In the depths of the universe, there may be outlandish entities similar to black holes that can redefine physics as we know it. A new study has calculated that in the coming years, gravitational wave observatories on Earth will be able to find these hypothetical eccentrics, known as exotic compact objects.
The US-based Laser Interferometer Gravitational Wave Observatory (LIGO) and its European counterpart, Virgo, were created to capture ripples in the fabric of spacetime emanating from massive objects such as black holes as well as neutron stars falling apart together. And yet there is always a chance that scientists may encounter something unexpected.
“We cannot be naive enough to assume we know everything that exists,” Luis Longo, PhD in Physics and Mathematics from the ABC Federal University in São Paulo, Brazil, told Live Science.
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Researchers have been pondering the possibilities of exotic compact objects for many years and trying to determine what they would look like for a gravitational wave detector, Longo added.
The term “exotic compact object” encompasses many different theoretical entities. Possible options include gravastars, which would look very similar to a regular black hole, but would be filled dark energy, a mysterious substance that causes the accelerated expansion of the universe. Another compact object that may be lurking in the Universe is a fluffy lump, a black hole-like knot of fundamental one-dimensional strings, proposed in the work. string theorywhich attempts to unify and replace current accepted theories in physics.
What the exotic compact objects have in common, Longo said, is that unlike a black hole, they shouldn’t have a region known as the event horizon. According to the theory of Albert Einstein relativity, the event horizon is the sphere surrounding the black hole beyond which any travel becomes one-way. Objects can slip into the event horizon, but nothing can come out of it – not even light.
But scientists know that one day Einstein’s theory of relativity will have to be replaced. Although the theory is unusually successful in describing gravity and massive cosmic entities, it says nothing about the behavior of subatomic particles. For this, physicists turn to quantum mechanics.
Hope will eventually get theory of quantum gravity it replaces both the theory of relativity and quantum mechanics. Exotic compact objects that resemble a black hole but lack an event horizon could help provide the information needed to begin building this theory of the future.
“They will violate general relativity because they will not lead to one of its key predictions,” Longo said, referring to the event horizon. “In this sense, we will be testing Einstein’s theory of gravity.”
When two black holes shatter and merge, they revolve around each other, bending spacetime and emitting gravitational waves that can impact LIGO detectors on Earth. After they meet, Longo said, the event horizon prevents additional waves from leaking out.
But since exotic compact objects will not have an event horizon, some gravitational waves can fall inward towards the center of the object and then bounce back, creating a gravitational echo that leaks outward, he added. These echoes are too weak for LIGO and Virgo to detect right now, but the equipment is currently being upgraded to improve sensitivity, and has been joined by the Kamioka Gravity Wave Detector (KAGRA) in Japan, which began operating last year.
Longo and his colleagues have calculated that during the next cycle of observations of gravitational wave detectors, due to begin in the summer of 2022, LIGO and its analogues may be sensitive enough to pick up the signal from one or two exotic compact objects, if they exist. … Longo will present his team’s results at American Physical Society April meeting on April 19.
Other researchers want to see if such a scenario could play out in the near future. “It looks like science fiction now,” Vitor Cardoso, a physicist at the Higher Technical Institute in Lisbon, Portugal, who was not involved in the work, told Live Science. “But he is rapidly moving from science fiction to established science.”
Cardoso would be thrilled if exotic compact objects turned out to be more than speculation. “We hate to see what we expect,” Cardoso said. “We hate boring science.”
However, even if LIGO detects echoes, it will likely take a long time before the scientific community confirms that they are indeed pointing to these hypothetical eccentrics, he added.
Longo would also be happy if observatories could find evidence for the existence of exotic compact objects. “This will be the first hint of the collapse of general relativity,” he said. “It would be a huge breakthrough and extremely exciting.”
Originally published on Live Science.