Astrophysicists do a 3-day long AMA about the discovery of gravitational waves
np.reddit.com
np.reddit.com
To get a better understanding of what LIGO is observing, does every massive object create a gravitational wave as it moves? Do gravitational waves act similarly as to how moving a charged particle creates magnetic flux? Do we know from LIGO if gravitational waves propagate at exactly the speed of light?
with just 2 "ears" I'd expect to be only able to determine a circle, but here is the picture they released: http://www.dailygalaxy.com/.a/6a00d8341bf7f753ef01b8d19e59ad...
Do i see a warped circle, or the bottom part of one? In the latter case I wonder how they found out.
Are the L-shape sensors capable of seeing some direction depending on which way the phases shift first/last?
If you'd build one of the sensors in reverse you'd see a reversed signal, no (and in between other amplitudes)?
Given that they will have optimized the orientations of both stations this is probably how it worked and I'm seeing just part of a circle, right?
That one lonely blob might be an unlikely mirrored version?
I know this is speculative, but do you think it is possible and/or plausible that measurement precision could be improved to the point where we generate gravity waves to transmit data much as we do with EM waves?
I saw somewhere that you adjusted for cosmological redshift.
Did you also adjust for gravitational redshift as the gravity wave left the gravity well of the black holes?
What about time dilation of the wave signal caused by gravity and orbital velocity?
I would guess there is not sufficient resolution. And maybe it's beyond what's possible. But, thinking of additional avenues for measurement, and something that might be extant or require less build-out.
And now, there would be something against which to compare anomalies, were they to be measurable.
More like once in 200'000 years, actually.
> Myself and one of my supervisors had a conversation about this a few weeks ago. We did some calculations which suggest that if you were in a space-ship close to the merging black holes you would feel a force which was pretty comparable to the force you feel by standing next to a loudspeaker at a music concert. You'd feel a vibration travelling through your body, but we were pretty confident it wouldn't hurt you!
Maybe the gravitational waves wouldn't hurt, but the gammas etc would be painful. I'm reminded of Greg Egan's Diaspora.
[0] https://www.astro.cf.ac.uk/research/gravity/tutorial/?page=4...
Edit: That tutorial also explains that black holes are very simple objects, so the chirps and ringdowns are likewise very simple. So black hole masses can be calculated very precisely. Also, amazingly:
> Just as optical radiation and radio waves, the luminosity of gravitational radiation falls off in inverse proportion to the square of the distance from the source. This makes binary black hole inspirals standard sirens: if we know what the masses of the two black holes are then we can infer the distance to the source by measuring its apparent luminosity. We can precisely measure the masses because the rate at which the frequency and amplitude of an inspiral increases depends only on the masses.
In any case, that emitted energy certainly wouldn't be good for any living tissue. I don't think you could expect to witness a black hole merger from the comfort of your spaceship a few thousands of miles away.
What's the best timing precision possible on the different reception times, to get better triangulation (if there was at least a 3rd LIGO)?
What's the odds of seeing one event when starting it up, and none since then?
How long will it take for any new events to be announced?
The resolution of time-of-flight between the two LIGO sites for the signal we just detected was about half a millisecond. This resolution is somewhat dependent on the signal strength and the location of the source relative to the detectors. With three sites we can localize most sources to tens of square degrees on the sky. This is still very large; the moon is a quarter of a square degree.
The odds are pretty good to observe only one event in 16 days of data, and the likelihood of seeing the event on the first day is the same as the likelihood as seeing it on the last day. The analysis of the remaining data from the first observing run (ended Jan 12th) will probably take a couple of months.
>How many signals we see has to do both with how sensitive our detectors are and how often events that can cause waves strong enough happen; because we observed one of these events in 18 days of observation, we can tell that there are between 2 and 400 of these events per year per gigaparsec cubed events like this in the space around us.
They have seen other events, this was just the biggest.
I read much discussion regarding the probability of a false alarm given the baseline model.[2] However, without an estimate of the probability of detecting a true signal during the same time frame, we cannot calculate the probability this is a false positive. Such an estimate would obviously require some prior estimates of the rate at which these black hole mergers occur and the percent that can get detected, etc.
[1] https://en.wikipedia.org/wiki/Base_rate_fallacy
[2] https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.11...
The rate inferred from GW150914 is on the high end of the rate estimates from astronomers, but it's completely consistent with prior observations. Certainly, if we had seen ten events in the first 16 days of data, it would not have made sense! But one event is well within expectations.
Then if the horizon distance is somewhat less than than 1 Gpc we need to scale this further. Say it was 0.5 Gpc, we scale by 0.5^3 to get ~5.475e-4 expected events. For 0.2 Gpc horizon we get ~3.5e-5! These values are getting dangerously close to the estimated background rate, at least using this crude calculation at the lower ends of the prior estimates.
It's mentioned a few times that the size of the black holes/other model parameters were "within expectations" and so were a good fit.
What are some of the specific quantities that these measurements will allow us to refine? Previous astronomical measurements have allowed us to put better and better estimates on things like the size of the sun, or the gravitational constant - do we have any idea what estimates this technology will allow us to improve?
In Figs 6 and 7 of the second paper you can see the constraints from GW150914 on what are known as the "post-Newtonian" expansion terms of Newtonian gravity. Previously, terms beyond first order were only loosed bound, mostly from observations of the Double Pulsar system J0737-3039.
Just from this one event, we can also constrain the mass of the graviton to an order of magnitude less than the previous best measurement.
The phenomenon detected was the collision of two black holes. Using the world’s most sophisticated detector, the scientists listened for 20 thousandths of a second as the two giant black holes, one 35 times the mass of the sun, the other slightly smaller, circled around each other.
At the beginning of the signal, their calculations told them how stars perish: the two objects had begun by circling each other 30 times a second. By the end of the 20 millisecond snatch of data, the two had accelerated to 250 times a second before the final collision and a dark, violent merger.
The observation signals the opening of a new window on to the universe.
A century of speculation, no wonder people are starving. Come on are u guys reading this? Are you just closing your eyes opening your mouth and letting them stick in what ever they want?tf? firstly i think there is bs going on but if i do accept this bs then we are way far behind in our spiritual growth. Dont forget what sting said... we are spirits in the material world....better get balanced soon or the world will do it for you. Or is that what you need?