Universe  ID: 13511

Distant Galaxy Group Caught Driving Ancient Cosmic Makeover

An international team of astronomers has found the farthest galaxy group identified to date. Called EGS77, the trio of galaxies dates to a time when the universe was only 680 million years old, or less than 5% of its current age of 13.8 billion years.

More significantly, observations show the galaxies are participants in a sweeping cosmic makeover called reionization. The era began when light from the first stars changed the nature of hydrogen throughout the universe in a manner akin to a frozen lake melting in the spring. This transformed the dark, light-quenching early cosmos into the one we see around us today.

The young universe was filled with hydrogen atoms, which so attenuate ultraviolet light that they block our view of early galaxies. EGS77 is the first galaxy group caught in the act of clearing out this cosmic fog.

While more distant individual galaxies have been observed, EGS77 is the farthest galaxy group to date showing the specific wavelengths of far-ultraviolet light revealed by reionization. This emission, called Lyman alpha light, is prominent in all members of EGS77.

In its earliest phase, the universe was a glowing plasma of particles, including electrons, protons, atomic nuclei, and light. Atoms could not yet exist. The universe was in an ionized state, similar to the gas inside a lighted neon sign or fluorescent tube.

After the universe expanded and cooled for about 380,000 years, electrons and protons combined into the first atoms — more than 90% of them hydrogen. Hundreds of millions of years later, this gas formed the first stars and galaxies. But the very presence of this abundant gas poses challenges for spotting galaxies in the early universe.

Hydrogen atoms readily absorb and quickly re-emit far-ultraviolet light known as Lyman alpha emission, which has a wavelength of 121.6 nanometers. When the first stars formed, some of the light they produced matched this wavelength. Because Lyman alpha light easily interacted with hydrogen atoms, it couldn’t travel far before the gas scattered it in random directions.

Intense light from galaxies can ionize the surrounding hydrogen gas, forming bubbles that allow starlight to travel freely. EGS77 has formed a large bubble that allows its light to travel to Earth without much attenuation. Eventually, bubbles like these grew around all galaxies and filled intergalactic space, reionizing the universe and clearing the way for light to travel across the cosmos.

Because the universe is expanding, Lyman alpha light from EGS77 has been stretched out during its travels, so astronomers actually detect it at near-infrared wavelengths. We can’t see these galaxies in visible light now because that light started out at shorter wavelengths than Lyman alpha and was scattered by the fog of hydrogen atoms.

Credits

Chris Smith (USRA): Lead Producer
Chris Smith (USRA): Lead Animator
Francis Reddy (University of Maryland College Park): Lead Science Writer
Please give credit for this item to:
NASA's Goddard Space Flight Center.
However, individual items should be credited as indicated above.

Short URL to share this page:
https://svs.gsfc.nasa.gov/13511

Mission:
Hubble

This item is part of these series:
Astrophysics Animations
Astrophysics Stills

Keywords:
SVS >> Galaxy
SVS >> Astrophysics
SVS >> Universe
SVS >> Space
SVS >> Reionization
NASA Science >> Universe
SVS >> Bubble