91–100 of 111 posts
> These are collisions that produce more power than is radiated as light by all the stars and galaxies in the universe at any given time. Astounding, especially given that these are happening at regular intervals in our "neighborhood".
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> - 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?
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.
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?
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Regarding #3, angular momentum is conserved, so it neither increases nor decreases.
Actually, can you shed angular momentum via gravitational waves?
[0] https://en.wikipedia.org/wiki/Gravitational_wave#Sources
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Black holes have mass, just like any other object in the universe - like a star, or a planet, or the sun. Consequently, they follow orbits just as any other mass would. In some cases, they're the local most massive object and any other masses move more in response. Other times they are near other black holes, and they orbit one another until they collide and merge. What makes black holes different is their density. T…
I guess this was the biggest question answering piece to me. When I think of a black hole, I assume it has a gigantic mass, enough that it's always the most massive local object, and subsequently pulls in all other things. I didn't realize that might not be the case. As black holes "absorb" everything that "falls" into them, do they continue to build mass then?
The sun is not pulling in the earth. Earth orbits a common barycenter with the sun. That barycenter happens to be inside the sun, but the sun is also orbiting around it.
So a small object orbiting a bigger object is an approximation. Orbiting their common center of mass is a better approximation. This is more easily visible in the pluto-charon system.[0]
The same of course applies to black holes. Them being heavier than most other objects in their vincinity does not render them immobile any less than the sun being the most massive object in the solar system renders it immobile.
[0] https://en.wikipedia.org/wiki/Charon_(moon)#/media/File:Plut...
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The actual space in which the planet resides stretches and shrinks as the gravitational wave passes through it. The fabric of space itself is the medium that the wave travels through. However, the affect is incredibly tiny, even though it was generated by two black holes colliding. The size of the distortion experienced here on Earth is 1000x smaller than the width of a proton! It's mind boggling. I think I remember…
The resolution of the detector is 1/1000th the width of a proton. The signal they see is much bigger: the length of 4km long arms stretch and then shrink about 1/10 the width of a proton. How do they know it is really space/time changing and not an earthquake? They have two detectors over 1000 miles apart from each other: https://en.wikipedia.org/wiki/LIGO#/media/File:Simplified_di...
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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.
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…
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The planet gets shorter, then longer, then shorter again... All that in a single direction, while the size on the other two directions stays the same.
That is incorrect. What you describe is a dipolar oscillation. The simplest gravitational waves woudl have a quadrupole moment: stretch in one direction while contracting in the direction perpendicular to it. Have a look at https://en.wikipedia.org/wiki/Gravitational_wave where there is an animation illustrating the simplest case.
Didn't think about that before.
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Actually, can you shed angular momentum via gravitational waves?
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
The paper describing the event is available to the public at https://dcc.ligo.org/LIGO-P170104/public The instrument data of this event is also available to the public at https://losc.ligo.org/events/GW170104/
Thanks >"GW170104 was first identified by inspection of low-latency triggers from Livingston data [15–17]. An automated notification was not generated as the Hanford detector’s calibration state was temporarily set incorrectly in the low-latency system . After it was manually determined that the calibration of both detectors was in a nominal state, an alert with an initial source localization [18,19] was distributed…
In terms of corroborating evidence, remember that the two independent LIGO detectors - 3000km apart - saw the event within 10ms of each other. That's enough corroborating evidence for a lot of people. The NASA text file you link shows no observed electromagnetic counterpart, but that's expected: unfortunately the best models so far for black hole coalescences predict very little or no electromagnetic emission - so although EM partners were informed, the chances of them seeing anything were slim. Other predicted sources of gravitational waves, like as-yet unseen binary neutron star coalescences, are more likely to emit EM radiation and stand a chance of being witnessed by conventional observatories as "corroboration".
#/media/File:Pluto-Charon_System.gif){kind=link}