// NASA BREAKING NEWS — SPAZIO & SCIENZA
Hubble Details Early Galaxy Transforming Neighborhood
Astronomers using NASA’s Hubble Space Telescope have found something they never expected — ultraviolet light from a galaxy that existed just 1.4 billion years after the big bang. That galaxy contains tightly clustered young stars that produce ionizing light capable of transforming the opaque, neutral gas within and immediately around the galaxy, clearing our view. This suggests that similar galaxies in the early universe were responsible for clearing the neutral fog of hydrogen gas that once filled the cosmos.
A paper describing this discovery was published June 23 in the Astrophysical Journal.
The galaxy, cataloged MXDFz4.4, existed at the end of the Era of Reionization, a transformative period in our universe. During roughly the first billion years of the cosmos, the gas between stars and galaxies was opaque to energetic ultraviolet light. As time wore on, gas everywhere became transparent or ionized. The changeover was not like an on/off switch, but likely took hundreds of millions of years. Researchers are still collecting evidence to fully understand how this happened, which is why MXDFz4.4 sets a critical precedent.
“Observing a galaxy like this was thought to be impossible,” said lead author Ilias Goovaerts, a postdoctoral fellow at the Space Telescope Science Institute (STScI) in Baltimore. “Researchers expected the ‘fog’ or neutral hydrogen that filled the early universe would be too thick and obscure our view of its ionizing light. Hubble not only spotted that light, but it also helped reveal incredible details about the galaxy’s characteristics.”
Young, massive stars emit ultraviolet light capable of ionizing hydrogen atoms. As this light traveled for over 12 billion years to reach Hubble, space expanded, and the light stretched or redshifted into visible light. Hubble’s wavelength coverage, combined with the sensitivity and resolution of its space-based vantage point, makes it the only telescope capable of capturing this ultraviolet light from the early universe.
“Astronomers have found many galaxies that existed at this point in the history of the universe, but we haven’t detected ionizing photons from any of them, making MXDFz4.4 one of a kind,” said Marc Rafelski, a co-author and Hubble deputy mission head at STScI.
Hubble’s long exposures, pulled from several existing surveys, revealed that the galaxy’s young, massive stars are the source of the ultraviolet light, which cleared the surrounding space. These stars formed in bursts within the last few million years of MXDFz4.4’s existence and are crammed together.
Amplifying this crowding effect, MXDFz4.4 is about 100 times smaller by area than our Milky Way galaxy, but is forming stars 10 times faster.
“A lot of young, hot, massive stars in a small space do a better job of blasting through opaque gas,” Goovaerts said. The researchers estimate that 50 to 100% of the young stars’ energetic ionizing light is escaping the surrounding gas.
Massive stars’ lifetimes also play a role, since they live for only a few million years. Many explode as supernovae, releasing gigantic amounts of energy and blowing colossal holes that allow even more light to escape.