How do they know it’s black holes colliding and not just large stars?
Astrophysicists unveil glut of gravitational-wave detections
41–50 of 108 posts
Re: Astrophysicists unveil glut of gravitational-wave detections
#42Interesting how, even with three LIGO observatories, there is still a 15% false positive rate. How many more observatories are needed to reduce this to a negligible number?
LIGO collaboration member here: this is a tunable knob, independent of the number of detectors, that we've set very intentionally based on feedback from astronomers who want to follow up with optical/gamma/neutrino instruments following our BNS detections. We could reduce our false positive rate to a negligible number today, at the cost of _not_ reporting many likely discoveries. Also, a minor point but there are onl…
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Re: Astrophysicists unveil glut of gravitational-wave detections
#43the Gravitational Observatories are so impressive to me - I can remember reading about them being theoretical well before LIGO ever started construction, and the fact that theyre here and working just like we expected is so amazing. I can't wait until we have LISA in space! But its so strange when we shut it off to do upgrades and stuff - like I totally understand why we have to do it, but its like we finally turned…
LIGO collaboration member here: we focus on maximizing the cumulative number of detections over time, and it turns out that by turning the detector off for a year to upgrade it, we can increase the sensitivity so much that a year after that we will have more total detections than if we had left it running continuous for two years. So you also have to think about all the distant/faint signals we would never be able to…
Thanks for the info! I expected it was something like this, that you expect the increased sensitivity is worth it. I just wish we had more observatories running in different sensitivities - we've just got to get the cost down, thats all :)
I didn't know about GEO, thanks for that!
Re: Astrophysicists unveil glut of gravitational-wave detections
#44Earlier quoted context omitted.
Has LIGO ever responded to Sabine Hossenfelder's claims? http://backreaction.blogspot.com/2019/09/whats-up-with-ligo....
I thought that 2019 article is now "answered" by the fact that we have multi-messenger observations of gravitational wave events that confirm fading light curves.
I believe we still only have one multi-messenger observation. One observation has infinite variance =P.
They're ALSO not independent observations, though. The LIGO observation was made, and then the directive was "go look for correlating events". That's a dependent observation.
To be truly independent, they would have to inject synthetic data (say 3x) into the observation reports and make sure that the multi-messenger results don't correlate with the synthetic data, much like GP says they did "at the beginning of LIGO" with internal (non-multimodal) signals.
This would have the side benefit of making the analysis pretty simple to do (just a chi-squared analysis) and you don't have to have a PhD in signals analysis with a specialization in the filters used by LIGO to believe with a high confidence that 1) GWs exist and 2) LIGO is actually measuring GWs.
Re: Astrophysicists unveil glut of gravitational-wave detections
#45the Gravitational Observatories are so impressive to me - I can remember reading about them being theoretical well before LIGO ever started construction, and the fact that theyre here and working just like we expected is so amazing. I can't wait until we have LISA in space! But its so strange when we shut it off to do upgrades and stuff - like I totally understand why we have to do it, but its like we finally turned…
> the thought that there are events that are going on right now that we will never be able to detect because we arent listening gives me major FOMO. I can relate to the sentiment but keep in mind that human timescales are downright puny compared to cosmological timescales. And there's lots of stuff going on all the time (lots is an understatement) so I would say you won't lose much turning off the detector for a year…
I totally understand this from a rational standpoint, but if you take that to its logical conclusion, you expect that nothing will happen in that year that is very interesting or rare, so why look at all?
Sure, our timescales are nothing, making what we have even more valuable, no? We've missed out on a whole lot of observations - we have a lot of catching up to do!
Re: Astrophysicists unveil glut of gravitational-wave detections
#46the Gravitational Observatories are so impressive to me - I can remember reading about them being theoretical well before LIGO ever started construction, and the fact that theyre here and working just like we expected is so amazing. I can't wait until we have LISA in space! But its so strange when we shut it off to do upgrades and stuff - like I totally understand why we have to do it, but its like we finally turned…
Why would you have FOMO? Why is any particular gravitational wave important enough that you'd worry about missing it? I'm not trying to hassle you here, I'm genuinely perplexed by this attitude.
I replied to a sister comment similarly, but the one resource that we are severely limited by is time. There were events that were far more common in the early universe that we may never see now. Rare things could happen at any time.
The reality is that we can't observe 100% of the time for resource constraints and that the cost/benefit of upgrading is totally worth it in the long run - rationally speaking its the right move. I will just always wonder what we are missing out on that we might never have the opportunity to observe again - or maybe not in our lifetimes.
Re: Astrophysicists unveil glut of gravitational-wave detections
#47How do they know it’s black holes colliding and not just large stars?
Maybe electromagnetic signals can disambiguate the two phenomena?
Re: Astrophysicists unveil glut of gravitational-wave detections
#48LIGO is a huge milestone. Turning it on is like the moment Galileo pointed his telescope to the moon. This is a new class of instruments observing the universe in a medium that was never utilized before. Using gravitational waves can observe things that cannot be seen before, like stars behind the dust clouds. It opens a new window to the world. We might finally be able to “see” dark matter. May be able to see the gr…
I hope to live long enough to see the evolution of interferometers that will be to LIGO as HST was to Galileo's telescope.
Re: Astrophysicists unveil glut of gravitational-wave detections
#49the Gravitational Observatories are so impressive to me - I can remember reading about them being theoretical well before LIGO ever started construction, and the fact that theyre here and working just like we expected is so amazing. I can't wait until we have LISA in space! But its so strange when we shut it off to do upgrades and stuff - like I totally understand why we have to do it, but its like we finally turned…
LIGO collaboration member here: we focus on maximizing the cumulative number of detections over time, and it turns out that by turning the detector off for a year to upgrade it, we can increase the sensitivity so much that a year after that we will have more total detections than if we had left it running continuous for two years. So you also have to think about all the distant/faint signals we would never be able to…
That makes me think of the "Wait calculation" in https://en.wikipedia.org/wiki/Interstellar_travel#Wait_calcu...
Re: Astrophysicists unveil glut of gravitational-wave detections
#50Earlier quoted context omitted.
Do you publish some number about how sure you are?
Yes, we carefully explain the statistical confidence of our detections in each discovery paper, and there are dozens of methods papers that go into excruciating detail on those techniques. Prior to our first detection, the overwhelming prime directive of our collaboration was _not to make a false detection_ and we went to insane lengths to avoid one; e.g., we had a small team of people secretly injecting false signal…
When I see LIGO graphs they always appear linear - the change in frequency is linear with time.
But with time dilation as black holes near each other, shouldn't the frequency change be exponential? Or does it cancel out - the frequency goes up as they get closer, and then time dilation lowers it back as it dilates into infinity?