XRISM Space Telescope: A Dead Star Is Feeding Off Its Companion's Wind — and NASA's New X-Ray Eye Just Caught It in the Act

A dead star is slowly consuming its companion. Right now, in a binary system thousands of light-years from Earth, a neutron star — the city-sized crushed remnant of a supernova explosion — is pulling the atmosphere of a living giant star toward itself. Atom by atom. The captured gas heats to tens of millions of degrees as it falls inward, screaming in X-rays across the galaxy.

This week, a joint NASA-Japan observatory called XRISM did something that's never been done before: it directly observed this process happening. Not in theory. Not in simulation. In data.

What is the XRISM space telescope?

XRISM — the X-ray Imaging and Spectroscopy Mission — launched on September 7, 2023 from Japan's Tanegashima Space Center. It's a partnership between JAXA (Japan's space agency) and NASA, and it carries one of the most sensitive X-ray instruments ever built: a calorimeter called Resolve that can measure X-ray energies with such extraordinary precision it can essentially "read" the chemical fingerprint of plasma hotter than a million degrees. Think of it as a spectrometer for the most violent processes in the universe.

How does a pulsar steal from a companion star?

When two massive stars are born close together, they orbit each other for millions of years — a slow cosmic dance. If the larger one dies first in a supernova, it leaves behind a neutron star: a city-sized object heavier than our Sun, with gravity so intense that space bends visibly around it.

The surviving companion is still alive — and it exhales. Every massive star continuously sheds its outer atmosphere in a stream of charged particles called a stellar wind. Moving at speeds up to 2,000 km/s, this outflow normally escapes into space. But near a neutron star, some of it gets captured. The stolen gas spirals inward, compresses, and heats to tens of millions of degrees — emitting X-rays intense enough to be detected from across the Milky Way.

What did XRISM actually find?

Using its Resolve instrument, XRISM captured the spectral "fingerprints" of the captured stellar wind — the specific X-ray energies that reveal which elements are present, how fast they're moving, and how they interact with the neutron star's magnetic field. This level of detail was previously impossible.

The result is the first direct observation of a stellar wind being captured by a compact object in this way. Earlier X-ray telescopes could see the glow. XRISM can read what's inside it — like the difference between seeing a fire and knowing exactly what's burning.

Why does this matter beyond the cool physics?

Stellar wind accretion is how the universe recycles its dead stars. When a neutron star captures enough material over millions of years, it gets spun up — rotating faster and faster — until it becomes a millisecond pulsar: a natural clock ticking hundreds of times per second with extraordinary precision. These objects are used to test general relativity and detect gravitational waves.

Understanding the feeding mechanism lets us trace the full life cycle of these systems. XRISM's data gives theorists real chemical fingerprints to test against models scientists have been refining since the 1970s. You can track the live orbit of X-ray observatories like XRISM on the SkyLens live tracker, which monitors more than 16,000 objects in real time.

Is the XRISM mission still active?

Yes — though it had a rocky start. Shortly after launch, the Xtend imaging camera experienced a partial detector failure, and the Resolve calorimeter required extra recovery steps to reach operating temperature. By early 2024, both instruments were fully nominal. Since then, XRISM has returned results on galaxy clusters, black hole accretion discs, supernova remnants, and now stellar wind capture in binary systems. It is expected to remain operational for years.

What does this look like from Earth?

Nothing. That's the point. X-rays are completely blocked by Earth's atmosphere — fortunate for us, because radiation this intense would be lethal at close range. From the ground, the night sky looks peaceful. From orbit, it's something else entirely: dying stars eating living ones, collapsed objects spinning hundreds of times per second, gas falling at speeds that could cross the Atlantic Ocean in under 4 minutes.

The only way to see any of this is from space. Right now, XRISM is up there — orbiting at roughly 550 km — quietly reading the universe's most violent correspondence in a language made of X-rays.

For more stories about the physics hiding above your head every night, explore the SkyLens blog — or visit the learn section for a deeper look at how orbital mechanics actually work.