As they target the massive gas cloud, astronomers notice changes in the thickness of the Milky Way galaxy

Space may seem vast and empty, but it is full of cosmological objects that are invisible to the human eye. From our vantage point on Earth, many of these objects fall between astronomers and what they hope to observe, influencing what they find. This scenario was recently encountered by scientists at the US National Science Foundation’s Green Bank Observatory (GBO), who were trying to study the Smith Cloud, embedded behind dense layers of gas and dust in our galaxy. Milky Way.

The Smith Cloud, which contains enough gas to fill a million suns, is expected to crash into the Milky Way – in about 27 million years. Astronomers have been intrigued by this monstrous high-velocity cloud since its discovery in the 1960s. The GBO’s Green Bank Telescope (GBT) and 20 Meter Telescope, along with NASA’s Hubble Telescope, are the primary instruments used to to study this massive and mysterious body of gas.

GBO scientist Toney Minter planned to observe where part of the Smith Cloud is now interacting with the Milky Way. At this distance, and on the other side of the Milky Way, this observation is tricky, even for a telescope as sensitive as the GBT.

Minter was looking for dust and faint emissions of hydroxyl (OH) molecules. The Smith Cloud should have very little or no dust and OH, while most clouds in the Milky Way contain both. If Minter found an accretion zone in the Milky Way where parts of the Smith cloud had begun to mix, he would see changes in their composition and learn more about this interaction.

He says, “I knew there was a low probability that I would find what I was looking for—and I didn’t,” laughs Minter, “But that’s all part of the scientific process. You learn from what you do and DON’T find.”

Instead, Minter’s observation revealed information about the structure of the interior of our home galaxy. While looking at the Milky Way to search for OH molecules in his target region, Minter determined the thickness of the layer of molecules in the inner galaxy. This revealed the height of the molecular gas scale in the inner Milky Way, measuring about 100 parsecs, or 330 light-years across. Observations of molecules in the outer parts of the Milky Way are about 200 parsecs, or twice as thick.

What does this mean for what scientists know about the Milky Way? Minter adds, “All I can say right now is that the data we see from this part of the inner galaxy shows that it is different from the outer galaxy. We need more observations to learn more about what it says. That’s why astronomy is exciting, knowledge is always evolving.”

Minter’s initial findings will be shared at a press conference Tuesday, June 11 at 10:15 a.m. CST at the 244th meeting of the American Astronomical Society June 9–13 in Madison, Wisconsin.