Milky Way’s giant gas bubbles in visible light

For the first time, scientists have observed visible light from enormous blobs of gas that sandwich the pancake flat part of our Milky Way galaxy. They’re known as Fermi bubbles. Astronomers had seen the bubbles since 2010, but never directly. The light they emitted is in wavelengths the human eye can’t see. At least, it hadn’t been until now.

Astronomer Dhanesh Krishnarao works at the University of Wisconsin–Madison. He was part of a team that spotted a new visible-light glow from the bubbles. It comes from hydrogen gas inside the bubbles that was electrically charged, or ionized. That ionization made the gas glow in colors our eyes can see.

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Credit: HST/NASA, and A. Field/STScI

Giant gas bubbles above and below the center of the Milky Way are illustrated here. The solar system is the bright, yellow spot at the right of the galaxy’s center. The gas moving toward the solar system looks bluer. Gas moving away from it appears redder.

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But these enormous gamma-ray emitting lobes aren't immediately visible in the Fermi all-sky map. By processing the data, a group of scientists was able to bring these unexpected structures into sharp relief.

Each lobe is 25,000 light-years tall and the whole structure may be only a few million years old. Within the bubbles, extremely energetic electrons are interacting with lower-energy light to create gamma rays, but right now, no one knows the source of these electrons.