Distant Galaxy Group Caught Driving Ancient Cosmic Makeover

  • Released Sunday, January 5, 2020
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This animation shows EGS77’s place in cosmic history, flies to the galaxies, and illustrates how ultraviolet light from their stars create bubbles of ionized hydrogen around them.

Credit: NASA’s Goddard Space Flight Center

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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.

Unlabeled version of the above video.

Credit: NASA’s Goddard Space Flight Center

Unlabeled version. This composite of archival Hubble Space Telescope visible and near-infrared images shows a part of the Extended Groth Strip, a well-studied area located between the constellations Ursa Major and Boötes, that includes the galaxy group EGS77 (lower left). The image is 5.4 arcminutes across. Credit: NASA, ESA, and V. Tilvi (ASU)

Unlabeled version. This composite of archival Hubble Space Telescope visible and near-infrared images shows a part of the Extended Groth Strip, a well-studied area located between the constellations Ursa Major and Boötes, that includes the galaxy group EGS77 (lower left). The image is 5.4 arcminutes across.

Credit: NASA, ESA, and V. Tilvi (ASU)

Labeled version. This composite of archival Hubble Space Telescope visible and near-infrared images shows a part of the Extended Groth Strip, a well-studied area located between the constellations Ursa Major and Boötes. The three galaxies of the EGS77 galaxy group, highlighted by green circles at lower left, lie at a redshift of 7.7, which means we’re seeing the galaxies as they were when the universe was just 680 million years old. The image is 5.4 arcminutes across. Credit: NASA, ESA, and V. Tilvi (ASU)

Labeled version. This composite of archival Hubble Space Telescope visible and near-infrared images shows a part of the Extended Groth Strip, a well-studied area located between the constellations Ursa Major and Boötes. The three galaxies of the EGS77 galaxy group, highlighted by green circles at lower left, lie at a redshift of 7.7, which means we’re seeing the galaxies as they were when the universe was just 680 million years old. The image is 5.4 arcminutes across.

Credit: NASA, ESA, and V. Tilvi (ASU)

GIF version. This composite of archival Hubble Space Telescope visible and near-infrared images shows a part of the Extended Groth Strip, a well-studied area located between the constellations Ursa Major and Boötes. The three galaxies of the EGS77 galaxy group, highlighted by the green circles, lie at a redshift of 7.7, which means we’re seeing the galaxies as they were when the universe was just 680 million years old. The image is 3.2 arcminutes across, or about one-tenth the apparent size of a full Moon. Credit: NASA, ESA, and V. Tilvi (ASU)

GIF version. This composite of archival Hubble Space Telescope visible and near-infrared images shows a part of the Extended Groth Strip, a well-studied area located between the constellations Ursa Major and Boötes. The three galaxies of the EGS77 galaxy group, highlighted by the green circles, lie at a redshift of 7.7, which means we’re seeing the galaxies as they were when the universe was just 680 million years old. The image is 3.2 arcminutes across, or about one-tenth the apparent size of a full Moon.

Credit: NASA, ESA, and V. Tilvi (ASU)

Inset: This illustration of the EGS77 galaxy group shows the galaxies surrounded by overlapping bubbles of ionized hydrogen. By transforming light-quenching hydrogen atoms to ionized gas, ultraviolet starlight is thought to have formed such bubbles throughout the early universe, gradually transitioning it from opaque to completely transparent. Background: This composite of archival Hubble Space Telescope visible and near-infrared images includes the three galaxies of EGS77 (green circles). Credit: NASA, ESA, and V. Tilvi (ASU)

Inset: This illustration of the EGS77 galaxy group shows the galaxies surrounded by overlapping bubbles of ionized hydrogen. By transforming light-quenching hydrogen atoms to ionized gas, ultraviolet starlight is thought to have formed such bubbles throughout the early universe, gradually transitioning it from opaque to completely transparent. Background: This composite of archival Hubble Space Telescope visible and near-infrared images includes the three galaxies of EGS77 (green circles).

Credit: NASA, ESA, and V. Tilvi (ASU)

This illustration of the EGS77 galaxy group shows the galaxies surrounded by overlapping bubbles of hydrogen ionized by ultraviolet light from their stars. By transforming light-quenching hydrogen atoms to ionized gas, UV starlight is thought to have formed such bubbles throughout the early universe, gradually transitioning it from opaque to completely transparent. Credit: NASA's Goddard Space Flight Center

This illustration of the EGS77 galaxy group shows the galaxies surrounded by overlapping bubbles of hydrogen ionized by ultraviolet light from their stars. By transforming light-quenching hydrogen atoms to ionized gas, UV starlight is thought to have formed such bubbles throughout the early universe, gradually transitioning it from opaque to completely transparent.

Credit: NASA's Goddard Space Flight Center

Labeled version. This illustration shows EGS77’s place in the history of the universe. We're seeing the galaxies as they were just 680 million years after the big bang (far left). The blue-green surface shows the cosmic microwave background, the light resulting from the formation of the first atoms 380,000 years after the universe was born.Credit: NASA’s Goddard Space Flight Center

Labeled version. This illustration shows EGS77’s place in the history of the universe. We're seeing the galaxies as they were just 680 million years after the big bang (far left). The blue-green surface shows the cosmic microwave background, the light resulting from the formation of the first atoms 380,000 years after the universe was born.

Credit: NASA’s Goddard Space Flight Center

Unlabeled version of the above illustration. Credit: NASA’s Goddard Space Flight Center

Unlabeled version of the above illustration.

Credit: NASA’s Goddard Space Flight Center

This visualization shows how ultraviolet light from the first stars and galaxies gradually transformed the universe. Hydrogen atoms, also called neutral hydrogen, readily scatter UV light, preventing it from traveling very far from its sources. Gradually, intense UV light from stars and galaxies split apart the hydrogen atoms, creating expanding bubbles of ionized gas. As these bubbles grew and overlapped, the cosmic fog lifted. Astronomers call this process reionization. Here, regions already ionized are blue and translucent, areas undergoing ionization are red and white, and regions of neutral gas are dark and opaque.

Credit: M. Alvarez, R. Kaehler and T. Abel (2009)

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This page was originally published on Sunday, January 5, 2020.
This page was last updated on Wednesday, May 3, 2023 at 1:45 PM EDT.

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