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LIGO Detects Gravitational Waves for Third Time

caltech.edu

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Re: LIGO Detects Gravitational Waves for Third Time

#21

Post by lnx01 »

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 black holes each a billion times as massive as the sun turning all their mass into energy in a couple of seconds.

10billion years to convert 99% of the mass of the sun to energy versus 10 seconds to covert 2 billion times the mass of the sun to energy. Now it makes sense that the power output is more in one second than the whole universe put together.

Solar fusion is on the cosmic scale a very slow way to convert mass to energy. It's so slow that we humans have been 'on the brink' of harnessing it for power generation for decades.

Now imagine if we could build two nano-black-holes and let them collide....

Re: LIGO Detects Gravitational Waves for Third Time

#22

Post by lnx01 »

teraflop wrote: post #18
shortstuffsushi wrote: post #9

Somewhat naive questions, as I know very little about astronomy. Do black holes "move?" How is it that they could merge if they're stationary, unless they're pulling each other in I guess? If black holes are indeed pulling in everything, does that mean the whole universe would eventually be one giant black hole?

> Do black holes "move?" Yes, like any other massive objects, black holes can have velocity and momentum. Two black holes, or a black hole and another object like a star, can orbit each other in a way that almost follows Newton's laws. > How is it that they could merge if they're stationary, unless they're pulling each other in I guess? This gets at what makes LIGO's findings interesting. Two black holes merge if the…

If we scale time to one-trillion-quadrillion years into the future, isn't is possible that all mass in the universe eventually coalesces into a massive universal super black hole? Or, does the expansion of the universe outstrip that?

Re: LIGO Detects Gravitational Waves for Third Time

#23

Post by BurningFrog »

wolfram74 wrote: post #2

Anyone familiar with this branch of astronomy want to explain why one detection in a volume on the order of 27 billion cubic light years is reasonable? Are they still processing data and will find more events? Is the sensitivity highly anisotropic so the detection volume is significantly smaller? Or are events like this just really conveniently rare that we get about 1 every data gathering interval?

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

Re: LIGO Detects Gravitational Waves for Third Time

#24

Post by dwaltrip »

eanzenberg wrote: post #20
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.

It's a balance between cost and sensitivity, and remember that 1 discovery would prove the experiment a "success". I think the way it was planned and executed was great. Also, I think the proof that gravitational waves is far more exciting than comparing gravity wave signatures among a sample of celestial collisions.

This is sort of like saying that "proving that stars emit light" is more exciting than using better and better telescopes to compare electromagnetic wave signatures of different light emitting celestial objects.

We will likely learn a great many things over the coming decades with this new way of looking at the universe, many of which we couldn't have even guessed we would learn!

Re: LIGO Detects Gravitational Waves for Third Time

#25

Post by shortstuffsushi »

lnx01 wrote: post #13
shortstuffsushi wrote: post #9

Somewhat naive questions, as I know very little about astronomy. Do black holes "move?" How is it that they could merge if they're stationary, unless they're pulling each other in I guess? If black holes are indeed pulling in everything, does that mean the whole universe would eventually be one giant black hole?

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?

Re: LIGO Detects Gravitational Waves for Third Time

#26

Post by ehsankia »

mturmon wrote: post #3

I was at a talk by Janna Levin, astrophysicist and author of a book Black Hole Blues that describes LIGO. (E.g., https://www.nytimes.com/2016/04/18/books/review-black-hole-b... ) She gave a neat analogy between GWs, as sensed by LIGO, and an electric guitar. In the sense that a distant pluck on the string is transmitted as a wave down the string to the pickup, which senses a little wiggle in the string and amplifies…

Except imagine you're embedded on the string itself and cannot actually sense the string "moving through space". The way you have to measure it is by sensing tiny changes in distance between the left and right side of the string as it wiggles around.

The actual detail of the experiment and the precision they reach is quite fascinating. Veratisium has a pretty good video explaining it in more laymen terms [0]

[0] https://www.youtube.com/watch?v=iphcyNWFD10

Re: LIGO Detects Gravitational Waves for Third Time

#27

Post by kstrauser »

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?

Re: LIGO Detects Gravitational Waves for Third Time

#29

Post by ChuckMcM »

BurningFrog wrote: post #23
wolfram74 wrote: post #2

Anyone familiar with this branch of astronomy want to explain why one detection in a volume on the order of 27 billion cubic light years is reasonable? Are they still processing data and will find more events? Is the sensitivity highly anisotropic so the detection volume is significantly smaller? Or are events like this just really conveniently rare that we get about 1 every data gathering interval?

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. :-)

Re: LIGO Detects Gravitational Waves for Third Time

#30

Post by privong »

yodon wrote: post #17
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.

It's not that physicists wouldn't love to capture all those events, it's that the cost of building instruments like LIGO is nearly prohibitively high and the cost is a strong function of the sensitivity of the instrument. If you aim too high in your sensitivity aspirations, the cost hits a point where the experiment simply can't be funded.

> If you aim too high in your sensitivity aspirations, the cost hits a point where the experiment simply can't be funded.

Agreed. I misunderstood your meaning then; I'd interpreted your wording to mean that "overpaid" was still within the bounds of reasonable expectations for funding. "Overpaid" didn't imply "too expensive to build", to me.

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