THIS week, scientists announced the first detection of gravitational waves from the collision between two neutron stars. Gravitational waves are ripples in space-time predicted by Einstein more than 100 years ago. The announcement was celebrated as the beginning of “multi-messenger astronomy,” the astronomy of observing cosmic events by detecting the light, particles, and now gravitational waves coming from them.
In addition to this important milestone, the detection can help shed light on some longstanding debates in astronomy, from the origin of the brightest cosmic flashes to the process that created the silver and gold in your jewelry.
The detection announced this week marks the 5th time gravitational waves were detected. The first four came from the merger of two black holes.
Black holes are objects so massive not even light can escape their pull. As a result, the first four detections were not accompanied by the detection of light. What makes the latest detection special is the fact that, for the first time, light and gravitational waves were detected coming from the same source.
The detection of the space-time ripples was made using the two detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States and the Virgo detector in Italy.
The three detectors allowed astronomers using light-gathering telescopes to turn their instruments and look for the light from the explosion. It’s as if a loud bang alerted them to fireworks—the bang would be the gravitational waves, the fireworks would be the light.
Some astronomers have compared the advent of multi-messenger astronomy with the transition from the age of silent films, when people only saw moving pictures, to the age of the talking film, when watching a movie means both seeing and hearing.
Current instruments were able to detect gravitational waves from colliding black holes and colliding neutron stars because such objects are massive, compact, and move at the frequency to which the instruments are sensitive.
Neutron stars are what remains after massive stars explode. A typical neutron star is half the size of Metro Manila, or about the size of Cebu City. However, they can have about twice the mass of the Sun. This means they are very dense objects. A teaspoon of neutron star weighs about 10 million tons!
Because of their extreme density, the collision of two neutron stars has long been proposed as the solution to at least two cosmic mysteries.
The first mystery is the origin of some of the brightest flashes in the universe called gamma-ray bursts (GRBs).
One top contender as a source of GRBs are supernovae, which are the explosive death of massive stars. Another contender are kilonovae, which are the result of the collision between two neutron stars.
When astronomers working at LIGO and Virgo detected gravitational waves from colliding neutron stars, they quickly alerted their counterparts working on light, who as a response turned their telescopes to the appropriate region of the sky.
Shortly after that, astronomers working at the Fermi-Gamma Ray Telescope and Integral Telescope detected a GRB coming from the target region. This shows that kilonovae are indeed sources of GRBs.
The second mystery is the origin of the heaviest elements in the universe.
The lightest elements in the universe, hydrogen and helium, were created during the birth of the universe some 13.8 billion years ago. Heavier elements such as carbon and oxygen are created inside stars. When stars die, they seed the universe with these elements. Since we are made of these elements, we are literally stardust!
Stars, however, can create elements only up to iron. Heavier elements, such as arsenic and selenium, are created in supernovae.
For a long time, astronomers have puzzled over the origin of the heaviest elements such as gold and uranium.
According to calculations, the lighter ones among them can be created by supernovae. However, the amount of these heavy elements in the universe can’t seem to be accounted for by supernovae alone.
To explain the observed abundance of heavy elements, astronomers theorized that neutron star collisions produce most of the gold, silver, and other heavy elements in the universe.
By combining the light and gravitational waves detected from the colliding neutron stars, astronomers were able to confirm this theory. In fact, according to calculations, the recently detected neutron star collision produced somewhere between a few tens to a hundred Earth masses worth of gold.
Just think about that for a moment. In the dawn of multi-messenger astronomy, we now have realized that the silver and gold in your jewelry were created along with the brightest flashes in the universe during the collision between two neutron stars.
And this is just the beginning. Expect a lot more mind-blowing discoveries to come.
Pecier Decierdo is the resident physicist and astronomer of The Mind Museum