![]() ![]() The key to spotting these earliest galaxies is a phenomenon called redshift. “So we’ll be able to detect the ones which are really bright, and the ones which are fairly rare.” “With Webb, we’re going to be able to identify thousands of galaxies from this period of time,” Kartaltepe says. Studying these very early galaxies is one of the key aims of the Webb science program overall, and it’s what COSMOS-Webb is aiming to achieve. These first stars formed the first galaxies, but there was more gas and fewer stars around compared to today, so the early galaxies looked very different too. It’s a very special population of stars,” Kartaltepe says. “They can become much more massive and much more extreme, and have very short lives. The different composition of this first generation of stars would make them behave differently to stars born today as well. Adrian Mann/Stocktrek Images/Stocktrek Images/Getty Images What were the first stars like? ![]() The telescopes aren’t to scale, but the differences between the viewing fields are, with Hubble on the left and Webb on the right. Today, stars also contain other heavier elements like oxygen, carbon, neon, silicon, magnesium, and iron - all synthesized in subsequent generations of stars via supernovae. ![]() “At that point, basically everything was hydrogen, with a little bit of helium,” Kartaltepe says, and these two elements were the building blocks of the earliest stars. The photon sources which switched on the lights of the universe were the earliest stars, which were rather different beasts from the stars we see today. That’s why it’s referred to as first light,” Kartaltepe says. “Once regions have enough of the medium ionized, then photons can now travel more freely. Eventually, some sources started giving off photons at a high enough energy that it ionized some of those atoms, breaking apart the protons and electrons. Light would soon arrive, however, in the form of the Epoch of Reionization. That’s why it’s opaque - because if there is a light source, any photons from it aren’t going to make it very far.” This early stage of the universe is often called the dark age for that reason. “Because of that, a photon can’t travel very efficiently through that medium as it gets absorbed right away. “The protons and electrons were bound together,” Kartaltepe says. This neutral state meant light couldn’t travel far because it made the universe dark and foggy. But as the universe cooled, it settled into a state of mostly neutral atoms of hydrogen and helium. Soon after the Big Bang, the universe was extremely hot and much of the material in it was ionized - meaning that atoms were gaining or losing electrons and had either a positive or negative charge. NASA, ESA, CSA, and STScI How far back in time can JWST look? On Monday, NASA, ESA, and CSA released this image of the SMACS 0723 deep field, an area previously imaged by Hubble, and one of several deep fields Webb will take over time. That means Webb can effectively look back in time to when the universe was in its infancy. “It’s so much more sensitive than what we’ve been able to do before,” Jeyhan Kartaltepe, co-leader of the COSMOS-Webb program, tells Inverse. It will cover some of the same area of the sky previously imaged by Hubble in its own COSMOS program, but at a different wavelength and higher resolution. The COSMOS-Webb program will use JWST’s NIRCam and MIRI instruments to collect images of extremely distant galaxies in the near-infrared and mid-infrared ranges. But Webb is just getting started when it comes to surveying the night sky in depth. It’s a sort of follow-up to one of the Hubble Space Telescope’s greatest contributions to astronomy: the Hubble Deep Fields, a series of images that show distant galaxies in incredible detail. On Monday, NASA - in tandem with the White House - released an incredible deep-field image taken by the James Webb Space Telescope (JWST), which demonstrates how this telescope will be able to look back at some of the earliest galaxies which lit up the cosmic dawn.
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