There are a lot of details about the two distant objects, especially if you consider that astrophysicists have only directly observed their extremely violent endings. The team rebuilt a city from a pile of dust. To deduce a lot from very little, they combined observations of neutron stars with insights gained from studying other stars and galaxies, creating a massive mathematical model. of both observed and hypothetical stars. The model contains detailed descriptions of the temperatures, chemical composition and other characteristics of 250,000 different types of stars, from their interior to their surface, and how these properties change as each star burns. fuel and eventually die. In addition, the model can simulate entire galaxies, each containing many star clusters of different ages and chemical compositions.
And so, to uncover the past of merging neutron stars, Stevance and her colleagues worked to reconstruct the data observed for the neutron stars in their model, which then can tell them the most likely scenarios before the two stars merge. For example, they concluded that stars share an envelope many times due to the time it takes for the two objects to collide. When two binary stars merge their envelopes, the gas in that common envelope creates drag that slows the stars’ orbits, which then causes the stars to spiral toward each other, rapidly closing the gap between them. they. To merge as quickly as their leftover cores, stars need to share the envelope multiple times.
The study of this neutron star merger builds on decades of astronomical research. Jan Eldridge, a lecturer in astrophysics at the University of Auckland and one of Stevance’s collaborators, says Stevance’s colleagues started building their star model 15 years ago to study celestial objects. in extremely distant galaxies. “When we first made this thing, it took us years to detect gravitational waves,” says Eldridge. In contrast, that 15-year-old model builds on stellar models that astronomers created in the 1970s. The work illustrates a long, often circular scientific process: generations of astronomers. Astronomy, which studies tangential questions about stars, unwittingly contributed to a new discovery decades later.
In addition, Stevance and her team have made their work open source, allowing additional researchers to rewind the clock to other operational excellence. Northwestern University’s Peter Blanchard, who was not involved in the work, said researchers could use the framework to study supernovae, bright explosions of massive stars. As astrophysicists study more about these different types of explosions, which are predicted to produce a variety of heavy elements, they can better explain the origin of all the elements in the universe. pillar. It seems that the death of the stars gave rise to gold and uranium, which would eventually combine with other elements to form the Earth, billions of years before we turned them into jewelry or weapons.
To predict the pedigrees of neutron stars, Stevance’s model must also infer properties of the galaxies that contain them, such as the types of elements the galaxy contains and whether they are evenly distributed in the galaxy. or not. Astrophysicist Hsin-Yu Chen of the University of Texas at Austin, who was not involved in the work, said this knowledge will guide where to look for other mergers in the future.
If researchers can find more neutron-star mergers, Chen wants to use them to find out how quickly the universe is expanding, which is needed to calculate its age. Chen was able to use the merger’s gravitational wave signal to calculate the distance from Earth to those neutron stars. Then, by analyzing the light emitted during the merger, she was able to estimate the speed at which neutron stars move away—providing the rate of expansion. So far, astrophysicists have calculated two opposite rates for the expansion of the universe using different methods, so they want to observe more mergers to try to reconcile. conflict.
The Laser Interferometer Gravitational Wave Observatory collaboration, which has detected neutron star mergers using two of its detectors in the US states of Washington and Louisiana, is expected to be active. Return to operation in May 2023 after two years of upgrades. When that happens, the researchers predict 10 neutron star mergers will be detected each year—which will provide many opportunities to dig deeper into the question of how old the universe is. “It will be very interesting in the next few years,” Blanchard said. It’s also been a very interesting few billion years.
