Photo: Contribution
If you’ve ever sat by a pond on a summer afternoon, you must have been watching the ripples.
When the fish emerges for a moment, the ripple pattern spreads. Reeds moving in the breeze also make ripples. So is the dragonfly. Touch the surface for a moment before flying. The whirligig beetle draws a tight circle to speed up and move the spiral ripples outward.
This behavior has a purpose. Ripples reflect on nearby objects, telling the beetle about threats and potential prey, and letting him or her be a smart, healthy and attractive beetle. You can place many sensors on the edge of the pond to measure the timing, size, and curvature of all ripples that reach the shore, and create an image of them moving around.
The same goes for those that move in space. Space is not “nothing”. It can be stretched, twisted and compressed. This pair is called “space-time” because time is closely related to space.
Just as the events of a pond create ripples, the events of space-time create ripples and waves that spread in all directions. These waves and ripples have come to be called “gravitational waves”. Exploding stars make ripples, much like throwing stones into a pond. Like ducks swimming across ponds and high-speed whirligig beetles, moving in space-time produces bow waves and wakes.
However, at the distance of the universe, the waves generated by the movement and collision of planets are too weak to detect. On the other hand, exploding stars, neutron stars, or black holes that orbit each other create detectable ripples in space-time.
As anyone who has rowed or rowed a boat knows, moving a boat through the water requires energy. Some of that energy will create waves. In other words, planets and objects orbiting other objects such as stars are losing energy as gravitational waves. This will slowly spiral inward until it collides.
Fortunately for a planet like us, the rate of energy loss from having to push through the universe is negligible. But for very large objects orbiting close to each other, such as neutron stars and black holes, that’s a completely different story. So much energy is put in to create the gravitational waves, the body spirals inward and moves faster and faster, like two whirligig beetles meet.
The combination of the two bodies into one is dramatic and produces more gravitational waves. As with the beetle, it receives one group of waves per revolution. These pulses of gravitational waves become faster and faster as the object approaches and takes less time to complete each rotation.
Given the size and mass of these objects, it is difficult to visualize the speed at which they sway with each other. Just before the collision, they are moving so fast that they only hear some kind of chirp and that’s it.
Observations made here on Earth using gravitational wave detectors can be seen here and here.
The existence of gravitational waves was predicted by Albert Einstein. But he suggested they would be too weak to actually detect. In 2015 he proved wrong. We are currently observing waves generated by high energy events such as black hole collisions.
For now, you can only detect the waves and get a rough idea of where the waves came from. There is a real hope that we will soon be able to do better.
Not so long ago, our optical and radio telescopes were only useful for studying individual objects of particular interest. Now you can image a vast area of the sky to capture a myriad of interesting objects.
At some point, the Laser Interferometer Space Antenna does that. You can capture the ripples of the pond in space and everything that makes it.
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• Jupiter, Venus, Mars, and Saturn are arranged in ascending order of brightness at dawn.
• The month will reach the last quarter on April 23rd.
This article was written by or on behalf of an outsourced columnist and does not necessarily reflect the views of castanets.
