GALEX J2339–0424
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GALEX J2339–0424 (GALEX J233917.0–042425, GALEX J2339) is a
white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
that is suspected to be polluted with material originating from an icy
exomoon Artist's impression of candidate exomoon Kepler-1625b I orbiting its planet. An exomoon or extrasolar moon is a natural satellite that orbits an exoplanet or other non-stellar extrasolar body. Exomoons are difficult to detect and confirm us ...
. This is evident from the first detection of
beryllium Beryllium is a chemical element; it has Symbol (chemistry), symbol Be and atomic number 4. It is a steel-gray, hard, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with ...
in this white dwarf, together with GD 378. GALEX J2339 was first identified as a possible
quasar A quasar ( ) is an extremely Luminosity, luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass rangi ...
with
GALEX Galaxy Evolution Explorer (GALEX or Explorer 83 or SMEX-7) was a NASA orbiting space telescope designed to observe the universe in ultraviolet wavelengths to measure the history of star formation in the universe. In addition to paving the way ...
in 2007. It was identified as a white dwarf candidate from
Gaia In Greek mythology, Gaia (; , a poetic form of ('), meaning 'land' or 'earth'),, , . also spelled Gaea (), is the personification of Earth. Gaia is the ancestral mother—sometimes parthenogenic—of all life. She is the mother of Uranus (S ...
and virtual observatory data in 2018. In 2020 it was identified as a DBAZ: white dwarf, which means that it had
helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...
,
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
and metal absorption lines. In 2021 the white dwarf was observed with Lick, Magellan 1 and Keck. The observations showed that the object had absorption due to hydrogen, helium, beryllium,
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
,
magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
,
silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
,
calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
,
titanium Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
,
chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...
,
manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
and
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
. The oxygen is present in excess, which indicates a
water ice Water ice may refer to: *Ice formed by water (as opposed to other substances) *In ice climbing, ice made from flowing water (as opposed to ice from precipitation) *The alternate term for various similar frozen fruit-flavoured desserts: ** Italian ic ...
-rich body. The accreted parent object had a
chondrite A chondrite is a stony (non-metallic) meteorite that has not been modified by either melting or planetary differentiation, differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar Syste ...
-like composition and was 85% water ice in volume. The accretion event lasted for 2–4 Million years and the parent body had a mass of 3 × 1020–1 × 1021 kg, or between about the mass of Vesta to about the mass of Ceres. Exomoons as a source of white dwarf pollution has been proposed since 2016/2017 and their fate around white dwarfs was further studied later, showing that around 1% of polluted white dwarfs should be polluted with exomoons. The presence of beryllium is thought to be the result of
spallation Spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection of material from a target during impact by a projectile. In planetary p ...
of heavier elements (especially oxygen) on the surface of an icy dust belt around a
giant planet A giant planet, sometimes referred to as a jovian planet (''Jove'' being another name for the Roman god Jupiter (mythology), Jupiter), is a diverse type of planet much larger than Earth. Giant planets are usually primarily composed of low-boiling ...
. The icy dust belts enriched in beryllium will then form exomoons, which might pollute white dwarf. These icy dust belts are comparable to Saturns rings and rings around
J1407b J1407b is a substellar object, either a Rogue planet, free-floating planet or brown dwarf, with a large circumplanetary disk or ring system. It was first detected by automated telescopes in 2007 when its disk eclipsed the star V1400 Cent ...
. Other scenarios are mentioned, such as the radiation of a Wolf-Rayet star. But these environments are less favourable to produce the observed beryllium excess. The spallation should also produce
lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...
and
boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...
, but (as of September 2024) these are not detected around GALEX J2339 or GD 378.


See also

* List of exoplanets and planetary debris around white dwarfs * List of exomoon candidates


References

{{Aquarius (constellation), state=collapsed White dwarfs Aquarius (constellation)