Kinematics, Galactic Age, Chemistry and Water Fraction of Asteroid-Polluted White Dwarfs from the Sloan Digital Sky Survey
Lead Research Organisation:
University of Cambridge
Department Name: Institute of Astronomy
Abstract
Of the nearly 800 extrasolar planets confirmed around other stars, only a small number of these are thought to be solid planets and thus similar in theory to Mercury, Venus, Earth, and Mars. These planets have been identified almost exclusively through NASA's Kepler mission, which detects the transit of the planet as it passes in front of the host star. The transit provides scientists with the size of the planet, and radial velocity observations from the ground can provide the mass in some case, thus giving the density and indicating a likely solid composition. However, the actual composition of these planets is unknown and no current or future means exist to make such measurements.
However, stars at the end of their lives -- called white dwarfs -- offer a unique advantage in the study of terrestrial exoplanetary systems. Over 95% of all stars in the Milky Way, including our Sun, will end their lives as white dwarf stars, gently shedding their outer layers, then shrinking to Earth-sized, slowly cooling embers. Owing to high gravities, heavy elements sink rapidly to the interior, leaving behind pure hydrogen or helium atmospheres in these stars. Those white dwarfs with rocky planetary systems can become chemically-enriched by small, but detectable amounts of heavy elements such as silicon, magnesium, and iron. In the last several years, astronomers have discovered white dwarfs ''polluted'' by rocky debris from asteroids, and been able to obtain the basic asteroid composition from the elements polluting the stellar atmosphere. In the Solar System, asteroids are the leftover building blocks of the terrestrial planets, and thus extrasolar asteroids at white dwarfs indicate the basic composition of their rocky exoplanets.
There have been three major epochs of star (and planet) formation in the Galaxy. The first stars formed 11-15 billion years ago and now lie in a spherical halo that encircles the disk of the Galaxy. The next stars formed 7-12 billion years ago and appear as a thick disk about the Galactic plane, while stars like our Sun formed 2-8 billion years ago and occupy a thin disk we recognize as the 'Milky Way' in the night sky. Each of these three star populations are chemically distinct as the material available was at first deficient in heavy elements, and then later enriched after one or more stages of nuclear processing within the interior of stars. The individual chemistry of these populations implies that the planets they built may differ substantially from those in our Solar System, and by studying their asteroids we can learn about the composition of solid planets built by the older halo and thick disk stars, as compared to younger, thin disk stars like our Sun. Such rocky planetary systems will be among the oldest in the Universe and represent the first and second waves of planet formation (and life, if present) in the Galaxy.
This project will identify hundreds of asteroid-polluted white dwarfs via the exploitation of large existing databases. The collected data will allow us to distinguish between thin disk, thick disk, and halo white dwarfs with remnant planetary systems by the stars' positions and motions in the sky. We can then assess the frequency of remnant, solid planetary systems as a function of Galactic age and study the asteroid composition within these stellar populations. Importantly, by focusing on white dwarfs with helium-dominated atmospheres and remnant planetary systems, we can assess the water content of their asteroids by studying the trace hydrogen in the stellar atmosphere. This in turn will give scientists a good handle on how much water is available for the construction of water-rich, habitable planets around other stars.
However, stars at the end of their lives -- called white dwarfs -- offer a unique advantage in the study of terrestrial exoplanetary systems. Over 95% of all stars in the Milky Way, including our Sun, will end their lives as white dwarf stars, gently shedding their outer layers, then shrinking to Earth-sized, slowly cooling embers. Owing to high gravities, heavy elements sink rapidly to the interior, leaving behind pure hydrogen or helium atmospheres in these stars. Those white dwarfs with rocky planetary systems can become chemically-enriched by small, but detectable amounts of heavy elements such as silicon, magnesium, and iron. In the last several years, astronomers have discovered white dwarfs ''polluted'' by rocky debris from asteroids, and been able to obtain the basic asteroid composition from the elements polluting the stellar atmosphere. In the Solar System, asteroids are the leftover building blocks of the terrestrial planets, and thus extrasolar asteroids at white dwarfs indicate the basic composition of their rocky exoplanets.
