APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

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APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby APOD Robot » Thu Sep 28, 2017 4:07 am

Image LIGO-Virgo GW170814 Skymap

Explanation: From around planet Earth three gravitational wave detectors have now reported a joint detection of ripples in spacetime, the fourth announced detection of a binary black hole merger in the distant Universe. The event was recorded on 2017 August 14, and so christened GW170814, by the LIGO observatory sites in Hanford, Washington and Livingston, Louisiana, and the more recently operational Virgo Observatory near Pisa, Italy. The signal was emitted in the final moments of the coalescence of two black holes of 31 and 25 solar masses located about 1.8 billion light-years away. But comparing the timing of the gravitational wave detections at all three sites allowed astronomers to vastly improve the location of the signal's origin on the sky. Just above the Magellanic clouds and generally toward the constellation Eridanus, the only sky region consistent with signals in all three detectors is indicated by the yellow contour line in this all-sky map. The all-sky projection includes the arc of our Milky Way Galaxy. An improved three-detector location of the gravitational wave source allowed rapid follow-up observations by other, more conventional, electromagnetic wave observatories that can search for potentially related signals. The addition of the Virgo detector also allowed the gravitational wave polarization to be measured, a property that further confirms predictions of Einstein's general relativity.

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby bystander » Thu Sep 28, 2017 4:46 am

Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby S_S » Thu Sep 28, 2017 7:14 am

What's the speed of these gravitational waves ? Same as light or slower (I guess nothing can go faster than light, right) ? And, how do they measure the speed ? Thanks in advance.

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby Boomer12k » Thu Sep 28, 2017 8:33 am

Reminds me of a "Yin-Yang" symbol... "Galactic Balance"... Ommmmmm...."What is the sound of two black holes merging in Space?"...."the vibration of their Gravitational Waves...." "The Five Waves deafen every ear...yet all we hear is silence"....

Parody of "Master Killer"....1978, and probably my favorite kung fu flick...Classic...

Looks like Al should get a posthumous Nobel....

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby neufer » Thu Sep 28, 2017 10:13 am

S_S wrote:
What's the speed of these gravitational waves ? Same as light or slower (I guess nothing can go faster than light, right) ? And, how do they measure the speed ? Thanks in advance.

Long range forces that drop off as 1/r2 like gravity & electrostatic
are always assumed to be mediated by waves that move at the speed of light.

The Δ-time delay between signals between any TWO gravitational telescopes:
Δ-time = [Δ-distance x cos(θ)]/c basically defines a θ-wide cone
shaped slice of the sky around the line between the two stations.

If Δ-time = [Δ-distance]/c then θ = 0º and the line between the two stations points directly to the source.
If Δ-time = 0 then θ = 90º and the source lies in a wide ring perpendicular to line between the two stations.

The time delays between signals between THREE gravitational telescopes taken two at a time
define THREE cone shaped slices of the sky that all intersect in the small region shown.

(If they didn't all intersect in a small region then
the speed of the gravitational wave would have to be artificially adjusted until they did so.)
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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby hamilton1 » Thu Sep 28, 2017 11:52 am

Using the American dating system to name these events is confusing for us Europeans. When I look at '170814' I think '17th August 2014' as opposed to the intended meaning. Using something like '14Aug2017' would be more appropriate, especially now that a European detector is also involved.

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby Guest » Thu Sep 28, 2017 12:16 pm

hamilton1 wrote:Using the American dating system to name these events is confusing for us Europeans. When I look at '170814' I think '17th August 2014' as opposed to the intended meaning. Using something like '14Aug2017' would be more appropriate, especially now that a European detector is also involved.


The method chosen is so that observation dates can be easily arranged numerically. Throwing month names in there would make this simple, logical arrangement impossible.

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby BobStein-VisiBone » Thu Sep 28, 2017 12:19 pm

What a fascinating read, that story Einstein's double reversal, about the changing minds over whether gravitational waves are real or abstract.

...in the end, Einstein had fully accepted the objections that had initially so upset him.


And then Feynman's contribution:

...after the introduction of the bead argument, any remaining doubts soon disappeared from the research literature.


How easy it is to be certain and wrong, and how hard that is to fix.

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby BDanielMayfield » Thu Sep 28, 2017 1:54 pm

BobStein-VisiBone wrote:How easy it is to be certain and wrong, and how hard that is to fix.


Profoundly true.

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby Chris Peterson » Thu Sep 28, 2017 1:55 pm

hamilton1 wrote:Using the American dating system to name these events is confusing for us Europeans. When I look at '170814' I think '17th August 2014' as opposed to the intended meaning. Using something like '14Aug2017' would be more appropriate, especially now that a European detector is also involved.

