A pair of stars circles each other. One is a dense white dwarf the size of Earth but with the mass of the Sun. Its companion is a regular star that transfers material onto the white dwarf. From time to time, the accumulated gas erupts like a giant hydrogen bomb, making the star thousands of times brighter for a while. This is the recurrent nova T Pyxidis, and it has erupted six times since 1890.
But what happens to the material during an eruption? Some of it is ejected into space, while some remains on the white dwarf. If the dwarf eventually accumulates mass above a certain limit, it will explode as a Type Ia supernova — the very 'standard candle' used to measure distances in the universe. So astronomers have long debated: does T Pyxidis gain or lose mass?
The new method turned out to be simpler and more reliable. Astronomers monitored the orbital period of the pair from 1986 to 2025. After the 2011 eruption, the period increased by 50 parts per million — a tiny change, but enough to calculate the mass of the ejected material. It turned out that in a single eruption, the star loses more than 2400 ten-millionths of a solar mass, and over the entire cycle, it loses more than 11 times more than it manages to accumulate.
This means T Pyxidis will never become a Type Ia supernova. This is already the seventh study to rule out popular candidate progenitors of such explosions. The question of what actually explodes as Type Ia supernovae remains open.
The 2011 eruption of the recurrent nova T Pyxidis was so bright that the star could be seen with a small telescope, even though it is usually hundreds of times fainter.