Astronomers have discovered a ring of large planetary debris in the habitable zone of a white dwarf for the first time. This means that many heavy-element-contaminated white dwarfs may have similar structures that are visible only with certain observation geometries. In the case of white dwarf 1054–226, the ring could be gravitationally influenced by an exoplanet whose existence has yet to be proven.
Observations of white dwarfs
Astronomers now have some evidence that many of the white dwarfs, which are compact remnants of stars, have planetary systems.
In particular, pollution of the photospheres of white dwarfs by planetesimals, asteroids, and fragments of planets destroyed by tidal forces has been repeatedly observed, which was confirmed by X-ray observations.
In addition, scientists have found candidates for Jupiter-like exoplanets in white dwarfs, which means that the planets are able to survive the transformation of their star into a red giant.
Astronomers studied an unusual object
A team of astronomers led by Jay Farihi of University College London has published the results of an analysis of observational data from a system of a relatively cold (effective temperature 7910 Kelvin) white dwarf WD 1054-226, located at a distance of 117 light-years from the Sun.
Earlier studies of this object revealed the contamination of its photosphere with Mg, Al, Ca, and Fe, it has a mass of 0.62 solar masses and a radius of 0.012 solar radii.
The scientists used data from the Spitzer and TESS space telescopes, the ULTRACAM camera installed on the 3.5-meter NTT telescope, and the UVES spectrograph installed on the VLT telescope complex.
The light curve of the dwarf turned out to be unique. The brilliance of the object is highly variable, with quasi-continuous eclipses that vary in depth, shape, and duration.
Similar events occur approximately every 23.1 minutes, but not always every 23.1 minutes, and the whole pattern of eclipse variability repeats almost perfectly every 25.02 hours, at least for several orbital cycles.
At the same time, there is not a single part on the light curve that would correspond to the light of the star outside of transit events (the passage of an object in front of the star, due to which its disk darkens).
The habitable zone of white dwarf 1054-226: there could be an exoplanet
Scientists have come to the conclusion that they are dealing with a situation where an Earth observer looks at a white dwarf through a ring of detrital material containing about 65 separate clouds and devoid of circumstellar gas and fine dust, which would be noticeable in excess infrared radiation.
The size of the largest bodies in the ring can reach 50 kilometers, provided that the density is comparable to that of asteroids. Among metal-rich white dwarfs, WD 1054–226 does not stand out in terms of mass, temperature, detected types of heavy elements, or their abundance – only transit events give out the presence of a circumstellar debris ring, which indicates that many polluted white dwarfs may have similar structures. which are difficult to find.
The orbital period of 25.02 hours indicates an orbit with a semi-major axis of 3.69 solar radii that lies in the habitable zone of WD 1054–226. Thus, this is the first time that a debris ring has been found in the habitable zone of a white dwarf.
However, the nature of the 23.1-minute brightness variations still has no exact explanation. It can be noted that the temperature of the circumstellar matter with such an orbital period would be close to 1300 kelvins.
Ideas that these are separate fragments formed during the breakup of a large parent body, or clumps of matter at the inner edge of the circumstellar disk, were rejected. It may be due to the external resonance of the 66:65 mean motion with an exoplanet rotating with a period of 25.02 hours, but this still needs to be proven.
Professor Jay Farihi, who led the research, gave the following statement:
“This is the first time that anything has been seen in the habitable zone of a white dwarf. And thus there is a possibility of life on another world orbiting it.”
Join the discussion and participate in awesome giveaways in our mobile Telegram group. Join Curiosmos on Telegram Today. t.me/Curiosmos
Sources:
• Crane, L. (2022, February 14). First hints of a planet orbiting in a white dwarf’s habitable zone. New Scientist.
• Farihi, J. (n.d.). Relentless and complex transits from a planetesimal debris disc . Academic.oup.com.
• Ghosh, P. (2022, February 11). Life could exist on planet orbiting ‘white dwarf’ star. BBC News.
