JWST is staring at the dark molecular clouds at the heart of the Milky Way

There is an unusual object near the heart of the Milky Way that astronomers call a “brick”. It is a huge cloud of gas called the Infrared Dark Cloud (IDC). The bricks are as dense and turbulent as the other types, but for some reason, they show few signs of star formation.

Why?

The Milky Way’s central molecular region (CMZ) can be a difficult region to study. And there are dark molecular clouds, which are giving birth to new stars. The CMZ is a huge complex of molecular clouds containing about 60 million solar masses of gas. Brick is one of those clouds. Astronomers are keen to better understand this region, and the James Webb Space Telescope has the ability to peer into the dense region, revealing some details.

The Brick is one of the most studied ICs in the Milky Way. It shows much less star formation than other clouds of similar mass. This is a mystery, and astronomers gravitate towards puzzles.

A team of researchers used the James Webb Space Telescope to study the brick, which is also called G0.253+0.015. But it is hard to see in the dense area. So, to study these clouds of gas, astronomers turn to carbon monoxide. Hydrogen is more abundant, but carbon monoxide is very bright and can be seen at certain wavelengths. It is watched by astronomers to track the movement and density of interstellar clouds.

The new study is titled “JWST Detects Large-scale Absorption of Ice and Carbon Dioxide in the G0.253+0.015 Galactic Center Cloud,” and is available at pre-publication arxiv.org. The lead author is Adam Ginsburg, assistant professor of astronomy at the University of Florida.

There are various explanations proposed for the bricks’ lack of clear star formation. It could be young, it could be very turbulent, it could be restricted by magnetic fields, or it could actually be many clouds in the same line of sight. “Each of these explanations is likely to play some role in the state and evolution of the cloud,” the authors explain.

While the rate of star formation may lag behind other similar clouds, there are still more than 56,000 stars out there.

Astronomers have put a lot of effort into understanding the presence, distribution, and behavior of gas in the Milky Way, including the CMZ. But they haven’t thoroughly studied frozen gases like carbon dioxide. This is because it takes powerful infrared potentials to study them.

Enter JWST’s NIRCam and its powerful and versatile filters.

The team of researchers used NIRCam to study the bricks more carefully. They found that the bricks contained more carbon dioxide ice than previously thought, and that although the carbon dioxide on the surface of the bricks may be in the gaseous phase, it is frozen inside. What does that tell us about bricks?

There is no firm conclusion yet regarding bricks. In the dense molecular regions within the bricks, carbon dioxide is the primary coolant in the cloud. Therefore, in the suburbs with lower cloud densities, the cooling effect of carbon dioxide should be stronger. Conversely, in the denser interior of the cloud, the carbon dioxide may have completely solidified, and the dust may be too sparse to replace the carbon monoxide as the dominant coolant.

Stars like to form when the gas is cool, so finding a large amount of carbon dioxide should indicate a high rate of star formation. But the gas inside the bricks is much warmer than the other clouds, despite all that ice.

These results tell us something about the galactic center in general. It changes our understanding of both the standard abundance of carbon dioxide in the GC and the ratio of gas to dust in the same region. According to these results, both are very low.

If there is more carbon dioxide in the bricks and at the galactic center than previously thought, this would have different implications for star formation models and could affect the bricks’ lower star formation rate.

There are standard models for the distribution of carbon dioxide in clouds, but like many things in astronomy and astrophysics, the James Webb Space Telescope is giving astronomers more detailed information than they had before, and also overturning some long-established ideas. The team behind this research suggests that if the central region of the Milky Way contains this much carbon dioxide, other galaxies are likely to, too.

This is just the team’s first paper based on observations from the James Webb Space Telescope of Brick. While he presents new findings for carbon monoxide, he draws no conclusions. But it does help cement Brick’s position as the most watched international data center.

A future paper will present MIRI (medium infrared instrument) observations of Brick, as well as MIRI and NIRCam observations of cloud C, another structure in the central molecular region.

More observations may lead to clarity, and astronomers may get their explanation for the low rate of star formation in the bricks.

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