Scientists may have found a way to use black hole collisions to measure the expansion rate of the universe and solve some of the mysteries surrounding dark energy, the mysterious force that drives the accelerating cosmic expansion.
Violent mergers of black holes releasing ripples in spacetime called gravitational wavesThe new technology measures the changes in these signals that occur when they directly experience the expansion of the universe.
Since the late 1990s, astronomers have realized that the universe is expanding at an accelerating rate, and they call the speed of this expansion Hubble constant. But when scientists calculate the Hubble constant based on observations of the universe and current theories, they end up with completely different values. So scientists hope to use cosmic collisions between pairs of tight binary black holes like what the team calls “spectral sirens” to provide an alternative measurement technique to the Hubble constant. Finally, settling this urgent cosmic concern can reveal in more detail how Universe It evolved and how it looked in its early years.
In particular, a better understanding of the evolution of the universe can help cosmologists solve some major puzzles dark energy. Dark energy makes up about 68% of the matter and energy content in the universe, and scientists want to determine when this mysterious force began dominating matter and why this switch occurred.
At the heart of the spectral siren method are gravitational waves — ripples in the fabric of space and time — emanating from powerful cosmic events such as the collision and merger of massive compact objects such as neutron stars and black holes.
On Earth, highly sensitive laser interferometers such as Laser Gravitational Wave Observatory (LIGO)The Italian Virgo Observatory and Japan’s Kamioka Gravitational Wave Detector (KAGRA) can measure these weak gravitational wave signals.
Since the first detection of gravitational waves in September 2015, LIGO and its partner instruments have collected data from nearly 100 distant mergers. Each discovery gives scientists a hint at the size of the black holes involved in the merger. For example, the first detection of gravitational waves arose from the collision of two black holes, each containing approximately 30 times the mass of the Sun.
The new spectroscopic siren method suggests that gravitational wave signals may encode other information as well. Specifically, as these ripples in space-time travel over enormous distances and on long time scales to reach Earth, the properties of their signals change as the universe expands.
“For example, if you take a black hole and place it in the early universe, the signal will change and it will look like a black hole is larger than it actually is,” said study co-author and University of Chicago astrophysicist Daniel Holes. a statement.
In order to unlock information about the expansion rate of the universe encoded in the gravitational wave data, scientists will need to know how the signal has changed since it was launched through space. Holz and colleagues believe that a group of newly discovered local black holes can be used as a tool to assess these changes.
“So we measure the masses of nearby black holes and understand their features, and then we look away and see how transformed those other holes are,” Jose Maria Izquiaga, co-author and also an astrophysicist at the University of Chicago said in the statement. “And that gives you a measure of the expansion of the universe.”
Because gravitational waves, like light, take time to travel from their source to a landDetecting these ripples from more distant black hole mergers allows scientists to look back in time. The study authors say that as LIGO and other detectors become more powerful and collect gravitational wave signals from distant events, researchers may one day be able to observe collisions that occurred 10 billion years ago — about 3.8 billion years later. the great explosion. This is also when researchers believe that dark energy is beginning to dominate other forms of matter and energy.
“About that time, we’ve gone from dark matter being the dominant force in the universe to dark energy being dominating, and we’re very interested in studying this critical transition,” Ezquiaga said.
Ezquiaga and Holz say the spectral siren method for measuring the Hubble constant could have advantages over other techniques, such as measuring the change in the frequency of light from afar. supernovaeOr exploding stars. (These methods are based on an understanding of the physics of stars and galaxies and, by extension, complex physics and astrophysics.)
However, this new technique relies on little more than Einstein’s well-established gravitational model – the General theory of relativity – It uses local black holes as a built-in calibration tool. This calibration will improve as more gravitational wave data is collected from colliding black holes.
“Thousands of these signals are preferred, which we should have in a few years, and even more in the next decade or two,” Holz concluded. “At that point, it would be an incredibly powerful way to learn about the universe.”
The duo’s research is discussed in a paper published on August 3 in physical review messages.
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