Astronomers have directly identified four previously hidden white dwarf stars in a nearby binary star system. All systems are within 65 light-years of Earth, and one contains the ninth closest known white dwarf to the Sun.
The discovery was made by researchers from the University of Warwick and the University of Colorado Boulder. Their discovery is Royal Astronomical Society Monthly Notices (MNRAS).
White dwarf hidden among bright friends
Each white dwarf orbits alongside a red dwarf. Red dwarfs appeared larger and brighter, making them appear to contain just one star system when viewed in visible light.
New observations reveal that all four nearby red dwarfs were hiding white dwarf companions.
Lead author Dr Mairi O’Brien, a research fellow at the University of Warwick, said: “Isolated white dwarfs are usually easy to spot nearby, but these four stars were difficult to see because their red dwarf companions were drowning out their light. “We couldn’t see it directly at wavelengths. This is a reminder that even in our own cosmic neighborhood, we can still find amazing things if we look in the right way and at the right wavelengths.”
Although astronomers have spent decades carefully cataloging the stars near the Sun, detecting white dwarfs in such systems remains difficult. The four systems attracted attention because their visible stars exhibited significant radial wobble.
This motion occurs when a star moves slightly towards or away from Earth as a giant invisible object pulls it during its orbit. This wobble suggested that each red dwarf had a hidden companion.
Hubble ultraviolet data reveals stars
The researchers used ultraviolet spectrometer data from the Hubble Space Telescope to examine the four systems in more detail.
White dwarfs are generally much easier to recognize in ultraviolet light. However, red dwarfs can produce powerful flares that mimic the ultraviolet signal of white dwarfs, making them more difficult to confirm.
To separate the true signal from the effects of stellar flares, the team developed a special calibration method. This analysis officially confirmed that all four star systems contain white dwarfs.
White dwarf hidden for 27 years
One system, G 203-47, was particularly puzzling. Although it is only 25 light-years away, it took astronomers 27 years to identify the hidden white dwarf after first detecting its radial wobble.
This object is currently recognized as the ninth closest white dwarf to the Sun.
G 203-47 also behaves differently than similar binary systems. A red dwarf orbits a white dwarf every 14.9 days, but it takes more than 100 days to complete one revolution.
Under normal circumstances, gravitational interactions between two closely orbiting stars are expected to synchronize their movements through tidal locking. The Moon and the Earth are a well-known example because the same side of the Moon always faces the Earth.
But in G 203-47, the red dwarf rotates too slowly to synchronize with its orbit.
“What’s interesting is that if G 203-47 formed in the same way as similar systems, it shouldn’t be rotating so slowly,” said co-author Dr. David Wilson, a University of Colorado Boulder researcher. Others, such as , experienced more benign and brief encounters.” That’s why they found themselves in this abnormal state. ”
Clues about binary star evolution
G 203-47’s unusual rotation suggests that not all white and red dwarf pairs developed through the same process.
Some star systems may have experienced long and intense interactions early in their history, causing the stars to become tidally locked. Others may interact for a shorter time and with less force, leaving the rotations unsynchronized.
The four discoveries also allowed astronomers to revise their census of white dwarf populations within 20 parsecs (65 light-years).
Previous population models predicted that there were approximately four to five closely orbiting white dwarf and red dwarf systems in this region. The researchers identified exactly four, and they closely matched their theoretical estimates.
There may be more hidden white dwarfs nearby
The discovery may not complete the picture. Most of the nearby red dwarfs have not been systematically investigated for hidden white dwarf companions.
Professor Pier Emmanuel Tremblay, from the Astronomy and Astrophysics Group at the University of Warwick, said: “Only about 30 per cent of red dwarfs within 20 parsecs have been systematically investigated for their hidden white dwarf companions. “We believe there may be as many as nine to 10 other undiscovered binary systems in our local stellar environment, and perhaps more could be found with more focused efforts to observe red dwarfs.” Such a surprise. ”
