cientists call this gravitational wave signal as well.
The signal itself may not look like much, but it contains multitudes. The shape and strength of the signal depends on the individual masses of the black holes, how far away they are from Earth, and also how quickly they merge. From all this the LIGO scientists (along with their VIRGO collaborators) found that they were 31 and 19 times the mass of the Sun each.
What gets the hair on the back of my neck standing on end is what happens at the moment of coalescence. The equations governing relativity predict that a large fraction of the masses of the black holes is converted into gravitational wave energy. The thing is, a tiny bit of mass converts into a lot of energy, thanks to that whole E being equal to mc2 thing. “c2” means the speed of light squared, and that’s an unholy huge number. So when you take a lot of mass and convert it to energy, the numbers get, well, terrifying.
Two times the mass of the Sun was converted to energy in this event. The mass of the Sun is 2x1030 kg, or, if you prefer, two octillion tons. Converted to energy, that’s 2x1047 Joules. How much energy is that?
It’s two thousands times the amount of energy the Sun emits over its entire lifetime. And these merging black holes blasted that much energy out in less than a second. In fact, for that brief fraction of a second, just this single event radiated away roughly as much energy as all the stars in the Universe combined. All of them. Everywhere.
I’m glad they were three billion light-years away. By the time the signal got here, it had weakened to the barest whisper of the roar it once was. But near the event, right there next to those black holes, this was the single most powerful event in the entire Universe. At that moment.
I have no words for this, and in fact I cannot comprehend it. Oh, I can do the math, put the numbers together, compare it to various other things. But to truly grasp this, to viscerally internalize it, is far, far beyond what our puny ape minds can handle.
The Universe dwarfs us.
But let me add something here, because it's beautiful.
Black holes spin. They have to; they form from stars that explode (usually), and these stars are spinning. When the stellar core collapses the spin is magnified for the same reason that an ice skater's spin increases rapidly when they draw their arms in. This is called "conservation of angular momentum," and basically says that when something is spinning, that spin rate will go up if the size of the object shrinks.
Both of the black holes that merged were spinning. But they were also in orbit around one another. Now, here's an amazing thing: If the two black holes were spinning in the same direction as they orbited each other (say, they both spun clockwise looking down from above, and their orbit around each other was also clockwise), then their merging will be a bit slower. It's tougher to slough off the angular momentum they have, so the merger is sluggish.
However, if one or both of their spins are not aligned with their orbital spin, the merger happens more quickly. This spin-orbit alignment (or lack thereof) is reflected in the signal we detect here on Earth; the speed of the merger tells us this. And in this case, although it's not rock-solid, it appears as though the spins were not aligned.
That's interesting. If these two stars formed together as a pair of normal but ridiculously massive stars orbiting each other, then their mutual gravity would align their spins over their brief lifetimes. The signal we saw seems to weigh against that.
Instead, it may be they formed separately in a dense cluster of stars. They exploded as supernovae separately (though, again, see my previous post about that), and over time their gravitational interaction with other stars in the cluster dropped them to the cluster center. It was there that they matched up, eventually becoming bound to each other, circling in a dance that would, after several billion years, result in the catastrophic merging and explosion of energy we detected billions of years after that