Identify the region in the image where light elements

IN DEPTH

Webb will address several key questions to help us unravel the story of the formation of structures in the Universe such as:

Webb's Role in Answering These Questions

To find the first galaxies, Webb will make ultra-deep near-infrared surveys of the Universe, and follow up with low-resolution spectroscopy and mid-infrared photometry (the measurement of the intensity of an astronomical object's electromagnetic radiation). To study reionization, high resolution near-infrared spectroscopy will be needed.

The Era of Recombination

Until around a few hundred million years or so after the Big Bang, the universe was a very dark place. There were no stars, and there were no galaxies.

After the Big Bang, the universe was like a hot soup of particles (i.e. protons, neutrons, and electrons). When the universe started cooling, the protons and neutrons began combining into ionized atoms of hydrogen and deuterium. Deuterium further fused into helium-4. These ionized atoms of hydrogen and helium attracted electrons turning them into neutral atoms. Ultimately the composition of the universe at this point was 3 times more hydrogen than helium with just trace amounts of other light elements.

This process of particles pairing up is called "Recombination" and it occurred approximately 240,000 to 300,000 years after the Big Bang. The Universe went from being opaque to transparent at this point. Light had formerly been stopped from traveling freely because it would frequently scatter off the free electrons. Now that the free electrons were bound to protons, light was no longer being impeded. "The era of recombination" is the earliest point in our cosmic history to which we can look back with any form of light. This is what we see as the Cosmic Microwave Background today with satellites like the Cosmic Microwave Background Explorer (COBE) and the Wilkinson Microwave Anisotropy Probe (WMAP). Following this are the cosmic dark ages - a period of time after the Universe became transparent but before the first stars formed. When the first stars formed, it ended the dark ages, and started the next epoch in our universe.

+

Brighter colors in the Cygus region indicate greater numbers of gamma rays detected by the Fermi gamma-ray space telescope. Credit: NASA/DOE/International LAT Team

SOURCES OF GAMMA RAYS

Gamma rays have the smallest wavelengths and the most energy of any wave in the electromagnetic spectrum. They are produced by the hottest and most energetic objects in the universe, such as neutron stars and pulsars, supernova explosions, and regions around black holes. On Earth, gamma waves are generated by nuclear explosions, lightning, and the less dramatic activity of radioactive decay.

DETECTING GAMMA RAYS

Unlike optical light and x-rays, gamma rays cannot be captured and reflected by mirrors. Gamma-ray wavelengths are so short that they can pass through the space within the atoms of a detector. Gamma-ray detectors typically contain densely packed crystal blocks. As gamma rays pass through, they collide with electrons in the crystal. This process is called Compton scattering, wherein a gamma ray strikes an electron and loses energy, similar to what happens when a cue ball strikes an eight ball. These collisions create charged particles that can be detected by the sensor.

GAMMA RAY BURSTS

Gamma-ray bursts are the most energetic and luminous electromagnetic events since the Big Bang and can release more energy in 10 seconds than our Sun will emit in its entire 10-billion-year expected lifetime! Gamma-ray astronomy presents unique opportunities to explore these exotic objects. By exploring the universe at these high energies, scientists can search for new physics, testing theories and performing experiments that are not possible in Earth-bound laboratories.

If we could see gamma rays, the night sky would look strange and unfamiliar. The familiar view of constantly shining constellations would be replaced by ever-changing bursts of high-energy gamma radiation that last fractions of a second to minutes, popping like cosmic flashbulbs, momentarily dominating the gamma-ray sky and then fading.

NASA's Swift satellite recorded the gamma-ray blast caused by a black hole being born 12.8 billion light years away (below). This object is among the most distant objects ever detected.

Credit: NASA/Swift/Stefan Immler, et al.

COMPOSITION OF PLANETS

Scientists can use gamma rays to determine the elements on other planets. The Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) Gamma-Ray Spectrometer (GRS) can measure gamma rays emitted by the nuclei of atoms on planet Mercury's surface that are struck by cosmic rays. When struck by cosmic rays, chemical elements in soils and rocks emit uniquely identifiable signatures of energy in the form of gamma rays. These data can help scientists look for geologically important elements such as hydrogen, magnesium, silicon, oxygen, iron, titanium, sodium, and calcium.

The gamma-ray spectrometer on NASA's Mars Odyssey Orbiter detects and maps these signatures, such as this map (below) showing hydrogen concentrations of Martian surface soils.

Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio

GAMMA RAY SKY

Gamma rays also stream from stars, supernovas, pulsars, and black hole accretion disks to wash our sky with gamma-ray light. These gamma-ray streams were imaged using NASA's Fermi gamma-ray space telescope to map out the Milky Way galaxy by creating a full 360-degree view of the galaxy from our perspective here on Earth.

Credit: NASA/DOE/International LAT Team

A FULL-SPECTRUM IMAGE

The composite image below of the Cas A supernova remnant shows the full spectrum in one image. Gamma rays from Fermi are shown in magenta; x-rays from the Chandra Observatory are blue and green. The visible light data captured by the Hubble space telescope are displayed in yellow. Infrared data from the Spitzer space telescope are shown in red; and radio data from the Very Large Array are displayed in orange.

Credit: NASA/DOE/Fermi LAT Collaboration, CXC/SAO/JPL-Caltech/Steward/O. Krause et al., and NRAO/AUI

Top of Page  |  Next: The Earth's Radiation Budget

Citation

APA

National Aeronautics and Space Administration, Science Mission Directorate. (2010). Gamma Rays. Retrieved [insert date - e.g. August 10, 2016], from NASA Science website: http://science.nasa.gov/ems/12_gammarays

MLA

Science Mission Directorate. "Gamma Rays" NASA Science. 2010. National Aeronautics and Space Administration. [insert date - e.g. 10 Aug. 2016] http://science.nasa.gov/ems/12_gammarays