The night sky seems almost unchanging: the Moon changes phases, the planets move slowly, and occasionally meteors streak past. But this serenity is an illusion. The human eye sees only a small part of the spectrum, and many cosmic events, including flares on stars and explosions of luminaries, manifest fully only in ultraviolet - radiation with a wavelength shorter than that of violet light.
To look into this invisible world, NASA is preparing the UVEX (UltraViolet EXplorer) space telescope. Launch is planned for 2031, and the mission is led by the California Institute of Technology (Caltech). The spacecraft will conduct a survey of the entire sky in near and far ultraviolet.
"UVEX is a bold step forward in exploring the ultraviolet Universe," the press release quotes Caltech President and professor of astronomy Ray Jayawardhana as saying.
Light of all wavelengths fills space. Understanding what produces this radiation is possible only by observing the entire spectrum. UVEX will fill a gap in observations, complementing surveys by other instruments such as the Nancy Grace Roman Space Telescope, the ground-based Vera Rubin Observatory and the European Euclid spacecraft.
Survey telescopes methodically scan the sky and create huge data sets that underpin modern astronomy. UVEX will contribute to this store, and will also be pointed at individual objects. Over two years of its primary mission, the telescope will conduct a multiple all-sky survey that will be 50-100 times deeper than that of its predecessor GALEX (a NASA ultraviolet telescope that completed operations in 2013). In addition, UVEX will repeatedly observe the Large and Small Magellanic Clouds - satellite galaxies of the Milky Way - respond quickly to sudden events, and obtain spectra - "fingerprints" of chemical composition - of individual stars and galaxies.
The mission rests on three key tasks. The first is studying nearby low-mass galaxies with a low content of heavy elements (metals). The observations will help understand how star formation proceeds under such conditions and how this affects the growth and evolution of galaxies. The second task is to study the "dynamic" Universe: UVEX will search for rapid ultraviolet flares, record the early stages of stellar explosions and monitor the aftermath of mergers of compact objects detected by gravitational waves. The third is to create an extensive archive of ultraviolet data open to researchers around the world, similar to what the European Gaia mission did.
Gravitational waves are ripples in space-time predicted by Einstein that arise when neutron stars or black holes merge. When detectors record such an event, astronomers point other telescopes at its source. After launch, UVEX will be able to join these observations in ultraviolet. "With UVEX, we will now be able to follow gravitational-wave events in ultraviolet light," explains team member Mansi Kasliwal, professor of astronomy at Caltech and director of Palomar Observatory. The spacecraft's detailed spectra will tell more about these events than ever before.
Every new telescope brings not only expected results but also surprises. "Every time you look at the sky in a new wavelength, you learn something new and unexpected," says Karim El-Badry, professor of astronomy at Caltech and a member of the UVEX team. UVEX will be the first new ultraviolet telescope in 20 years and the first mission to create deep maps of the sky in ultraviolet.