by In 2015, the iconic Laser Interferometer Gravitational Observatory (LIGO) made the first ever tangible detection of gravitational waves. The waves were the result of two black holes colliding far away in the universe; since then, a wealth of such signals have been seen from black hole mergers, neutron stars and even a few mixed mergers between the two.
But, despite the success of LIGO — based at two US sites supported by the Virgo detector, based in Italy, and Japan’s Kamioka Gravitational-Wave Detector (KAGRA) — astronomers were only able to detect one of the events confirm this gravitation that produces waves. using “traditional” light-based astronomy. That event was the merger of two neutron stars, producing the signal of GW170817’s gravitational waves.
Now, a team of scientists from the University of Minnesota has developed software upgrades that will help alert astronomers to merger events just 30 seconds after gravitational waves are picked up on Earth. This early warning system should allow further merger events to be followed up with light-based astronomy.
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“With this software, we can detect the gravitational wave from neutron star collisions that are usually too small to see unless we know exactly where to look,” Andrew Toivonen, team member and Ph.D. student at the University of Minnesota Twin Cities School of Physics and Astronomy, said in a statement. “Finding the gravitational waves first will help detect the collision and help astronomers and astrophysicists do more research.”
What are gravitational waves?
Gravitational waves are tiny ripples in the fabric of space and time, both of which are united as a single four-dimensional entity called “space-time.” Such a leak was first predicted by Albert Einstein in his 1915 theory of gravity, general relativity.
General relativity predicts that gravity arises from objects with mass that thicken the fabric of spacetime. The greater the mass, the more extreme the curve, thus explaining why stars have a greater gravitational influence than planets.
Einstein also theorized that when things accelerate, space-time collapses. These flips are only detectable when extremely massive objects — things like neutron stars and black holes that orbit each other in binary systems — emit gravitational waves as they do so. This continuous emission of gravitational waves, Einstein said, would build up angular momentum and pull the ultradense objects together and eventually merge, a collision that sends out a high-pitched “scream” of gravitational waves.
However, Einstein thought that even gravitational waves from objects significant enough to generate them would be too small to ever be detected here on Earth.
Fortunately, he was wrong.
Still, seeing gravitational waves is no mean feat. After all, neutron stars and black hole binaries are located millions (sometimes even billions) of light years away, and gravitational waves lose energy as they travel through the cosmos.
To enable LIGO to detect gravitational waves from these events, this giant laser interferometer consists of two L-shaped arms, each 2.5 miles (4 kilometers) long. In phase, a laser light shines down each of these limbs. This means that when the beams meet, the peaks and troughs of their waves line up, and the laser light is amplified, which is called “constructive interference.”
However, if a gravitational wave passes one of these lasers and space is compressed and stretched, then the laser passing this part of space would be out of phase, meaning that troughs meet peaks, and vice vice versa, resulting in “destructive interference” and thus no amplification.
The changes that LIGO picks up are “hearing” gravitational waves 0.0001 times the width of protons, particles that sit at the heart of atomic nuclei. To put this in “standard” astronomical terms, this is equivalent to measuring the distance to the nearest star, Proxima Centauri, about 4.2 light years away, with a quantitative precision equal to the width of a human hair.
LIGO, Virgo and KAGRA are currently in their fourth operational run, which began on 24 May 2023, and is scheduled to last until February 2025. Between each of the previous operational runs, scientists in the LIGO/Virgo collaboration have made upgrades /KAGRA is the software used to detect the shape of gravitational wave signals, track how the signal evolves, and then estimate the mass of the neutron stars or black holes that collided to create the signal. This software also sends out an alert to other scientists.
Thanks to simulations created using data collected from one to three observing periods, as well as artificially generated gravitational signals, the team now knows that it is possible to upgrade the observing software that allows for alerts to go out within 30 seconds of detecting gravitational waves during an observation. . Such upgrades will affect observation period four.
That should help astronomers track the locations of these events in the sky with light-based astronomy, which no current gravity detector can do, and determine how collisions between the most exotic and mysterious objects evolve in the cosmos over time.
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This is unlikely to be the end of the upgrades to gravitational wave detection alerts. At the end of this current operation, scientists of the LIGO/Virgo/KAGRA collaboration will use data collected in almost two years of “listening” to a universal symphony of colliding black holes and neutron stars to further improve the speed of alerts.
The team’s research was published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).
