The merger of two galaxies is a spectacular but slow process. It can completely change the shape of a galaxy but can take up to a billion years. This hardly affects the individual stars, but their central black holes are pulled and pushed until they collide. And according to a new study, this happens very quickly in astronomical terms.
An international team has created a detailed simulation of galaxy mergers and discovered that merging supermassive black holes start emitting gravitational waves just 10 million years after the merger begins.
“The result is surprising,” explained Lucio Mayer, from the Institute for Computational Science of the University of Zurich, in a statement. “The merging of the two black holes already triggered the first gravitational waves after 10 million years – around 100 times faster than previously assumed.”
In a paper, published in the Astrophysical Journal, the researchers discussed the details of the intricate simulation, which took more than a year to complete. The team modeled two 3-billion-year-old galaxies lying quite close to each other and each sporting a 100-million-solar-mass black hole.
The researchers aimed to create the most realistic simulation they could. They were able to create a representative scenario of how the black holes would move and how the galaxies should genuinely interact.
“Our calculations therefore allow a robust forecast for the merging rate of supermassive black holes in the early stage of the universe,” explains Mayer. “They may help assess the gravitational waves eLISA is bound to find in the near future more effectively.”
eLISA is the space gravitational wave observatory that ESA is planning to launch in 2034 after the precursor technology has been successfully tested this year. The instrument will follow in the footstep of LIGO, which observed gravitational waves for the first time last year, but it will be a lot more sensitive. eLISA will detect the supermassive black holes during the spiraling phase as they move towards each other, which produce gravitational waves at lower frequencies compared to the final collision.
Galaxies might seem unchanging but they live active lives growing, changing, and sometimes colliding with each other. These collisions happen often enough to play a key role in galaxy evolution and have long-lasting impacts that we can see with our instruments.