eROSITA finds large-scale bubbles in the halo of the Milky Way

Gigantic hot gas structures above and below the galactic disc are probably due to shock waves generated by past energetic activity in the center of our galaxy.

The first all-sky survey performed by the eROSITA X-ray telescope on-board the Spektrum-Roentgen-Gamma (SRG) observatory has revealed a large hourglass-shaped structure in the Milky Way.

These "eROSITA bubbles" show a striking similarity to the Fermi bubbles, detected a decade ago at even higher energies. The most likely explanation for these features is a massive energy injection from the galactic center in the past, leading to shocks in the hot gas envelope of our galaxy.

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. Credit: University of Tübingen

The SRG/eROSITA all-sky map as a false color image (red for energies 0.3-0.6 keV, green for 0.6-1.0 keV, blue for 1.0-2.3 keV).

The original image, with a resolution of about 12”, was smoothed in order to generate the above picture.

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Credit: University of Tübingen

The eROSITA bubbles. In this false-color map the extended emission at energies of 0.6-1.0 keV is highlighted.

The contribution of the point sources was removed and the scaling adjusted to enhance large-scale structures in our galaxy.

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Credit: University of Tübingen

Schematic view of the eROSITA (yellow) and Fermi bubbles (purple). The galactic disk is indicated with its spiral arms and the location of the Solar System is marked.

The eROSITA bubbles are considerably larger than the Fermi bubbles, indicating that these structures are comparable in size to the whole galaxy.

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Credit: University of Tübingen

Illustration of the eRosita and Fermi bubbles (blue/green and orange respectively) of how they could look, if our vision were extended beyond visible light – and if Tübingen was located closer to the equator. Actually only the Northern part of the eRosita bubbles is above Tübingen.

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Using data from NASA's Fermi Gamma-ray Space Telescope, scientists have discovered a gigantic, mysterious structure in our galaxy. This never-before-seen feature looks like a pair of bubbles extending above and below our galaxy's center.

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.

Are the bubbles remnants of a massive burst of star formation? Leftovers from an eruption by the supermassive black hole at our galaxy's center? Or or did these forces work in tandem to produce them? Scientists aren't sure yet, but the more they learn about this amazing structure, the better we'll understand the Milky Way.