Scientists discover four new stars right next to Earth: White dwarfs were hiding behind brighter red dwarfs; discovery made using Hubble's ultraviolet camera

Space has a way of surprising us even when we think we have already mapped the neighbourhood. Astronomers have spent decades cataloguing the stars closest to Earth, and most researchers assumed that anything within 65 light-years was reasonably well understood. Turns out, four stars had been hiding there the whole time, and nobody noticed.

A team from the University of Warwick and the University of Colorado Boulder has directly observed four white dwarf stars for the first time, all of them sitting quietly in binary systems within our immediate cosmic vicinity. The findings have been published in the Monthly Notices of the Royal Astronomical Society.

What exactly is a white dwarf?


A white dwarf is what remains after a star like our Sun exhausts its fuel and sheds its outer layers. What is left behind is an incredibly dense, Earth-sized core that gradually cools over billions of years. They are common across the galaxy, but they are also faint, which makes them easy to miss.

In this case, they were even harder to spot because each of the four white dwarfs was paired with a red dwarf, a larger and significantly brighter companion star. From our vantage point, the red dwarfs were hogging all the attention, making each system look like a single, unremarkable star.

How did astronomers finally find them?

The team's first clue came from an unusual wobble.

Each of the four systems displayed what astronomers call a radial wobble, a subtle back-and-forth motion in a star that typically signals something massive is orbiting it. That wobble suggested a hidden companion, but confirming it was another matter entirely.

To cut through the glare of the red dwarfs, the researchers turned to the Hubble Space Telescope and its ultraviolet spectrograph. White dwarfs glow strongly in ultraviolet light, a wavelength range where red dwarfs are far less dominant. Even then, the work was not straightforward. Red dwarfs are prone to intense flaring events that can mimic a white dwarf's ultraviolet signature, so the team developed custom calibration techniques to separate the real signal from the noise.

The result: four confirmed white dwarfs, all within 65 light-years of Earth, all previously hiding in plain sight.

First author Dr Mairi O'Brien, a Research Fellow at the University of Warwick, said the discovery was a reminder that even familiar territory can hold surprises. The team could not detect these stars in visible wavelengths because their red dwarf companions were simply drowning out their light, she noted.

The star that took 27 years to confirm

One of the four systems stands out from the rest.

G 203-47 sits just 25 light-years away, practically next door in cosmic terms. Astronomers first noticed its radial wobble back in the late 1990s, which suggested something was orbiting the red dwarf at its centre. It then took 27 years to confirm what that something actually was.

The answer turned out to be a white dwarf, and G 203-47 is now officially the ninth closest white dwarf to our Sun.

But the system is odd in another way too. The red dwarf in G 203-47 orbits its white dwarf companion once every 14.9 days. Normally, gravitational forces in a system like this would tidally lock the two stars so that they spin and orbit in sync, much like how the Moon always shows the same face to Earth. Instead, the red dwarf in G 203-47 takes over 100 days to complete a single rotation, far too slow for tidal locking to have taken hold.

Co-author Dr David Wilson from the University of Colorado Boulder said the system's slow rotation suggests it had a very different history compared to similar binary pairs. Some of these systems went through violent, prolonged early interactions that locked them tidally. G 203-47 appears to have had a gentler, briefer encounter, leaving it in this unusual and unexplained state.

What this means for our stellar census

Beyond the individual discoveries, the findings carry a broader implication for how well we actually know our cosmic neighbourhood.

Population models had previously predicted that roughly four to five closely orbiting white dwarf and red dwarf pairs should exist within 65 light-years of Earth. The Warwick team found exactly four, which lines up almost perfectly with theoretical predictions.

But here is the catch: only about 30 per cent of red dwarfs within that range have been systematically surveyed for hidden companions. Professor Pier-Emmanuel Tremblay of the University of Warwick's Astronomy and Astrophysics Group estimates that as many as nine or ten additional binary systems could still be lurking out there, undetected and uncatalogued.

The tools to find them already exist. What is needed, the researchers say, is more targeted effort, pointing telescopes at red dwarfs with the right wavelengths and looking for the same telltale wobbles that gave these four away.

As Dr O'Brien put it, you just have to look in the right way, at the right wavelengths.