NASA's New UV Space Telescope Will Launch in 2031

To the human eye, the night sky can seem almost unchanging. The Moon moves through its phases. The planets drift slowly across the sky. Satellites and the International Space Station pass overhead for a few moments. A meteor may flash briefly. If we are very lucky, we might see a bright comet, such as Halley's Comet, or a rare visitor like Hale-Bopp. A much smaller number of people might witness a distant supernova.

Yet this quiet appearance is an illusion. It comes from a selection bias: human eyes can detect only visible light. The universe is actually full of sudden and violent events. Many of these events, including stellar flares and exploding stars, reveal themselves most clearly in ultraviolet (UV) light. UV light lies beyond what people can see without special technology.

A new space telescope will soon study the sky in that hidden range. NASA has announced that UVEX, the UltraViolet EXplorer, will launch in 2031. The mission will be led by Caltech and will conduct an all-sky survey in near and far ultraviolet light.

"UVEX is a bold leap forward in our exploration of the ultraviolet universe," said Caltech President and professor of astronomy Ray Jayawardhana.

Light reaches us from across the universe in many wavelengths, from radio waves to gamma rays. To understand what produces all of this light, astronomers need to observe as much of it as possible. UVEX will help fill a gap by surveying the whole sky in UV. Its data will complement surveys by other telescopes, including the Nancy Grace Roman Space Telescope, the Vera Rubin Observatory, and the European Space Agency's Euclid Space Telescope.

People often picture telescopes as instruments that magnify distant objects and produce beautiful images of nebulae and galaxies. Survey telescopes, however, play a different and equally important role. The Nancy Grace Roman Space Telescope will carry out three infrared surveys. The Vera Rubin Observatory will image the night sky repeatedly over a decade. Euclid is conducting three deep-field surveys in visible light and will capture more than 10 billion sources. Another NASA telescope, SPHEREx, is surveying the whole sky in near-infrared light.

These large datasets have become essential in modern astronomy. UVEX will add to this growing picture of the universe. It will also make focused observations of individual targets.

In its two-year baseline mission, UVEX will perform a multi-cadence synoptic all-sky survey. According to a white paper about the mission, it will be 50 to 100 times deeper than GALEX in near- and far-ultraviolet light. It will also conduct cadenced surveys of the Large and Small Magellanic Clouds, rapid follow-up of targets of opportunity, and spectroscopic follow-up of samples of stars and galaxies. GALEX was a NASA ultraviolet space telescope whose mission ended in 2013. UVEX will be up to 100 times more sensitive than GALEX.

UVEX will observe nearby low-mass galaxies that are bright in ultraviolet light. Those observations will complement work by the James Webb Space Telescope and the Nancy Grace Roman Space Telescope.

Low-mass galaxies matter because of the role they play in the universe. In a paper describing the UVEX mission, the authors explained that the mission rests on three pillars. The first is low-mass galaxies.

"First, UVEX will explore the low-mass, low-metallicity galaxy frontier through imaging and spectroscopic surveys," the authors wrote. These surveys will probe how star formation and stellar evolution at low metallicities affect the growth and evolution of low-mass galaxies in the local universe. This galaxy population contains half of the universe's mass, and these galaxies are analogs for the universe's first galaxies.

"Second, UVEX will explore the dynamic universe through time-domain surveys," the authors explain. Its prompt spectroscopic follow-up will probe the environments, energetics, and emission processes in the early aftermaths of gravitational-wave-discovered compact object mergers. It will also discover hot, fast UV transients and diagnose the early stages of stellar explosions.

Third, UVEX will generate a vast treasure trove of UV data. Like other survey missions, it will make that data available to researchers studying a wide range of objects and phenomena. This is similar to what the European Space Agency's recently completed Gaia mission did. Gaia's data is used in many research areas and will likely be relied upon for a long time.

UVEX will reveal objects and events that were too dim to be seen before. Explosions, stellar mergers, tidal disruption events, and other transient events will become visible more than ever. These events are among the most dramatic happenings in the universe. Along with its steady surveying work, UVEX will be able to turn quickly toward a transient event and watch it unfold.

Several powerful telescopes have launched in recent years, but UVEX is the first new UV telescope in 20 years. It will also be the first UV mission to create deep-sky maps in ultraviolet light. With its extreme sensitivity and spectrograph, it will separate the different wavelengths of light coming from distant objects. That will help clarify which chemical elements are present.

UVEX will also complement gravitational-wave observatories. Gravitational waves are ripples in space-time, predicted by Einstein, that are generated when extremely dense objects such as neutron stars and black holes merge. When gravitational waves are detected, alerts go out to other telescopes, which then observe the events in wavelengths including radio and gamma rays. Once UVEX is launched, it will add ultraviolet observations.

"With UVEX, we will now be able to follow up on gravitational-wave events in ultraviolet light," explains UVEX team member Mansi Kasliwal, professor of astronomy at Caltech and director of the Palomar Observatory. UVEX's detailed spectra will reveal more information than ever about these events.

Every new mission and telescope is launched with clear goals and expected results. But as telescopes such as the James Webb Space Telescope have shown, each new instrument can also produce surprises.

"Every time you look at the skies in a new wavelength," said Kareem El-Badry, associate professor of astronomy at Caltech and a member of the UVEX team, "you learn something new and unexpected."