UVEX Will Map the Ultraviolet Universe and Cosmic Explosions

Harrison said that glow would make the nearby systems easier to distinguish from distant look-alikes, which optical light often makes hard to separate.

For astronomers, the planned gain is a broad ultraviolet map of nearby galaxies and faster access to some cosmic explosions.

How will UVEX follow supernovae and neutron-star mergers?

A supernova occurs when a massive star exhausts the fuel for nuclear fusion, the process that powers a star, and can no longer resist gravity’s inward pull. Its core collapses and the outer layers explode outward. Such explosions also mark the birth of neutron stars and black holes.

The explosions fling heavy elements forged inside stars into surrounding galaxies. That material can become the building blocks for later stars and planets and may contribute to life. UVEX will study both the explosions and the stellar remnants they leave behind.

A neutron star packs one to two times the Sun’s mass into a width of about 12 miles (20 kilometers). If a teaspoon of that material reached Earth, it would weigh more than 1 billion tons. That is equivalent to stacking about 9 million adult blue whales on a spoon.

When two neutron stars in a binary system—a paired stellar system—spiral together and merge, they create the only environment in the universe where scientists are certain that elements heavier than lead, including gold, silver and platinum, can form.

Scientists detect these mergers through gravitational waves, ripples in spacetime, then watch the aftermath in electromagnetic light from high-energy gamma rays to low-energy radio waves. UVEX would add ultraviolet observations. Caltech scientist and UVEX team member Mansi Kasliwal said: “With UVEX, we will now be able to follow up on gravitational-wave events in ultraviolet light.”

Kasliwal said researchers have only a small number of spectra, or measurements of light, from short-lived events in their infancy phase. Although Hubble can observe ultraviolet light, it cannot pivot quickly toward real-time events. UVEX’s maneuverability should let it observe explosive events very shortly after they happen, an advantage over other instruments, including Hubble.

UVEX should fill the early-time ultraviolet gap by recording neutron-star mergers soon after gravitational-wave detections.

What will ultraviolet light expose inside stars?

Ultraviolet observations will also target blue stars whose companion has stripped away their outer layers of hydrogen. Removing that envelope exposes stellar interiors that the outer layers normally hide. These stars offer researchers a distinct way to study matter inside stars.

Caltech associate professor of astronomy Kareem El-Badry said UVEX would show what lies inside these stripped stars. Astronomers know only a small number now, but the mission should find hundreds, expanding the sample they can compare.

El-Badry also said that every new wavelength has revealed something new and unexpected when astronomers looked through it. UVEX may therefore uncover objects or phenomena beyond its planned targets, although its core program remains focused on nearby low-mass galaxies, supernovae, neutron-star mergers and stripped stars.

For astronomers, UVEX’s main practical promise is speed: it should catch cosmic events before older instruments can turn toward them.