Astronomers have dated one of the oldest stars in the galaxy. Here’s how to see it
To find Indi, head out at night and look west. Find the brightest dot you can see, close down by the horizon. That’s Venus, second planet from the sun.
Shift your eyes along the horizon to the south, towards the Southern Cross. Midway between Venus and the Cross you’ll spot a bright star.
That’s Indi. You’re looking at a galactic ancient.
Scientists work out the age of stars using asteroseismology: the study of star vibrations.
Stars are giant nuclear furnaces. The explosions within them make them constantly vibrate, like a ringing bell.
“They are basically big gongs,” says Associate Professor Dennis Stello, a physicist with the University of NSW who was part of the team that made the discovery.
That vibration causes their brightness to flicker slightly, like a candle in the wind. That flickering is tiny – but it can be detected by the sensitive telescopes on NASA’s TESS satellite, currently in high-Earth orbit.
As stars age, the pattern of their vibrations – and their flickering – changes. Know a star’s vibration and you know its age. Indi’s vibration pattern makes it 11 billion years old.
There are several stars astronomers think are older, but none of them have been dated with such precision.
Then there is its chemistry. Indi contains high levels of titanium atoms. Most titanium was made by supernovae, or the explosion of stars, in the universe’s early days. After those supernovae blew, the titanium-rich gas congealed into new stars – like Indi. That’s a further clue the star is a stellar ancient.
Finally, there is the course the star is charting through space.
In the early days of the Milky Way, our galaxy was little more than a small blob of stars. Over its several-billion-year history it has swallowed up other smaller blobs.
About the time Indi was formed, the Milky Way was merging with a dwarf galaxy called Gaia-Enceladus.
Could Indi have been from Gaia-Enceladus? It was certainly old enough. To find out, the team used the European Space Agency’s Gaia space telescope, which is orbiting between the sun and Earth.
Gaia is capable of detecting the speed and direction of stars moving through the galaxy. Using that data, the team could see their star was moving in the same direction as other stars from the old Milky Way – suggesting Indi had been an original member of our galaxy.
But Gaia’s observations also show Indi has been pushed and shoved around. Its orbit is not quite right. The research team say that suggests it took a buffeting when the Milky Way collided with Gaia-Enceladus.
“This was a very chaotic time, when lots of lumps of stars merged together,” says Dr Stello.
“We want to understand our home. And that’s the Milky Way. And to understand how it formed, we need to understand these early events.”
The research was published on Tuesday in Nature Astronomy.
Liam is The Age and Sydney Morning Herald’s science reporter