The very first results from the James Webb Space Telescope seem to indicate that massive, luminous galaxies had already formed within the first 250 million years after the Big Bang. If confirmed, this would seriously challenge current cosmological thinking. For now, however, that’s still a big “if.”
Shortly after NASA published Webb’s first batch of scientific data, the astronomical preprint server arXiv was flooded with papers claiming the detection of galaxies that are so remote that their light took some 13.5 billion years to reach us. Many of these appear to be more massive than the standard cosmological model that describes the universe’s composition and evolution.
“It worries me slightly that we find these monsters in the first few images,” says cosmologist Richard Ellis (University College London).
Young, massive stars in newborn galaxies emit vast amounts of energetic ultraviolet radiation. As this light moves through expanding space for billions of years, the wavelengths stretch (redshift) all the way into the infrared – radiation that Webb’s instruments are sensitive to.
It takes careful spectroscopic measurements – either by Webb’s spectrometers or by the ground-based ALMA observatory that operates at even longer wavelengths – to precisely determine the redshifts, which tells you how far out into space — and thus how far back in time — you’re looking. But there’s a quick (albeit less reliable) workaround that gives a rough idea.
Neutral hydrogen atoms in intergalactic space absorb ultraviolet radiation at wavelengths shorter than 91.2 nanometers. For remote objects, this threshold also redshifts to longer wavelengths, into the infrared for the most distant galaxies.
Since Webb’s near-infrared camera NIRCam takes measurements through a large number of filters, each covering a different wavelength band, a galaxy may be visible in some channels but not in others. The wavelength band in which the galaxy disappears roughly indicates its redshift, and the corresponding look-back time. READ MORE...
