Hubble Discovers Ancient Galaxy That Helps Explain the Universe's Fog

NASA's Hubble Space Telescope captured ultraviolet light from an ancient galaxy that existed about 1.4 billion years after the Big Bang or Big Bang. This finding provides new clues about how the early universe changed from opaque to transparent.

Launching NASA's official website, quoted Thursday, June 25, the galaxy named MXDFz4.4 contains dense and very hot young stars. The stars emit ionizing light, i.e. high-energy light that can turn neutral hydrogen gas into transparent.

This finding strengthens the idea that the early galaxies helped clear the hydrogen fog that once filled the universe. The results of the study were published on June 23 in the journal Astrophysical Journal.

MXDFz4.4 comes from the end of the Reionization Era, a time when the universe began to become clearer to light. In the first billion years or so after the Big Bang, the intergalactic space was still filled with neutral hydrogen gas that blocked high-energy light. The process of change is estimated to have taken place gradually over hundreds of millions of years.

"Observing galaxies like this was previously thought to be impossible," said the study's lead author, Ilias Goovaerts, a postdoctoral researcher at the Space Telescope Science Institute (STScI), as reported on the NASA website.

According to Goovaerts, the hydrogen fog in the early universe was originally estimated to be too thick so that the ionizing light from galaxies such as MXDFz4.4 would not be visible. However, Hubble managed to capture the light and helped reveal the character of the galaxy.

The light captured by Hubble was emitted more than 12 billion years ago. During its journey to Earth, the expansion of the universe caused its wavelength to shift from ultraviolet to visible light. This phenomenon is known as the redshift.

Marc Rafelski, one of the study's authors and deputy head of the Hubble Mission at STScI, said astronomers have found many galaxies from the same period. However, they have never detected ionizing photons, that is, high-energy light particles, from these galaxies. That makes MXDFz4.4 an important finding.

Hubble observations show that the light comes from a cluster of massive young stars that were only formed a few million years ago. Although its area is about 100 times smaller than the Milky Way Galaxy, MXDFz4.4 forms stars about 10 times faster.

"Many hot, massive young stars in a tight space are more effective at penetrating the opaque gas," said Goovaerts.

The research team estimates that 50 to 100 percent of the ionizing light from the young stars managed to escape the gas around the galaxy. Supernova explosions from massive stars are also thought to form large gaps that make more light come out.

In a report published on the NASA website, the conclusion was strengthened by data from the James Webb Space Telescope which observed near-infrared light and the Very Large Telescope (VLT) of the European Southern Observatory which observed visible light.

James Webb data helped scientists calculate the mass of the galaxy, study old stars, and piece together the history of star formation in MXDFz4.4. Meanwhile, VLT data confirmed that the galaxy originated from a time when the universe was only 1.4 billion years old.

Before this discovery, astronomers had only identified galaxies emitting ionizing light from a time when the universe was about 1.6 billion years old. Some other examples come from the age of the cosmos about 2 billion years after the Big Bang.

According to Rafelski, the observation of MXDFz4.4 allows scientists to test their hypothesis closer to the Era of Reionization. The discovery of similar galaxies in subsequent epochs will help explain what made the early universe's fog eventually disappear.

For more than three decades, Hubble has continued to contribute important findings to astronomy. This time, the old telescope showed again that the light trail from small and distant galaxies can help humans read the first chapter of the history of the universe.