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Can anyone explain how I should be reading that graph? I'm surprised that the gravity anomaly is coming from a large region of space. And it's a curve. Is that

Can anyone explain how I should be reading that graph? I'm surprised that the gravity anomaly is coming from a large region of space. And it's a curve. Is that expected? Why is it happening? A black hole merge is coming from a single point in space, so I would have expected there to be a single point. But I'm definitely missing something.

petschge 7y ago
It does come from a single point but they can not tell where inside the shaded area of space the single point was. As far as I can tell from their website the event was seen by Virgo and only one of the Ligo detectors (Livingston), which makes localization in the sky rather uncertain. No clue at the moment why the second Ligo detector (Hanford) did not see it.
- turndown 7y ago
  From what I understand a lack of detection can also tell you something about where the point of origin is.
  - petschge 7y ago
    If you had a working detector taking good data than not hearing it also tells you something. But if the detector was not taking good data for whatever reason (local seismic event, high surface winds, technical glitch), then it doesn't help you. Also afaik (and I am not an expert) the first automatic pipeline doesn't use non-detections.
- SiempreViernes 7y ago
  If not all of them see it and they have this shitty sky location, the one missing was either offline or its data was unusable for other reasons (ie someone left their phone on one of the mirrors and got a call).
gus_massa 7y ago
It is easier to understand if you imagine that they are "hearing" the gravitational waves instead of "seeing" the gravitational waves. Analyzing how the waves affect both detectors and the delay, they can get a rough idea of the direction. The origin was in a single point that is probably in the dark zone in the bottom left. I'm not sure of the reason of the shape, but resolving equations in sphere usually give curved solutions, and then projecting it to a planisphere add more distortion. [I'm interested to read a more detailed explanation. Also, why the longitude is in hours?]
- petschge 7y ago
  That's probably not longitude, but right ascension which is typically given in hours (and minutes and seconds).
SiempreViernes 7y ago
The short version is "we heard something, but we don't know were from, somewhere over there probably waves at the sky"
pfdietz 7y ago
The localization was particularly poor because LIGO Hanford apparently wasn't up(?), and didn't contribute data for this event.

petschge 7y ago

It does come from a single point but they can not tell where inside the shaded area of space the single point was. As far as I can tell from their website the event was seen by Virgo and only one of the Ligo detectors (Livingston), which makes localization in the sky rather uncertain. No clue at the moment why the second Ligo detector (Hanford) did not see it.

turndown 7y ago
From what I understand a lack of detection can also tell you something about where the point of origin is.
- petschge 7y ago
  If you had a working detector taking good data than not hearing it also tells you something. But if the detector was not taking good data for whatever reason (local seismic event, high surface winds, technical glitch), then it doesn't help you. Also afaik (and I am not an expert) the first automatic pipeline doesn't use non-detections.
SiempreViernes 7y ago
If not all of them see it and they have this shitty sky location, the one missing was either offline or its data was unusable for other reasons (ie someone left their phone on one of the mirrors and got a call).

gus_massa 7y ago

It is easier to understand if you imagine that they are "hearing" the gravitational waves instead of "seeing" the gravitational waves. Analyzing how the waves affect both detectors and the delay, they can get a rough idea of the direction. The origin was in a single point that is probably in the dark zone in the bottom left. I'm not sure of the reason of the shape, but resolving equations in sphere usually give curved solutions, and then projecting it to a planisphere add more distortion. [I'm interested to read a more detailed explanation. Also, why the longitude is in hours?]

petschge 7y ago
That's probably not longitude, but right ascension which is typically given in hours (and minutes and seconds).

SiempreViernes 7y ago

The short version is "we heard something, but we don't know were from, somewhere over there probably waves at the sky"

pfdietz 7y ago

The localization was particularly poor because LIGO Hanford apparently wasn't up(?), and didn't contribute data for this event.