“Fermi Bubbles” have astrophysicists scratching their heads

Using data from NASA’s Fermi Gamma-ray Space Telescope, scientists recently discovered a gigantic, mysterious structure in our Milky Way galaxy comprised of two enormous gamma-ray emitting bubbles. (Image courtesy of NASA)

About a year ago, astronomers using NASA’s Fermi Gamma-Ray Space Telescope announced an astonishing discovery. I regard it as the single strangest object in the entire universe.

Emanating from the center of our Milky Way galaxy are two bubbles made solely of gamma rays. This would have been strange enough if the bubbles, expanding at 2.2 million miles an hour, were concentric – a bubble within a bubble – with both centered at the galaxy’s core. But no; the two enormous spheres each hover in seemingly empty space above and below the black hole in the Milky Way’s nucleus. They are tangent to each other, meaning that they touch at the galactic center to form a squat hourglass shape. The entire structure looks like the number eight.


Gamma rays are the bad boys of the electromagnetic spectrum – the highest-energy light in the universe. Because of this, they do not reliably reflect off objects the way that visible light does. Rather, they are penetrating. Such photons drill through bodies at the speed of light, damaging chromosomes all along the way.

Fortunately, few gamma rays reach us here at Earth’s surface. Stars usually don’t emit them, and in any case our atmosphere blocks them. The only gamma rays flying near Earth have come from distant violent events like supernovae. This is why a dense gamma-ray swarm at our own galaxy’s center is so puzzling. It’s the unmistakable sign of extreme violence. And yet, these days, the Milky Way’s core is about as energetic as a steamy Florida lunchtime.

The bubbles are sharp-edged and well-defined and nothing short of enormous. The top and bottom of the figure-eight extend from 25,000 light-years north of the galactic plane to the same distance beneath it. From our sideways viewpoint 25,000 light-years from the center, the hourglass stands a whopping 45 degrees above and below the galactic core in Sagittarius. It takes up half of our southern sky.

Theorists need to explain more than just what could have produced this kind of extreme energy, which is equivalent to 100,000 supernovae exploding all at once. They must also explain the off-center nature of the bubbles, since each seemingly surrounds nothingness.

This gargantuan hourglass – which is starting to be called the Fermi Bubbles in honor of the orbiting gamma-ray telescope launched in 2008 that found them – is now regarded as an entirely new type of astronomical object. In trying to come up with some explanation for our galaxy blowing bubbles surrounding nothingness at temperatures of 7 million degrees Fahrenheit, many astrophysicists simply say, “I have no idea.” Others, starting perforce from Square One, have posited a couple of vague causes.

For example, what if the heavy black hole at our galaxy’s center had a brief feasting frenzy when much of its captured material was flung away at super-high speeds? Then, perhaps, that black hole could have developed something that it does not have at present: twin jets of outrushing material. We see such blue jets exploding from the supermassive black holes in some other galaxies. These jets could have possibly deposited energetic material above and below the galactic plane – although how bubbles then emanated from those positions is anyone’s guess.

The ultimate answer could be even stranger: Might these be the long-sought signs of dark matter? Could dark matter be meeting its opposite entity (whatever that is) in total annihilation, the way that matter and antimatter do? More likely, however, this is something else entirely – some new phenom that will actually get in the way of the dark matter hunt.

As Fermi research team leader Douglas Bookbeiner put it, “This just confuses everything.”


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