YYMMDD is most certainly not the American dating convention, which would almost always be MMDDYY (whether the month was specified numerically or by name). The system used is standard for scientists everywhere, however, since the ordered field significance allows for logical sorting. (And it is a fairly popular convention outside of science in much of Europe.)
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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby BDanielMayfield » Thu Sep 28, 2017 2:11 pm

This merger instantly converted 3 solar masses into gravitational wave energy :!:
I wonder what the effect would be if, rather than being 1.8 billion light years away, it had happened inside the Milky Way, say, 18,000 ly away? Could such an event trigger earthquakes, for example?

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby Chris Peterson » Thu Sep 28, 2017 2:27 pm

BDanielMayfield wrote:This merger instantly converted 3 solar masses into gravitational wave energy :!:
I wonder what the effect would be if, rather than being 1.8 billion light years away, it had happened inside the Milky Way, say, 18,000 ly away? Could such an event trigger earthquakes, for example?

I don't think it would be detectable except with sensitive gravitational wave detectors. In any case, such mergers produce gravitational waves with lengths from thousands to tens of thousands of kilometers- much larger than fault systems, so unlikely to interact with them strongly.
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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby geckzilla » Thu Sep 28, 2017 2:53 pm

Chris Peterson wrote:
hamilton1 wrote:Using the American dating system to name these events is confusing for us Europeans. When I look at '170814' I think '17th August 2014' as opposed to the intended meaning. Using something like '14Aug2017' would be more appropriate, especially now that a European detector is also involved.

YYMMDD is most certainly not the American dating convention, which would almost always be MMDDYY (whether the month was specified numerically or by name). The system used is standard for scientists everywhere, however, since the ordered field significance allows for logical sorting. (And it is a fairly popular convention outside of science in much of Europe.)

I'm disappointed it isn't YYYYMMDD. APOD is going to have problems starting in 2095, which is but a single human lifetime away. The editors will one day retire. Will they hand over APOD to someone new?
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby Chris Peterson » Thu Sep 28, 2017 2:57 pm

geckzilla wrote:
Chris Peterson wrote:
hamilton1 wrote:Using the American dating system to name these events is confusing for us Europeans. When I look at '170814' I think '17th August 2014' as opposed to the intended meaning. Using something like '14Aug2017' would be more appropriate, especially now that a European detector is also involved.

YYMMDD is most certainly not the American dating convention, which would almost always be MMDDYY (whether the month was specified numerically or by name). The system used is standard for scientists everywhere, however, since the ordered field significance allows for logical sorting. (And it is a fairly popular convention outside of science in much of Europe.)

I'm disappointed it isn't YYYYMMDD. APOD is going to have problems starting in 2095, which is but a single human lifetime away. The editors will one day retire. Will they hand over APOD to someone new?

APOD can always end with "DD", but the gravitational wave identifications may have to add "HH" in the not too distant future, as more than a single detection in a day becomes increasingly likely.
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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby BDanielMayfield » Thu Sep 28, 2017 3:37 pm

Chris Peterson wrote:
BDanielMayfield wrote:This merger instantly converted 3 solar masses into gravitational wave energy :!:
I wonder what the effect would be if, rather than being 1.8 billion light years away, it had happened inside the Milky Way, say, 18,000 ly away? Could such an event trigger earthquakes, for example?

I don't think it would be detectable except with sensitive gravitational wave detectors. In any case, such mergers produce gravitational waves with lengths from thousands to tens of thousands of kilometers- much larger than fault systems, so unlikely to interact with them strongly.

So no threat to the Earth from such mergers. Good. But, since the power falls off with the inverse square of the distance the signal would be 10 billion times stronger for a 18 kly event, so wouldn't it at least peg LIGO's meters?

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby Ann » Thu Sep 28, 2017 4:03 pm

Chris Peterson wrote:YYMMDD is most certainly not the American dating convention, which would almost always be MMDDYY (whether the month was specified numerically or by name).


I know. :roll:

The system used is standard for scientists everywhere, however,


It is???

since the ordered field significance allows for logical sorting.


It does???

(And it is a fairly popular convention outside of science in much of Europe.)


Really????

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby BobStein-VisiBone » Thu Sep 28, 2017 4:34 pm

Ann wrote:
Chris Peterson wrote:since the ordered field significance allows for logical sorting.

It does???
Ann


That YYMMDD date code is "monotonic" in the sense that you can compare two codes alphabetically and know which one refers to an earlier time. So "171231" is less than "180101" in the same way that 31-Dec-2017 came before 01-Jan-2018.

