How black hole collisions will help us understand the expansion rate of the universe

(ORDO NEWS) — Information, as a rule, disappears in black holes without a trace. But chances are, scientists have found a way to use her last moments before her disappearance to learn more about the history of the universe.

In a new study published in the journal Physical Review Letters, two astrophysicists from the University of Chicago have developed a method to use the collision of two black holes to measure the expansion rate of our universe – and thus understand how the universe evolved, what it is made of, and where it is going.

In particular, scientists believe that a new method called “spectral siren” can tell us about the “teenage” years of the universe, which might otherwise remain a mystery.

Measuring tape for space

One of the main ongoing scientific discussions is how fast the universe is expanding, a value called the Hubble constant.

So far, the available methods provide slightly different indicators, and scientists are striving to find alternative ways to measure it.

The accuracy of this value is extremely important, as it affects our understanding of fundamental questions such as the age, history, and composition of the universe.

A new study suggests a way to do this calculation, using special detectors that pick up cosmic echoes from black hole collisions.

Periodically, black holes collide with each other – this event is so powerful that it literally creates ripples in space-time that spreads throughout the universe.

From here, from Earth, the American Laser Interferometric Gravitational Wave Observatory (LIGO) and the Italian Virgo Observatory can pick up these fluctuations – gravitational waves.

Over the past few years, LIGO and Virgo have collected collision data from nearly 100 pairs of black holes.

The signal from each collision contains information about how massive the black holes were. But during the time that this signal was traveling in space, the Universe expanded, and this factor changes the properties of the signal.

“For example, if a black hole is placed earlier in the Universe, then this signal will change and give its size larger than it really is,” explained Daniel Holtz, an astrophysicist from the University of California, Daniel Holtz, one of the authors of the article.

If scientists can find a way to measure how this signal has changed, they can calculate the expansion rate of the universe. The problem lies in the calibration: how do you know how much it has changed compared to the original?

In their new paper, Holtz and his co-author José María Esquiaga suggest that they can use newfound knowledge about the entire population of black holes as a calibration tool.

For example, current evidence suggests that the mass of most discovered black holes exceeds the mass of our sun by 5-40 times.

“We study the masses of nearby black holes and their features, and then we look at how much those farther away have shifted,” said Eskiaga, a NASA postdoctoral fellow and fellow at the Kavli Institute of Cosmological Physics who works with Holtz at the University of Chicago. “Thus, we determine the expansion of the universe.

The authors call this the “spectral siren” method, a new approach to the “standard siren” method that Daniel Holtz and colleagues developed. (The name is a reference to the “standard candle” method, also used in astronomy.)

The development is inspiring because, in the future, as LIGO expands its capabilities, this approach could shed light on the “teenage” years of the universe – about 10 billion years ago – which difficult to study by other methods.

Researchers can use the CMB to look at the earliest moments of the universe, and learn its more recent history through the study of galaxies near our own. But the interim period is more difficult to cover and is an area of ​​special scientific interest.

“We have just shifted the focus from dark matter as the predominant force in the universe to dark energy, and we are very interested in studying this significant transition,” Eskiaga shared.

Another advantage of this method, according to the authors, is that current gaps in our scientific knowledge will cause fewer uncertainties.

“Using the entire population of black holes, the method can calibrate itself by directly detecting and correcting errors,” explained D. Holtz.

Other methods used to calculate the Hubble constant are based on our current understanding of stars and galaxies, which includes many complex aspects of physics and astrophysics.

This means that the measurements can be slightly distorted in case we don’t know something yet.

This new method of studying black holes is based almost entirely on Einstein’s theory of gravity, and it has been carefully studied and withstood repeated and unsuccessful attempts to refute it.

The more data you can collect on all black holes, the more accurate this calibration will be.

“It would be optimal to receive thousands of such signals, which is feasible in the next few years, and even more will come out in the next decade or two,” says D. Holz. “By then, we will have achieved an incredibly powerful method for studying the universe.


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