One of the things that has been puzzling astrophysicists concerning Sagittarius A* – the massive black hole at the center of the Milky Way – is its seeming lack of activity, when compared to similar objects in other galaxies. Now, experts are analyzing what would happen if the black hole were to wake up.Over time, scientists measured Sagittarius A*'s mass at around 4 million solar masses, which makes it relatively small by comparison. For a galaxy the size of the Milky Way – 120,000 light-years across – one would expect to detect a supermassive black hole at least billions of solar masses in weight.
At the same time, high-energy measurements of the radio source have established that its level of radiation activity is several billion times weaker than it should be. Experts have always associated this with some kind of slumber. However, there are evidences that object occasionally returns to life.
Evidences collected from the very structure of the Milky Way appear to indicate that Sagittarius A* had an intense outburst about three centuries ago, producing an extremely massive and powerful flare.
However, confirming these theories is not as easy as proposing them. The galactic core is obscured by tremendously large clouds of hydrogen and dust, so conducting astronomical observations is extremely difficult. This is also true if scientists use infrared, X-ray, radio or gamma-ray telescopes.
Distance is another factor, since our location is around 24,000 light-years away from Sagittarius A*. However, by combining the multi-wavelength observation powers of several telescopes, it is possible to pierce the galactic core, and observe the black hole in its natural habitat.
“We have wondered why the Milky Way’s black hole appears to be a slumbering giant. But now we realize that the black hole was far more active in the past. Perhaps it’s just resting after a major outburst,” Kyoto University investigator Tatsuya Inui explains, quoted by Daily Galaxy.
He and his team used the European Space Agency's (ESA) XMM-Newton X-ray Observatory, the NASA Chandra X-ray Observatory, and the Japan Aerospace Exploration Agency's (ESA) Suzaku and ASCA X-ray satellites to conduct this investigation.
Seeing how only 300 years passed since the last time Sagittarius A* flared up, it stands to reason that the object would want to take a break before resuming its activities. At the same time, researchers observed the seeds of future flare-ups.
These were X-ray emissions originating just outside the black hole's event horizon, where matter accumulates before feeding the giant structure. As this happens, the material is heated up to millions of degrees, which causes it to release energetic radiations.