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A box-shaped cloud of opaque dust that sits at the center of our galaxy has long puzzled scientists, and observations revealing new details about its composition are adding to the mystery — perhaps shedding light on what known about the way stars form.
The cloud, known as “the Brick” because of its obscurity and rectangular shape, was previously estimated to have more than 100,000 times the mass of the sun. And such a dense blob should be churning out massive new stars, based on researchers’ current understanding of star formation.
But it is not.
The Brick is largely dormant. And the latest observations, made using the James Webb Space Telescope, did not reveal any hidden young stars.
The new Webb data revealed instead that the Brick is not made up of gas alone. It’s also littered with frozen carbon monoxide — far more than previously thought — according to a study published Monday in the Astrophysical Journal. And more ice is forming deeper into the Brick.
The results could have major implications for how scientists analyze this region in the future. More carbon monoxide ice inside the Milky Way could dramatically change the way researchers study and measure dark clouds in the center of the Milky Way.
“We are (now) closer to understanding what exactly is happening in the Brick and where the mass is,” said University of Florida astronomer Adam Ginsburg, lead author of the study. “But we opened up more questions than we closed with this.”
Among those questions: Why and where is this carbon monoxide being frozen in the ice?
Another mystery surrounding this region remains unanswered: Why don’t we see any new stars forming? Is the Brick not as dense as scientists once believed? And what are the strange ridge and filament features shown within the Brick?
“We have more to investigate before we can be sure what’s going on,” Ginsburg said. “I would say that we are in the hypothesis formation phase, not the conclusions phase.”
What Webb revealed
Ginsburg and his fellow researchers, including University of Florida graduate students, got their hands on this new Webb data for the first time in September 2022.
It was a crucial moment. As the most powerful space telescope ever built, Webb could provide unprecedented insights into the Brick. But right off the bat, Ginsburg and his team found that the data needed a lot of work. The Webb telescope orients itself using a map, deciding which direction it is pointing by referencing where it is relative to known stars.
The trouble was, “there are so many stars at the galactic center that it gets confusing,” Ginsburg said. So, researchers had to spend months cleaning up the data, orienting it to match up properly with the existing maps of the sky.
Then, looking at the Brick, they discovered that the images from Webb were turning out the wrong color.
“All the stars were coming out a little too blue,” Ginsburg said, prompting researchers to wonder if there was something wrong with the data.
But it turned out, he said, the problem was with their assumptions. Scientists didn’t expect there to be so much carbon monoxide ice – and that’s what caused the color change, according to the study.
Learning that the ice exists could have broad ripple effects for all kinds of research in the center of the Milky Way, said Dr. Natalie Butterfield, an assistant scientist at the National Radio Astronomy Observatory, who was not involved in the study.
Butterfield said her own research – which includes the study of supernovae and the radiation between star systems – could be changed forever by understanding the existence of this carbon monoxide ice. It could change the way scientists estimate the mass of all the clouds in the galactic center.
Why is carbon monoxide important
There are some perplexing things about all this carbon monoxide ice. For example, the area is relatively warm – around 60 Kelvin (minus 351.67 degrees Fahrenheit) – and carbon monoxide usually freezes at 20 Kelvin.
The dust inside the Brick may be much cooler than the gas, causing the carbon monoxide around the dust particles to turn solid. Or, Ginsburg said, the water could be freezing, trapping carbon monoxide inside.
The answer is important.
All the ice in a region like the Brick can give scientists new insights into our solar system — even our home planet.
The ice and water that exists on Earth, for example, probably arrived here via comets. So, when ice is in the universe and how it forms, it can help researchers understand where these comets come from and how they collected the materials they deposited.
Where are the stars?
And then there is the great mystery of why there is a lack of star formation within the Brick.
Scientists already know that new stars are brewed from clouds of dust and hydrogen molecules. But scientists can’t directly observe hydrogen molecules inside the Brick – or anywhere else in the universe – because they are invisible to telescopes.
However, scientists also know that there is likely to be a certain amount of carbon monoxide for every hydrogen molecule. And carbon monoxide is visible – so scientists can measure it as a proxy for how many hydrogen molecules there are in a given area.
Researchers have been using this method to measure hydrogen molecules for 50 years, Ginsburg said.
But they always assumed that carbon monoxide was a gas — not solid ice, as Webb’s data showed. This finding opens up a new can of worms, Ginsburg said.
Ginsburg noted that understanding what state of matter the carbon monoxide is in — gas or solid — is critical for researchers to find the right answers.
Each new piece of information about the Brick and its composition better explains why this opaque cloud is not producing stars, even though – by most accounts – it should be one of the most active star nurseries in the galaxy.
“It’s a natural place for new stars,” Ginsburg said. “But we haven’t found many – just a tiny handful.”
There are several possible answers that Ginsburg and other researchers are trying to explore: Maybe the Brick is more spread out — less dense — than scientists once thought. Or maybe he’s too young, and his star-making days are ahead of us.
Those are questions, Ginsburg and Butterfield said, that Webb can continue to help researchers answer.
“It’s just an impressive, impressive telescope,” Butterfield said. “I think this is just the first of many unique results coming out of the JWST for the galactic center.”
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