14:39 GMT28 January 2021
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    The universe is not only expanding, but doing so increasingly faster, leaving scientists puzzling over the reasons and the exact rate, and proposing a plethora of theories for the “missing piece to the puzzle”.

    A team of scientists have carried out supercomputer simulation of merging black holes sending out gravitational waves to come up with a theory potentially offering to provide the missing clue to our understanding of the cosmic forces at play in our Universe.

    In the paper, published on 21 December in Physical Review D, co-authored by physicists from the University of Chicago in the United States and the Max Planck Institute for Gravitational Physics in Germany, lay out how LIGO (Laser Interferometer Gravitational-Wave Observatory) gravitational waves could be scrambled to offer the information scientists have been seeking.

    The study, “Gravitational wave lensing beyond general relativity: Birefringence, echoes, and shadows,” claims that this would depend on finding “ripples” through space and time heading towards Earth after having been “bent” by travelling through supermassive black holes or large galaxies.

    Riddle of the Universe

    Cosmology scientists have long been pondering the mystery of why the Universe is expanding faster and faster over time. Astrophysicists have proposed diverse theories for what the missing answer to the conundrum might be.

    “Many of these rely on changing the way gravity works over large scales. So gravitational waves are the perfect messenger to see these possible modifications of gravity, if they exist,” said Dr. Jose María Ezquiaga, a postdoctoral researcher in the Kavli Institute for Cosmological Physics and Enrico Fermi Institute at the University of Chicago.

    Whenever black holes or neutron stars collide in the Universe, they create gravitational waves –a ripple through the fabric of “space-time”. As the waves travel across space they carry the signature of whatever made it, such as two black holes or two neutron stars merging together. Since 2015 scientists have been able to pick up these ripples using the LIGO observatories.

    ​If such waves hit a supermassive black hole or a cluster of galaxies on their way to Earth, their signature would change, claim Ezquiaga and his co-author Miguel Zumalacarregui, a scientist at the Max Planck Institute.

    Furthermore, if there were a difference in gravity compared to Albert Einstein’s theory, the evidence would be “embedded” in that signature.

    Extra Particle

    One of the suggested theories to explain the missing “piece of the puzzle” pertaining to the Universe is the existence of an extra particle that would generate a “background” around large objects.

    In that case, once a gravitational wave hits a supermassive black hole, it would generate waves that would get intertwined with the gravitational wave itself.

    ​Accordingly, the gravitational wave signature would carry an “echo” of this impact, or show up “scrambled”.

    “This is a new way to probe scenarios that couldn’t be tested before,” Dr. Ezquiaga said, adding:

    “In our last observing run with LIGO, we were seeing a new gravitational wave reading every six days. But in the entire Universe, we think they’re actually happening once every 5 minutes. In the next upgrade, we could see… hundreds of events per year,” said Ezquiaga.

    According to the team, increased numbers suggest it is likely that one or more waves will have “travelled through a massive object”. This will provide researchers with ample material for follow-up studies as they seek clues to the missing components.


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    Max Planck Institute, Laser Interferometer Gravitational-Wave Observatory (LIGO), Laser Interferometer Gravitational-wave Observatory (LIGO), Albert Einstein, galaxy, black holes, black hole, black hole, gravitational waves
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