A team of scientists from China, Japan, the Netherlands and the US have used data obtained from the US National Aeronautics and Space Agency’s Chandra X-ray space telescope to identify the first known example in our own galaxy (the Milky Way) of an unusual type of stellar explosion, known as a Type Iax supernova. It is designated Sagittarius A East (Sgr A East) and it is a supernova remnant which lies very close to Sagittarius A•, which is the supermassive black hole in the centre of the Milky Way.

There are different types of supernovas. The best known are those triggered by the collapse of massive stars. But they can also be triggered by the collision of two white dwarf stars (which are the collapsed remnants of smaller stars, such as our Sun) or by a white dwarf which pulls too much material from a second, still active, companion star. White dwarf supernovas are usually designated as Type Ia supernovas. 

White dwarf supernovas are one of the most important sources of chromium, iron and nickel in the universe. All elements in the universe, except hydrogen and some helium, were manufactured in the hearts of stars. Nearly everything your body is made of was created inside a star and then blasted across the universe in a supernova.

Type Iax supernovas, which have previously been identified in other galaxies, produce different relative quantities of elements to those produced by Type Ia supernovas. The study of the data on Sgr A East showed that the relative quantities of elements it had produced fitted the profile for Type Iax and not Type Ia. 

Studies of other galaxies indicate that Type Iax supernovas happen at a rate of some 33% of that for Type Ia supernovas. The cause of Type Iax supernovas has not yet been established. The current leading theory is that the thermonuclear reactions within the white dwarf, that cause the supernova, move more slowly through the star than is the case with Type Ia supernovas. The result is weaker explosions, and so different quantities of elements produced in the explosions. It could also result in some of the white dwarf remaining afterwards.

“This supernova remnant is the the background of many Chandra images of our galaxy’s supermassive black hole taken over the last 20 years,” pointed out Nanjing University, China, scientist and study co-author Zhiyuan Li. “We finally may have worked out what this object is and how it came to be.”