Our Milky Way galaxy is a secretive snacker. A huge blob of gas is falling towards the supermassive black hole at the centre of our galaxy, but so far the predicted feeding frenzy has been a quiet affair. The main meal will come a bit later than previously expected, with the bulk of the cloud getting closest to the black hole some time in March.
Astronomers first spotted the cloud, called G2, in 2011 and determined that it will skim unusually close to the black hole鈥檚 maw. Originally it looked like the cloud would make its closest approach in September 2013, spurring excitement over the possibility of getting our first good look at our black hole鈥檚 feeding habits.
This could help solve a number of puzzles. Seeing the black hole eat would give us a close-up view of how matter reacts to extreme gravitational fields, perhaps offering clues to physics beyond Einstein鈥檚 relativity. We could also learn more about how black holes grow to supermassive sizes.
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鈥淏lack holes need to grow, and we think they grow by accreting mass,鈥� Leo Meyer at the University of California, Los Angeles (UCLA), said today at a meeting of the in Maryland. 鈥淭his is potentially an experiment where we can watch in nearly real time how this material falls into a black hole. This is a fundamental process that is not well understood.鈥�
But monitoring efforts searching for bright X-rays and radio signals 鈥� signs of active feeding 鈥� have so far come up empty, in part because the cloud has not actually made its closest approach. Updated calculations have now shifted the black hole鈥檚 dinnertime to March 2014.
Spaghettification
In the meantime, astronomers have been able to track the cloud鈥檚 movements in near-infrared images. A series of snapshots taken by the in Chile have revealed that G2 is getting stretched like a lump of by the black hole鈥檚 powerful gravity as it creeps closer to its doom.
鈥淚t is showing tidal shear and beautiful spaghettification,鈥� says at the Max Planck Institute for Extraterrestrial Physics in Munich, Germany, who presented his team鈥檚 at the American Astronomical Society meeting this week. The most recent images show that a trickle of material from the front of the cloud has made it to the black hole鈥檚 lips, although it is not enough to spark any significant activity, Gillessen says.
For now it鈥檚 anyone鈥檚 guess what will happen when the bulk of G2 reaches the black hole. It could be ripped apart without triggering much active feeding. Or the Milky Way鈥檚 normally inactive, faint central black hole might consume enough of the cloud鈥檚 material to ignite dramatic X-ray flares as matter falling in heats up and spews radiation. Its fate depends in part on what the cloud is made of and where it came from, but that is also a hotly debated topic.
Shrouded star
Some groups argue that it could be a simple gas cloud, says at UCLA. Simulations suggest that a gas cloud would be quickly torn up by the black hole and would rain large amounts of material into it, possibly yielding X-ray fireworks and giving us a clear view of what happens when a black hole eats.
Others think G2 could be a young star obscured by a disc of material left over from its birth, which would make the object much less gassy. That would reduce the black hole鈥檚 meal to a snack and reduce the chances of dramatic flares. 鈥淚t is possible this dietary supplement is really nothing,鈥� says Meyer.
The only way to know for sure will be to see the cloud鈥檚 demise in action. Multiple telescopes in space and on the ground are gearing up for the next round of observations, perhaps starting in a few weeks, and theorists continue to model a range of potential outcomes.
鈥淲ill there be fireworks? The clear answer has to be: maybe,鈥� says Meyer. 鈥淏ut this is a unique opportunity to learn something new in astrophysics.鈥�
