Some of the oldest stars in the universe have just been discovered orbiting the Milky Way

Mention the Milky Way and most people will imagine a very large spiral galaxy billions of years old. It is thought to be a galaxy that formed billions of years after the Big Bang. Research by astronomers has shown that echoes of an earlier time can be heard around us.

A team of astronomers from MIT has found three ancient stars orbiting the Milky Way’s halo. The team thinks these stars formed when the universe was about a billion years old and were once part of a smaller galaxy that was consumed by the Milky Way.

The Milky Way is our home system within which our entire solar system and an estimated 400 billion other stars reside. It spans 100,000 light-years from left to right and is home to almost everything else we can see in the sky with the naked eye.

The Milky Way
MIT astronomers discovered three of the oldest stars in the universe, and they live in our own galactic neighborhood. The stars are located in the Milky Way’s ‘halo’ – the cloud of stars surrounding the main galactic disk – and appear to have formed between 12 and 13 billion years ago, when the very first galaxies took shape. (Serge Brunier/NASA)

On a clear, dark night, we can see that the combined light of all the stars in the Milky Way forms a beautiful band of hazy light that runs across the sky from horizon to horizon. If you could view the Milky Way from the outside, its broad shape would resemble two fried eggs stuck back to back.

The story of the discovery takes us back to 2022 during a new Observational Stellar Archeology course at MIoT, when students learned how to analyze ancient stars.

They then applied them to stars that have not yet been analyzed. Working with data from the Las Campanas Observatory’s 6.5-meter Magellan-Clay Telescope, they were looking for stars that formed shortly after the Big Bang.

At this point in the evolution of the universe there was mainly hydrogen and helium with traces of strontium and barium. The team therefore looked for stars with spectra that indicate these elements.

Precision manufacturing is at the heart of the Giant Magellan Telescope. The surface of each mirror must be polished to a fraction of the wavelength of light. (Giant Magellan Telescope Organization)

They based it on just three stars that had been observed in 2013 and 2014 but had not been analyzed before, so it was a great study for the students.

After completing their analysis (which took several hundred hours on a computer), the team determined that the stars had very low strontium and barium contents, as predicted if they were old stars.

The stars they studied are estimated to have formed between 12 and 13 billion years ago. What wasn’t clear was the origin of the stars. How did they end up in the Milky Way since it was relatively new and young?

The team decided to analyze the orbital characteristics of the stars to see how they moved. The stars were all in different locations in the Milky Way’s halo and were all thought to be about 30,000 light-years away from Earth.

Comparing the motion with data from the astrometric Gaia satellite, they found that the stars were moving in the opposite direction than most other stars in the Milky Way. We call this retrograde motion and it suggests that the stars came from somewhere else and did not form together with the Milky Way.

The chemical signatures of the stars, coupled with their motion, lend strong credence to the likelihood that these ancient stars are not native to the Milky Way.

Now that they’ve developed their approach to identifying old stars, the students are eager to expand their search to see if any others can be located.

However, with 400 billion stars in the Milky Way, a slightly more efficient method must be found.

This article was originally published by Universe Today. Read the original article.

Leave a Reply

Your email address will not be published. Required fields are marked *