New discoveries ALMA studies ‘pregnant’ clouds in the Milky Way Read time: 3 minutes If you see a woman with a big baby bump, you know she’s pregnant. Pretty soon, she will give birth to her child. But much earlier in her pregnancy, it’s not so easy to tell. Yes, there is a baby growing inside her belly, but you can’t see it. Unless you use special medical equipment. More or less the same is true with dark clouds of gas molecules and dust particles in our Milky Way galaxy. These molecular clouds contract under their own weight, and fall apart in numerous smaller ‘cores’. Some of these cloud cores will eventually give birth to new stars. If the baby star is already well-developed, it becomes visible as a so-called proto-star. But if you don’t see a proto-star, it doesn’t mean that the cloud core isn’t ‘expecting’. It may well be in the very first stage of stellar ‘pregnancy’. Here, too, special equipment can tell you what’s happening inside the cloud core. In this case it’s not a medical instrument, but a huge array of radio antennas: ALMA. By studying the millimeter waves from cloud cores in a star-forming region, astronomers can learn about the internal structure of the cloud. That makes it possible to say if a cloud core is ‘pregnant’ or not. Japanese astronomers studied 41 cloud cores in the Taurus Molecular Cloud. Nine of them already contain proto-stars. They are like pregnant women with a big baby bump: they will soon give birth to a full-grown star. The other 32 cloud cores are dark and do not show evidence of a growing star inside. They are like women without a clear baby bump: some may be pregnant, but it’s still too early to tell. The ALMA observations revealed that 12 of these dark cloud cores show evidence of internal structure, suggesting that the growth of a new star has already started, albeit invisible to normal telescopes. These are the ‘pregnant’ cloud cores. The other 20 do not appear to have much internal structure. Apparently, they are not yet forming new stars, probably because the central gas density isn’t yet high enough. In one case, the astronomers also found evidence of streams of gas in two opposite directions from the center of the cloud core. Such ‘bipolar flows’ are also hallmarks of a growing baby star. The new research helps astronomers to learn more about the birth of stars and what happens before. It’s really like a doctor who studies the development of babies before they are actually born! What was observed? The Taurus Molecular Cloud is the nearest large ‘star factory’ in our Milky Way galaxy. Its distance is only some 430 light-years. It started to form its first stars just 1 to 2 million years ago. Many young stars are easily visible in the region, but countless new ones are still being formed in dense cores – relatively small cloud patches with a higher-than-average density. Who observed this? A large group of Japanese astronomers studied the Taurus Molecular Cloud using a small subset of ALMA antennas known as the Morita Array. The team was led by Kazuki Tokuda of the Osaka Prefecture University and the National Astronomical Observatory of Japan (NAOJ). The new results are published in two articles, one in The Astrophysical Journal, and the other in Astrophysical Journal Letters. Original Link