Yes, I've seen this coding, and similar ones, used in many places. This is one of those tricks that us software developers foist on humanity to save us work, and because we aren't worshipped like gods enough already.

Incidentally I use a bigger monotonic date code formatted like YYYY.MMDD.HHMM, where 2017.0928.1234 means 12:34pm, 28 September 2017.

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby geckzilla » Thu Sep 28, 2017 4:48 pm

Another very typical way to store a date is by the numbers of seconds which have elapsed since the UNIX epoch, which is at 00:00:00 UTC on January 1st, 1970. Each APOD could easily be indexed like this. Today's would be 1506556800, tomorrow's would be 86400 seconds later at 1506643200, and so on. 170814 is comparatively quite a lot easier for a human to read. Count yourself lucky!

And Chris, you kinda lost me. We can just serialize in the same 24 hour intervals them until APOD is nothing but gravitational wave detections. So what if we end up weeks, months, and eventually years behind the results.
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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby Chris Peterson » Thu Sep 28, 2017 5:29 pm

geckzilla wrote:And Chris, you kinda lost me. We can just serialize in the same 24 hour intervals them until APOD is nothing but gravitational wave detections. So what if we end up weeks, months, and eventually years behind the results.

I just meant that one day resolution is all APOD should ever need, but gravitational wave detections may need finer than that.
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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby geckzilla » Thu Sep 28, 2017 5:30 pm

Chris Peterson wrote:
geckzilla wrote:And Chris, you kinda lost me. We can just serialize in the same 24 hour intervals them until APOD is nothing but gravitational wave detections. So what if we end up weeks, months, and eventually years behind the results.

I just meant that one day resolution is all APOD should ever need, but gravitational wave detections may need finer than that.

I still can't tell if we're joking or not.
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby Chris Peterson » Thu Sep 28, 2017 5:48 pm

geckzilla wrote:
Chris Peterson wrote:I just meant that one day resolution is all APOD should ever need, but gravitational wave detections may need finer than that.

I still can't tell if we're joking or not.

No. Just considering that the inadequacy of the gravitational wave nomenclature lies at both ends- a lack of the century on the left, and the lack of an hour on the right.

Looking at similar nomenclature elsewhere in astronomy, I'd guess that a second detection on the same day would get a "b" appended. But the time is a little more elegant, IMO.
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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby BobStein-VisiBone » Thu Sep 28, 2017 5:49 pm

geckzilla wrote:
Chris Peterson wrote:I just meant that one day resolution is all APOD should ever need, but gravitational wave detections may need finer than that.

I still can't tell if we're joking or not.


Some days I wish there were an APOH.

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby tomatoherd » Thu Sep 28, 2017 5:59 pm

BobStein-VisiBone wrote:
geckzilla wrote:
Chris Peterson wrote:I just meant that one day resolution is all APOD should ever need, but gravitational wave detections may need finer than that.

I still can't tell if we're joking or not.


Some days I wish there were an APOH.


Some folks would not get anything done.

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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby bystander » Thu Sep 28, 2017 6:34 pm

Ann wrote:
Chris Peterson wrote:YYMMDD is most certainly not the American dating convention, which would almost always be MMDDYY (whether the month was specified numerically or by name).

I know. :roll:
The system used is standard for scientists everywhere, however,

It is???
since the ordered field significance allows for logical sorting.

It does???
(And it is a fairly popular convention outside of science in much of Europe.)

Really????

ISO 8601 - International Standard for Date and Time
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Re: APOD: LIGO-Virgo GW170814 Skymap (2017 Sep 28)

Postby Guest » Thu Sep 28, 2017 6:41 pm

Chris Peterson wrote:
geckzilla wrote:
Chris Peterson wrote:YYMMDD is most certainly not the American dating convention, which would almost always be MMDDYY (whether the month was specified numerically or by name). The system used is standard for scientists everywhere, however, since the ordered field significance allows for logical sorting. (And it is a fairly popular convention outside of science in much of Europe.)

I'm disappointed it isn't YYYYMMDD. APOD is going to have problems starting in 2095, which is but a single human lifetime away. The editors will one day retire. Will they hand over APOD to someone new?

APOD can always end with "DD", but the gravitational wave identifications may have to add "HH" in the not too distant future, as more than a single detection in a day becomes increasingly likely.


They're already (almost) following ISO-8601 for the date order, they can keep following it to add higher resolution. YYYYMMDDThhZ or YYYYMMDDThhmmZ.


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