Most people think of the space between galaxies — if they think of it at all — as fairly empty.

After all, the distance between the Milky Way and its nearest spiral neighbor, the Andromeda Galaxy, is 2.3 million light-years. No stars occupy that unimaginably vast expanse.

But new research using the Keck Observatory atop Mauna Kea shows that galaxies in some instances generate serious exhaust as they speed through space.

And like a hot rod with a bad tailpipe, they leave a distinct cloud far afield.

In fact, so productive is one particular galaxy, 5 billion light-years away, that astronomers gave it a pertinent name: Makani, Hawaiian for wind.

“Naming in astronomy is typically a dry task, usually involving some sort of catalog label,” recalled lead researcher David Rupke of Rhodes College in Memphis, Tenn., writing for the journal Nature. “Some subfields of astronomy have more fun with this than others (there are lots of asteroids named after people, and of course the planets!). Astronomers who study galaxies — let’s just say names are not done, mostly. But this galaxy and its nebula seemed special, at least to us. So we thought, why not? At worst, we’re the only ones who end up calling it Makani. And at best, it has a moniker which reflects why it’s scientifically important and also speaks to the origin of the data itself.”

The journey began in early November 2018, when Rupke and colleagues Alison Coil and Gene Leung of UC San Diego were beginning their third observing run with a new instrument on the Keck Observatory, the Keck Cosmic Web Imager. Their main mission was to study the size of gas outflows from nearby galaxies with hungry supermassive black holes.

After spending most of the night doing that, they turned their attention to another group of star-forming galaxies with fast out- flowing winds.

They picked a target that had a broad chemical signature for oxygen, which often accompanies strong galactic winds. They found some interesting structures but assumed that they had to do with the strong tides left over from the galaxy’s origin — the merger of two others.

Weeks later Coil emailed Rupke, asking whether he had had a chance to do more careful computer analysis of the data. He promised to do so.

Again at the Keck on New Year’s Eve 2018, he compared the oxygen emissions with an image of the galaxy’s stars.

“The result seemed different than our casual inspection from two months earlier, because the gas was now on much larger scales than the starlight,” he recalled. “‘OK, I must have calculated it wrong,’ I thought to myself. ‘Let’s do this again.’ When I recalculated the image scales and again found the gas nebula was enormous compared to the starlight, it was the ‘aha’ moment of discovery.”

Coil was ecstatic at the news, he said.

“Galactic winds have been studied for decades, and a lingering question has been how far they extend from their host galaxies,” Rupke said. “The discovery of such an enormous galactic wind brought me into a new collaboration with a group that had been working on these galaxies for over a decade, starting in 2007.”

One of them, James Geach of the University of Hertfordshire in England, looked at the mysterious new galaxy with the Atacama Large Millimeter Array, or ALMA.

“He immediately found that our galaxy had a molecular outflow, as well,” Rupke said.

The wind has formed an hourglass-shaped nebula that extends 326,000 light-years across at its greatest width, they said.

The first part of the gas cloud dates back 400 million years and is traveling at 870 miles per second. The second eruption is 7 million years old and drives gas at 1,300 miles per second, the scientists said.

Their findings appear in the Oct. 30 issue of Nature.

Geach was the one to suggest the name “Makani.”

In a statement, Coil said that most of the gas in the universe mysteriously appears in the regions surrounding galaxies — not in the galaxies themselves. Typically, when astronomers observe a galaxy, it is not in a turbulent state with collisions, the creation or rearrangements of stars or huge, fast winds.

“While these events may occur at some point in a galaxy’s life, they’d be relatively brief,” she said. “Here, we’re actually catching it all right as it’s happening through these huge outflows of gas and dust.”