There have been three major epochs of star (and planet) formation in the Galaxy. The first stars formed 11-15 billion years ago and now lie in a spherical halo that encircles the disk of the Galaxy. The next stars formed 7-12 billion years ago and appear as a thick disk about the Galactic plane, while stars like our Sun formed 2-8 billion years ago and occupy a thin disk we recognize as the 'Milky Way' in the night sky. Each of these three star populations are chemically distinct as the material available was at first deficient in heavy elements, and then later enriched after one or more stages of nuclear processing within the interior of stars. The individual chemistry of these populations implies that the planets they built may differ substantially from those in our Solar System, and by studying their asteroids we can learn about the composition of solid planets built by the older halo and thick disk stars, as compared to younger, thin disk stars like our Sun. Such rocky planetary systems will be among the oldest in the Universe and represent the first and second waves of planet formation (and life, if present) in the Galaxy.
This project will identify hundreds of asteroid-polluted white dwarfs via the exploitation of large existing databases. The collected data will allow us to distinguish between thin disk, thick disk, and halo white dwarfs with remnant planetary systems by the stars' positions and motions in the sky. We can then assess the frequency of remnant, solid planetary systems as a function of Galactic age and study the asteroid composition within these stellar populations. Importantly, by focusing on white dwarfs with helium-dominated atmospheres and remnant planetary systems, we can assess the water content of their asteroids by studying the trace hydrogen in the stellar atmosphere. This in turn will give scientists a good handle on how much water is available for the construction of water-rich, habitable planets around other stars.
Planned Impact
The following non-academic entities will benefit from the proposed research.
The Postdoctoral researcher supported on the grant through career development and training.
The UK economy via the provision of highly trained Ph.D. students and postdoctoral researchers associated with the research undertaken as part of the grant.
The wider UK public through the active Outreach programme undertaken at the Insititute of Astronomy.
The Postdoctoral researcher supported on the grant through career development and training.
The UK economy via the provision of highly trained Ph.D. students and postdoctoral researchers associated with the research undertaken as part of the grant.
The wider UK public through the active Outreach programme undertaken at the Insititute of Astronomy.
Organisations
People |
ORCID iD |
Jay Farihi (Principal Investigator) |
Publications
Bergfors C
(2014)
Signs of a faint disc population at polluted white dwarfs
in Monthly Notices of the Royal Astronomical Society
Bonsor A
(2017)
Infrared observations of white dwarfs and the implications for the accretion of dusty planetary material
in Monthly Notices of the Royal Astronomical Society
Boyajian T
(2018)
The First Post-Kepler Brightness Dips of KIC 8462852
Boyajian T
(2018)
The First Post- Kepler Brightness Dips of KIC 8462852
in The Astrophysical Journal
Cauley P
(2018)
Evidence for Eccentric, Precessing Gaseous Debris in the Circumstellar Absorption toward WD 1145 + 017
in The Astrophysical Journal Letters
Cunningham T
(2021)
Horizontal spreading of planetary debris accreted by white dwarfs
in Monthly Notices of the Royal Astronomical Society
Del Santo M
(2014)
The puzzling source IGR J17361-4441 in NGC 6388: a possible planetary tidal disruption event
in Monthly Notices of the Royal Astronomical Society
Dennihy E
(2020)
A Word to the WISE: Confusion is Unavoidable for WISE-selected Infrared Excesses
in The Astrophysical Journal
Dey A
(2019)
Overview of the DESI Legacy Imaging Surveys
in The Astronomical Journal
Farihi J
(2018)
Magnetism, X-rays and accretion rates in WD 1145+017 and other polluted white dwarf systems
in Monthly Notices of the Royal Astronomical Society
Farihi J
(2013)
Evidence for water in the rocky debris of a disrupted extrasolar minor planet.
in Science (New York, N.Y.)
