Why the biggest explosions come from the smallest galaxies

Scientists have noticed that the bigger explosions out come from the smaller galaxies. If star size were purely random, bigger galaxies with more stars would have larger explosions. Find out why small galaxies produce massive booms.

Plenty of people have heard of white dwarf stars (stars that burn out and never nova) and brown dwarfs (stars too small for nuclear fusion to be sustained in their core), but there are also whole dwarf galaxies. No, they're not so named because they contain a lot of dwarf stars. Astronomers are tricky that way. They're just very, very small galaxies, about a thousand times lower in mass than the Milky Way.

Before astronomers knew about these galaxies, it seemed like massive supernovae were happening out of the clear black sky. The galaxies were so small, and so relatively dark, that telescopes didn't even see them. They had to go back for a closer look to see the galaxies around these huge releases of energy. They examined them using many tools, including ultraviolet light. The amount of UV light given off by a galaxy is a good indication that star formation is happening close by. The little dribbles of ultraviolet given off by the dwarf galaxies indicated that not many stars were being formed, making the huge explosions even more curious. Clearly these places weren't making many stars.

They found out that these small galaxies supported the making of giant stars. They were younger, and hadn't had that many supernovae before the massive explosions. Since heavier atoms are almost all made by the fusion of light atoms inside stars, these low-mass galaxies didn't have many heavy atoms interspersed with the stars. Heavy atoms around a galaxy tend to bleed nearby stars of mass. Older, larger galaxies sucked the mass off their larger stars, while light, small, young galaxies let the stars keep all their fat as they aged. The results were huge, spectacular explosions when the stars finally did blow themselves apart.

Image credit: NASA/JPL-Caltech/STScI . Via Nasa.