Lawrence Krauss, a cosmologist at Arizona State university, tweeted that he had received independent confirmation of a rumour that has been in circulation for months, adding: “Gravitational waves may have been discovered!!”
The excitement centers on a longstanding experiment known as the Advanced Laser Interferometer Gravitational-Wave Observatory (Ligo) which uses detectors in Hanford, Washington, and Livingston, Louisiana to look for ripples in the fabric of spacetime.
According to the rumors, scientists on the team are in the process of writing up a paper that describes a gravitational wave signal. If such a signal exists and is verified, it would confirm one of the most dramatic predictions of Albert Einstein’s century-old theory of general relativity.
Krauss said he was 60% confident that the rumor was true, but said he would have to see the scientists’ data before drawing any conclusions about whether the signal was real or not. Researchers on a large collaboration like Ligo will have any such paper internally vetted before sending it for publication and calling a press conference.
So this is pre-buzz for a researcher paper which may not be any good or conclusive
Einstein predicted that the waves would be produced in extremely violent events, such as collisions between two black holes. As gravitational waves spread out, they compress and stretch spacetime. The ripples could potentially be picked up by laser beams that measure minute changes in the lengths of two 4km-long pipes at the Ligo facilities.
Gabriela Gonzalez, professor of physics and astronomy at Louisiana State University, and the spokesperson for the LIGO collaboration, told the Guardian: “The LIGO instruments are still taking data today, and it takes us time to analyse, interpret and review results, so we don’t have any results to share yet.
Physicist working with LIGO looked for them from 2002 to 2010, with the initial incarnation of the observatory, which consists of two gargantuan L-shaped optical instruments in Hanford, Washington, and Livingston, Louisiana. To detect the stretching of space itself, researchers compare the lengths of an interferometer’s two 4-kilometer-long arms to within a billionth the width of an atom.
From 2010 to 2015, LIGO researchers completely rebuilt their instruments, aiming to make them up to 10 times more sensitive. They resumed their hunt for a fleeting source of gravitational waves on 18 September 2015. Then the rumor mill revved up.
By mid-September 2016 “the world’s largest gravitational-wave facility” would have completed a 5-year US$200-million overhaul and a would have a total cost of $620 million. LIGO is the largest and most ambitious project ever funded by the NSF.
Its sensitivity will be further enhanced until it reaches design sensitivity around 2021
The LIGO Laboratory started the first Observing Run ‘O1’ with the Advanced LIGO detectors in September 2015 at a sensitivity roughly 4 times greater than Initial LIGO for some classes of sources (e.g., neutron-star binaries), and a much greater sensitivity for larger systems with their peak radiation at lower audio frequencies.
Based on current models of astronomical events, and the predictions of the general theory of relativity, gravitational waves that originate tens of millions of light years from Earth are expected to distort the 4 kilometer mirror spacing by about 10^−18 meters, less than one-thousandth the charge diameter of a proton. Equivalently, this is a relative change in distance of approximately one part in 10^21. A typical event which might cause a detection event would be the late stage inspiral and merger of two 10 solar mass black holes, not necessarily located in the Milky Way galaxy, which is expected to result in a very specific sequence of signals often summarized by the slogan chirp, burst, quasi-normal mode ringing, exponential decay.
During LIGO’s fifth Science Run in November 2005, sensitivity reached the primary design specification of a detectable strain of one part in 10^21 over a 100 Hz bandwidth. The baseline inspiral of two roughly solar-mass neutron stars is typically expected to be observable if it occurs within about 8,000,000 parsecs (26,000,000 ly), or the vicinity of the Local Group, averaged over all directions and polarizations. Also at this time, LIGO and GEO 600 (the German-UK interferometric detector) began a joint science run, during which they collected data for several months. Virgo (the French-Italian interferometric detector) joined in May 2007. The fifth science run ended in 2007. After extensive analysis data from this run did not uncover any unambiguous detection events.
Further Observing runs will be interleaved with commissioning efforts to further improve the sensitivity.
SOURCES – Twitter, Guardian UK, Science Magazine, Wikipedia