Black hole week ends today (May 10), and there’s no better way to mark the occasion than with “egg-casual” black hole science.
Using gravitational wave measurements made by the US-based Laser Interferometer Gravitational Wave Observatory (LIGO) and the Virgo and KAGRA detectors in Italy and Japan, scientists found that the orbits of some binary black holes may be eggs. shaped and exhibits an interesting wobble.
This research is more than just curiosity (and an “egg excuse” to solve some bad egg-related puns). The discovery of these oval-shaped orbits in binary black hole systems could help researchers determine how each of these systems formed.
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“We found that the majority of binary black holes are expected to be in so-called ‘semi-circular’ orbits. ‘Semi-circular’ simply means that the separation of black holes decreases over time due to the emission of gravitational waves.” Nihar Gupte, lead author of the study from the Max Planck Institute for Gravitational Physics in Germany and the University of Maryland, told Space.com.
“Our study shows that several of the observed binary black holes may be in ‘eccentric’ orbits,” Gupte said. he added. “This means that black holes orbit in an oval or ‘egg’ shape.”
The team also discovered that the tip of the egg-shaped oval orbit can rotate as black holes revolve around each other, the researcher said.
“Also, if you analyze these events using a non-eccentric model,
“We overestimate the masses of black holes,” Gupte added.
What can we learn from egg-shaped black hole orbits?
Gupte and colleagues, in the LIGO-Virgo-KAGRA collaboration, examined 57 binary black hole pairs detected via gravitational waves. Gravitational waves are ripples in space-time that were first predicted by Albert Einstein in his famous theory of general relativity in 1915.
General relativity proposes that objects with mass create a curvature in the fabric of space and time and coalesce into a four-dimensional entity called “spacetime.” Gravity results from this curvature, which becomes more extreme as the masses of objects increase. Therefore, stars have a greater gravitational effect than planets, and galaxies have a greater gravitational effect than stars.
Einstein also predicted in this revolutionary theory of gravity that when objects accelerate, they will send out tiny ripples (gravitational waves) that propagate through space-time. However, these fluctuations are insignificant until the domain of extremely dense objects such as neutron stars and black holes is reached.
When binary neutron stars, or black holes, orbit each other, they constantly emit gravitational waves, which remove energy from the system in the form of angular momentum. The loss of angular momentum causes the orbits of these objects to narrow, holding them together until gravity takes over. Eventually they collide and merge, finally sending out high-pitched gravitational waves.
Einstein thought that even these gravitational waves would be too weak to be detected on Earth. Fortunately, in September 2015, LIGO proved the great scientist wrong by detecting GW150914, the gravitational wave signal from a black hole binary merger 1 billion light-years away.
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As detections of gravitational waves continue to fluctuate, scientists like Gupta are learning how to use them to reveal details about the objects that create them, as this new research shows.
Gupta explained that using gravitational waves to understand the orbits of binary black holes is akin to paleontologists examining bones to reconstruct how dinosaurs may have lived. Physicists can thus study the properties of binary black hole mergers to understand how binary black holes come together in the first place.
This can happen in two different ways. Dynamic interactions occur when a black hole binary encounters and interacts with another black hole or even another black hole binary system.
Binaries, on the other hand, can be isolated and formed more simply from two stars orbiting each other and becoming black holes, or from one black hole wandering too close to another and colliding and forming a binary before merging.
“The idea is that if we observe a dyad with eccentricity, it is likely to result from a dynamic interaction,” Gupta said. said. “These chaotic interactions can tear the binary apart and eject the black holes that formed them from their host galaxies and galaxy clusters. But sometimes they can narrow the distance between two black holes, causing eccentricities and causing them to merge on short time scales.”
In addition to using orbital eccentricity to tell the story of black hole binaries, the scientist and his team are also interested in studying what the oval nature of the orbits does to the gravitational wave emissions of these systems.
“When you have eccentricity, it means that at some points in the orbit the black holes are closer together,” Gupta explained. “When black holes are closer to each other, they have a larger acceleration, which means they emit more gravitational waves. On the other hand, if they are further away, they have a smaller acceleration, which means they emit fewer gravitational waves.”
“So you start to see little dots in the amplitude of the waveform [the total pattern of gravitational waves]It occurs as a result of black holes approaching and moving away from each other!”
It would be incredibly difficult to determine the nature and history of binary black holes without the use of gravitational waves. An alternative method of understanding the origin of binary black holes is to look for “common envelope” events with standard light-based astronomy.
These events begin when a star and a black hole revolve around each other and that star grows and turns into a red giant. The outer layers of the swollen star form a common envelope around both inhabitants of the binary system, causing friction between the black hole and the star. This narrows the orbit of the binary, and after it eventually collapses into a red giant black hole, this leads to the merger of a binary black hole.
“The problem is that observing this critical period is difficult with electromagnetic observations. This is because massive stars are rare and short-lived, so the critical evolutionary stages of compact object mergers occupy a small fraction of these systems,” Gupta said. “On the other hand, we can understand the final moments of the binary merger by studying gravitational waves. This could allow us to trace the history of the merger and hypothesize what might have created it.”
Gravitational waves are particularly useful in this regard, he added, because they are an “extremely clean probe,” or distant events. This refers to the fact that these ripples in space-time can travel very large distances without interference from anything between the binary system and the Earth.
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“While we do not claim that these are definitive detections of eccentric binary black holes, these results do point to eccentricity [in the] “Current population,” Gupte said. “This is an important consideration for current Earth-based gravitational wave detector observation work, as well as future ground- and space-based gravitational wave detectors.
“We do not currently have enough data to pinpoint the origins of binary black holes. But if we observe more eccentric binary black holes in the future, we can begin to place constraints on what mechanisms form these systems.”
The team’s paper has not yet been published in a peer-reviewed journal. You can read a preprint of this in the online repository arXiv.