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The uncertainty of science: Sagittarius A* (pronounced A-Star), the Milky Way’s supermassive central black hole, has shown signs of increased activity in recent months.
The new study reveals that Sagittarius A* (Sgr A* for short) has been producing one bright X-ray flare about every ten days. However, within the past year, there has been a ten-fold increase in the rate of bright flares from Sgr A*, at about one every day. This increase happened soon after the close approach to Sgr A* by a mysterious object called G2.
“For several years, we’ve been tracking the X-ray emission from Sgr A*. This includes also the close passage of this dusty object” said Gabriele Ponti of the Max Planck Institute for Extraterrestrial Physics in Germany. “A year or so ago, we thought it had absolutely no effect on Sgr A*, but our new data raise the possibility that that might not be the case.”
G2 was first thought to be a cloud that would be ripped apart as it passed close to Sgr A*, causing an outburst of activity. When it wasn’t ripped apart and there was no immediate increase in activity astronomers concluded that G2 was a star surrounded by dust which was generally unaffected by its close fly-by of the black hole.
The timing of this new activity now is puzzling. It comes much later than it should have if it was caused by G2, but astronomers don’t have any other explanation for it. It might be because of G2’s fly-by, or maybe the activity is just the natural variability of this poorly understand object. Either way it illustrates how little we really know about the behavior of giant black holes.