## New Model Explains Unexpected Heat and Orbital Behavior of White Dwarf Binaries
White dwarfs โคare the dense remnants left behind after a star stops producing energy through nuclear fusion, a stage our own sun will reach far inโฃ the future. Theseโ stellar remnants behave in unusual ways,sinceโค their internal structure โmakes them shrink as they gain mass,which is why they are known as degenerate stars.
Recent observations have revealed a puzzling phenomenon in some white dwarf โbinary systems – pairs of โwhite dwarfs orbiting each other in very close proximity. These systems, typically ancientโ and cooled to around 4,000โค Kelvin, are exhibiting unexpectedly high โคtemperatures (10,000-30,000 Kelvin) and are roughly twice the size predicted by current โmodels. Manyโ complete โan โorbit in less than an hour, furtherโฃ deviating from established expectations.
Tidal Heating โฃas a Key โFactor
To explain this discrepancy, a team led โคby Lucy Olivia โMcNeill of Kyoto โคuniversity investigated the roleโฃ of โคtidal forces. Just as tides on โEarth areโ caused by the gravitational pull of the Moon,close orbits between stars generate critically important tidal forces that can distort and heat the stars involved.
“We wondered: to what extent can tidalโค heating explain โคthe temperatures of white dwarfs in short โขperiod binaries?” asks McNeill,drawing a parallel to โthe successful application of tidal heating models โฃto explain the behavior ofโ “Hot Jupiters”โค orbiting their stars.
The team developed a new theoretical model to estimate โthe amount of heating experiencedโฃ by white dwarfs in these tightโค binary systems. This model is designed to predict both temperature evolution andโฃ future orbital changes.
Reshaping Our understanding of White Dwarf Evolution
the analysis revealed that tidal interactions are a significant driver of white โคdwarf evolution. the gravitational pull between the starsโ generates internal โขheat within the larger,โข less massive white dwarf, causing it toโ expandโค and reach temperatures of at least 10,000 Kelvin.
Thisโ expansion hasโ critically important implications for when the starsโค begin to exchange material -โข a process called mass transfer. The researchers believeโ white dwarfsโ are likely to be twice the predictedโ size โat the onset of mass โtransfer, โmeaning these binary systems may begin interacting atโค orbital periodsโ three times longer than previously thought.
“We expected tidal heating would increase theโ temperatures of these white dwarfs, but โฃwe were surprised toโข see how much the orbital period โreduces for the oldest โฃwhite dwarfs when their Roche lobes come into contact,” explains McNeill.
Implications for Stellar Explosions and Future Research
These tightly orbiting white dwarf systems are potential precursors to dramatic cosmic โevents like type Ia supernovae and cataclysmic variables,whichโ emit gravitational radiation as they interact. Understanding their evolution is thusโ crucial.
The team plans to apply their model to binary systems composed of carbon-oxygen white dwarfs, aiming to better understand the pathways leading to type Ia supernovae and to determine โif realistic temperature predictionsโ support the “double degenerate” (merger) scenario for these explosions.