Fragile molecules survive in the shade
If you want to enjoy an ice cream, you’d better not put it outside in the sun on a hot day. The ice will melt, and you’re left with a small puddle of liquid. It’s best to keep your ice cream indoors, in a cold place.
There are no ice creams in space, but some molecules are as vulnerable to radiation as your ice cream is to sunlight.
Molecules are compounds of various atoms. Some molecules – like water molecules – consists of only three atoms. More complicated molecules in space may consist of five, six or even more atoms, including hydrogen, carbon and nitrogen. When such large organic molecules are exposed to high-energy radiation, they will easily fall apart and get destroyed.
Surprisingly, astronomers have found such large molecules in a violent region of another galaxy, close to the galaxy’s central black hole. Gas that spirals into the black hole gets extremely hot before it finally disappears. The hot gas emits huge amounts of energetic ultraviolet radiation and X-rays.
You’d expect that this fierce radiation destroys fragile organic molecules in the neighborhood. But ALMA observations of the galaxy have revealed the existence of complicated molecules with funny names like cyanoacetylene and acetonitrile close to the black hole. It’s as if your ice cream is out in the sun, but doesn’t melt.
Further from the black hole, where there’s less energetic radiation, ALMA also detected a wide variety of molecules. These molecules are located in a ‘starburst ring’, surrounding the galaxy’s core at a distance of some 3,500 light-years. But the survival of fragile molecules in the galaxy’s central region came as a surprise.
The astronomers believe that some regions in the core of the galaxy are shielded from the energetic radiation by dense clouds of gas and dust. Thanks to this shielding effect, the large organic molecules are able to survive.
Next time you’re out in the sun with an ice cream, you can try it for yourself. If you find yourself a cooler and darker place, for instance in the shadow of a building, the ice will not melt as fast.
The molecules have been found in a large spiral galaxy known as M77 (of NGC 1068). This galaxy is at a distance of 47 million light-years, in the direction of the constellation Cetus the Whale. Like most galaxies, it has a large, supermassive black hole in its core, surrounded by a disk of gas and dust. Further away from the galaxy’s center is a ‘starburst ring’ – a region where large numbers of new stars are being born.
The ALMA measurements of M77 were carried out by a team of mainly Japanese astronomers, led by Shuro Takano of the National Astronomical Observatory of Japan and Taku Nakajima of Nagoya University. Shuro and Taku had already studied the galaxy with the 45-meter Nobeyama radio telescope in Japan. However, the ALMA observations revealed much more information, although only 16 of the 66 ALMA antennas were used in this research. The results have been published in two articles in the Publications of the Astronomical Society of Japan.