Across the universe, violent collisions of cosmic beasts like black holes call the space-time key, producing ripples called gravitational waves. For most of history, humans have ignored those celestial babbles. Today we detected dozens of them.
The first came in 2015, when scientists at the Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, detected gravitational waves arising from the fusion of two black holes. That event shook the bones of the cosmos, shaking the underlying structure of space and time. Detection also provoked astronomy, providing a new way to observe the universe and verified a prediction of Albert Einstein's general theory of relativity (SN: 2/11/16).
But like a lone ripple in a vast sea, a single detection can only tell scientists. Now, LIGO and its partner observatory Advanced Virgo have collected 50 sets of gravitational waves. Most of these space-time waves resulted from two black holes spiraling inward before colliding. Some arose from collisions of dense stellar corpses called neutron stars. Two collisions involve celestial bodies that cannot be identified with confidence, suggesting that scientists were able to see the first fusion of a neutron star with a black hole (SN: 23/06/20).
Each gravitational wave event detected to date, on a graph
Scientists have detected 50 collisions of massive objects in space. Explore the details of these smashups below.
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The farther away the Earth's collision is, the later the gravitational waves arrive. Some detected ripples were born when the universe was only half its current age of 13.8 billion years. The less massive mergers of the collection tend to take place in the more recent past; they are closer to Earth. This is because LIGO and Virgo are harder to see in small smashups.
Some of the 50 collisions left behind surprisingly large black holes, including the largest known fusion, which created the first definitive example of a class of medium-sized black holes (SN: 9/2/20). The data also revealed that some black holes rotate rapidly before merging and that fusions can occur between objects with very different masses (SN: 20/04/20). That information could help scientists understand how pairs of black holes form.
With so much data, there are many questions to explore. Gravitational wave sets have even become analog sound waves, allowing an auditory appreciation of these enigmatic events.
Future detections will further illuminate the furtive movements of these mysterious objects. Welcome to a new era of astronomy in which black holes and neutron stars regularly communicate their secrets to Earth.