Hubble Sees Our Galaxy Sucking Up a Mysterious Amount of Gas

Artist’s concept of gas clouds flowing in and out and how Hubble observes it
Artist’s concept of gas clouds flowing in and out and how Hubble observes it
Illustration: NASA, ESA, and D Player

The Milky Way seems to be gobbling up a mysterious amount of gas—more than it spits back out, according to a new paper.


Our galaxy maintains a level of “stuff” through a feedback process: It eats up gas from the surrounding environment to form stars, and then it spits the gas back out via supernovas and stellar winds. Using data from the Hubble Space Telescope, a team of astronomers calculated that more mass appears to be flowing in than is flowing out—an unexpected result, according to a Hubble press release.

The researchers collected data from 270 views taken by the Cosmic Origins Spectrograph instrument on the Hubble Space Telescope. Specifically, they were interested in speedy clouds of gas that moved too quickly to be orbiting with the Milky Way. These clouds appear as features that absorb ultraviolet light passing from behind them, like shadows on specific light wavelengths. Doppler shifts—the clouds absorbing longer or shorter wavelengths than expected—allow the researchers to determine whether the clouds are flowing out or in. They found 187 of these clouds.


When the researchers calculated the rate that mass was flowing into the galaxy versus out of it, they found the scales tipped—the galaxy sucks up more gas than it spits out, according to the paper published in the Astrophysical Journal. The Milky Way could simply be in an inflow-dominated part of its life, the researchers write in the paper, but the presence of mass moving in either direction lends credence to ideas that the galaxy used gas from its surrounding environment to produce stars, then recycles it back into the environment once the stars die.

So, where’s the extra mass coming from? Study author Andrew Fox from the Space Telescope Science Institute suggested that perhaps the Milky Way was slurping up mass from the intergalactic medium, as well as its smaller satellite galaxies, according to the release.

The authors note that the calculations are based on solely a snapshot of the Milky Way today, and that caution should be taken when trying to extrapolate the rates that mass is flowing over time, according to the paper. Additionally, the ultraviolet absorption by these high-velocity clouds is just one way to measure the rate that the galaxy is eating and spitting out gas. These measurements present a higher rate of gas flowing inwards than radio-based measurements. Plus, the authors write, they only looked at fast-moving clouds; maybe the slow-moving clouds would reveal a different story.

Ultimately, though a mystery is exciting, studies like these serve a more profound purpose: to understand how our galaxy and others fit into the grander scheme of the universe, and how they get the necessary material to form stars and, in turn, planets.


Science Writer, Founder of Birdmodo

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Here’s the amazing part: by the time the sun exits the main sequence, the galaxy will barely be half-way through its first percent of its life span, depending on how many galaxies it consumes or is consumed by as we go. By the time the white dwarf left behind by our dying sun is frozen solid and cold, the galaxy will only be entering its third percent of its lifespan. By the time the last star grows cold and dead in our galaxy, the universe will be just 2-3% of its projected maximum age. And by the time the last black hole decays into nothingness... the universe won’t even be 1/4 of the way through its lifespan as measured when the last erg of photonic energy finally reaches is base state and decays into nothingness.

We are brief - we don’t even register as sparks as individuals. We are too small and too insignificant. Our delusions of grandeur mean nothing so long as we squander our moment and believe that some power or being grants us dominion over all of this. We don’t even have dominion over ourselves. Astronomy shows us our place in the universe and challenges us to understand that universe and ourselves - because there is nobody else to do so... as Carl Sagan put it: “In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.”

What I see as a challenge, most people see as an inevitability. They cling strongly to their beliefs, war and fight over them. Kill over them. They do not care for tomorrow, or their children’s tomorrow. They only care for their now and themselves. That is the greatest threat our civilization has ever faced: greed and apathy swathed in shades of Faith and Belief.

But here is the universe giving us a mystery to solve. And some of us believe in looking out there and asking “Why is that the way it is?” This gives me hope in our future. That some of us can even ask that question means we are not all consumed by this “folly of human conceit”, again as stated by Dr. Sagan.

And hope is the greatest thing there is. Civilizations are built from hope. They fall when all hope is lost. And they rise again when hope shines brightly. And even the tiniest, briefest, most insignificant spark of hope can change the universe. Even if we die completely in the next eyeblink... there will be more. Even if they never see these words, they will have words similar to it. And if we are gone, then maybe they will succeed where we failed.  But as I said, I have hope - and hope is a power that can change the universe.  And we are not dead yet.