White dwarf star devours its companion in record feeding frenzy

Astronomers have caught a nearby stellar duo in a dramatic act. A super-dense white dwarf star is siphoning material from its larger companion at a pace never seen before.

The system, known as V Sagittae (V Sge), sits about 10,000 light-years away and orbits so tightly that the two stars whirl around each other every 12.3 hours.

As the white dwarf feeds, the pair blazes far brighter than similar systems – a century-old mystery that a new study says it has finally cracked.

Led by Pasi Hakala from the University of Turku in Finland, the team used the European Southern Observatory’s Very Large Telescope in Chile to probe V Sge’s extreme behavior. The results point to a runaway case of “stellar cannibalism.”

White dwarf in a feeding frenzy

White dwarfs are the ultra-compact embers left behind when sun-like stars exhaust their fuel. On their own, they glow faintly. Paired with a close companion, they can become voracious, as gravity from the white dwarf pulls gas – mostly hydrogen – off the neighboring star.

As that gas piles up, it heats to extraordinary temperatures and ignites thermonuclear burning on the dwarf’s surface.

The study concludes that V Sge’s famous overbrightness comes from this very process operating at ferocious rates. It turns the white dwarf’s outer layers into a sustained, nuclear-powered beacon.

The V Sge system has baffled astronomers since its discovery in 1902 because it outshines its peers so dramatically. The study argues the system is in a “feeding frenzy,” with mass transfer exceeding what the white dwarf can absorb.

Luminous halo signals instability

One of the team’s most striking finds is a broad ring of gas – a luminous halo encircling both stars. That ring appears to be the overflow.

The system rips material from the companion that the white dwarf can’t accrete and flings it outward to form a circumbinary shroud.

The sheer energy released in the process, the researchers say, is also jostling the system, contributing to the erratic, “wild” motion seen in monitoring data.

That halo isn’t just window dressing. It’s a clue that V Sge is being pushed toward instability. When the inflow of fuel momentarily overwhelms the white dwarf’s ability to burn it steadily, pressure can build until the surface layers detonate in a thermonuclear flash.

A rare outburst on the horizon

The team warns that V Sge is primed for a classic nova – a powerful, but non-destructive outburst triggered when accumulated hydrogen ignites on the white dwarf’s surface.

If that happens in the coming years, the system could brighten enough to be visible to the naked eye. It would be a rare treat for skywatchers.

Farther down the line, the endgame could be even more spectacular. As the stars spiral inward and the white dwarf gains mass, they may collide or reach a catastrophic limit.

In that scenario, V Sge would explode as a supernova – an event so luminous it would be visible even in daylight. That fate isn’t guaranteed, and it may be centuries away. But the current feeding rate and the presence of the gas ring suggest this binary is on a dangerous trajectory.

A star system in real time

For decades, astronomers struggled to explain why V Sge was the brightest system of its kind.

By tying its glare to sustained thermonuclear burning driven by extreme mass transfer – and by revealing the telltale, system-wide gas ring – the new study provides a coherent picture of how this oddball works.

It also offers a living laboratory where scientists can study how close binaries evolve and how novae trigger. It may even explain how some white dwarfs cross the threshold into supernovae.

Most of the time, stellar evolution plays out slowly, across eons. V Sagittae is a rare exception: a nearby, rapidly changing system writing its next chapter in real time. Keep an eye on the southern sky. The next burst from this hungry white dwarf could be bright enough for all of us to see.

The research is published in the journal Monthly Notices of the Royal Astronomical Society.

Image Credit: University of Southampton

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