An international team of astronomers has discovered four white dwarfs — "dead" stellar remnants — that were hidden in the glare of their brighter red dwarf companions. This is the first detection of such binary systems in the Sun's immediate cosmic neighborhood.

How they were found

White dwarfs are compact and relatively dim objects that are very difficult to spot next to brighter red dwarfs. Astronomers were able to detect them thanks to characteristic "wobbles" (radial velocity variations) in the red dwarfs, caused by the gravitational influence of an invisible companion.

Lead researcher Mary O'Brien from the University of Warwick (UK) explained that the nearest isolated white dwarfs are usually easy to find, but these four stars could not be seen directly in the visible spectrum because their red dwarf companions completely outshone them.

To confirm the discovery, the scientists used Hubble Space Telescope data in the ultraviolet range with special calibration to eliminate interference from red dwarf flares.

The unique system G 203-47

One of the detected systems — G 203-47, located just 25 light-years from Earth — turned out to be particularly interesting. The red dwarf in this pair rotates on its axis once every 100 Earth days, even though its orbital period around the white dwarf is only 15 days. In such systems, stars are usually synchronized (tidally locked), but here this has not occurred.

David Wilson from the University of Colorado Boulder noted that this suggests these binary systems had very different evolutionary histories.

Significance of the discovery

The finding helps to better understand how many white dwarfs exist in our Galaxy. Earlier models predicted roughly 4–5 such close pairs within 65 light-years of the Sun. The discovery of four objects confirms the accuracy of current theoretical models.

Study participant Pierre-Emmanuel Tremblay noted that only about 30% of red dwarfs within 20 parsecs (65 light-years) have been systematically surveyed, suggesting that another 9–10 such systems may still be hidden in the immediate vicinity.

The next step could be a more targeted search for hidden white dwarfs around red dwarfs.

The study was published on July 14 in the journal Monthly Notices of the Royal Astronomical Society (MNRAS).

In brief

Astronomers have discovered four white dwarfs hidden behind the glare of red dwarf companions within 65 light-years of Earth. The discovery was made possible by characteristic wobbles in the red dwarfs and Hubble telescope observations. One of the systems — G 203-47 — has unusual rotation characteristics. The finding confirms theoretical models and indicates that several more such pairs may be hidden in nearby space. The work was published in the journal MNRAS.