Another two white-dwarfs in Universe

Thanks to the Hubble Space Telescope, a team of astronomers found chemical signatures of debris of rocky planets around two white dwarfs, one constellation not far from us. So far it has been very difficult to observe planets within the clusters, but the same method could allow us to discover many more.

An Earth-like planet placed where we wouldn’t just expect: the atmosphere around a couple of old stars now reduced to white dwarfs in a cluster of stars in our vicinity. The Hubble Space Telescope has uncovered that there are at least debris, which suggests that the formation of rocky planets may be very common in star clusters. The two white dwarfs – the remains of stars that once were similar to the Sun – are located 150 light-years away in the cluster Hyades in the constellation of Taurus. The constellation is relatively young, born just 625 million years ago.



Astronomers believe that all stars are formed in clusters. However, so far the search for planets within the clusters did not go well – of the approximately 800 known extrasolar planets, only four are in orbit around stars that are part of clusters. This lack could be due to the nature of the stars within the clusters, young and active, its surrounding area being difficult to study in detail. A new study by Jay Farihi from University of Cambridge, published in the Monthly Notices of the Royal Astronomical Society has allowed observing stars that “retire” within the clusters, looking for signs of planet formation.

Spectroscopic observations conducted with Hubble identified silicon in the atmospheres of two white dwarfs, an important ingredient of the rock material that forms the Earth and other terrestrial planets of the Solar System. The silicon in question could have come from asteroids “crushed” by the gravity of white dwarfs. The rocky debris is likely to have formed a ring around the white dwarf, ending up being concentrated inwards. But if there were any asteroids, it most likely means that there were rocky planets around these stars formed early in their history.



“We have identified the chemical evidence of the presence of brick rocky planets,” says Farihi. “When these stars were born, they formed planets, and there is a good chance that currently retains some. The traces of rocky debris that we see are the proof. “In addition to finding silicon in the atmospheres of stars in the Hyades, Hubble also detected low levels of carbon, another sign of the rocky nature of the debris: in fact, astronomers know that the levels of carbon must be very low in rock materials of terrestrial nature. Find its weak chemical signature required the use of the powerful Hubble’s Cosmic Origins Spectrograph (COS): carbon footprints can only be detected in ultraviolet light, which cannot be studied by ground-based telescopes.

The team now plans to analyze other white dwarfs with the same technique to identify not only the composition of the rocks, but also the star around which they orbit. “The beauty of this technique is that no matter what the universe is doing, we will be able to measure it,” said Farihi. “So far we have used the solar system as a sort of map, but we do not know what happens in the rest of the Universe. We hope that with Hubble and his powerful spectrograph COS- ultraviolet light, and with the next ground-based telescopes from 30 – 40 meters, we will be able to tell other parts of the story.”

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