Tag Archives: LISA

Success of test mission paves way for orbiting gravitational wave detector

The success of LISA Pathfinder during the past year to test the technology for building an orbiting gravitational wave detector has now made it possible for Europe to approve construction of the full scale telescope, set to launch in the 2030s.

The LISA Pathfinder mission, launched in late 2015, beat its precision target by a factor of 1,000 and quieted critics who have doubted its potential, says project scientist Paul McNamara, an astrophysicist at ESA in Noordwijk, the Netherlands. “This is not the impossible task that some people believed it was.”

Currently set to fly in 2034, the full-scale Laser Interferometer Space Antenna (LISA) will be the space analogue of the Laser Interfero-meter Gravitational-Wave Observatory (LIGO), two machines in the United States — each with a pair of 4-kilometre-long arms — that first detected the ripples by ‘hearing’ the merger of two black holes. LISA’s three probes will fly in a triangle, millions of kilometres apart, making the mission sensitive to much longer gravitational waves, such as the ripples produced by the collisions of even larger black holes.

The article also notes that the European Space Agency also approved two other large missions, one to launch in 2022 and go the moons of Jupiter, another an X-ray observatory that will launch in 2028.

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First direct detection of a gravitational wave

The science team from the Laser Interferometer Gravitational-wave Observatory (LIGO) announced today that on September 14, 2015 they made the first direct detection of a gravitational wave, produced by the merging of two distant black holes.

Based on the observed signals, LIGO scientists estimate that the black holes for this event were about 29 and 36 times the mass of the sun, and the event took place 1.3 billion years ago. About three times the mass of the sun was converted into gravitational waves in a fraction of a second — with a peak power output about 50 times that of the whole visible universe. By looking at the time of arrival of the signals — the detector in Livingston recorded the event 7 milliseconds before the detector in Hanford — scientists can say that the source was located in the Southern Hemisphere.

According to general relativity, a pair of black holes orbiting around each other lose energy through the emission of gravitational waves, causing them to gradually approach each other over billions of years, and then much more quickly in the final minutes. During the final fraction of a second, the two black holes collide at nearly half the speed of light and form a single more massive black hole, converting a portion of the combined black holes’ mass to energy, according to Einstein’s formula E=mc2. This energy is emitted as a final strong burst of gravitational waves. These are the gravitational waves that LIGO observed.

Because of the faintness of the wave signal, I suspect that the scientists involved have spent the last four months reviewing their data and the instrument very carefully, to make sure this was not a false detection. That they feel confident enough to make this announcement tells us that they think the detection was real.

Recently ESA launched Lisa Pathfinder, a prototype space-based gravitational wave detector designed to test the technology for building a larger in-space observatory that would be far more sensitive that LIGO. Funding for that larger detector has dried up, Today’s announcement will likely help re-energize that funding effort.

More information here.

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