Six Gravitational-Wave Breakthroughs Scientists Can’t Wait to See

After years of downtime for upgrades, the world’s premier gravitational-wave observatories are coming back online with big hopes for transformative discoveries

On May 24, the Laser Interferometer Gravitational-Wave Observatory (LIGO) will continue to hunt for gravitational waves – small periodic variations in the curvature of space and time created by events. The universe is as distant and violent as the collision of two black holes.

Some would call gravitational wave scientists lucky, based on the series of remarkable, transformative discoveries in their field that took place in less than a decade. During each of their first three observations, the gravitational wave detectors found or confirmed a new astrophysical phenomenon. First, in 2015, the collision of black holes, two years later the collision of microscopic dead stars called neutron stars, and then in 2019, of zero-mass objects. is believed to exist in the universe.

Past performance is not an indicator of future success. However, as LIGO lights up this month (followed by two more detectors:
Virgo in Italy and KAGRA in Japan), there are good reasons to be optimistic that this trend of cosmic exploration will continue. 

Given how productive these detectors are, why would astronomers turn them on and off in the first place? The simple answer is that gravitational wave observations rely on rapidly developing advanced technology. This allows scientists to detect gravitational waves over a region of the universe with magnitudes greater than they would have been able to detect directly for the first time. However, upgrading gravitational wave detectors is a complex and time-consuming task. It cannot be done in parallel with observations. Hence the observation stages:
scientists alternate between improving their detectors and listening to the sky.

Probing this vastly expanded universe virtually guarantees that observers will find new skeletons in the cosmic closet – discoveries that could transform astrophysics and science at large. . Here, we’ve listed six potential breakouts we’re looking forward to:

1. The heaviest black holes. The heaviest black hole we’ve detected to date with gravitational waves about 100 times the mass of our sun. However, thanks to the upgrade, our detectors are now sensitive to gravitational waves emitted by colliding black holes 1,000 times more massive than our sun. The discovery of these much more massive black holes would be a game changer; this will tell us how black holes grow and how some of them grow to supermassive sizes millions or billions of times larger than our parent star. We know of such supermassive black holes at the centers of large galaxies, but their origin is currently a mystery.
2. The collision of radiating black holes. Black holes are special because nothing, not even light, can escape them. However, suppose two black holes collide in the middle of an interstellar gas cloud. Such a collision could create cosmic fireworks in this surrounding material. Detecting the electromagnetic signature or possibly even neutrinos of such collisions, as well as gravitational waves, would be a major discovery. With such data, we were able to determine with great accuracy where and how the crash occurred, capturing vivid new details about the previously inaccessible harsh space environment. The precise location of this gravitational wave signal could also provide astronomers with a new, independent way to measure the expansion rate of the universe.
3. The origin of gold and platinum in the universe. While most elements in the universe are forged inside stars by fusion fusion, heavier elements, such as gold, platinum or uranium, require a special creation process. . In 2017, scientists observed both gravitational waves and light emitted simultaneously from a pair of colliding neutron stars, revealing how and to what extent these events produce heavy elements like So. It is not clear whether neutron star collisions are really the main source of cosmic gold, but what is certain is that the detection and study of these collisions will resolve the ongoing fierce debate and will allow us to better understand the stress conditions of neutron stars where and when. because life as we know it can appear in the universe. 
4. Supernova explosion nearby. At the end of their life cycles, the most massive stars explode into supernovae, creating one of the most spectacular events in the universe. These explosions actually start with an explosion:
   A stellar core collapses under its own gravity as it reaches critical mass, resulting in a massive energy release that abruptly blows up the entire star. Detecting the gravitational waves of such a “core collapse” will allow us to peer into the center of the explosion, revealing its early stages that we would otherwise be hidden deep below. the surface of the dying star. This can tell us how matter behaves at a density greater than the nucleus of an atom, that is, at a density greater than 100 million tons per tablespoon of matter.
5. Breaking Einstein’s theory of general relativity. Scientists suspect that our current theory of gravity and spacetime is incomplete because we cannot reconcile it with the quantum mechanical description of reality. Part of the problem is the lack of possible experiments that simultaneously test both strong gravity and the small spatial scales where most of the effects of quantum mechanics manifest themselves. Black holes are probably the closest to these two extremes. That means finding deviations from general relativity in highly accurate gravitational wave observations could rewrite some of our basic understanding of space and time.
6. The unknown “unknown”. History tells us that we should expect the unexpected whenever we broaden our horizons. It would be no different for gravitational wave astrophysics. The most interesting game changer would be if we discovered a new kind of cosmic object or phenomenon that surprised us in some way. Fortunately, scientists are well prepared for this possibility. Gravitational wave data are searched not only for known and well understood signal types, but also for real unknowns. 

What’s next? While these six potential breakthroughs may be reached during the upcoming observation period of the LIGO, Virgo and KAGRA detectors, it is worth noting that the future is even brighter. Over the coming decades, scientists and policy makers shall continue exploring the possibilities of a new generation of ambitious gravitational-observatories, some of them space-based. Such observatories could expand our scientific and cosmic horizons far beyond what is currently achievable. These pioneering projects are not aimed merely at probing farther, but aspire to be able to detect black hole collisions from virtually the entire universe. For the future, the greatest surprise would be if there were no surprises.

This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of Scientific American.