From our perspective inside the Milky Way, it's hard to really understand its large-scale structure. Now, astronomers have peered towards the center of the galaxy using the ESA's X-ray telescope XMM-Newton, and discovered two colossal "chimneys" pumping huge amounts of energy and gas out into intergalactic space.
Black holes – especially the supermassive variety like Sagittarius A* at the heart of the Milky Way – are known for being ravenous, to the point that not even light can escape their gravity. But they don't necessarily swallow up everything that comes their way. Black holes are messy eaters, throwing dust, gas, energy and matter away, and as a result, the center of the Milky Way is a turbulent region.
But that energy and matter doesn't stay there, and now we know where it goes. The new study discovered what are essentially the galaxy's exhaust pipes – two gigantic channels of hot matter streaming away from Sagittarius A*, carrying charged particles from the center of the galaxy to the outskirts.
If you picture the Milky Way as more or less a flat disk, these two chimneys stretch out from the top and bottom, each spanning over 500 light-years long. They seem to connect to two huge bubbles that sit above and below the galaxy that contain high-speed particles that have basically blown away the gas that otherwise surrounds the Milky Way.
These bubbles, stretching as far as 25,000 light-years across, were discovered in 2010 by NASA's Fermi Gamma-ray Space Telescope, but until now it wasn't entirely known where the charged particles came from. The discovery of the chimneys helps fill that void, revealing that the particles originated in the center of the galaxy.
The chimneys were discovered when an international team of astronomers set out to map the Milky Way center in X-rays with the XMM-Newton telescope. By examining images of the region taken in 2012 and then again between 2016 and 2018, the chimneys were given away by their bright X-ray emissions.
"This outstanding result from XMM-Newton gives us an unprecedented view of what's really happening at the core of the Milky Way, and presents the most extensive X-ray map ever created of the entire central region," says Norbert Schartel, XMM-Newton Project Scientist.
The team says this mechanism could help us understand the formation and evolution of our own galaxy and others. The Milky Way is usually considered to be comparatively quiet, so the astronomers suggest these outflows could be relics of a time long past in which it was much more active. Or it may tell us that even the quiet ones can be energetic.
"We know that outflows and winds of material and energy emanating from a galaxy are crucial in sculpting and altering that galaxy's shape over time – they're key players in how galaxies, and other structures, form and evolve throughout the cosmos," says Gabriele Ponti, lead author of the study. "Luckily, our galaxy gives us a nearby laboratory to explore this in detail, and probe how material flows out into the space around us."
The research was published in the journal Nature.