Gaia’s all-sky view of our Milky Way galaxy and neighbouring galaxies, based on measurements of nearly 1.7 billion stars. Photo: Gaia/ESA
A decade ago, the Gaia space mission was launched by the European Space Agency (ESA) with the ambition of creating a 3D map of our galaxy.
After observing some 1.8 billion stars, and having a near complete map of the Milky Way, scientists realised a crucial gap: They did not have a clear view of parts of the sky that were packed with stars.
So the scientists operating the Gaia space observatory decided to take a better look at super-conglomerations of stars called globular clusters.
The study was a reanalysis of old data they had previously collected. ESA called for help from amateur astronomers to help with the analysis.
They focussed on the Omega Centauri cluster, some 17,090 light years from Earth.
The study revealed half a million new stars in just this one cluster. It also found cosmic objects so heavy they bend light itself.
What are globular clusters?
Globular clusters are a dense collection of hundreds of thousands of stars. They are some of the oldest objects in the universe.
Spotting these clusters helped scientists realize that the sun was not at the centre of the spiral Milky Way galaxy.
The majority of the galaxy’s globular clusters are situated near the centre of the Milky Way. Using their locations, they found that the sun (and Earth) was in the open clusters found in one of the galaxy’s spiral arms — the Sagittarius arm.
Astronomers have been charting the Milky Way for centuries but the sheer number of stars in them can sometimes overwhelm telescopes and our ability to read them properly.
Bright stars in the clusters often outshine their weak neighbours, and some stars are too close to each other to be defined separately.
Gaia has rendered a clearer picture of these clusters than ever before.
Why did Gaia choose Omega Centauri?
Omega Centauri is the largest known globular cluster in the Milky Way that can be seen from Earth. It appears to be almost as big as a full Moon when observed from dark, remote areas.
It has a sprawling diameter of 150 light years. It is estimated to be four million times as heavy as the sun and spread across some 10 million stars.
Scientists working on Gaia mapped the cluster by observing its core every time it came into view.
The half million new stars revealed in Omega Centauri mean it is the most crowded region explored by Gaia so far.
The data can help us understand how the stars of the Milky Way are distributed and why some parts of the universe, like these clusters, have more mass than others.
Universe through gravitational lens
Light tends to get warped when it passes through heavy objects like globular clusters.
These heavy clusters have a greater gravitational pull. So they bend light in a phenomenon called gravitational lensing.
The clusters behave like a giant magnifying glass, or lens, that can amplify the light and cast multiple images of the faraway source onto the sky.
Gaia has recently found 381 cases where evidence for gravitational lensing was observed. ESA scientists say this means that the Omega Centauri cluster’s gravity bent light coming from distant sources called quasars.
Quasars are remote sources of bright light that could be powered by black holes.
Gaia has been able to observe these faraway quasars because they are lensed through the Omega Centauri cluster.
Co-author Christine Ducourant of Laboratoire d’Astrophysique de Bordeaux, France, and a member of the Gaia collaboration described Gaia as “a real lens-seeker.”
In the next data release in 2025, Gaia will give information about eight more such star-packed regions of the sky.
Scientists hope this will help confirm the age of our galaxy, locate its centre, verify how stars change through their lifetimes and ultimately infer the possible age of the universe itself.
This article was originally published on DW.