The confirmed detection today of gravitational waves by the LIGO Scientific Collaboration ushers in a new era in astronomy, as momentous as Galileo’s first observations of the heavens with his small refractor.
Our knowledge of the universe is based on the evidence from observations of light of all wavelengths (radio, microwave, IR, visible, UV, x-ray, gamma-ray) and detection of neutrinos and cosmic rays. By the time this observed light reaches Earth, it is incredibly faint, requiring increasingly larger and more sophisticated instruments to see further and fainter. This light is also affected or blocked by intervening material and objects.
Gravitational waves are like “hearing” the universe for the first time! They are vibrations in the actual fabric of space-time itself, providing undistorted information from the far reaches of the cosmos. The detectors used in this experiment are impressive. Before its recent upgrade, LIGO could record local space-time distortions of 1/1000th the diameter of a proton – equivalent to measuring the distance to the nearest star (Alpha Centauri; 4.2 light-years away) to the accuracy of the width of a human hair! But this was not enough to find gravitational waves. It is now ten times more sensitive, and that magnitude increase made all the difference.
Even with this sensitivity, it took the merging of two black holes of 36 and 29 solar masses each – producing as much energy at that moment 50 times greater than all the stars in the universe combined – for successful detection. The resulting singularity is 62 solar masses, with the 3 solar mass difference radiated away in the energy of the gravitational waves (remember E = mc2).
The two LIGO installations are 3002km apart. The waves arrived at Louisiana first and Washington 7 milliseconds later, indicating the source is in the southern sky.
The half-second signal was actually recorded last September 14th. The investigators went to great lengths to ensure their results would stand the closest scrutiny before publishing their peer-reviewed findings. To help avoid false positive results they looked for possible computer hacking, and even inserted deliberate false signals to test the scientists.
This success confirms the predictions of gravitational waves in Einstein’s equations 100 years ago. It also validates the work of Kiwi theoretical physicist Roy Kerr in 1963 who solved the equations describing rotating black holes.
This is just the beginning. The first extrasolar planets discovered were massive and close to their parent star, but we are gradually closing in on finding another Earth-like planet as methods and instruments improve.
Gravitational wave detection will also improve. The two LIGO observatories and the European VIRGO observatory in Italy are forging initial steps towards a global network, and there are tentative plans for a fourth detector in India.
The signal from the merging black holes has been described as a “chirp”. One day soon the “pops and crackles” from a supernova or the “sizzle” of the Big Bang may be on the top playlists of all who wonder at the universe.