Two fascinating structures in the Milky Way just became even more interesting.
The Fermi bubbles stretch above and below the center of our galaxy like a giant hourglass. These massive orbs of heated plasma have been pushing out from the galactic center for millions of years. They reach about 50,000 light-years across, making them towering giants compared to our galaxy’s length.
Researchers at the U.S. National Science Foundation’s Green Bank Telescope in West Virginia recently made a surprising find within these bubbles. They discovered immense clouds of cold hydrogen gas that somehow survived in this extreme environment. This strange combination raises intriguing questions.
According to lead author Rongmon Bordoloi, an astrophysicist at North Carolina State University, these clouds are likely leftovers from much larger structures that the galaxy’s center expelled millions of years ago. Bordoloi compares it to adding a big ice cube to boiling water; while smaller ice cubes melt quickly, larger ones take longer to disappear. The cold hydrogen clouds seem to have retained their size in an environment where they shouldn’t have.
“These clouds provide a kind of ‘cosmic clock’ that suggests the Milky Way’s central black hole spewed out material more recently than we thought—just a few million years ago,” Bordoloi explained. This finding, published in The Astrophysical Journal Letters, changes our understanding of the black hole’s activity.
The Fermi bubbles were first spotted in 2010 using NASA’s Fermi Gamma-ray Space Telescope. They’re visible only in gamma rays and seem to be linked to another mysterious set of structures called the eROSITA bubbles. The plasma in these Fermi bubbles reaches temperatures over a million kelvins (nearly 2 million degrees Fahrenheit). Scientists believe these bubbles emerged from a violent explosion at the center of the Milky Way, ejecting matter in twin jets and pushing nearby material outward.
The newly identified cold clouds range from about 13 to 91 light-years wide—much larger than our solar system. For these clouds to persist in such a hot environment, they must have started much larger when they were caught in the turbulence of the bubbles. Bordoloi noted, “In principle, these clouds shouldn’t be here, yet they are, suggesting a far more active past for our galaxy’s center.”
This discovery helps expose the mysteries surrounding the Fermi bubbles, suggesting that the Milky Way’s black hole may have experienced violent outbursts more frequently than previously believed. A recent survey published by the European Space Agency confirmed that black holes are often much more active than earlier studies suggested, especially when large amounts of material fall into them.
“The Fermi Bubbles and eROSITA Bubbles indicate that the center of our galaxy has been bustling with activity in the recent geological past,” Bordoloi concluded. “Understanding this helps us piece together the chaotic history of our galaxy.”
With ongoing exploration, each discovery reveals a bit more of the Milky Way’s hidden dynamics, inviting curiosity and wonder about our place in the universe.
