Transcripts of 13314_Dark_Energy

[Music throughout] What makes up most of the cosmos? Not stars or planets, or even atoms. It’s something scientists call dark energy. And so far, no one has a good handle on what it actually is. Dark energy, first discovered in 1998, is an enigmatic pressure pushing the universe apart at an ever-faster clip. Scientists suspect it began flexing its muscles around five billion years ago – beyond that, we know very little. Learning more about dark energy is one of the primary reasons NASA is building WFIRST, a new space telescope whose measurements will help us home in on this mysterious cosmic component. Without a better understanding of dark energy, our knowledge of the past and future evolution of the universe is incomplete. WFIRST will tackle the dark energy problem using different yet complementary wide-field surveys. A key aspect of them is a measurement called “redshift.” Because space itself is expanding, the farther we look, the faster galaxies are moving away from us. This results in a measurable shift in an object’s light toward redder colors. This redshift indicates how fast the expanding universe is carrying galaxies away from us. If we can also figure out a galaxy’s distance by other methods, we can use both pieces of information to measure how the universe expanded while the galaxy’s light was traveling to us. WFIRST will map out the positions and distances of millions of galaxies. This will allow astronomers to see how the distribution of galaxies has changed, revealing how dark energy has evolved over cosmic time. An alternative way to measure dark energy is by using exploding stars called type Ia supernovas. These blasts are caused by the total destruction of a white dwarf star and each one emits similar amounts of light. But the farther away they are, the fainter the explosions look. By measuring how bright type Ia supernovas appear to be, we have a way to measure their distances. It was comparing supernovae redshifts to their apparent brightness that astronomers discovered dark energy. These studies showed that explosions at greater redshifts were dimmer than they should be in any model where the expansion of the universe was not speeding up. WFIRST will study thousands of explosions reaching to even greater distances to measure dark energy’s influence over time. A quirk of the early universe provides another way to pin down dark energy. In it’s first half-million years, the universe consisted of a hot, dense expanding fluid. Small density changes in the fluid excited sound waves that traveled throughout it. Although the waves, called baryonic acoustic oscillations, eventually ceased, astronomers have observed their faint imprint in the way that galaxies cluster together. This provides another way to measure galaxy distances. WFIRST will measure how this imprint changes through cosmic history, allowing astronomers to map the expansion of the universe in more detail and probe dark energy’s effects over time. With each technique cross-checking the other, WFIRST’s surveys will peer deeply into dark energy, providing important data to help scientists figure out what, exactly, it is, and how it will determine the ultimate fate of the universe. [Explore: Solar System & Beyond] [NASA]