“WFIRST’s surveys don’t require that we know exactly where and when to look to make exciting discoveries—we won’t be limited to looking under the cosmic lamppost,” says Goddard’s Julie McEnery, the WFIRST deputy project scientist about NASA’s new set of infrared eyes on the universe. “The mission will turn on the floodlights so we can explore the universe in a whole new way.”
While Hubble views the cosmos in infrared, visible and ultraviolet light, WFIRST will be tuned to see a slightly wider range of infrared light than Hubble can observe. Detecting more of the spectrum of light allows Hubble to create a more comprehensive picture of many processes at work in individual objects in the cosmos. WFIRST is designed to expand on Hubble’s infrared observations specifically, because conducting enormous surveys of the infrared universe will let us see vast numbers of cosmic objects and subtler processes in regions of space that would otherwise be difficult or impossible to view.
WFIRST will help unravel mysteries surrounding dark energy and the evolution of galaxies by peering across enormous stretches of the universe—even farther than Hubble is capable of seeing. These studies require precise infrared observations because light shifts into longer wavelengths, from ultraviolet and visible into infrared, as it travels across vast astronomical distances due to the expansion of space.
WFIRST’s infrared capabilities will also provide a new view into objects that are closer to home. The heart of our Milky Way galaxy is densely populated with rich targets, but shrouded in dust that obscures visible light. As an infrared telescope, WFIRST will essentially use heat-vision goggles to peer right through the dust, giving us a new view into the inner workings of the galaxy.
These observations will allow astronomers to study stellar evolution—the births, lives and deaths of stars. WFIRST will also expand our inventory of exoplanets—planets outside our solar system—by revealing thousands of worlds that astronomers expect will be very different from most of the 4,100 now known. Most of the currently known exoplanets are either very close to their host stars, or large planets orbiting farther away. Hubble has observed some of these planets directly using coronagraphs, which block the glare from stars. WFIRST will build upon that technology to make an active coronagraph that is much better at suppressing starlight—a demonstration of technology that, when further advanced, will enable future space telescopes to image Earth-size exoplanets.
Pinpointing Extreme Objects
This image, comparing the apparent sizes of the Andromeda galaxy and the Moon in the sky, demonstrates the type of observation WFIRST will produce. It took Hubble more than 650 hours between 2010 and 2013 to produce the portion of the image outlined in teal, but calculations suggest WFIRST could observe the same area in three hours or less. WFIRST’s infrared observations will also allow us to see through obscuring dust to help us gain further insights into the natures of planets, stars and galaxies. Background image: Digitized Sky Survey and R. Gendler; Moon image: NASA, GSFC and Arizona State University; WFIRST simulation: NASA, STScI and B. F. Williams (University of Washington)
Scientists will also use WFIRST’s cosmic surveys to obtain enormous samples of some of the most extreme objects in the universe, including quasars—active galaxies with super-bright centers. Pinpointing their locations will allow Hubble and other telescopes to follow up for detailed observations. These investigations will enable astronomers to piece together the history of galaxy growth and the evolution of the universe.
To make these studies possible, WFIRST will operate much farther away from Earth than Hubble does. While Hubble orbits about 340 miles above us, WFIRST will be located about 930,000 miles (1.5 million km) away from Earth in the direction opposite the Sun. At this special place in space, called the second Sun-Earth Lagrange point, or L2, gravitational forces from the Sun and Earth balance to keep spacecraft in relatively stable orbits.
Near L2, WFIRST will orbit the Sun in sync with Earth, using a sunshield to block sunlight and keep the spacecraft cool. Since infrared light is heat radiation, if WFIRST is warmed by radiation from Earth, the Sun or even its own instruments, it will overwhelm the infrared sensors. From this vantage point, WFIRST can view large swaths of sky smoothly over long periods of time.
Panoramic Views of the Unknown
To collect as much light as possible, telescopes need large primary mirrors. Since both WFIRST and Hubble have a primary mirror that is 2.4 meters (7.9 feet) across, they gather the same amount of light. While the same size, WFIRST’s mirror is only one-fourth the weight of Hubble’s thanks to advancements in technology.
With Hubble’s similar light collection, resolution and an overlap in infrared capabilities, it can help set expectations for WFIRST. For example, Hubble produced a panoramic image of our neighboring Andromeda galaxy as part of the Panchromatic Hubble Andromeda Treasury (PHAT) program. Scientists compiled the PHAT image from 7,398 exposures taken over the course of three years. WFIRST could replicate Hubble’s PHAT image more than 1,000 times faster. This type of observation will reveal how stars change with time and influence the galaxy in which they reside.
Like Hubble, WFIRST will also offer a General Observer program to support the astronomical community, allowing scientists to take advantage of the mission’s unique capabilities by proposing new, competitively selected observations. As with Hubble, the pursuit of investigations not even contemplated before launch will likely become the primary legacy of the WFIRST mission. The entire trove of WFIRST data will be publicly available within days of being taken—a first for a NASA astrophysics flagship mission. WFIRST will have a robust archival research program to allow scientists to take full advantage of these vast datasets.
WFIRST benefits from an additional 30 years of major technological advances, however Hubble will continue to transform our understanding of the universe. In the coming years, WFIRST’s enormous infrared surveys will reveal interesting targets for follow up by other missions. Hubble can view the targets in additional wavelengths of light and will provide the only high-resolution view of the ultraviolet universe. The James Webb Space Telescope can make detailed observations that go even further into the infrared with its high-resolution, zoomed in view. Combining the WFIRST’s findings with Hubble’s and Webb’s could revolutionize our understanding in a multitude of cosmic pursuits.
The Daily Galaxy, via Ashley Balzer, NASA’s Goddard Space Flight Center
Image at top of page: Goddard, annotated view of a curious supernova SN1995E in NGC 2441.