DISCOVERY
Hubble Detects Elusive Ultraviolet Light from Ancient Galaxy
Using the Hubble Space Telescope, astronomers detected ultraviolet light from the galaxy MXDFz4.4, which existed just 1.4 billion years after the big bang. This galaxy contains tightly clustered young stars that produce ionizing light capable of clearing the opaque neutral gas within and around the galaxy. The findings were published June 23 in the Astrophysical Journal.
Between 50% and 100% of the galaxy's ionizing light escapes the surrounding gas, directly impacting the universe's transparency.
Key Details
- Timeline: MXDFz4.4 existed at the end of the Era of Reionization, a period when the universe's neutral hydrogen gas became ionized and transparent to ultraviolet light.
- First of Its Kind: Hubble's observations captured ionizing photons from this galaxy—a feat that had not been achieved from galaxies at this earlier epoch.
- Size and Speed: The galaxy is about 100 times smaller in area than the Milky Way but forms stars 10 times faster.
- How It Works: Young, massive stars emitted ultraviolet light that ionized hydrogen atoms. The light stretched into visible wavelengths due to cosmic expansion.
- Escape Rate: Between 50% and 100% of the ionizing light escapes the galaxy's surrounding gas.
- Supporting Data: Supplementary observations came from the James Webb Space Telescope (near-infrared) and the Very Large Telescope's MUSE instrument (visible light).
Significance
MXDFz4.4 provides direct evidence for how galaxies may have cleared the neutral hydrogen fog during the Era of Reionization, which occurred roughly the first billion years of the universe.
Previous examples of galaxies emitting ionized light existed only from later epochs—1.6 billion years after the big bang or later.
Statements from Researchers
Lead author Ilias Goovaerts (Space Telescope Science Institute) stated that observing such a galaxy was previously thought impossible due to expected obscuration by neutral hydrogen.
Co-author Marc Rafelski noted that MXDFz4.4 is unique among galaxies found at this epoch in emitting detectable ionizing photons.
This article is based on a NASA press release about research published in the Astrophysical Journal.