The experiment that made the first direct detection of gravitational waves is once again hunting for these space-time ripples, Space.com reported.
The Laser Interferometer Gravitational-wave Observatory (LIGO) stopped collecting data in January for a scheduled period of upgrades to its two detectors, located in Hanford, Washington, and Livingston, Louisiana. Now, the machines are back on, looking for gravitational waves coming from distant cosmic sources.
The LIGO collaboration announced the first direct detection of gravitational waves in February 2016 and announced a second detection in June. In both cases, the waves were created by sets of black holes colliding and merging together in space.
Since the end of LIGO's last science run in January, "engineers and scientists have been evaluating LIGO's performance and making improvements to its lasers, electronics and optics —resulting in an overall increase in LIGO's sensitivity," scientists at the California Institute of Technology, which operates LIGO together with the Massachusetts Institute of Technology, said in a statement.
The detection of gravitational waves has been compared to "hearing" the universe for the first time; the waves in space-time are similar to vibrations on the surface of a drum. These ripples provide an entirely new kind of information about the universe, and have the potential to reveal previously invisible features of the cosmos.
Indeed, some scientists have hailed the discovery of these waves as the start of a new era. The two black-hole mergers detected by LIGO very likely did not emit any light and, therefore, would have been invisible to other observatories and telescopes, LIGO scientists said.
"With our improved sensitivity, and a longer observing period, we will likely observe even more black-hole mergers in the coming run and further enhance our knowledge of black-hole dynamics," Caltech's David Reitze, executive director of the LIGO Laboratory, said in the statement. "We are only just now, thanks to LIGO, learning about how often events like these occur."
LIGO's detection of two black-hole mergers came as somewhat of a surpriseto astrophysicists, based on estimations of the frequency of these mergers in the cosmos.
"As more black-hole mergers are detected by LIGO, scientists will start to get their first real understanding of black-hole pairs in the universe — including their population numbers, masses and spin rates," the scientists said in the statement. "LIGO may also detect the merger of neutron stars — the dense cores of exploded stars. Knowledge of both black-hole and neutron-star mergers will improve our understanding of stellar evolution and death."