Hunt Is On For Sun’s Lost Siblings

Astronomers at the Very Large Telescope (VLT) Observatory’s hotel in the Atacama Desert in Chile take a moment to gaze up at the Milky Way. Our galaxy may have up to 400 billion stars. Lost among them are the original members of the star cluster of which our sun was once a member. ESO/Luis Calcada/Herbert Zodet

Did you know that the sun once had brothers and sisters? Like most stars, it was born in a nebula, a cloud of gas and dust that collapsed under its self-gravity to form a cluster of stars. That all happened 4.6 billion years ago. Earth’s sky back then would have been positively glowing from all those solar neighbors which may have numbered in the thousands. Fast-forward to the present time when we find ourselves alone. The nearest star, the Alpha Centauri system, is 4.5 light years away and unrelated to our birth mates.

There’s hope that may change. Australian astronomers have collected spectra (rainbows of light imprinted with a star’s chemical makeup) from more than 340,000 stars across the Milky Way as part of the Galactic Archaeology project called GALAH. They’re hoping to identify stars that have the same chemical signature as that of the sun which would indicate they were born from the same cloud. Brothers and sisters, yeah!

The star cluster NGC 457, better known as the “E.T. Cluster” for its resemblance to the Steven Spielberg movie character, will one day dissipate as the stars go their separate ways. Hunter Wilson

Star clusters like the Pleiades don’t stay together forever. They orbit the galactic center and stray from the group. Massive clouds of hydrogen in the Milky Way’s disk tug at them, picking clusters apart, separating family members over time. The sun’s cluster has long since scattered.

So far, astronomers have used the custom-built HERMES spectrograph attached to the Australian Astronomical Observatory’s 3.9-meter (153.5-inch) telescope to collect spectra over 280 nights. No other survey has been able to measure as many elements for as many stars.

“Every star in that cluster will have the same chemical composition, or DNA,” said Sarah Martell of the University of New South Wales in Sydney, leader of the GALAH survey observations. “These clusters are quickly pulled apart by our Milky Way Galaxy and are now scattered across the sky. The GALAH team’s aim is to make DNA matches between stars to find their long-lost sisters and brothers.”

Just like checking in on our own family members, we hope someday to do the same with the sun’s former cluster buddies. Too bad that no reunion will ever be possible, but it would sure be nice to know what’s become of the family.