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A box-shaped cloud of opaque dust located at the center of our Milky Way has long baffled scientists, and observations that reveal a new detail about its composition deepen the mystery and potentially upend knowledge of star formation .
The cloud, nicknamed “the Stone” because of its visual impenetrability and rectangular appearance, was previously estimated to be more than 100,000 times the mass of the Sun. And such a dense blob should produce massive new stars, based on researchers’ current knowledge of star formation.
But that is not it.
The Brick is largely inactive. And the latest observations, made using the James Webb Space Telescope, revealed no hidden, young stars.
The new Webb data instead revealed that the Brick is not just made of gas. It’s also littered with frozen carbon monoxide — far more than previously expected — according to a study published Monday in The Astrophysical Journal. And even more ice forms deeper in the Brick.
The findings could have drastic implications for how scientists analyze this region in the future. More carbon monoxide ice in the Brick could dramatically change the way researchers study and measure dark clouds in the center of the Milky Way.
“We are (now) better able to understand 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 have opened more questions than we have closed.”
One of those questions: why and where does this carbon monoxide freeze into ice?
Other mysteries looming for this region also remain unanswered: Why can’t we see new stars forming? Is the brick not as compact as scientists once believed? And what are the strange edge and filament-like features that appear in the Brick?
“We need to investigate more before we really know for sure what’s going on,” Ginsburg said. “I would say we are in the hypothesis-forming phase, not the conclusion-drawing phase.”
What Webb revealed
Ginsburg and his fellow researchers, including graduate students from the University of Florida, first obtained this new Webb data in September 2022.
It was a crucial moment. As the most powerful space telescope ever built, Webb was able to provide never-before-seen insights into the Brick. But Ginsburg and his team immediately discovered that the data required a lot of work. The Webb telescope orients itself using a map and determines which direction it is pointing by referring to where it is in relation to known stars.
The problem was, “There are so many stars in the galactic center that it’s getting confused,” Ginsburg said. So researchers had to spend months cleaning the data and orienting it so that it aligned correctly with existing maps of the sky.
When they looked at the stone, they discovered that Webb’s images were the wrong color.
“All the stars were a little too blue,” Ginsburg said, leading researchers to wonder if there was something wrong with the data.
But it turned out, he said, that the problem was their assumptions. The scientists didn’t expect there to be so much carbon monoxide ice – and that was the cause of the color change, according to the study.
Learning of the ice’s existence could have major implications for all kinds of research into 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 studying supernovae and the radiation between galaxies — could be forever changed if she understood 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 carbon monoxide is important
There are several baffling things about all this carbon monoxide ice. For example, the area is quite warm – about 60 Kelvin (minus 351.67 degrees Fahrenheit) – while carbon monoxide typically freezes at 20 Kelvin.
It may be that the dust in the stone is much colder than the gas, causing the carbon monoxide around the dust particles to solidify. Or, Ginsburg said, it could be that the water freezes, trapping carbon monoxide in it.
The answer is important.
All the ice in a region like the Brick could give scientists new insight into our solar system – even our home planet.
The ice and water on Earth probably arrived here via comets. So where ice is in the universe and how it forms can help researchers understand where these comets came from and how they collected the materials they deposited.
Where are the stars?
And then there is the big mystery of why there is a lack of star formation in the Brick.
Scientists already know that new stars form from clouds of dust and hydrogen molecules. But scientists cannot directly observe hydrogen molecules in the Brick – or anywhere else in the universe – because they are invisible to telescopes.
However, scientists also know that for every hydrogen molecule, there is likely some amount of carbon monoxide present. And carbon monoxide is visible, so scientists can measure it as a benchmark for identifying how many hydrogen molecules are in a given area.
Researchers have been using this method to measure hydrogen molecules for 50 years, Ginsburg said.
But they always assumed the carbon monoxide was gas and not solid ice, as the Webb data showed. This finding opens a whole new can of worms, Ginsburg said.
Ginsburg noted that it is critical for researchers to understand what state the carbon monoxide is in – gas or solid – to arrive at the right answers.
Each new piece of knowledge about the Brick and its composition better explains why this opaque cloud isn’t producing stars, even though – by most accounts – it should be one of the most active star nurseries in the Milky Way.
“It’s a very natural place for new stars,” Ginsburg said. “But we didn’t find very many – just a very, very small handful.”
There are some possible answers that Ginsburg and other researchers would like to explore: Maybe the rock is more spread out — less dense — than scientists once thought. Or maybe it’s just too young and the star formation days are just around the corner.
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 to come from the JWST for the galactic center.”
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