited in their growth by the initial small magnitudes of the overdensities, the cosmic scale on which the overdensities are found (and the time it takes the gravitational force to traverse them), and also by the presence of radiation that’s still energetic, which prevents structure from growing any faster. It takes tens-to-hundreds of millions of years to form the first stars; small-scale clumps of matter exist long before that, however. Until stars form, the atoms in these clumps remain neutral, requiring ionizing, ultraviolet photons to render them transparent to visible light. (Credit: Aaron Smith/TACC/UT-Austin)
Energetic, ultraviolet photons are required to reionize atoms.
An artist’s conception of what a region within the Universe might look like as it forms stars for the first time. As they shine and merge, radiation will be emitted, both electromagnetic and gravitational. But the conversion of matter into energy does something else: it causes an increase in radiation pressure, which fights against gravitation. Surrounding the star-forming region is darkness, as neutral atoms effectively absorb that emitted starlight, while the emitted ultraviolet starlight works to ionize that matter from the inside out. (Credit: Pablo Carlos Budassi/Wikimedia Commons)
Determining how early stars and galaxies reionized the Universe is a cosmic challenge.
One of the science goals of the JWST UNCOVER survey is to track galaxy evolution across cosmic time. Here, a selection of nine galaxies pulled from the survey itself are highlighted in context with the cosmic time from which their light was emitted. JWST is shedding a whole new light on the story of galaxy evolution within our Universe, and is also helping us determine which types of galaxies, and when, helped our Universe transition from an opaque state to one transparent to light. (Credit: R. Bezanson et al., ApJ submitted, JWST UNCOVER Treasury Survey, 2023)
The galaxies that compose Pandora’s Cluster, Abell 2744, are present within the three separate cluster components easily visually identifiable, while the remaining background sources are scattered all throughout the Universe, including many from the first ~1 billion years of cosmic history. This field of view is now known to contain many of the earliest galaxies ever found, as well as the youngest proto-cluster of galaxies ever discovered to date: just 650 million years after the Big Bang. (Credit: R. Bezanson et al., ApJ submitted, JWST UNCOVER Treasury Survey, 2023)
This gravitational lensing map shows the reconstructed magnification contours from JWST data owing to the lensing profile of the three bright components of Abell 2744, Pandora’s Cluster. All galaxy clusters have their own unique lensing magnification properties, providing maximum enhancement along specific contours. (Credit: L.J. Furtak et al., MNRAS Submitted/arXiv:2212.04381, 2022)
This huge mass collection bends and distorts the surrounding spacetime.
