Star-spawning ‘peacock clouds’ hint at galaxy interaction
New discoveries

Star-spawning ‘peacock clouds’ hint at galaxy interaction

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The two images shown here look like the beautifully colored tails of peacocks, don’t you think?
Well, think again. In reality, these are giant clouds of gas in a neighboring galaxy. The ‘feathers’ are long filaments of gas. Deep within the two clouds, the gas is compressed into several very massive stars, according to new observations by ALMA.
Low-mass stars like our own Sun are born from huge clouds of cool gas and dust. But astronomers don’t know how very massive stars are born. To form a star ten times the mass of the Sun, you need to compress a lot of gas into a small region. That’s hard to do: the gas would heat up and expand again.
The two ‘peacock clouds’ hint at a solution to this problem. The existence of the feathery filaments tell you that the clouds have been stirred up a lot. Because of all the turbulent motion, some parts of the cloud became very dense. Dense enough to start the formation of massive stars.
So what caused all the stirring-up? Astronomers think it was due to the interaction between two small galaxies – the Magellanic Clouds. From the southern hemisphere, you can see these two galaxies as hazy patches of light in the night sky.
The two ‘peacocks’ are located within the Large Magellanic Cloud. Today, the Large and Small Magellanic Clouds are pretty far apart. But some 200 million years ago, they passed each other at a much smaller distance.
During this near-miss encounter, gas from the Small Magellanic Cloud was ripped off and flowed into the other galaxy. This flow of hydrogen gas then collided with the existing gas in the Large Magellanic Cloud. The collision would have caused the chaotic, filamentary structures that allowed the birth of massive stars.
Thus, the new ALMA observations reveal a possible link between galaxy interactions and the formation of stellar heavyweights.
And what about the beautiful ‘peacocky’ colors in the ALMA images? Well, they are not real, unfortunately. They are only used to show variations in the composition and the velocity of the gas.


The two star-forming regions imaged by ALMA are part of a huge stellar nursery known as N159. N159 sits in the Large Magellanic Cloud, which is about 167,000 light-years away. The region on the left is called the N159E-Papillon Nebula; the one on the right is known as N159W South. The two clouds are some 150 light-years apart. Yet, they show a very similar structure, and they both harbor several massive baby stars of similar age. That’s why astronomers believe that they must result from one single cause: a close encounter between the Large and the Small Magellanic Clouds, some 200 million years ago.


The ALMA observations of the two peacock-shaped star-forming regions in the Large Magellanic Cloud were carried out by a large international team of astronomers. The team was led by Yasuo Fukui of Nagoya University and Kazuki Tokuda of Osaka Prefecture University, both in Japan. Yasuo and Kazuki worked together with colleagues from Japan, the United States, France, and Germany. They published their results in two articles – one for each ‘peacock cloud’ – in The Astrophysical Journal.