A supernova is the final explosion of a massive star, scattering its material over light-years. Inside the expanding shell, a neutron star remains, and the shell itself continues to plow through interstellar gas for thousands of years. It is in such a shell, left behind by an explosion, that the ALMA telescope has for the first time spotted hot molecular cores — compact clumps of gas where new stars are born. The discovery was made inside the remnant RX J1713.7-3946, a young remnant about 1600 years old, located in the constellation Scorpius.
The hot core HC1, studied in detail, resembles a tightly packed backpack: gas density there reaches 10 million particles per cubic centimeter, and temperatures exceed 100 Kelvin, like a hot sauna. This compact knot, less than 500 astronomical units across (one astronomical unit is the distance from Earth to the Sun), is stuffed with complex organic molecules: methyl formate, dimethyl ether, and acetaldehyde. The same cocktail is found in hot cores of quiescent star-forming regions, far from any cataclysms.
Why hasn't the aggressive environment spoiled the chemical composition? The authors propose two explanations. The first is time: the cloud sits at the outer edge of the shell and has only recently come under fire from energetic particles and radiation. Chemical reactions simply haven't had time to adjust. The second is a magnetic shield: the supernova shock wave can amplify magnetic fields, which deflect cosmic-ray streams like an umbrella in a downpour. As a result, the molecular filling remains untouched, like food in a refrigerator during a power outage, if you don't open the door.
Methyl formate (HCOOCH₃), found in the hot core HC1, gives raspberries their flavor. In interstellar space, of course, it cannot smell, but the very presence of such a complex molecule in such a harsh place is astonishing.
In Fred Hoyle's novel "The Black Cloud," an intelligent interstellar cloud uses chemistry to transmit signals. Hot cores like HC1 are natural laboratories where complex organics arise on their own, without the involvement of life.