Last month the big news in the astronomy and physics world was the detection of gravitational waves.
This detection is a big deal because it opens the door to a new type of astronomy – gravitational waves can potentially reveal a lot about our universe that is just not possible with light-wave-based astronomy, including clues to what happened in the very earliest moments of the universe, and how gravity actually works.
Understanding gravity matters! Its effects permeate everything - we see the small-scale effects of gravity around us every day, including the ocean tides and the existence of the very atmosphere that we breathe, and on a larger scale it's responsible for much of the structure and movement of the universe such the orbiting motions of moons, planets and stars, the shapes of galaxies, and even the way that all these objects are spread throughout the universe. The way that it actually works is not well understood, but in simple terms, the more massive an object is, the greater its gravitational pull; and its pull, although diminishing with distance, can stretch across vast reaches of space and is theoretically infinite!
Tides are a fascinating effect of gravity and can appear in many different forms. For example, we all know that the Moon's gravity causes the ocean tides. But the Earth's gravity also affects the Moon - as a result, the Moon and Earth are moving apart. What's more, research published late last year has shown that Earth's gravity has tidal effects on the Moon - with no water on its surface to absorb the strain, the Moon's rocky crust itself is becoming fractured due to the stress.
This effect is even more extreme on Jupiter's rocky moon Io – this small satellite orbits so close to Jupiter that its rocks become repeatedly stretched and compressed by its parent's gravity, causing them to become molten in places and erupt as volcanoes.
A breath of air
We also have gravity to thank for a crucial feature of our planet, the atmosphere – without sufficient gravity most of it would simply evaporate into space, a fate that has befallen other smaller planets in the solar system, such Mars and Mercury.
Gravity is also a very powerful tool for exploring the universe in many different ways. Just a couple of examples: In our our neighbourhood, spacecraft exploring the solar system, such as the Cassini mission to Saturn, can use the power of gravity by doing a 'gravity assist'' around one or more others planet in order to gain enough momentum to reach their final destination.
And at the other end of the distance scale, astronomers studying distant targets often make use of the 'gravitational lensing' effect, whereby light from distant objects can be distorted and magnified by the gravity of massive objects near the line of sight, making very faint objects detectable.
So, going back to Gravitational Waves, what are they exactly, and how were they detected? This phenomenon was predicted a century ago by Einstein's theory of relativity, when his calculations showed that massive accelerating objects would cause spreading ripples in the fabric of space/time itself, just like the concentric ripples of water around a dropped pebble. But although scientists have been searching for evidence for decades, the effect is so tiny that only now, with the advent of modern super-sensitive technology, have they succeeded in detecting a gravitational wave effect.
The principle of the detector set-up is simple: two very precisely measured laser beams of equal lengths at right angles to each other – as the gravitational wave passes, their length changes very slightly and at a slightly different time. This particular event, caused by the collision of two black holes. was picked up by two totally different detectors on opposite sides of North America. This image shows how the signals exactly match each other exactly (bottom graph), with just a very small time offset, because the signal reached the Livingstone dectector first by a margin of a few milliseconds.
Plans are now in progress to develop a space-based detector of gravitational waves, the first step being ESA's LISA Pathfinder spacecraft, launched last December in order to test the proposed method of detection. Watch this space!
Faults and tidal effects on the Moon http://www.nasa.gov/press-release/goddard/shrinking-moon-tides
Dectectiom of gravitational waves: https://www.ligo.caltech.edu/detection
Gravity assist technique: http://saturn.jpl.nasa.gov/mission/missiongravityassistprimer/
LISA Pathfinder mission: http://sci.esa.int/lisa-pathfinder/
Image Credits:
1.ISS Crew Earth Observations Experiment and Image Science & Analysis Laboratory/Johnson Space Center.
2 NASA/LRO/Arizona State University/Smi
3.Courtesy Caltech/MIT/LIGO Lab