On June 30, 2001, NASA launched the Wilkinson Microwave Anisotropy Probe (WMAP), a satellite that has since been used to map cosmic microwave background (CMB) radiation. CMB radiation is billions of years old, a byproduct of the Big Bang that scientists detect in the form of radio waves. CMB radiation yields insights into the early history of the universe, showing what it looked like when it was as young as a few hundred thousand years old. And by examining the spread of CMB radiation, scientists can find out how the universe has developed since the Big Bang and how it will continue to develop -- or even end.
Until the giant galactic void was further studied by the University of Minnesota researchers, it was known as the "WMAP Cold Spot" because NASA scientists measured colder temperatures in the region than in surrounding areas. The temperature difference only amounted to a few millionths of a degree, but that was enough to indicate something was much different about that section of space.
In order to understand why galactic voids show up as cooler, it's important to consider the role of dark energy. Like dark matter, dark energy is prevalent throughout the known universe. But in an area lacking dark energy, photons (originating from the Big Bang) pick up energy from objects as they approach them. As they move away, the gravitational force of those objects takes that energy back. The result is no net change in energy.
An area where dark energy is present works differently. When photons pass through space containing dark energy, the dark energy gives the photons energy. Consequently areas with a lot of photons and dark energy show up on scans as more energetic and hotter. Photons lose some of their energy if they pass through a galactic void lacking in dark energy. Those areas in turn emit cooler radiation. A giant void where little matter or dark energy is present, like the WMAP Cold Spot, causes significant drops in radiation temperature.
Both dark matter and dark energy remain rather mysterious to scientists. Much scientific research is underway to examine these substances and their roles in various cosmic processes. Dark energy may be even less understood than dark matter, but scientists do know that dark energy serves an important role in accelerating the universe's growth, especially in recent cosmological history. We also know that photons passing through dark energy allow for the kind of energy changes that produce varying temperatures that are in turn represented in the CMB map. Examining these temperature fluctuations allows scientists to learn how the universe is growing and developing. And considering that dark energy is the most common type of energy in the universe, it should continue to occupy a prominent role in cosmological research for years to come.
For more information about voids, dark energy and related topics, please check out the links on the next page.