The origin of binary black holes may be hidden in their spins, study suggests: ScienceAlert

In a recent study published in Astronomy and astrophysics lettersa team of researchers at the Massachusetts Institute of Technology (MIT) used different computer models to examine 69 confirmed binary black holes to help determine their origins and found their computer results changed based on the model’s configurations.

Essentially, the input consistently changed the output, and the researchers want to better understand both how and why this happens and what steps can be taken to get more consistent results.

“When you change the model and make it more flexible or make other assumptions, you get a different answer about how black holes formed in the universe,” Sylvia Biscoveanu, an MIT graduate student working in the LIGO laboratory and a co-author on the study, it says in a statement.

“We’re showing that people need to be careful because we’re not yet at the stage with our data where we can believe what the model is telling us.”

Like binary stars, binary black holes are two massive objects orbiting each other, both of which have the ability to potentially collide – or merge – together, with another common characteristic being that black holes are sometimes born from the collapse of dying massive stars, also known as a supernova.

But how binary black holes arose remains a mystery, as there are two current hypotheses regarding their formation: “field binary evolution” and “dynamical assembly”.

Field binary evolution involves when a pair of binary stars explode, resulting in two black holes in their space, which continue to orbit each other in the same way as before.

Since they originally orbited each other as binary stars, it is assumed that their spins and tilts should also be aligned.

Scientists also hypothesize that their aligned spins indicate that they originate from a galactic disk, given the relatively peaceful environment.

Dynamical assembly involves when two individual black holes, each with their own unique tilt and spin, are eventually brought together by extreme astrophysical processes, to form their own binary black hole system.

It is currently thought that this merger is likely to occur in a dense environment such as a globular cluster, where thousands of stars in close proximity can force two black holes together.

The real question is: What fraction of binary black holes originates from each respective method? Astronomers believe that this answer lies in the data, particularly spin measurements of black holes.

Using the 69 confirmed binary black holes, astronomers have determined that these massive objects can originate from both globular clusters and galactic disks.

The LIGO Laboratory in the US has collaborated with its Italian counterpart, Virgo, to determine the spins (rotational periods) of the 69 confirmed binary black holes.

“But we wanted to know, do we have enough data to make this difference?” Biscoveanu said. “And it turns out that things are messy and uncertain, and it’s harder than it looks.”

For the study, the researchers continually fine-tuned a series of computer models to determine whether the results matched each model’s predictions.

One such model was configured to assume that only a fraction of binary black holes were produced with aligned spins, with the rest having random spins. Another model was configured to predict a moderately contrasting spin direction.

Finally, their findings indicated that results consistently changed in accordance with the fitted models.

Essentially, the results consistently changed based on the model’s adjustments, meaning that more data than the 69 confirmed binary black holes is likely needed to have more consistent results.

“Our paper shows that your result depends entirely on how you model your astrophysics, rather than the data itself,” Biscoveanu said.

“We need more data than we thought if we want to make a claim that is independent of the astrophysical assumptions we make,” said Salvatore Vitale, associate professor of physics, member of the Kavli Institute of Astrophysics and Space Research. at MIT, and lead author of the study.

But how much more data will the astronomers demand? Vitale estimates that the LIGO network will be able to detect one new binary black hole every few days when the network returns to service in early 2023.

“The measurements of the spins that we have now are very uncertain,” Vitale said.

“But as we build up many of them, we can get better information. Then we can say, no matter the details of my model, the data always tells me the same story – a story that we could then believe.”

This article was originally published by Universe Today. Read the original article.

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