A new study has found that part of our Milky Way galaxy is much older than previously thought, dating back only 800 million years after the Big Bang.
Astronomers have shown that the “thick disk” of the Milky Way began to form 13 billion years ago – about two billion years earlier than expected.
The spiral disk of our galaxy can be divided into two parts: a thin inner disk of young stars, to which our Sun belongs, and a thick disk, which includes several older stars that extend further from the plane of the galactic spiral.
The surprising result came from an analysis by Maosheng Xiang and Hans-Walter Rix of the Max Planck Institute for Astronomy in Heidelberg, Germany.
A new study has found that part of our Milky Way galaxy is much older than previously thought, dating back only 800 million years after the Big Bang. Astronomers have shown that the “thick disk” began to form 13 billion years ago – about two billion years earlier than expected.
HOW MUCH IS THE MILKY WAY?
One solar mass is equivalent to 2 times 10 in the 30th part of one kilogram.
The entire galaxy is 1.5 trillion times bigger (1.5 times ten to the power of 12) than this.
This means that the Sun weighs 3 x 10^42 kg.
This corresponds to 3 x 10^39 tons.
In non-mathematics, this means that the weight of the Milky Way is therefore 3,000 trillion trillion trillion tons.
Using data from the European Space Agency’s Gaia Observatory, the researchers were able to build a timeline for the formation of the Milky Way, identifying subgiant stars in different regions.
They took brightness and position data from a survey of nearly a quarter of a million stars and combined them with their chemical composition to determine the age of the stellar bodies.
In subgiant stars, energy has ceased to be generated in the core of the star and has moved into a shell around the core as the star itself becomes a red giant.
Because the subgiant phase is a relatively short evolutionary phase in a star’s life, astronomers say it allows a star’s age to be determined with great accuracy.
However, this is still a tricky calculation because it cannot be measured directly.
Instead, it should be inferred by comparing the characteristics of the star with computer models of stellar evolution, and what the star is made of helps with this.
The universe was born almost exclusively from hydrogen and helium, while other chemical elements, collectively known to astronomers as metals, are produced inside stars.
They are ejected back into space at the end of a star’s life, where they can be incorporated into the next generation of stars.
This means that older stars contain less metals and are said to have lower metallicities.
Together, brightness and metallicity allow astronomers to determine the age of a star from computer models.
Prior to Gaia, astronomers often worked with an uncertainty of 20 to 40 percent, which could result in a given age being inaccurate by a billion years or more.
But the release of early data Gaia 3 (EDR3) changed that.
“With Gaia brightness data, we can determine the age of a subgiant star to within a few percent,” Maosheng said.
Armed with the exact age of a quarter of a million subgiants scattered throughout the galaxy, he and Hans-Walter began their analysis.
Our galaxy is made up of different components, which can be divided into a halo and a disk. The halo is a spherical region surrounding a disk and is traditionally considered the oldest component of a galaxy.
Our galaxy is made up of different components, which can be divided into a halo and a disk. The halo is a spherical region surrounding a disk and is traditionally considered the oldest component of a galaxy.
The disk consists of two parts: a thin disk and a thick disk.
The thin disk contains most of the stars we see as a hazy band of light in the night sky called the Milky Way, while the thick disk contains only a few percent of the Milky Way’s stars in the Sun’s vicinity.
By identifying subgiant stars in these different regions, the researchers were able to plot a timeline for the formation of the Milky Way – and here they were in for a surprise.
The stellar ages have clearly shown that the formation of the Milky Way took place in two separate phases.
In the first phase, starting just 0.8 billion years after the Big Bang, the thick disk began to form stars.
The interior parts of the halo may have also begun to assemble at this stage, but the process quickly accelerated and ended about two billion years later when the dwarf galaxy known as Gaia-Sausage-Enceladus merged with the Milky Way.
It filled the halo with stars and, as the new work clearly shows, caused the nascent thick disk to form most of its stars.
The researchers said that the thin disk of stars that holds the Sun formed during the subsequent, second phase of galaxy formation.
The spiral disk of our galaxy can be divided into two parts: a thin inner disk of young stars, to which our Sun belongs, and a thick disk, which includes older stars that extend further from the plane of the galactic spiral.
This earlier formation of the thick disk points to a different picture of our galaxy’s early history.
“Since the discovery of the ancient Gaia-Sausage-Enceladus confluence in 2018, astronomers have suspected that the Milky Way already existed before the halo formed, but we had no clear idea of what that Milky Way looked like. Maosheng said.
“Our results provide detailed information about this part of the Milky Way, such as its birthday, star formation rate, and history of metal enrichment.
“Combining these discoveries using Gaia data will revolutionize our understanding of when and how our galaxy was formed.”
New observations may emerge in the near future, including with NASA’s James Webb Space Telescope, which was designed to detect the earliest Milky Way-like galaxies in the universe.
Gaia will also publish more stellar age and metallicity data this summer.
“With each new analysis and data release, Gaia allows us to piece together the history of our galaxy in even more unprecedented detail,” said Timo Prusti, Gaia Project Scientist for ESA.
“With the release of Gaia DR3 in June, astronomers will be able to enrich the story with even more detail.”
The study is published in the journal Nature.
WHAT IS THE EUROPEAN SPACE AGENCY GAIA PROBE AND WHAT IS IT FOR?
Gaia is an ambitious mission to map our Milky Way galaxy in 3D and reveal its composition, formation and evolution.
Gaia has orbited the Sun nearly a million miles from Earth’s orbit since its launch by the European Space Agency (ESA) in December 2013.
On its journey, the probe discreetly took pictures of the Milky Way, identifying stars from smaller galaxies long swallowed up by our own.
Gaia is expected to detect tens of thousands of previously undiscovered objects, including asteroids that could one day threaten Earth, planets orbiting nearby stars, and exploding supernovae.
An artist’s impression of Gaia displaying the stars of the Milky Way. Gaia displays the position of the stars in the Milky Way in several ways. It pinpoints the location of stars, but the probe can also track their movement by scanning each star about 70 times.
Astrophysicists also hope to learn more about the distribution of dark matter, the invisible substance thought to hold the observable universe together.
They also plan to test Albert Einstein’s general theory of relativity by observing how light is deflected by the Sun and its planets.
The satellite’s billion-pixel camera, the largest ever in space, is so powerful that it can measure the diameter of a human hair at a distance of 621 miles (1,000 km).
This means that nearby stars have been detected with unprecedented accuracy.
Gaia displays the position of the stars in the Milky Way in several ways.
An all-sky view of our Milky Way Galaxy and neighboring galaxies taken by Gaia based on measurements of almost 1.7 billion stars. The map shows the overall brightness and color of stars observed by the ESA satellite in each part of the sky between July 2014 and May 2016. Brighter areas indicate denser concentrations of especially bright stars, while darker areas correspond to areas of the sky where there is less bright stars are observed. The color representation is obtained by combining the total amount of light with the amount of blue and red light recorded by Gaia in each area of the sky.
It pinpoints the location of stars, but the probe can also track their movement by scanning each star about 70 times.
This is what allows scientists to calculate the distance between the Earth and each star, which is the most important measure.
In September 2016, the ESA released the first batch of data collected by Gaia, which included information on the brightness and position of over a billion stars.
In April 2018, it was expanded to high-precision measurements of nearly 1.7 billion stars.