LIGO Detects Gravitational Waves for Third Time • Hacker News Board

Re: LIGO Detects Gravitational Waves for Third Time

#41

Post by Cerium » Thu, Jun 01, 2017, 5:41 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?

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...

Re: LIGO Detects Gravitational Waves for Third Time

#42

Post by lnx01 » Thu, Jun 01, 2017, 5:42 PM UTC

CodeCube wrote: post #32

nurettin wrote: post #28

How does LIGO separate vibrations caused by a nearby truck from whatever reading that is required for gravitational waves?

This is a complete guess, as I don't have any firsthand knowledge ... but I can only imagine that they have a whole array of seismographs on the premises, which they can use to clear noise from the main LIGO readings they are interested in. Curious to know if this is the case from anyone who happens to know one way or the other :) edit: the more I think about it, the more I think that random vibrations from passing t…

Actually, I think it's measuring the intensity of light between two points. It has two perpendicular lasers of some wavelength which then interfere with one another. If they interfere perfectly you measure a zero, if the interference is off by some amount you measure a deviation in intensity from the i^ or the j^ direction.

You can eliminate passing trucks, earth tremors, mining, asteroid impacts etc simply by applying a band-pass filter that excludes measurement frequencies outside of the range predicted by the equations.

No expert though, just guessing.

Re: LIGO Detects Gravitational Waves for Third Time

#43

Post by lifeformed » Thu, Jun 01, 2017, 5:42 PM UTC

lnx01 wrote: post #22

teraflop wrote: post #18

Earlier quoted context omitted.

> 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?

It would take far long than that, and I think all the black holes would evaporate before then.

Re: LIGO Detects Gravitational Waves for Third Time

#44

Post by russdill » Thu, Jun 01, 2017, 5:43 PM UTC

netcraft wrote: post #35

Great veritasium video about this latest wave: https://www.youtube.com/watch?v=NVKO7UCIlgs What is involved with increasing sensitivity I wonder? Is it purely lengthening the arms? or are there other advancements required? Hopefully one day we can have these things in space, isolated from noise and curvature of the earth and no need for vacuum equipment.

Secret signals? What secret signals?

Re: LIGO Detects Gravitational Waves for Third Time

#45

Post by [deleted] » Thu, Jun 01, 2017, 5:47 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?

[deleted]

Re: LIGO Detects Gravitational Waves for Third Time

#46

Post by iaw » Thu, Jun 01, 2017, 5:49 PM UTC

mudil wrote: post #40

Here's what I don't understand. In the first detection, they mentioned that two black holes collapsed, emitted gravitational waves, and the resulting combined mass was less than then sum of two previous masses because energy was spent on gravitational wave generation. Hence it means, that due to gravitational interactions, objects leak mass. Now, we know that every object in the universe is gravitationally related to…

E = mc^2

"Mass" in a blackhole is not the same as mass here on earth. The likely answer to your question is that the mass was converted to energy in the form of gravitational waves.

Re: LIGO Detects Gravitational Waves for Third Time

#47

Post by iaw » Thu, Jun 01, 2017, 5:50 PM UTC

lnx01 wrote: post #42

CodeCube wrote: post #32

Earlier quoted context omitted.

This is a complete guess, as I don't have any firsthand knowledge ... but I can only imagine that they have a whole array of seismographs on the premises, which they can use to clear noise from the main LIGO readings they are interested in. Curious to know if this is the case from anyone who happens to know one way or the other :) edit: the more I think about it, the more I think that random vibrations from passing t…

Actually, I think it's measuring the intensity of light between two points. It has two perpendicular lasers of some wavelength which then interfere with one another. If they interfere perfectly you measure a zero, if the interference is off by some amount you measure a deviation in intensity from the i^ or the j^ direction. You can eliminate passing trucks, earth tremors, mining, asteroid impacts etc simply by applyi…

This is pretty close to the setup I recall. It blows my mind that they have a visual link that long.

Re: LIGO Detects Gravitational Waves for Third Time

#48

Post by smortaz » Thu, Jun 01, 2017, 5:58 PM UTC

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]

Re: LIGO Detects Gravitational Waves for Third Time

#49

Post by nonbel » Thu, Jun 01, 2017, 5:58 PM UTC

eaq wrote: post #6

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 to collaborating astronomers [20] for the purpose of searching for a transient counterpart. About 30 groups of observers covered the parts of the sky localization using ground- and space-based instruments, spanning from γ ray to radio frequencies as well as high energy neutrinos [21]." https://dcc.ligo.org/LIGO-P170104/public

Regarding the earlier detection:

>"At 11:23:20 UTC, an analyst follow-up determined which auxiliary channels were associated with iDQ’s decision. It became clear that these were un-calibrated versions of h(t) which had not been flagged as “unsafe” and were only added to the set of available low latency channels after the start of ER8. Based on the safety of the channels, the Data Quality Veto label was removed within 2.5 hours and analyses proceeded after re- starting by hand." http://ligo.elte.hu/magazine/LIGO-magazine-issue-8.pdf

So both times humans had to take special action for the detection to "count". I really wonder about whether the null model they are using is appropriate/relevant here.

Also, the other thing I have been concerned about is the lack of any corroborating evidence that these signals are truly generated by inspiraling black holes(gamma ray bursts, etc). Apparently, in this case the above-mentioned miscalibration has impeded that effort:

>"The event candidate was not reported by the low-latency analysis pipelines because re-tuning the calibration of the LIGO Hanford detector is not yet complete after the holiday shutdown. This resulted in a delay of over 4 hours before the candidate could be fully examined. We are confident that this is a highly significant event candidate, but the calibration issue may be affecting the initial sky maps. We will provide an update in approximately 48 hours which may include an improved sky map." https://gcn.gsfc.nasa.gov/other/G268556.gcn3

I can't tell from that text file whether they got corroborating evidence or not. IANAP though.

Re: LIGO Detects Gravitational Waves for Third Time

#50

Post by lnx01 » Thu, Jun 01, 2017, 5:59 PM UTC

mudil wrote: post #40

Here's what I don't understand. In the first detection, they mentioned that two black holes collapsed, emitted gravitational waves, and the resulting combined mass was less than then sum of two previous masses because energy was spent on gravitational wave generation. Hence it means, that due to gravitational interactions, objects leak mass. Now, we know that every object in the universe is gravitationally related to…

Objects do no leak mass due to gravitational interaction, but gravitational interaction always expends some energy. The earth orbiting the sun expends some energy in the form of gravitational waves but it's miniscule. It is enough though that the earth's orbit decays measurably.

This experiment is designed to detect the waves carrying away that lost energy, but you need a cataclysmic event like the collision of two black holes for the event to be energetic enough that you can measure it and measure it on astronomical scales.

This is the reason why LIGO must be so sensitive, we hope not to experience a nearby black hole collision for as long as we're alive, so we must measure a distant one.

Mass and energy are interchangeable but they both must be conserved.

They didn't leak mass, the missing mass became energy in the form of emission (photons and some kinetic) and gravitational waves, which until recently we could not detect. The equations suggested they were there though, and that's why these experiments were funded, a way to find out if the uncertainties in the standard model were true or not. At this point, our model seems to predict what we track in reality with this experiment.

Of course, there are gaps in the standard model and they must all be tested. LHC is also looking at the gaps, and confirming/invalidating them.