galactic-center

In 2010, NASA's Fermi telescope found two colossal gamma-ray structures erupting from the center of the Milky Way, each 25,000 light-years tall. In 2020, an X-ray telescope found even larger versions of the same structures. Nobody fully agrees on what made them.

Within 500 parsecs of the Milky Way's center lies a region unlike anything else in the galaxy — the Central Molecular Zone. It contains roughly 10% of the entire galaxy's molecular gas compressed into less than 0.1% of its volume. Star formation there should be rampant, but it is strangely quiet. Giant molecular clouds orbit at velocities that defy simple physics. A cloud called the Brick should have already collapsed into thousands of stars, yet it has not. Understanding the CMZ means understanding what keeps the center of our galaxy from exploding with new stars — and what occasionally makes it erupt instead.

The Milky Way is a barred spiral galaxy containing 200–400 billion stars, spanning ~100,000 light-years. Its four major spiral arms — Perseus, Norma-Cygnus, Scutum-Centaurus, and Sagittarius — host most star formation. The galactic centre harbours Sagittarius A*, a 4.15 million solar mass black hole, imaged directly by the Event Horizon Telescope in 2022. The Sun orbits at 26,000 light-years from the centre, completing one revolution in ~225 million years.