(ORDO NEWS) — Astronomers from the University of Warwick have identified the oldest star in our galaxy. The star is accreting debris from rotating planetesimals, making it one of the oldest rocky and icy planetary systems found in the Milky Way.
Scientists have found that the faint white dwarf, located 90 light years from Earth, as well as the remnants of its orbital planetary system, is more than 10 billion years old.
For this study, a team of astronomers created models of two unusual white dwarfs that were discovered by ESA’s GAIA space observatory.
Both stars are contaminated with planetary debris, with one found to be unusually blue while the other is the dimmest and reddest star found to date in the local galactic neighborhood. The team subjected both stars to further analysis.
To determine the age of WDJ2147-4035, scientists used GAIA spectroscopic and photometric data, the Dark Energy Survey, and the X-Shooter at the European Southern Observatory. As a result, astronomers found that the star is about 10.7 billion years old, of which 10.2 billion it cools.
By analyzing the spectrum of WDJ2147-4035, the team detected the presence of the metals sodium, lithium, potassium, and tentatively detected carbon being consumed by the star. Thus, this star is the most metal-polluted white dwarf.
The second star WDJ1922+0233 is only slightly younger than WDJ2147-4035. It was contaminated with planetary debris, the composition of which is similar to that of the Earth’s continental crust.
The scientific team concluded that the blue color of WDJ1922+0233, despite its low surface temperature, is due to the star’s unusual mixed helium-hydrogen atmosphere.
The debris found in the atmosphere of the red star WDJ2147-4035 belongs to an old planetary system that survived the star’s evolution into a white dwarf.
“These metal-polluted stars show that the Earth is not unique, there are other planetary systems with planetary bodies similar to the Earth.
97% of all stars will become white dwarfs, and they are so common throughout the universe that they are very important to study, especially those that are extremely cold.
Formed from the oldest stars in our galaxy, cool white dwarfs provide information about the formation and evolution of planetary systems around the oldest stars in the Milky Way,” said Abigail Elmes, lead author of the paper.
Astronomers can also use the spectra of a star to calculate how quickly metals sink into the star’s core, which makes it possible to determine how much of each of these metals was in the original planetary body.
By comparing this number to astronomical bodies and planetary material found in the solar system, scientists can guess what these planets were like before the star died and turned into a white dwarf, but in the case of WDJ2147-4035, this proved to be a daunting task.
“The red star WDJ2147-4035 is a mystery, because the accumulated debris of the planets is very rich in lithium and potassium, and is not like anything known in our solar system.
This is a very interesting white dwarf, as its ultra-cold surface temperatures, its contaminating metals, its advanced age, and the fact that it is magnetic make it extremely rare,” Abigail said.
“When these old stars formed over 10 billion years ago, the universe was less rich in metals than it is now, because metals are formed in evolved stars and in giant stellar explosions.
The two observed white dwarfs provide an opportunity to study the formation of planets in a metal-poor, gas-rich environment that was different from the conditions under which the solar system formed.”
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