The oldest planetary debris has been found in our galaxy in a new study

Artist’s impression of ancient white dwarfs WDJ2147-4035 and WDJ1922+0233 surrounded by orbiting planetary debris, which would accumulate on the stars and pollute their atmospheres. WDJ2147-4035 is red and very dim, while WDJ1922 + 0233 is unusually blue. Credit: University of Warwick / Dr. Mark Garlick. Credit: University of Warwick / Dr. Mark Garlick

Astronomers led by the University of Warwick have identified the oldest star in our galaxy that is accumulating debris from planetary-orbiting minor planets, making it one of the oldest rocky and icy planetary systems ever discovered in the Milky Way.

Their findings were published today (November 5) in Monthly Notices of the Royal Astronomical Society He concluded that a faint white dwarf located 90 light-years from Earth, as well as the remnants of its orbiting planetary system, are more than 10 billion years old.

The fate of most stars, including those similar to our Sun, is to become a white dwarf. A white dwarf is a star that has burned off all its fuel and shed its outer layers and is now undergoing a process of shrinkage and cooling. During this process, any planets in their orbit will be disrupted, and in some cases destroyed, leaving their debris to collect on the surface of the white dwarf.

For this study, a team of astronomers led by the University of Warwick modeled two unusual white dwarfs discovered by the European Space Agency’s GAIA space observatory. Both stars are contaminated with planetary debris, with one found to be unusually blue, while the other is the faintest and redder so far found in the local galactic region – the team subjected both to further analysis.

Using spectroscopic and photometric data from GAIA, the Dark Energy Survey and the European Southern Observatory’s X-Shooter instrument to see how long it has cooled, the astronomers found that the “red” star WDJ2147-4035 is about 10.7 billion years old, of which 10.2 billion years were spent cooling as a dwarf. white.

Spectroscopy involves analyzing light from a star of different wavelengths, which can detect when elements in a star’s atmosphere absorb light of different colors and help determine and quantify which elements are present. By analyzing the spectrum of WDJ2147-4035, the team found the presence of the minerals sodium, lithium, potassium and carbon initially detected on the star – making this the oldest mineral-contaminated white dwarf discovered to date.

The second “blue” star WDJ1922+0233 is slightly smaller than WDJ2147-4035 and was contaminated with planetary debris of similar composition to Earth’s continental crust. The scientific team concluded that WDJ1922+0233’s blue color, despite its cold surface temperature, is caused by an unusually mixed atmosphere of helium and hydrogen.

Debris in the near-pure, highly gravitational atmosphere of the red star WDJ2147-4035 is from an ancient planetary system that survived the star’s evolution into a white dwarf, leading astronomers to conclude that this is the oldest. Discover a planetary system around a white dwarf in the Milky Way.

Lead author Abigail Elms, Ph.D. A student in the Department of Physics at the University of Warwick said, “These metal-tainted stars show that Earth is not unique, there are other planetary systems with planetary bodies similar to Earth. 97% of all stars will become white dwarfs and they are so ubiquitous around the universe that it is important They are very well understood, especially the very fascinating ones. Cold white dwarfs are composed of the oldest stars in our galaxy, and provide information about the formation and evolution of planetary systems around the oldest stars in the Milky Way.”

“We find the oldest stellar remnants in the Milky Way that were contaminated by Earth-like planets once upon a time. It is amazing to think that this happened on a scale of 10 billion years, and that these planets died before the Earth was formed.”

Astronomers can also use the star’s spectra to determine how quickly these minerals sink into the star’s core, allowing them to look back in time and determine how abundant each of these minerals was in the original planetary body. By comparing this abundance to astronomical objects and planetary material found in our solar system, we can guess what those planets were like before the star died and became a white dwarf—but in the case of WDJ2147-4035, that proved challenging.

Abigail explains: “The red star WDJ2147-4035 is a mystery because the accumulating planetary debris is very rich in lithium and potassium and unlike anything known in our solar system. This is a very interesting white dwarf as its surface temperature is extremely cold, the minerals that pollute it and its aging and the fact that it is magnetic makes it magnetic Extremely rare.”

Professor Pierre-Emmanuel Tremblay from the University of Warwick’s Department of Physics said, “When these ancient stars formed more than 10 billion years ago, the universe was less metal-rich than it is now, because minerals form in advanced stars and giant starbursts. The two white dwarfs provide Their observations are an exciting window into planet formation in a mineral-poor, gas-rich environment that was different from conditions when the solar system formed.”

more information:
Abigail Elms et al., Spectroscopy of ultra-cool white dwarfs contaminated with planetary debris, Monthly Notices of the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac2908

Presented by the University of Warwick

the quote: The oldest planetary debris in our galaxy is found in a new study (2022, November 5) on November 6, 2022 from https://phys.org/news/2022-11-oldest-planetary-debris-galaxy.html

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