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Almost nothing can escape the strong gravitational pull of a black hole, but now scientists plan to use colliding black holes to understand the age of the universe and its evolution.
In a new study published in Physical Review Letters, University of Chicago astrophysicists have developed a method to use pairs of colliding black holes to measure how fast the universe is expanding, and with it, how the universe has evolved and where it is going. Scientists are particularly interested in using the new technique of “spectral sirens” to learn more about the “teenage years” of the universe.
Sometimes two black holes collide in spectacular collisions. Such powerful events send out space-time waves across the universe. These ripples, called gravitational waves, can be detected by ground-based observatories such as the American Laser Interferometer Gravitational-Wave Observatory and Italy’s Virgo Observatory.
The signal from these collisions contains important information about the size of black holes. But because this signal travels vast distances through space, the expansion of space changes its properties. “For example, if you took a black hole and placed it earlier in space, the signal would change and make it look like a bigger black hole than it actually is,” explained astrophysicist Daniel Holz, one of the paper’s two authors. in a UChicago press release.
Scientists need to figure out a way to measure how these signals have changed, and it could help them calculate the rate at which the universe is expanding. The problem lies in understanding how much the signal has changed from the original.
Current evidence suggests that most black holes we have detected are 5 to 40 times the mass of our Sun. Holz and first author Jose María Ezquiaga plan to use this and other newfound knowledge about the black hole population as a calibration tool.
As the capabilities of LIGO and other interferometer observatories expand, they will be able to observe “weaker” gravitational waves. This excites scientists because this data, combined with the Silent Siren method, can potentially offer a unique insight into what is called the “coming of age” years: a period about 10 billion years ago. This is interesting because this particular period is difficult to study with current methodologies.
Astrophysicists can use the cosmic microwave background radiation to look at the earliest moments of the universe. They can also look around at galaxies near our own Milky Way to study the recent history of the universe. But the interim period is a tough nut to crack.
“Around that time, we transitioned from dark matter being the dominant force in the universe to dark energy taking over, and we are very interested in studying this critical transition,” Ezquiaga said in a press statement.
According to Holz, the new method could be an “incredibly powerful method” for learning about the universe if it could be used with data from thousands of such signals.