Hubble finds dead stars 'polluted' with planetary debris

May 09, 2013
This illustration is an artist's impression of the thin, rocky debris disc discovered around the two Hyades white dwarfs. Rocky asteroids are thought to have been perturbed by planets within the system and diverted inwards towards the star, where they broke up, circled into a debris ring, and were then dragged onto the star itself. Credit: NASA, ESA, STScI, and G. Bacon (STScI)

(Phys.org) —The NASA/ESA Hubble Space Telescope has found signs of Earth-like planets in an unlikely place: the atmospheres of a pair of burnt-out stars in a nearby star cluster. The white dwarf stars are being polluted by debris from asteroid-like objects falling onto them. This discovery suggests that rocky planet assembly is common in clusters, say researchers.

The stars, known as white dwarfs—small, dim remnants of stars once like the Sun—reside 150 light-years away in the Hyades star cluster, in the constellation of Taurus (The Bull). The cluster is relatively young, at only 625 million years old.

Astronomers believe that all stars formed in clusters. However, searches for planets in these clusters have not been fruitful—of the roughly 800 known, only four are known to orbit stars in clusters. This scarcity may be due to the nature of the cluster stars, which are young and active, producing stellar flares and other outbursts that make it difficult to study them in detail.

A new study led by Jay Farihi of the University of Cambridge, UK, instead observed "retired" cluster stars to hunt for signs of planet formation.

Hubble's identified silicon in the atmospheres of two white dwarfs, a major ingredient of the rocky material that forms Earth and other in the Solar System. This silicon may have come from asteroids that were shredded by the white dwarfs' gravity when they veered too close to the stars. The likely formed a ring around the dead stars, which then funnelled the material inwards.

The debris detected whirling around the white dwarfs suggests that terrestrial planets formed when these stars were born. After the stars collapsed to form white dwarfs, surviving gas giant planets may have gravitationally nudged members of any leftover asteroid belts into star-grazing orbits.

This video is not supported by your browser at this time.
This animation is an artist's impression of the thin, rocky debris disc discovered around the two Hyades white dwarfs. Rocky asteroids are thought to have been perturbed by planets within the system and diverted inwards towards the star, where they broke up, circled into a debris ring, and were then dragged onto the star itself. Credit: NASA, ESA, STScI, and G. Bacon (STScI).

"We have identified for the building blocks of ," says Farihi. "When these stars were born, they built planets, and there's a good chance that they currently retain some of them. The signs of rocky debris we are seeing are evidence of this—it is at least as rocky as the most primitive terrestrial bodies in our Solar System."

Besides finding silicon in the Hyades ' atmospheres, Hubble also detected low levels of carbon. This is another sign of the rocky nature of the debris, as astronomers know that carbon levels should be very low in rocky, Earth-like material. Finding its faint chemical signature required Hubble's powerful Cosmic Origins Spectrograph (COS), as carbon's fingerprints can be detected only in ultraviolet light, which cannot be observed from ground-based telescopes.

"The one thing the white dwarf pollution technique gives us that we won't get with any other planet detection technique is the chemistry of solid planets," Farihi says. "Based on the silicon-to-carbon ratio in our study, for example, we can actually say that this material is basically Earth-like."

This new study suggests that asteroids less than 160 kilometres across were gravitationally torn apart by the white dwarfs' strong tidal forces, before eventually falling onto the .

The team plans to analyse more using the same technique to identify not only the rocks' composition, but also their parent bodies. "The beauty of this technique is that whatever the Universe is doing, we'll be able to measure it," Farihi said. "We have been using the Solar System as a kind of map, but we don't know what the rest of the Universe does. Hopefully with Hubble and its powerful ultraviolet-light spectrograph COS, and with the upcoming ground-based 30- and 40-metre telescopes, we'll be able to tell more of the story."

Explore further: Study finds white dwarf stars may hold the key to detecting life on other planets

Related Stories

Watery, rocky planets may be common in the Milky Way

Apr 13, 2010

(PhysOrg.com) -- An international team of astronomers have discovered compelling evidence that rocky planets are commonplace in our Galaxy. Leicester University scientist and lead researcher Dr Jay Farihi ...

Solar systems around dead Suns?

Apr 20, 2009

(PhysOrg.com) -- Using NASA’s Spitzer Space Telescope, an international team of astronomers have found that at least 1 in 100 white dwarf stars show evidence of orbiting asteroids and rocky planets, suggesting ...

Dead Stars Tell Story of Planet Birth

Jan 05, 2009

(PhysOrg.com) -- Astronomers have turned to an unexpected place to study the evolution of planets -- dead stars. Observations made with NASA's Spitzer Space Telescope reveal six dead "white dwarf" stars littered ...

Recommended for you

Quest for extraterrestrial life not over, experts say

17 hours ago

The discovery of an Earth-sized planet in the "habitable" zone of a distant star, though exciting, is still a long way from pointing to the existence of extraterrestrial life, experts said Friday. ...

Continents may be a key feature of Super-Earths

22 hours ago

Huge Earth-like planets that have both continents and oceans may be better at harboring extraterrestrial life than those that are water-only worlds. A new study gives hope for the possibility that many super-Earth ...

Exoplanets soon to gleam in the eye of NESSI

Apr 18, 2014

(Phys.org) —The New Mexico Exoplanet Spectroscopic Survey Instrument (NESSI) will soon get its first "taste" of exoplanets, helping astronomers decipher their chemical composition. Exoplanets are planets ...

User comments : 0

More news stories

Impact glass stores biodata for millions of years

(Phys.org) —Bits of plant life encapsulated in molten glass by asteroid and comet impacts millions of years ago give geologists information about climate and life forms on the ancient Earth. Scientists ...

Health care site flagged in Heartbleed review

People with accounts on the enrollment website for President Barack Obama's signature health care law are being told to change their passwords following an administration-wide review of the government's vulnerability to the ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.