April 17, 2008

New Project Will Detect Gravitational Waves

The U.S. Laser Interferometer Gravitational-wave Observatories (LIGO) is getting a $205 million upgrade by the National Science Foundation (NSF). Dubbed the "Advanced LIGO Project", the upgrade will enable the new field of gravitational wave astronomy.

The National Science Board approved the seven-year project in its March 27 meeting, and the  NSF will provide an initial $32.75 million in funding this year via the Major Research Equipment and Facilities Construction (MREFC) budget account. The Caltech-MIT LIGO Laboratory will carry out the project.

Regular detections of gravitational waves would bring about a new era in astronomy that is not dependent on the observation of light.  This is critical, since  most of the cosmos is "dark" and the majority of its matter cannot be seen with traditional telescopes.

The upgrade will increase the sensitivity of the LIGO instruments by a factor of 10, which represents a one thousand-fold increase in the number of astrophysical candidates for gravitational wave signals. Researchers believe the changes will allow detections of waves to become a regular occurrence, perhaps on a daily basis.

"We anticipate that this new instrument will see gravitational wave sources possibly on a daily basis, with excellent signal strengths, allowing details of the waveforms to be observed and compared with theories of neutron stars, black holes, and other astrophysical objects moving near the speed of light," said Jay Marx of the California Institute of Technology, executive director of the LIGO Laboratory.

Gravitational waves are ripples in the fabric of space and time produced by violent events in the distant universe--for example, by the collision of two black holes or the mergers of super-dense stars.  The waves are emitted by accelerating masses much in the same way as radio waves are produced by accelerating charges-- such as electrons in antennas.

Confirmation of the waves' existence will provide a different perspective of the Universe.  Eventually, scientists hope to be able to investigate these ripples to better understand what happened just fractions of a second after the Big Bang itself. 

"These ripples in the space-time fabric travel to Earth, bringing with them information about their violent origins and about the nature of gravity that cannot be obtained by other astronomical tools," said David Reitze of the University of Florida, spokesperson for the LIGO Scientific Collaboration.

Albert Einstein predicted the existence of the waves in 1916 as part of his general theory of relativity.  But it has only been since the 1990s that technology has become powerful enough to detect and harness them for science.

Although they have yet to be directly detected, the influence of gravitational waves on a binary pulsar system (two neutron stars orbiting each other) has been measured accurately and is in excellent agreement with predictions, giving scientists a high degree of confidence that gravitational waves exist.  A direct detection will conclusively confirm Einstein's vision of the waves, and allow a fascinating view of cosmic cataclysms.

The Advanced LIGO detector will be installed at the LIGO Observatories in Hanford, Washington, and Livingston, Louisiana.   They will use existing infrastructure, but replace the present detector, transforming gravitational wave science into a real observational tool. 

"The improvement of sensitivity will allow the data set generated after one year of initial operations to be equaled in just several hours,"  said David Shoemaker of MIT, the project's leader.

The detector's increased sensitivity comes along with a significant increase in the sensitive frequency range and the ability to tune the instrument for specific astrophysical sources.  This will allow Advanced LIGO to view the last minutes of life of pairs of massive black holes as they spiral closer, coalesce into one larger black hole, and then vibrate much like two soap bubbles becoming one.

It will also allow the instrument to pinpoint periodic signals from many known pulsars.  Recent results from the Wilkinson Microwave Anisotropy Probe have shown the depth of information that comes from looking at the photon, or infrared cosmic background, which originated some 400,000 years after the Big Bang.

Advanced LIGO can also be optimized to search for the gravitational cosmic background, allowing scientists to test theories about the development of the universe only 10-35 seconds after the Big Bang.

From their beginning, the LIGO Observatories were built to support the continuing development of this new science. The upgrade will provide changes in the lasers, optics, seismic isolation systems and in how the microscopic motion of test masses are detected.  Several of these technologies are significant advances in their fields. 

Testing and practice installation will allow the new detectors to be brought online with minimal interruption in observation, and the instruments will be operational in 2014.

The instrument's design comes from scientists throughout the 50-institution, 600-person LIGO Scientific Collaboration, an international group that conducts instrument development and scientific data analysis for LIGO.   In the United States, these efforts are supported by the NSF.

Several international partners have already approved funding for significant contributions of equipment, labor, and expertise.

The British contribution, funded by its Science and Technology Facilities Council (STFC), is the suspension assembly and some optics for the mirrors whose movements register the passage of the gravitational waves.

Germany is contributing the high-power, high-stability laser whose light measures the actual movements of the mirrors.   This has been funded via the Max Planck Society in Munich.
"We in the German-British GEO project are excited that our long-standing partnership with LIGO allows us to contribute to Advanced LIGO some of the key technologies we have developed and tested in our GEO600 instrument," said Bernard F. Schutz, director of the Albert Einstein Institute in Germany.

""Advanced LIGO will be one of the most important scientific instruments of the 21st century. For the first time, it will let us listen in on the sounds of the universe, as unseen explosions, collisions, and whirlpools shake the fabric of space-time and send out the ripples that Advanced LIGO will measure," he added.

"The UK and Germany made a big difference in getting Advanced Ligo funded; the fact that both countries were willing to put money into it," Professor Jim Hough of the University of Glasgow told BBC News.  Hough is a member of the international LIGO Scientific Collaboration.

"There is another $30m, which is the UK-German contribution, on top of the $205m," he added.

Much of the new technology that will go into the updated LIGO has undergone trials at the German-UK observatory known as GEO-600.   This includes the high-powered lasers that catch the waves and the mechanisms that hold the "test mass" mirrors at the ends of the tunnels.

Some interim enhancements at LIGO are planned to go online later this year.  At that time, the US installations will be joined by the French-Italian observatory known as Virgo.  This will allow GEO-600 to engage in a period of research and development work.

"When a discovery is made we will want to see signals in all the observatories. It will give us confidence; we will know it is not some spurious random event," said Professor Hough.

The University of Florida and Columbia University are also taking part in the design and construction of Advanced LIGO.  Other members of the LIGO Scientific Collaboration (LSC), with NSF or other funding, will participate in all phases of the project.


On the Net:

LIGO Project

University of Florida

Columbia University