That Gas Cloud Near Our Black Hole Is Not What We Thought It Was
I’m very disappointed.
The huge chunk of gas (called G2) that was supposed to be engulfed by the supermassive black hole at the center of our galaxy in a wonderful display of pyrotechnics never did and now they think they know why. It’s really a star.
In 2011 astronomers noticed a fuzzy hot smear that appeared to be a cloud of gas near our 4 million solar mass, black hole called Sagitarius (Sag A). That wasn’t the exciting part though. Orbital calculations revealed that it could be swallowed in 2014 by the black hole or its accretion disk, putting on a once in a lifetime display before disappearing forever. This got them very excited because such an event has been observed before but only in distant galaxies many trillions of times farther away. Sag A does have snacks fairly often but they’ve only been antepasto; this time it would be a full plate of lasagna with the little meatballs inside.
This year everyone was ready for this to happen. Countless land and space-based observatories were ready to watch and record this amazing event. When the time came for G2 to be pulled into the black hole’s maw………nothing happened, not one tiny flare was observed, not even a gratified burp.
So what the hell happened?
It looks now to be fairly certain that the cloud of gas is actually what some astronomers have suspected for a while, a star. Not just an ordinary star though, they would have known that from the get go. It appears to be a star that was once a binary pair that has merged into a much bigger single star. This star in turn is surrounded by an envelope of gas and dust. A simple diffuse cloud would likely have never survived this last go-round around the black hole which would have ripped it apart with its immense tidal forces. To see what this would have looked like check out this beautiful (but now irrelevant) video simulation. The much more gravitationally compact star however apparently had the fortitude to withstand this close encounter, escaping with only minor damage astronomers described as a “bruise”.
Other large stars in the neighborhood may also be similar merged beasts meaning that this could be a new class of star that is created from a binary system that has been thrown together by the gravity of the super-massive black hole it is bound to.
So, even though it was mighty disappointing that we didn’t have an extra-special fireworks display this summer at least…..umm…at least….I got nothing.
Image Credit: ESO/S. Gillessen/MPE/Marc Schartmann