Astronomers analyzing James Webb Space Telescope data have discovered an overabundance of bright galaxies in the early universe, prompting researchers at the Flatiron Institute’s Center for Computational Astrophysics and the University of Texas at Dallas to propose that ultraviolet radiation from young stars acted like a cosmic leaf blower to clear away light-blocking gas and dust.
When the James Webb Space Telescope began capturing images of the early universe, researchers noticed far more bright galaxies than expected in the few hundred million years following the Big Bang. Explaining those observations requires understanding both how rapidly the galaxies formed stars and how much of their light could escape surrounding gas and dust.
To solve the mystery, Flatiron Institute research fellow Shyam Menon and University of Texas at Dallas assistant professor of physics Aaron Smith investigated how Lyman-alpha radiation—a form of ultraviolet light produced by hydrogen gas around young stars—affected early star clusters, according to Miragenews. A Lyman-alpha photon can scatter repeatedly between hydrogen atoms before escaping or meeting dust. Each photon bounces back and forth like a ping-pong ball, transferring momentum with every collision,
Smith said. Those repeated pushes add up, so each photon packs a much stronger punch than it would in a single interaction.
Simulating Radiation Pressure in Dense and Low-Density Regions
Because modeling each individual interaction makes Lyman-alpha radiation computationally challenging to simulate, researchers analyzed snapshots from an existing simulation of an early-universe star-forming region to calculate the force exerted by the radiation pressure on gas and dust. In the densest structures, the outward pressure was not strong enough to counteract gravity, allowing enough material to remain to fuel ongoing star formation. In less-dense regions, however, the outcome differed significantly.
Our results show Lyman-alpha radiation can push low-density gas and dust away really, really fast,
Menon said. It can sort of clear the ‘fog,’ allowing us to see stars in the early universe much more clearly than we would otherwise.
Smith compared the effect to landscaping equipment: If you think about a leaf blower, it’s not moving trees. But it is very effective at clearing away loose leaves.
The research was published Nov. 4 in The Astrophysical Journal. Funding was provided in part by the Space Telescope Science Institute program JWST-AR-08709, operated by the Association of Universities for Research in Astronomy under NASA contract NAS 5-03127, with computing resources from the Simons Foundation and additional support from the National Science Foundation through the Kavli Institute for Theoretical Physics.
Supernova Winds Hinder Early Cosmic Reionization
The role of stellar feedback in shaping early cosmic transparency forms the core of a separate study published in Nature Astronomy using data from the Hubble Space Telescope, according to Science Daily. For years, scientists theorized that powerful winds from supernovae pushed gas aside to help ultraviolet radiation escape and drive reionization, the period roughly 13 billion years ago when ionizing radiation cleared the neutral hydrogen fog filling the universe.
However, an international research team examining nearby starburst galaxies found that stronger galactic winds associated with supernovae actually correlated with less escaping ionizing radiation. It appears that energy input from supernovae has stirred up the surroundings and increased, rather than decreased, the coverage of neutral gas and dust that suppresses ionizing radiation escape,
said Stephan McCandliss, senior author of the study and director of the Center for Astrophysical Sciences at Johns Hopkins University.
Instead, researchers conclude that ultraviolet photons from young, massive stars escape their galaxies before those stars explode and generate winds. Basically, how these galaxies were leaking ionizing radiation isn’t what we thought,
said Carr. Our observations show that these photons are escaping before galactic winds form.
Earlier coverage: Frontier Supercomputer Powers New Simulation of First Galaxies