Bench Press

I’ve mentioned before that I’m a sucker for the indirect observational techniques that one engages in when doing astronomy/astrophysics. One phenomena that astronomers have yet to be able to observe in any depth is also one of the most fascinating consequences of Einstein’s theory of General Relativity: gravitational waves.

A rigorous understanding of gravitational waves is far beyond the scope of this post (and also far far far far far far beyond my limited comprehension), but the basic concept comes from Einstein’s idea that gravity as we know it is actually a “bending” in spacetime that happens wherever there is mass. This curvature is what causes most of the effects of gravity that we can observe (i.e. you feel a pull towards the center of the Earth because the Earth’s mass bends the neighboring spacetime that you are in). As the Earth moves around the Sun (and as the Sun moves around the Milky Way galaxy and as the Milky Way moves…), the curvature in spacetime also moves with it. In certain types of motion (i.e. when an object is part of a binary orbiting system), this movement in spacetime curvature actually results in “waves” of spacetime curvature emanating outwards, kind of like ripples in a pond. These “waves” are called gravitational waves and, because they carry energy, are also called gravitational radiation. Because of the nature of these waves, they have three unique properties which make them interesting tools in the study of astronomy:

• they move at the speed of light
• unlike light, these waves don’t get significantly scattered/blocked
• they don’t require the existence of matter (so they can be used to study black holes)

The problem? They are extremely difficult to detect, because their effects are remarkably small. In fact, the first indirect observation of gravitational waves, found in the change in orbits of the Hulse-Taylor binary system (pictured above-right) won the researchers the 1993 Nobel Prize in Physics.

So, what to do? While there have been many attempts to do this, they are plagued by the difficulty of detecting such weak waves in the presence of as much noise on Earth. Potential solution? The use of a multinational space-borne laser interferometry setup called LISA (Laser Interferometer Space Antenna). With the use of laser light and interferometry (which allows you to measure small changes in distance by observing interference between a beam of light and a reflection), three identical solar-powered spacecraft will be set up in an equilateral triangle orbiting the sun at an angle relative to where the plane of the orbit of the other planets in the solar system (see below).

What’s especially remarkable is the precautions NASA is taking with the LISA spacecraft to correct for error and insure greater accuracy and precision in their measurements:

• Use of microthrusters to maintain drag-free flight by constantly monitoring the position of the test-weights the LISA spacecraft is flying around (and maintaining position of the instruments relative to the test-weights of ~10nm)
• Use of a transponder (which calculates the phase of an incoming beam of laser light and electronically setting the phase of the outgoing beams) instead of a mirror for interferometry to avoid diffraction (light scattering) from a traditional reflection approach
• Use of time-delay interferometry and continuous frequency monitoring/stabilization to correct for the effects of frequency noise

Given the technology and the theory involved, LISA’s potential to change astronomy could potentially rival the Hubble telescope’s, opening up new ways to study distant astronomical phenomena and potentially some of the more exotic topics in physics like string theory and strong-field gravity. There’s a lot more information on the potential topics of scientific inquiry which LISA could be used to study on NASA’s LISA science page.

Let’s cross our fingers that it will stay on schedule for launch in the 2018-2020 range and deliver not only concrete observations of gravitational waves but a whole wealth of information on the universe we live in.

(Image credit: NASA) (Image credit: NASA)