[cletus]

The numbers here are just staggering:

- Black hole merger occurred 3 billion light years away

- Two solar masses were converted to energy

- Briefly 10^34 megatons of energy were released every second

This is hard to intuitively wrap your head around because we think of space as constant. Something like this can distort space itself. Amazing stuff.

[kstrauser]

> - Briefly 10^34 megatons of energy were released every second

That quote caught my eye too. What's the full unit on that? Is that literally the "m" you'd plug into E=mc^2, or was there an elided "...of TNT", like we'd use to describe nuclear weapons?

[Cerium]

It appears it is "... of TNT". Wolfram Alpha converts "10^56 ergs to imperial megatons" to a value of: 1.095×10^23 long megatons (using E = mc^2). While it converts "10^56 ergs to megatons" to a value of "2.39×10^33 megatons of TNT" which is much more like that number.

Peak luminosity from https://losc.ligo.org/events/GW170104/ Query: https://www.wolframalpha.com/input/?i=10%5E56+ergs+to+megato... Query: https://www.wolframalpha.com/input/?i=10%5E56+ergs+to+imperi...

[Florin_Andrei]

It must be TNT equivalent. One solar mass is 1.99 × 10^30 kilograms, and we know that 2 solar masses were converted in total, so 4 x 10^30 kilograms, which is far less than the "megatons" mentioned, in terms of pure mass.

I wish folks would avoid mixing military units and general relativity units like this, it's confusing.

[nategri]

I don't think it's that ambiguous.

"Megaton" isn't really used anywhere except for explosive yields, where it always means TNT. As far as the 'native unit' astrophysicists will tend to use ergs for events like supernovae.

https://en.wikipedia.org/wiki/Erg

[kstrauser]

I thought it was ambiguous in the context of an article talking about converting mass to energy. Without running the numbers, I couldn't tell if that was a unit of the input mass or the output energy.

[vog]

Or, at least give the SI unit first, then a day-to-day formulation in parentheses.

The SI units are not just more useful for scientific minded readers, but also for international readers in general, who don't share the same cultural background and hence have no feeling for these "day-to-day formulations" anyway, because it isn't their day-to-day. For example, a German author might write:

| The area is as large as 7.2 km², which are 1000 football fields.

Without the SI unit (7.2 km²), this would be very confusing. Of course, the author meant association football (soccer) fields, not American football fields. But who in the international audience would have caught that, especially if I didn't state author's national background upfront? Even more importantly, which percentage of the international readership has developed a intuition about the size of a football field?

[billforsternz]

A football field is pretty univerally understandable, it doesn't really matter what kind of football it is.

[InclinedPlane]

One kiloton of TNT equivalent in energy release is 4.2 terajoules (a megaton is 4.2 petajoules). And yes, this is the unit most commonly used for the yield of nuclear weapons.

[mowenz]

Anyone familiar enough in this area that can help me answer these questions:

-gravitational waves also propogate at c so how did they escape the event horizons from which they originated?

-what and where was/is the "more energy than all stars emit as light in the universe"--10^34 megatons--released from? From matter in the accretion disk orbiting the black holes?

-the article says these two were spinning non-uniformly. Can we know if the bh's are spinning or just the stuff around them?

[breadbox]

1. The waves didn't originate from inside the event horizons, but from the area around the black holes, where space is still very heavily warped.

2. Imagine you have two serious dents in some stiff plastic sheet. By tapping on the plastic with a hammer, you can't get rid of them, but you can sort of move the dents around. Now imagine that you maneuver the dents towards each other, so they merge into one bigger dent, and as that happens the sheet makes a dull thumping sound as the rigid material snaps into a radically different shape. That's a little like what happened here.

3. Yes, black holes maintain the spin they had before they became black holes (and in fact their angular momentum is vastly increased in the process, just like any spinning thing that reduces its radius).

[ISL]

Regarding #3, angular momentum is conserved, so it neither increases nor decreases.

[jessriedel]

He clearly means that the spin rate increases.

[andrewflnr]

Actually, can you shed angular momentum via gravitational waves?

[the8472]

Since black holes are rotationally symmetric they cannot shed angular momentum via gravitational waves since the production of those requires some asymmetry[0]. But as a sibling post pointed out they can impart some of their angular momentum on objects within the ergosphere which then may escape and carry away the energy.

[0] https://en.wikipedia.org/wiki/Gravitational_wave#Sources

[andrewflnr]

I was thinking of the two-black-hole system right before merging.

[jcims]

Sort of? http://wikipedia.org/wiki/Rotating_black_hole

[prawn]

How would a non-rotating black hole be possible? Wouldn't it be impossible for any source material to lack spin entirely? Or is it a purely theoretical thing?

[mowenz]

I like your analogy on #2, but To get to a more precise answer to the question, can't we just say the energy that was released came from the potential energy between the two?