Last summer, an enigmatic gas cloud had space scientists at the edge of their seats as it migrated perilously close to our galaxy’s colossal black hole. The dusty cloud’s predicted doom was set to be one of the main astronomical events of the year, but perplexingly it seemed to have escaped the black hole’s gravitational clutches. Now, after analyzing the best images collected so far of the cloud, scientists have confirmed that it made its closest approach in May last year and indeed survived the encounter seemingly unscathed. The findings have been published in Astrophysical Journal Letters.
At the center of the Milky Way lies a supermassive black hole, known as Sagittarius A* (Sgr A*), with a mass four million times that of our sun. Back in 2011, scientists discovered a dusty cloud of gas, later named G2, several times the mass of Earth that appeared to be zooming fast towards this object. After tracking G2’s path, it seemed to be undergoing spaghettification, or the noodle effect, whereby the black hole’s extreme gravitational field was grossly stretching and elongating the cloud, much like pasta.
In fact, the cloud appeared to be so distended that the approach was not a single event, but rather a process extending over a period of one year. Scientists therefore predicted that the hungry black hole would dramatically tear apart G2 as it made its daring encounter, possibly as early as 2013. But, perhaps disappointedly for those expecting fireworks, G2 survived its passage and continued merrily on its orbit around Sgr A*, completely unaffected by the event.
This resilience led scientists to reevaluate G2’s identity since a free-floating gas cloud would not have made it through the encounter. At first, astronomers postulated that it could be a pair of binary stars (two stars orbiting around a common center of mass) that merged into a huge star. But several years of observations using ESO’s Very Large Telescope (VLT) and other instruments have led scientists to believe it could be a young, compact star with a massive core that is still attracting more matter, or accreting material.
Interestingly, despite earlier data suggesting that the cloud was being dramatically stretched by Sgr A*, the latest observations in infrared show that G2 was in fact compact both before and after its closest approach, as it swerved around the black hole. This ties in with other measurements from the VLT, which show that the behavior of the material being accreted into Sgr A* seems to be stable and not disturbed by material from G2. If the colossal black hole was indeed being fed by matter from the cloud, we would expect to see flaring and increased activity.
“It was amazing to see that the glow from the dusty cloud stayed compact before and after the close approach to the black hole,” lead author Monica Valencia-S. said in a statement.
Alongside providing us with the most detailed images so far of the event, VLT data also allowed scientists to estimate G2’s velocity during its encounter. As it sped towards Sgr A*, the cloud was travelling away from us at around 10 million kilometers (6 million miles) per hour, but after it swung around the black hole, it was headed in our direction at speeds of 12 million kph (7.5 million mph).
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