Can Fermi bubbles be produced in non-spiral galaxies?
We don’t know the answer because we don’t know with certainty the origin of the Fermi bubbles seen in our own galaxy. The Fermi bubbles are bilobular structures that emerge north and south from the galactic plane in the vicinity of the galactic nucleus. The original discoverers of the bubbles – and many other astrophysicists since – have favoured an interpretation that the bubbles are manifestations of a previous period of activity. This could have occurred something like a few million years ago. External galaxies which host flaring supermassive black holes are known as active galactic nuclei (AGN).
Other researchers have promoted the idea that the bubbles are signatures of the intense star formation that occurs around the supermassive black hole in the galaxy’s Central Molecular Zone, or CMZ. This is a region only 0.01 per cent the area of the galaxy’s disc that hosts about ten per cent of the molecular hydrogen – and a similar fraction of all the star formation in the galaxy. In this scenario the bubbles are inflated much more slowly and gently by this sustained but intense star formation than in the AGN scenario.
If the Fermi bubbles were manifestations of a recent AGN phase in the Milky Way, then we might expect them in elliptical galaxies, which tend to host the universe’s largest black holes and create giant radio- and gamma-ray-emitting lobes on larger scales than the Fermi bubbles. On the other hand, if the bubbles are energised by CMZ star formation then we would really only expect their exact analogues in spiral galaxies, because these are the only galaxies in the local cosmos that host sufficiently intense star formation.