Black holes are not theoretical. They’re real. The first ever identified, and still the surest, floats directly overhead these nights at 9:30 p.m. It’s Cygnus X-1, so named because intense X-rays stream from that spot as material from a companion star spirals into the black hole’s accretion disk, giving off yelps of protest.
But let’s not fool around with a mere 12-solar-mass black hole. This weekend it’s truly easy to find the biggest one in our entire galaxy. That’s the supermassive black hole named Sagittarius A star – which is written Sagittarius A*.
There’s probably a supermassive black hole in the core of every galaxy. Ours has the weight of four million Suns. It marks the spot around which everything you see in the night sky revolves, once every 240 million years or so. Well, not quite everything; there’s a single smudgy spot directly overhead these nights at about 1:30 a.m., and this alone does not circle that black hole. That’s because that little smudge is the only naked-eye object not in our galaxy. It’s our sister galaxy, Andromeda – but we won’t let her distract us.
Here’s how to stare at the center of our galaxy, at the black hole. Friday night or Saturday night, September 14 or 15, look at the first bright star to the left of the Moon. That’s the planet Saturn, and it is floating right in front of that supermassive black hole. If you could travel at the speed of light, it would take one hour to reach Saturn, and if you continued at that velocity beyond the ringed planet and kept going for another 25,000 years, you would reach Sagittarius A* in the galaxy’s core.
It’s cool to be able to salute the spot around which every naked-eye object in the heavens revolves. And yet, that supermassive black hole is unusually quiet. Unlike the much smaller one overhead, it does not emit X-rays, because these days it is not gobbling up atoms from any stars. There are truly weird things in its vicinity, such as a double bubble of lethal gamma rays that is so large, it occupies half of our southern sky these nights! Also in its vicinity are violent electromagnetic emissions that are the signature of antimatter colliding with ordinary matter. Yet these powerful antimatter geysers are not emanating from the Milky Way’s central black hole, but from a puzzling empty region not too far from it.
So there’s lots of mystery in that direction behind Saturn: deep, troubling enigmas. And yet that four-million-solar-mass black hole just sits there quietly and heavily, as innocent as Jabba the Hutt.
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