6 ms·

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 meg

by cletus 9y ago

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 9y ago
> - 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 9y ago
  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/ https://losc.ligo.org/events/GW170104/ Query: https://www.wolframalpha.com/input/?i=10%5E56+ergs+to+megatons https://www.wolframalpha.com/input/?i=10%5E56+ergs+to+megato... Query: https://www.wolframalpha.com/input/?i=10%5E56+ergs+to+imperial+megatons https://www.wolframalpha.com/input/?i=10%5E56+ergs+to+imperi...
- deleted 9y ago
  [deleted]
- Florin_Andrei 9y ago
  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 9y ago
    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 https://en.wikipedia.org/wiki/Erg
    - kstrauser 9y ago
      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 9y ago
    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 9y ago
      A football field is pretty univerally understandable, it doesn't really matter what kind of football it is.
- InclinedPlane 9y ago
  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 9y ago
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 9y ago
  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 9y ago
    Regarding #3, angular momentum is conserved, so it neither increases nor decreases.
    - andrewflnr 9y ago
      Actually, can you shed angular momentum via gravitational waves?
      - jcims 9y ago
        Sort of? http://wikipedia.org/wiki/Rotating_black_hole http://wikipedia.org/wiki/Rotating_black_hole

by cletus 9y ago

kstrauser 9y ago

> - 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 9y ago
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/ https://losc.ligo.org/events/GW170104/ Query: https://www.wolframalpha.com/input/?i=10%5E56+ergs+to+megatons https://www.wolframalpha.com/input/?i=10%5E56+ergs+to+megato... Query: https://www.wolframalpha.com/input/?i=10%5E56+ergs+to+imperial+megatons https://www.wolframalpha.com/input/?i=10%5E56+ergs+to+imperi...
deleted 9y ago
[deleted]
Florin_Andrei 9y ago
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 9y ago
  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 https://en.wikipedia.org/wiki/Erg
  - kstrauser 9y ago
    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 9y ago
  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 9y ago
    A football field is pretty univerally understandable, it doesn't really matter what kind of football it is.
InclinedPlane 9y ago
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 9y ago

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 9y ago
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 9y ago
  Regarding #3, angular momentum is conserved, so it neither increases nor decreases.
  - andrewflnr 9y ago
    Actually, can you shed angular momentum via gravitational waves?
    - jcims 9y ago
      Sort of? http://wikipedia.org/wiki/Rotating_black_hole http://wikipedia.org/wiki/Rotating_black_hole