Molecular variety in distant dust clouds stuns astronomers
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Suppose there are eight trees in the street you live in. They’re all the same kind of tree, and they’re also the same size. Surely you would expect them to host the same types of insects, right? But what if some of the trees carry just a small number of different insects, and one tree has a huge variety of them? Wouldn’t you be surprised, and curious about the cause of the difference?
That’s the case for a team of Japanese astronomers. No, they didn’t study insects in trees. Instead, they used ALMA to study molecules in giant clouds of gas and dust. The eight clouds are located in the core region of another galaxy, known as NGC 253. They’re close to each other, and they are about the same size, just like the trees in the street. But they differ widely in the types and number of molecules they contain.
Molecules are chemical combinations of different atoms. For instance, a water molecule consists of two hydrogen atoms and one oxygen atom (H2O). Hydrogen cyanide (HCN) has one atom of hydrogen, one of carbon, and one of nitrogen. Each and every molecule produces its own telltale kind of radiation at millimeter wavelengths – the type of radiation that ALMA can ‘see’. By studying distant gas clouds, ALMA can measure what kind of molecules the clouds contain.
Surprisingly, the eight clouds in the galaxy all have a very different chemical makeup. Some contain just a small number of different molecules. Others present a much richer ‘mix’, with up to 19 different molecules, including hydrogen cyanide and formaldehyde (H2CO). No two clouds are the same, even if they are very close together – just a few tens of light-years.
In the darkest, dustiest parts of the clouds, new stars are born. The molecules in the cloud probably form thanks to the energy from those baby stars. But astronomers do not know why some clouds contain a much larger variety of molecules than others. By studying the clouds in detail, they hope to learn more about the birth of stars in ‘active’ galaxies like NGC 253.
What?
NGC 253 is a galaxy like our own Milky Way galaxy, containing many billions of stars. It is located in the constellation Sculptor, at a distance of 11 million light-years. There’s one big difference with the Milky Way: NGC 253 is an active star-forming galaxy. For some reason, the birth rate of new stars in the galaxy is much higher than it is in our own Milky Way. Most new stars are born in giant clouds of dust and molecular gas, measuring some 30 light-years across. ALMA was able to study eight of these clouds in detail.
Who?
The ALMA observations of the molecular clouds in the core region of the galaxy NGC 253 were carried out by a large team of Japanese astronomers, led by Ryo Ando. Ryo is a graduate student at the University of Tokyo in Japan. To study the distant clouds in as much detail as possible, the ALMA antennas were used in the widest possible configuration, at mutual distances of many kilometers. The new results have been published in The Astrophysical Journal, a professional astronomy magazine.
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