Last gorge for galaxy’s central black hole gauged

About two million years ago, the supermassive black hole at the Milky Way’s center went on a feeding frenzy. It was the galactic core’s last big gorge, and it left behind a fiery flare that astronomers can still see evidence of today.

That glimmer comes from the Magellanic Stream. In this lacy gas filament, ultraviolet light splits hydrogen atoms into protons and electrons. When those particles recombine, the electrons give off a signature glow called an H-alpha emission. Stars in the Milky Way don’t produce enough light to account for this glow, and the stars never have.

That fact led a team of astronomers to conclude that the glow represents a relic of a past eruption from the black hole at the galactic center. The relic light suggests that about two million years ago, the black hole was 100 million times more powerful than it is today, the team suggests.

The researchers presented the results September 24 at the Galaxy Zoo meeting in Sydney. A paper describing the results will also appear in an upcoming issue of the Astrophysical Journal.