An “Unattainable” White Dwarf Recognized in Kepler Knowledge

August 15, 2019 - Comment

Although Kepler’s major mission ended years in the past, the ensuing dataset stays an enormous playground by which astronomers proceed to find new surprises in stellar gentle curves. The newest? Proof of a white dwarf that defies all expectations. On this artist’s illustration of self-lensing, a white dwarf transits in entrance of a companion star,


Although Kepler’s major mission ended years in the past, the ensuing dataset stays an enormous playground by which astronomers proceed to find new surprises in stellar gentle curves. The newest? Proof of a white dwarf that defies all expectations.

Lensing white dwarf

On this artist’s illustration of self-lensing, a white dwarf transits in entrance of a companion star, gravitationally lensing the star behind it.
NASA / JPL-Caltech

Forming a Light-weight

White dwarf binary

Artist’s impression of a particularly low-mass white dwarf (foreground) orbiting a extra typical white dwarf (background).
CfA / David A. Aguilar

White dwarfs are available a spread of various sizes. A typical white dwarf could be round zero.6 photo voltaic mass and come up when an remoted star of maybe a number of occasions the mass of the Solar expands right into a pink big, exhausts its gas provide, and puffs off its outer layers, forsaking its useless, dense core.

However some noticed white dwarfs have a lot decrease plenty — say, between zero.15 and zero.three photo voltaic mass. To supply such a small remnant mass, the mass of the preliminary progenitor star would additionally must be very low. However this poses an issue: smaller stars take longer to evolve, so a star of such low mass would want longer than the age of the universe to exhaust its gas provide!

Since remoted stellar evolution can’t clarify extraordinarily low-mass white dwarfs, astronomers have settled on one other rationalization: binary interactions. On this state of affairs, the shut orbit of two stars in a binary leads to materials being stripped away from the progenitor star, accelerating its mass loss and permitting it to evolve into a really low-mass white dwarf.

To this point, this rationalization has match our observations. However now, the invention of a brand new low-mass white dwarf is difficult our understanding.

Instance diagram of a special self-lensing binary system, KOI-3278. When the white dwarf passes between us and the first star, gravitational magnification causes a brightening within the gentle curve that we detect. For KIC 8145411, we don’t observe an occultation, as a result of the sunshine from the white dwarf is simply too faint to detect immediately.
Eric Agol

Self-Lensing Shock

In a brand new publication, a group of scientists led by Kento Masuda (NASA Sagan Fellow at Princeton College) current the invention of the binary system KIC 8145411 from Kepler information. This distinctive binary is one in every of solely 5 identified self-lensing techniques: one object within the binary gravitationally lenses the sunshine of the opposite because it passes in entrance as soon as per orbit.

Masuda and collaborators use follow-up observations from the Fred Lawrence Whipple Observatory in Arizona and the Subaru telescope in Hawaii to pin down the properties of the system, confirming that we’re a zero.2 solar-mass white dwarf orbiting a Solar-like star in an edge-on, eclipsing orbit.

However right here’s the catch: KIC 8145411’s orbit is kind of huge, at 1.28 AU (a interval of ~450 days) — ten occasions too huge for the first and the white-dwarf progenitor to have interacted in the best way we’d anticipate. How, then, did this “inconceivable” white dwarf come to exist?

Tip of the Iceberg

White dwarf orbital periods vs. masses

Plenty of identified white dwarfs in binaries and their orbital durations. The KIC 8145411 system is a transparent outlier, having each a low mass and a really huge orbit. Click on to enlarge.
Masuda et al. 2019 / Astrophysical Journal Letters 2019

Masuda and collaborators focus on a number of proposed formation mechanisms — like interactions with a since-ejected or swallowed tertiary object — however none of them are particularly satisfying.

So what’s subsequent? The authors level out that we had solely a 1 in 200 likelihood of detecting this specific system, because of its edge-on orientation — which possible signifies that KIC 8145411 is simply the tip of the iceberg. Now that we all know what we’re in search of, devoted searches could flip up many extra of those techniques sooner or later — hopefully serving to us to clarify why this white dwarf is feasible in any case!

Quotation

“Self-lensing Discovery of a zero.2 M⊙ White Dwarf in an Unusually Large Orbit round a Solar-like Star,” Kento Masuda et al 2019 ApJL 881 L3. doi:10.3847/2041-8213/ab321b

This publish initially appeared on AAS Nova, which options analysis highlights from the journals of the American Astronomical Society.



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