In 2015, the iconic Laser Interferometer Gravitational Wave Observatory (LIGO) made the first concrete detection of gravitational waves. The waves were the result of the collision of two black holes far away in the universe; Since then, numerous such signals have been detected from mergers of black holes, neutron stars, and even a few mixed mergers between the two.
But despite the success of LIGO, based at two sites in the United States and powered by the Virgo detector in Italy and Japan’s Kamioka Gravitational Wave Detector (KAGRA), astronomers have only been able to confirm one of these gravitational wave-producing events. using “conventional” light-based astronomy. This event was the merger of two neutron stars that produced the GW170817 gravitational wave signal.
Now, a team of scientists at the University of Minnesota has developed software upgrades that could help alert astronomers to merger events just 30 seconds after gravitational waves are received on Earth. This early warning system should allow more merger events to be tracked with light-based astronomy.
Relating to: Gravitational waves reveal first-of-its-kind merger between neutron star and mysterious object
Team member and Ph.D. “With this software, we can detect the gravitational wave resulting from neutron star collisions, which are normally too weak to see unless we know exactly where to look,” said Andrew Toivonen. A student at the University of Minnesota Twin Cities School of Physics and Astronomy made a statement. “Detecting gravitational waves first will help pinpoint the location of the collision and enable astronomers and astrophysicists to complete further investigations.”
What are gravitational waves?
Gravitational waves are tiny ripples in the fabric of space and time; They both merge into a single, four-dimensional entity called “space-time”. Such fluctuations were first predicted by Albert Einstein in his 1915 theory of gravity, general relativity.
General relativity predicts that gravity arises from objects with mass that distort the fabric of space-time. The greater the mass, the more extreme the curve, which explains why stars have a greater gravitational influence than planets.
Einstein also theorized that when objects accelerate, they cause space-time to fluctuate. These fluctuations can only be detected when truly massive objects—objects that orbit each other in binary systems, such as neutron stars and black holes, and emit gravitational waves as they do so—accelerate. Einstein said that this sustained emission of gravitational waves would carry angular momentum and cause extremely dense objects to come together and eventually coalesce, a collision that would send out a high-pitched “scream” of gravitational waves.
But Einstein thought that even gravitational waves from objects significant enough to generate them would be too weak to be detected here on Earth.
Fortunately he was wrong.
However, detecting gravitational waves is still no easy feat. After all, neutron star and black hole binaries are millions (sometimes even billions) of light-years away, and gravitational waves lose energy as they move through the cosmos.
To enable LIGO to detect gravitational waves from these events, this massive laser interferometer consists of two L-shaped arms, each 2.5 miles (4 kilometers) long. While in phase, laser light shines towards each of these arms. This means that when the beams meet, the peaks and troughs of the waves align and the laser light is amplified; this is called “constructive interference”.
However, if a gravitational wave passes over one of these lasers and space becomes compressed and stretched, then the laser passing over that part of space becomes out of phase, meaning troughs meet peaks and vice versa, resulting in “destructive interference”. and hence no amplification.
The changes that LIGO captures to “hear” gravitational waves are 0.0001 times the width of the proton particles at the heart of the atomic nucleus. To put this in “standard” astronomy terms, this is equivalent to measuring the distance to Proxima Centauri, the nearest star about 4.2 light-years away, with a quantitative accuracy equal to the width of a human hair.
LIGO, Virgo and KAGRA are currently in their fourth operational run, which started on May 24, 2023 and is planned to last until February 2025. Scientists in the LIGO/Virgo/KAGRA collaboration made upgrades between each of the previous operational studies. Software used to detect the shape of gravitational wave signals, watch how the signal evolves, and then estimate the masses of the neutron stars or black holes that collided together to create the signal. This software also sends an alert to other scientists.
Thanks to data collected from the first to third observation periods and simulations created using artificially generated gravitational wave signals, the team now knows that upgrades to the observing software can be made during the observation, allowing alerts to be sent within 30 seconds of gravitational wave detection. Such improvements will affect the fourth observation period.
This will help astronomers track the locations of these events in the sky with light-based astronomy, which no gravitational wave detectors can currently do, and determine how collisions between the most exotic and mysterious objects in the cosmos evolve over time.
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This is unlikely to be the end of upgrades to gravitational wave detection alerts. At the end of this current study, scientists in the LIGO/Virgo/KAGRA collaboration will use data collected over nearly two years of “listening” to the universal symphony of colliding black holes and neutron stars to further increase the rate of stimulation.
The team’s research was published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).