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Ripples of anticipation
Henze, NASA
Upfront an idea of the event’s distance and the masses of the bodies, but not where they are in the sky. So the LIGO team asks astronomers at 75 observatories worldwide to scan for more traditional signals: visible light, gamma rays, even neutrinos. If a gravitational wave event is like the elusive Cheshire cat, then finding these counterparts is seeing the grin. Although the results of these searches are not public, whether or not they have taken place is – and so
“The first gravitational wave sighting could have fallen into LIGO’s lap before it formally started looking”
Ripples of anticipation NEVER mind the rumours. The most-sensitive ever search for gravitational waves seems to have glimpsed its quarry before it even started looking officially, New Scientist has found. Gravitational waves are ripples in space-time predicted by Einstein’s theory of general relativity. Massive objects like black holes and neutron stars warp space-time around themselves, and when two such behemoths collide, the distortions ripple outward at the speed of light. Although we are pretty confident this happens, no one had detected the waves themselves. As New Scientist went to press, rumours were flying that the Laser Interferometer Gravitational-Wave Observatory (LIGO) team was about to announce just such a detection. The source was said to be the merger of two black holes, each about 30 times the mass of the sun. The team has called a press conference for 11 February, but we already have reason to believe this
6 | NewScientist | 13 February 2016
is the real deal. By analysing public observation logs, New Scientist discovered that the team had followed up on at least three possible sources since it started listening to the sky last September. LIGO’s detectors, 3000 kilometres apart in Hanford, Washington, and
What did did LIGO LIGO see? see? What
Livingston, Louisiana, aim to spot passing gravitational waves by picking up stretches and contractions in space-time as small as one tenthousandth the diameter of a proton. The signal from the merger of two massive objects rises in frequency, then falls abruptly. Analysing it gives
Follow-upobservations observations by by the the European European Southern Follow-up Southern Observatory Observatorysuggest suggestthat that LIGOmay mayhave haveseen seenthree three gravitational gravitational wave wave signals. LIGO signals. The The map mapshows showsareas areas of sky swept by the ESO, superimposed on the cosmic microwave background of sky swept by the ESO, superimposed on the cosmic microwave background theembers embersof ofthe thebig big bang bang –– as as mapped mapped by ––the by NASA's NASA's WMAP WMAP September2015 2015 September
BACKGROUND SOURCE: BACKGROUND NASA / WMAPSOURCE: SCIENCE TEAM NASA / WMAP SCIENCE TEAM
December 2015/January 2015/January 2016 December 2016
are the coordinates. New Scientist focused on searches by the European Southern Observatory (ESO), a set of telescopes in Chile that can detect the flash of light that may accompany a gravitational wave signal. We found that ESO began a search on 17 September, starting in the constellation Dorado and veering across other parts of the southern sky. LIGO’s observing run officially began the very next morning, but the team had spent the previous few weeks collecting data in preparation. The first rumour of a signal appeared just a week later, to the consternation of team members. It seems the first sighting fell into LIGO LIGO’s lap before the experiment LIGOon onthe thelooko look formally started. LIGO may have seen LIGO may have seenatatlea le ininmid-September and Two other ESO searches – one mid-September andtw tw below shows their locatio around the constellation Aries, below shows their locati background – –the theembers ember the other in the rough background vicinity of Hydra – both began on 28 December and continued until the end of the LIGO run on 14 January. Taken together, the three searches suggest LIGO has been unbelievably lucky. The LIGO team is known to create false signals to test its analysis. In 2010, before LIGO was upgraded to its present sensitivity, an apparent signal turned out to be one of these deliberate fakes. This time, given the team’s scheme for introducing fakes, it’s likely that at least one of the signals is real. Joshua Sokol n
Upfront an idea of the event’s distance and the masses of the bodies, but not where they are in the sky. So the LIGO team asks astronomers at 75 observatories worldwide to scan for more traditional signals: visible light, gamma rays, even neutrinos. If a gravitational wave event is like the elusive Cheshire cat, then finding these counterparts is seeing the grin. Although the results of these searches are not public, whether or not they have taken place is – and so
“The first gravitational wave sighting could have fallen into LIGO’s lap before it formally started looking”
Ripples of anticipation NEVER mind the rumours. The most-sensitive ever search for gravitational waves seems to have glimpsed its quarry before it even started looking officially, New Scientist has found. Gravitational waves are ripples in space-time predicted by Einstein’s theory of general relativity. Massive objects like black holes and neutron stars warp space-time around themselves, and when two such behemoths collide, the distortions ripple outward at the speed of light. Although we are pretty confident this happens, no one had detected the waves themselves. As New Scientist went to press, rumours were flying that the Laser Interferometer Gravitational-Wave Observatory (LIGO) team was about to announce just such a detection. The source was said to be the merger of two black holes, each about 30 times the mass of the sun. The team has called a press conference for 11 February, but we already have reason to believe this
6 | NewScientist | 13 February 2016
is the real deal. By analysing public observation logs, New Scientist discovered that the team had followed up on at least three possible sources since it started listening to the sky last September. LIGO’s detectors, 3000 kilometres apart in Hanford, Washington, and
What did did LIGO LIGO see? see? What
Livingston, Louisiana, aim to spot passing gravitational waves by picking up stretches and contractions in space-time as small as one tenthousandth the diameter of a proton. The signal from the merger of two massive objects rises in frequency, then falls abruptly. Analysing it gives
Follow-upobservations observations by by the the European European Southern Follow-up Southern Observatory Observatorysuggest suggestthat that LIGOmay mayhave haveseen seenthree three gravitational gravitational wave wave signals. LIGO signals. The The map mapshows showsareas areas of sky swept by the ESO, superimposed on the cosmic microwave background of sky swept by the ESO, superimposed on the cosmic microwave background theembers embersof ofthe thebig big bang bang –– as as mapped mapped by ––the by NASA's NASA's WMAP WMAP September2015 2015 September
BACKGROUND SOURCE: BACKGROUND NASA / WMAPSOURCE: SCIENCE TEAM NASA / WMAP SCIENCE TEAM
December 2015/January 2015/January 2016 December 2016
are the coordinates. New Scientist focused on searches by the European Southern Observatory (ESO), a set of telescopes in Chile that can detect the flash of light that may accompany a gravitational wave signal. We found that ESO began a search on 17 September, starting in the constellation Dorado and veering across other parts of the southern sky. LIGO’s observing run officially began the very next morning, but the team had spent the previous few weeks collecting data in preparation. The first rumour of a signal appeared just a week later, to the consternation of team members. It seems the first sighting fell into LIGO LIGO’s lap before the experiment LIGOon onthe thelooko look formally started. LIGO may have seen LIGO may have seenatatlea le ininmid-September and Two other ESO searches – one mid-September andtw tw below shows their locatio around the constellation Aries, below shows their locati background – –the theembers ember the other in the rough background vicinity of Hydra – both began on 28 December and continued until the end of the LIGO run on 14 January. Taken together, the three searches suggest LIGO has been unbelievably lucky. The LIGO team is known to create false signals to test its analysis. In 2010, before LIGO was upgraded to its present sensitivity, an apparent signal turned out to be one of these deliberate fakes. This time, given the team’s scheme for introducing fakes, it’s likely that at least one of the signals is real. Joshua Sokol n