March Skywatch

I’ve been promising a column for a couple months now that offers a basic introduction to telescope optics and usage. I plan to keep that promise, but exciting news keeps breaking out in the astronomical world. Last month it was the alignment of the planets in the early morning skies and the announcement of the possible existence of a new, ninth planet in the solar system. Now it’s even bigger news, as scientists have reported the first confirmed detection of gravity waves, which not only provide a further confirmation of Einstein’s theory of general relatively but more importantly have opened a completely new avenue for learning about the universe.

Up to this point in our history, everything we’ve known about distant objects in space has come from light, whether telescopes set up in backyards or research observatories on mountaintops or even instruments beyond the surface of the Earth like the Hubble Space Telescope. All of these gather types of light (which includes all portions of the electromagnetic spectrum, from the visible light we see up to high-energy gamma rays and down to low-energy radio waves). Light can tell us a lot about the universe, from the velocity of galaxies to the chemical make-up and temperatures of stars. Until now, all discovery related to the distant universe has been through studying light.

But a century ago Einstein predicted that there may be another means of learning about the universe. According to his theory of general relativity, massive moving objects should give off gravity waves, distortions in space that spread outward at the speed of light like ripples on a pond. These waves would be a completely new way of giving us information about objects in space. It would be as though having only before seen distant objects in space, now we would be able to “hear” them as well.

The problem was that gravity waves would be incredibly, almost unimaginably weak and thus very, very hard to detect. As a gravity wave moves through space, it contracts space slightly along one direction while stretching it in a perpendicular direction. This contraction and stretching is tiny, amounting to something like a thousandth of the thickness of a single proton. To detect such miniscule variations in length, scientists have had to build some of the most sensitive detectors ever.

How do you detect the warping of space caused by gravitational waves? There are several detectors around the world, but the two in the U.S. that detected this first confirmed signal (which passed through the planet—and all of us—last September) were the twin detectors of LIGO, the Laser Interferometer Gravity wave Observatory, located in Washington state and Louisiana. LIGO reflects a beam of light down two 2.5-mile tunnels at right angles to each other and by analyzing the beams can detect a tiny difference in the lengths of the tunnels caused by gravitational waves. This past September they both received a signal, and after months of analysis scientists were confident that it was indeed a gravity wave.

Aerial view of the LIGO Hanford Observatory, courtesy LIGO Image Gallery,

This particular signal appears to have come from two black holes billions of light years away in the process of colliding and merging to form one larger black hole. Scientists are able to predict how such an event would “sound” (that is, what sort of gravity waves it would give off), and the signal detected matches this prediction. Scientists are also able to triangulate using the detection at the two different sights to get an idea of where in the sky the signal came from, though it’s far too distant to observe with visible light.

But that’s exactly the point: with this confirmation, we now have a completely new way of observing the universe. We’re in a similar situation to when Galileo first turned a telescope—at the time a completely new scientific instrument—to the heavens. We have a new tool, and we’re not sure what we’ll discover.

Yet our very first observation has already shown us something exciting: double black holes that eventually collide have long been predicted but never before observed. It turns out the very first thing we’ve “heard” with our new ears on the universe is itself something new.

This column first appeared in the Kankakee Daily Journal.


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