Ripples in the structure of space and time provide new clues to the shape of a black hole

Ripples in the structure of space and time provide new clues to the shape of a black hole

Black holes are one of the most fascinating objects in the universe. On a surface known as the “event horizon”, gravity is so strong that even light cannot escape. In general, black holes are quiet, quiet creatures that swallow up getting too close. However, when two black holes collide and merge, one of the most catastrophic events in the universe is created. black hole As they are born and reach their final form, they release a huge amount of energy. This phenomenon offers astronomers a unique opportunity to observe rapidly changing black holes and explore gravity in its most extreme form.

Colliding black holes do not produce light, but astronomers have detected Gravitational wave -Waves rise in the structure of space and time. Scientists speculate that the behavior of the black hole remaining after impact is important to understanding gravity and should be encoded in the emitted gravitational wave.

Black hole cuff

The artist’s painting at the black hole bridge. Credits: C. Evans; JC Bustillo

In the article posted on Communication physics (Nature), a team of scientists led by OzGrav graduate Professor Juan Calderón Bustillo (now’La Caixa Junior Leader-Marie Curie Fellow’ at the Institute of High Energy Physics in Galicia (Santiago de Compostela, Spain)) revealed how gravitational waves work. It encodes the shape of the black hole that merges when the black hole settles into its final form.

Christopher Evans, a graduate student and co-author at the Georgia Institute of Technology, USA, says: “We used a supercomputer to perform a black hole collision simulation and then compared it to a gravitational wave that emits the shape of a rapidly changing residual black hole. We can learn more about the greatly changing shape of the final black hole by discovering that these signals are much richer and more complex than you would normally think.”

Black hole merger stage

First, the two black holes orbit each other slowly approaching during the inspiratory phase. Second, the two black holes merge to form a distorted black hole. Finally, the black hole reaches its final form. b: The frequency of the gravitational wave signal observed as a function of time at the top (leftmost) of the collision and at various locations on the equator (rest). The first signal shows a typical “chipping” signal whose frequency rises as a function of time. The remaining 3 show that after a collision (at t = 0) the frequency drops and rises again, creating a second “chirp”. Source: C. Evans, J. Calderón Bustillo

Gravity waves from colliding black holes are very simple signals known as “chirps”. As the two black holes approach each other, they emit signals of increasing frequency and amplitude that represent the speed and radius of the orbit. According to Professor Calderón Bustillo, “As the two black holes approach faster and faster, the pitch and amplitude of the signal increase. After the collision, the last remaining black hole emits a signal of constant pitch and attenuating amplitude, like the sound of a bell.” This principle is consistent with all observations of gravitational waves so far when studying collisions from above.

However, this study found that if a collision was observed at the “equator” of the final black hole, something completely different would happen. “When we observed a black hole at the equator, we found that the final black hole emits a more complex signal, which goes up and down several times before it dies,” explains Professor Calderón Bustillo. In other words, a black hole is actually chirping multiple times.”

Black hole shape left after collision

The shape of the black hole remaining after the black hole collision is described in detail as’chestnut shape’. A strong gravitational emission (yellow) cluster area near the cusps. This black hole rotates, creating a cusp point for all nearby observers. Source: C. Evans, J. Calderón Bustillo

The team found that this had to do with the shape of the final black hole, which acts like a kind of gravitational wave lighthouse. “When the two original’parent’ black holes are of different sizes, the final black hole initially looks like this: It’s a chestnut tree with a vertex on one side and a wider, softer back on the other,” says Bustillo. “Black holes have been found to emit stronger gravitational waves through the most curved areas, the area surrounding the cusps. This is because the remaining black hole is also spinning, and its ends and backs repeatedly point to all observers, generating multiple tweets.”

“The relationship between gravitational waves and the behavior of the final black hole has long been speculated,” said co-author Pablo Laguna, professor of physics at the Georgia Institute of Technology and now a professor at the University of Texas at Austin. , Our research gives the first clear example of this kind of relationship.”

See also: October 8, 2020, Communication physics.
DOI: 10.1038 / s42005-020-00446-7

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