Hubble Telescope Reveals White Dwarf Consuming Pluto-Like Icy World: Implications for Habitable Exoplanets

An early stage of an icy body being torn apart by the intense gravity of a white dwarf

Astronomers utilizing the Hubble Space Telescope have detected a white dwarf - a compact stellar remnant - consuming an icy celestial body similar to the dwarf planet Pluto. This discovery carries significant implications for understanding the potential habitability of exoplanetary systems.

The white dwarf is situated within our Milky Way galaxy approximately 255 light-years from Earth, relatively nearby in cosmic distance, possessing about 57% of the sun's mass. A light-year represents the distance light travels in one year, equivalent to 5.9 trillion miles (9.5 trillion km).

White dwarfs rank among the universe's most dense objects, though less compact than black holes. Stars with masses up to eight times that of our sun typically conclude their lifecycle as white dwarfs. These stars eventually exhaust their hydrogen fuel supply. Gravitational forces then cause them to collapse and expel their outer layers during a "red giant" phase, ultimately leaving behind a dense core - the white dwarf.

Our sun is predicted to transform into a white dwarf billions of years in the future. The particular white dwarf examined in this study originates from a star estimated to have been 50% more massive than our sun. In its current compressed state, its diameter roughly matches Earth's despite being approximately 190,000 times more massive than our planet.

Scientists have previously documented how white dwarfs, through their powerful gravitational attraction, consume - or accrete - rocky bodies such as planets, moons, and asteroids. Researchers identify these events by detecting materials composed of elements from these consumed objects on the white dwarf's surface.

In this case, researchers identified a chemical signature indicating that the consumed object was primarily icy rather than rocky. They theorize that the white dwarf's gravitational forces dismembered a Pluto-like world, with the resulting fragments cascading onto its surface.

"The white dwarf likely accreted fragments from the crust and mantle of a Pluto-like icy world," explained Snehalata Sahu, a postdoctoral research fellow in astrophysics at the University of Warwick in England and lead author of the study published this month in the Monthly Notices of the Royal Astronomical Society.

"If not an entire Pluto, it would be a fragment chipped off a Pluto-like world by the collision with some other body. Either way, once this body gets sufficiently close to the white dwarf, roughly within a distance comparable to the size of the sun, the strong gravity would tidally distort the body, and it eventually would crack and disintegrate," added University of Warwick astrophysicist and study co-author Boris Gansicke.

Chemical analysis confirmed that the object was not a comet, another type of icy celestial body.

"The key evidence comes from the unusually high abundance of nitrogen we observed, much higher than in typical cometary material, and consistent with the nitrogen-rich ices that dominate Pluto's surface," Sahu stated.

According to Gansicke, nitrogen detection was accomplished using Hubble's Cosmic Origins Spectrograph instrument, which observes ultraviolet light to investigate the formation and evolution of galaxies, stars, and planetary systems.

Material was falling onto the white dwarf at a rate equivalent to approximately the mass of an adult blue whale every second, continuing for at least the past 13 years, according to Sahu.

These observations provide evidence that icy bodies similar to those in our solar system exist in other planetary systems. Our solar system contains numerous such objects, particularly in the cold region beyond Neptune populated by dwarf planets like Pluto, comets, and other icy bodies.

Water represents a vital component for life. However, the process by which rocky planets like Earth acquire substantial quantities of water remains debated.

"In our solar system, icy bodies such as comets are thought to have played a key role in delivering water to the rocky planets, including Earth. Along with water, they also supplied other volatile and organic compounds such as carbon, sulfur and complex organics that are essential for prebiotic chemistry and, ultimately, the emergence of life," Sahu explained.

"Similarly, in other planetary systems, water-rich bodies are expected to serve as carriers of these fundamental building blocks, potentially contributing to the development of habitable environments," Sahu continued. "Detecting water-rich bodies around other stars provides observational confirmation that such reservoirs exist beyond our solar system."