✨ Three stars in Mercury's orbit!

Stellar groupings sometimes lead to extremely dense associations, but how far can orbital distances shrink? A recent observation shows a case that contradicts everything that was previously considered.

NASA's TESS satellite has enabled the identification of a stellar system named TIC 120362137, which constitutes the most compact quadruple configuration ever recorded. This system has a unique architecture, with three closely linked stars and a fourth more distant one.


During the analysis of TESS data, researchers initially interpreted the signals as coming from a pair of stars regularly eclipsing each other. Tamás Borkovits from the University of Szeged specified that additional drops in brightness led to the highlighting of a third star, and finally a fourth, confirmed by ground-based spectroscopic observations.

This configuration is so compact that the three inner stars would fit inside Mercury's orbit around the Sun (approximately 36 million miles or 57.9 million kilometers in radius), while the outer star is at a distance comparable to that of Jupiter (approximately 484 million miles or 778 million kilometers from the Sun). This makes it a remarkable specimen of a hierarchical system, where multiple bodies evolve in a confined space.

The three central stars are more massive and hotter than the Sun, while the fourth is cooler and similar to our star. Numerical simulations indicate that in approximately 276 million years, the inner stars will gradually merge to eventually form a white dwarf.

Evolution Towards White Dwarfs

Stars, like all astronomical objects, follow an evolutionary cycle. After exhausting their nuclear fuel, intermediate-mass stars, similar to those in TIC 120362137, enter a red giant phase.

During this period, they expand and can coalesce with close companions if the orbits are sufficiently tight. These mergers alter the mass and composition of the stars, leading to the emergence of new stellar objects.

At the end of this process, the stars expel their outer envelopes and contract into white dwarfs, dense and hot remnants. This transformation releases a significant amount of energy and can modify the surrounding stellar environment.