LIGO Detects Gravitational Waves for Third Time • Hacker News Board

Re: LIGO Detects Gravitational Waves for Third Time

#61

Post by onebigbug » Thu, Jun 01, 2017, 6:56 PM UTC

lnx01 wrote: post #21

gjem97 wrote: post #10

> 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".

It's like the difference between an explosion of TNT and a atomic bomb, but on a much larger scale. Stars like our sun spend ~10billion years turning a portion of their mass into energy. Most stars are like ours, small, dim and weak in power output. Our sun will not go supernova and will not collapse into a black hole when it dies, it will simply go nova and end up as a dwarf star in a nebula. But, now imagine two bl…

> But, now imagine two black holes each a billion times as massive as the sun turning all their mass into energy in a couple of seconds.

Sure, lemme just take off my "good at socializing with apes and running for long periods of time after antelope" hat and put on my "Cosmological scale" hat.

Huh, I seem to have misplaced that one. And the one I'm currently wearing is oddly well affixed.

Re: LIGO Detects Gravitational Waves for Third Time

#62

Post by kevin_thibedeau » Thu, Jun 01, 2017, 7:14 PM UTC

ChuckMcM wrote: post #29

BurningFrog wrote: post #23

Earlier quoted context omitted.

These waves are extremely small, and we've just managed to build instruments sensitive enough to detect the very biggest ones. Earth bound instruments will no doubt get better, but to get a real jump in quality, you need instruments in the stillness of space: http://www.einstein-online.info/spotlights/eLISA

The info on eLISA is great. I am just waiting for the $10,000 shielding for high end speakers to keep gravity waves from interfering with the acoustic purity of the sound they produce. :-)

You absolutely must keep your record player suspended from glass fiber in a vacuum chamber to avoid any unwanted coloration. Just takes 30 minutes to pump down when you want to flip sides.

Re: LIGO Detects Gravitational Waves for Third Time

#63

Post by marcosdumay » Thu, Jun 01, 2017, 7:35 PM UTC

castis wrote: post #57

When a gravitational wave hits the earth, does the planet oscillate in place for the duration, or is our position in the cosmos displaced, or something else altogether?

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.

Re: LIGO Detects Gravitational Waves for Third Time

#64

Post by japhyr » Thu, Jun 01, 2017, 7:40 PM UTC

smortaz wrote: post #48

FYI - if you want to check out the data, the code, even an audio of the wave checkout: https://notebooks.azure.com/roywilliams/libraries/LIGOOpenSc... It's a Jupyter notebook that anyone can clone and run. [edit: updated link]

It's just awesome to see these notebooks released. I'm not going to play with them, but I love that people are able to. It makes me much more confident in the results that are announced, and I hope this approach to doing science becomes the norm.

Re: LIGO Detects Gravitational Waves for Third Time

#65

Post by nategri » Thu, Jun 01, 2017, 7:49 PM UTC

Florin_Andrei wrote: post #58

kstrauser wrote: post #27

Earlier quoted context omitted.

> - 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.

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

Re: LIGO Detects Gravitational Waves for Third Time

#66

Post by Sharlin » Thu, Jun 01, 2017, 8:19 PM UTC

shortstuffsushi wrote: post #25

lnx01 wrote: post #13

Earlier quoted context omitted.

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 the most massive local object in the solar system, by a very large margin, but does not pull in all other things. Or, well, it does pull, obviously, but it turns out that objects under gravity end up on Keplerian orbits if they have sideways velocity to begin with.

Re: LIGO Detects Gravitational Waves for Third Time

#67

Post by privong » Thu, Jun 01, 2017, 8:22 PM UTC

specialp wrote: post #37

privong wrote: post #14

Earlier quoted context omitted.

> If you're getting 10 events/second with a device like this, you probably overpaid for sensitivity Aside from issues processing and disentangling the overlapping events in a situation with that high of an event rate, more events would not be bad, so I'm not sure I'd call it "overpaying". Imagine the kind of population demographics that could be built up if we were detecting that many events.

Keep in mind that when LIGO was built at tremendous expense, gravitational waves were never conclusively detected, and just to get to this sensitivity it was a feat of engineering. It was unknown how long it would be or if they would ever detect a wave. Just detecting the initial wave was one of the most important measurements in the history of physics. Now that we know that gravitational waves exist, and can give us…

I'm aware of the context for the GW detections and the expense, etc. I was making a general philosophical point about "overpaid", not commenting specifically on the LIGO cost-benefit analysis.

Re: LIGO Detects Gravitational Waves for Third Time

#68

Post by dwaltrip » Thu, Jun 01, 2017, 8:29 PM UTC

castis wrote: post #57

When a gravitational wave hits the earth, does the planet oscillate in place for the duration, or is our position in the cosmos displaced, or something else altogether?

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 hearing that there is immense distortion in the area immediately around the collision, but I'm not certain.

Re: LIGO Detects Gravitational Waves for Third Time

#69

Post by InclinedPlane » Thu, Jun 01, 2017, 8:33 PM UTC

kstrauser wrote: post #27

cletus wrote: post #12

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.

> - 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?

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.

Re: LIGO Detects Gravitational Waves for Third Time

#70

Post by danbruc » Thu, Jun 01, 2017, 8:44 PM UTC

lnx01 wrote: post #21

gjem97 wrote: post #10

> 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".

It's like the difference between an explosion of TNT and a atomic bomb, but on a much larger scale. Stars like our sun spend ~10billion years turning a portion of their mass into energy. Most stars are like ours, small, dim and weak in power output. Our sun will not go supernova and will not collapse into a black hole when it dies, it will simply go nova and end up as a dwarf star in a nebula. But, now imagine two bl…

I think your numbers are a bit off. I am not sure about the exact numbers but I think the sun will only burn about half or so of its mass over its lifetime. Also the black holes we observed merging are stellar black holes with masses on the order of tens of solar masses, not galactic black holes with millions or billions of solar masses.