Farihi J
(2018)
Dust production and depletion in evolved planetary systems
in Monthly Notices of the Royal Astronomical Society
Farihi J
(2013)
Evidence of rocky planetesimals orbiting two Hyades stars
in Monthly Notices of the Royal Astronomical Society
Farihi J
(2022)
Relentless and complex transits from a planetesimal debris disc
in Monthly Notices of the Royal Astronomical Society
Farihi J
(2016)
Circumstellar debris and pollution at white dwarf stars
in New Astronomy Reviews
Farihi J
(2017)
A circumbinary debris disk in a polluted white dwarf system
in Nature Astronomy
Farihi J
(2018)
Dust production and depletion in evolved planetary systems
Farihi J
(2014)
ALMA and Herschel observations of the prototype dusty and polluted white dwarf G29-38
in Monthly Notices of the Royal Astronomical Society
Farihi J
(2013)
Orbital and evolutionary constraints on the planet hosting binary GJ 86 from the Hubble Space Telescope
in Monthly Notices of the Royal Astronomical Society
Farihi J
(2016)
Solar abundances of rock-forming elements, extreme oxygen and hydrogen in a young polluted white dwarf
in Monthly Notices of the Royal Astronomical Society
Gentile Fusillo N
(2017)
Trace hydrogen in helium atmosphere white dwarfs as a possible signature of water accretion
in Monthly Notices of the Royal Astronomical Society
Gentile Fusillo N
(2021)
White dwarfs with planetary remnants in the era of Gaia - I. Six emission line systems
in Monthly Notices of the Royal Astronomical Society
Gänsicke B
(2016)
HIGH-SPEED PHOTOMETRY OF THE DISINTEGRATING PLANETESIMALS AT WD1145+017: EVIDENCE FOR RAPID DYNAMICAL EVOLUTION
in The Astrophysical Journal Letters
Gänsicke B
(2018)
Broadening of Ly a by neutral helium in DBA white dwarfs
in Monthly Notices of the Royal Astronomical Society
Hallakoun N
(2018)
Periodic optical variability and debris accretion in white dwarfs: a test for a causal connection*
in Monthly Notices of the Royal Astronomical Society
Hallakoun Na'ama
(2018)
Periodic optical variability and debris accretion in white dwarfs: a test for a causal connection
in Monthly Notices of the Royal Astronomical Society
Hermes J
(2014)
Heavy metals in a light white dwarf: abundances of the metal-rich, extremely low-mass GALEX J1717+6757
in Monthly Notices of the Royal Astronomical Society
Hoskin M
(2020)
White dwarf pollution by hydrated planetary remnants: hydrogen and metals in WD J204713.76-125908.9
in Monthly Notices of the Royal Astronomical Society
Izquierdo P
(2021)
GD 424 - a helium-atmosphere white dwarf with a large amount of trace hydrogen in the process of digesting a rocky planetesimal
in Monthly Notices of the Royal Astronomical Society
Izquierdo P
(2018)
Fast spectrophotometry of WD 1145+017
in Monthly Notices of the Royal Astronomical Society
Koester D
(2014)
The frequency of planetary debris around young white dwarfs
in Astronomy & Astrophysics
Manser CJ
(2019)
A planetesimal orbiting within the debris disc around a white dwarf star.
in Science (New York, N.Y.)
Raddi R
(2015)
Likely detection of water-rich asteroid debris in a metal-polluted white dwarf
in Monthly Notices of the Royal Astronomical Society
Redfield S
(2017)
Spectroscopic Evolution of Disintegrating Planetesimals: Minute to Month Variability in the Circumstellar Gas Associated with WD 1145+017
in The Astrophysical Journal
Rocchetto M
(2015)
The frequency and infrared brightness of circumstellar discs at white dwarfs
in Monthly Notices of the Royal Astronomical Society
Swan A
(2021)
Collisions in a gas-rich white dwarf planetary debris disc.
in Monthly notices of the Royal Astronomical Society
Swan A
(2019)
Interpretation and diversity of exoplanetary material orbiting white dwarfs
in Monthly Notices of the Royal Astronomical Society
Swan A
(2019)
Most white dwarfs with detectable dust discs show infrared variability
in Monthly Notices of the Royal Astronomical Society: Letters
Swan A
(2019)
The unbiased frequency of planetary signatures around single and binary white dwarfs using Spitzer and Hubble
in Monthly Notices of the Royal Astronomical Society
Tremblay P
(2020)
Gaia white dwarfs within 40 pc - I. Spectroscopic observations of new candidates
in Monthly Notices of the Royal Astronomical Society
Walters N
(2021)
A test of the planet-star unipolar inductor for magnetic white dwarfs
in Monthly Notices of the Royal Astronomical Society
Wilson D
(2019)
Multiwavelength observations of the EUV variable metal-rich white dwarf GD 394
in Monthly Notices of the Royal Astronomical Society
Wilson D
(2016)
Carbon to oxygen ratios in extrasolar planetesimals
in Monthly Notices of the Royal Astronomical Society
Wyatt M
(2018)
Fast spectrophotometry of WD1145+017
Wyatt M
(2014)
Stochastic accretion of planetesimals on to white dwarfs: constraints on the mass distribution of accreted material from atmospheric pollution
in Monthly Notices of the Royal Astronomical Society
Xu S
(2018)
Infrared Variability of Two Dusty White Dwarfs
in The Astrophysical Journal