Carl Sagan one speculated that if we didn’t have the intellectual stagnation of the Early Middle Ages, we’d be flying in starships today.
Now, I’m not saying that the Italian scientist Galileo would have had an X-ray telescope by 1609. But if he did he would have noted a burst of X-rays from the heart of our galaxy. (Yes, it really happened 27,000 years ago because the galactic core is 27,000 light-years away, but the energy didn’t first reach us until the Renaissance period.)
Fortunately, because of the finite nature of the speed of light, we can still witness this outburst hundreds of years later. This is because X-rays from the blast that rebounded off dark clouds of molecular hydrogen near the black hole are reaching us as a light echo, or rather an X-ray echo.
This “echo” was first detected as simply several mysteriously bright sources of X-rays in the vicinity of the galactic center. They come from dark clouds that are not hot enough to produce X-rays.
What’s more, the X-rays flicker like a searchlight bouncing off of blotchy evening cloud-cover. This also means the interstellar clouds aren’t producing X-rays but reflecting them from a nearby source.
That source could be several types of astronomical fireworks such as X-ray binary stars erupting flares, or stellar collisions.
But Masayoshi Nobukawa and co-investigators at Kyoto University report that the intense X-rays are too powerful to come from anything other than the gargantuan 3-million solar mass black hole at the heart of our galaxy. They calculated that the Renaissance flare was at least 10,000 times brighter than what an X-ray binary could unleash.
This conclusion is based on several years worth of observations from Japan’s Suzaku X-ray telescope. The space observatory shows the flare fading but at different intervals for specific clouds. This can be explained if the clouds at different distances from the flare, and so the echoes arrive at different times – just like sound waves echoing through a canyon.
The dark molecular clouds are a few hundred light years from the black hole. So the arrival time of the outburst has been delayed by a few hundred years due to the light echo effect. Therefore the flare must have erupted between the 14th and 17th centuries.
Astrophysicists propose that flares periodically blast out from the black hole as chunks of matter fall into it from an accretion disk of debris madly whirling around the black hole. Hubble Space Telescope witnessed the decaying “light-train” of one such infalling piece around a stellar mass black hole in 2001.
Or, possibly immense magnetic fields around the black hole triggered the flare. Like the fields around our sun, the black hole’s magnetic fields should periodically “reconnect.” This would explosively propel material away from the black hole.
NASA’s Chandra X-ray observatory has witnessed the central black hole hiccuping X-ray flares. But they are that are about 1/100,000th the intensity of the Renaissance super-burst say the researchers.
Will the central black hole repeat this superstar performance in the near future? “Stay tuned” say the researchers.
Image (top): The X-ray “echo” as detected by researchers at Kyoto University (Masayoshi Nobukawa et al.). Other images credited to NASA.