When extreme dead stars, such as neutron stars or black holes, collide, they create a cataclysmic event with a fascinating aftermath. Here's what happens to the wreckage:
1. Kilonova: A brilliant burst of light called a kilonova occurs. This is much brighter than a typical supernova and releases enormous amounts of energy. Kilonovae are responsible for creating most of the universe's heavy elements, such as gold, platinum, and uranium.
2. Gravitational Waves: The collision sends out ripples in spacetime known as gravitational waves. These waves were first detected in 2015, confirming a major prediction of Einstein's theory of relativity.
3. Remnant: The exact nature of the remnant depends on the type of stars involved:
Two Neutron Stars: The merger can result in either a more massive neutron star or a black hole.
Neutron Star and Black Hole: The neutron star is usually disrupted and its material accretes onto the black hole, forming a hot accretion disk.
Two Black Holes: The merger creates a larger black hole.
4. Accretion Disk: In some cases, a rapidly spinning ring of matter called an accretion disk forms around the remnant. This disk contains a small amount of the system's mass but a significant portion of its angular momentum.
5. Ejecta: The collision ejects a vast amount of material into space. This material can include heavy elements created in the kilonova, as well as neutron-rich matter.
6. Gamma-Ray Burst: In some cases, particularly when a rapidly rotating neutron star is involved, the merger can trigger a short-duration gamma-ray burst, one of the most powerful explosions in the universe.
7. Pulsar Wind Nebula: If a highly magnetized neutron star (a pulsar) survives the merger, it can create a pulsar wind nebula as it interacts with the surrounding material.
Image of a kilonova
Image of a neutron star merger:
The study of these extreme events provides valuable insights into the formation of heavy elements, the nature of gravity, and the evolution of the universe.