Majestic strings of interstellar gas and dust, formed by star births, supernova explosions and the whims of a supermassive black hole. The Northern Chilean telescope ALMA mapped these structures in the center of the Milky Way in unprecedented detail. Not in visible light, where bright stars and hot gas would steal the show, but in wavelengths of a few millimeters. It is precisely that light that is rich in ‘fingerprints’ of all kinds of molecules in the cold gas from which stars are formed. Astrochemists, astronomers who specialize in remote chemistry, can deduce many local conditions from the presence of certain molecules.
“We are seeing the heart of the Milky Way like we have never seen it before,” says astrochemist Kasia Dutkowska. At Leiden University she already found twenty-four different molecules in the data, of which this image shows five, each in a different color. “The entire image is about six hundred light-years wide, but we can observe details down to less than a quarter of a light-year in size. We can see star births happening on those smallest scales.”
Just right of center, in the bright yellow and purple region, is the supermassive black hole Sagittarius A*. Don’t look too long, the giant cannot be seen in these wavelengths of light. But its influence does: the enormous gravity, plus the energy released when absorbing mass, determine everything for the gas clouds around it. Dutkowska: “The center of the Milky Way is not an average piece of the universe. Nowhere in our galaxy will you find more supernova explosions per volume. In terms of ‘busyness’ and radiation, it is somewhat similar to the conditions in which our sun was formed, when the universe was younger. That makes it interesting to study in such detail.”
If you zoom in far, you can distinguish small round structures in the gas. These can indicate the death or birth of a star, depending on their size and which molecules you find there. Larger bubbles are remnants of supernova explosions, which slowly expand and mix with the surrounding gas clouds. The little ones point to newborn protostars: they are still eating away at the gas cloud from which they originated and, as it were, hollowing it out. “The photo includes all stages of stellar evolution,” says Dutkowska with satisfaction. “Exactly what we need to test our theories.”
Four of the total sixty-six antennas that make up the Atacama Large Millimetre Array (ALMA). The antennas are spread across the northern Chilean Atacama Desert. The maximum distance between antennas is sixteen kilometers, allowing the telescope to capture the sky in extremely high resolution.
Photo ESO/José Francisco Salgado (josefrancisco.org)
