A new model of star formation supports the theory that most, if not all, stars are born in a litter with at least one sibling.
Our own star at the center of the Solar System is most likely no exception, and some astronomers believe that the Sun’s estranged twin might be to blame for the dinosaurs’ extinction.
Do all stars form as binaries?
After analyzing data from a radio survey conducted on a dust cloud in the Perseus constellation, two researchers from UC Berkeley and the Harvard-Smithsonian Astrophysical Observatory concluded back in 2017 that all Sun-like stars are most likely born with a companion.
“We ran a series of statistical models to see if we could account for the relative populations of young single stars and binaries of all separations in the Perseus molecular cloud, and the only model that could reproduce the data was one in which all stars form initially as wide binaries,” said UC Berkeley astronomer Steven Stahler in June 2017.
For years, astronomers have wondered if our galaxy’s large number of binary and triple star systems are formed close to one another, or if they merge after they form.
The ‘born together’ hypothesis has been the most popular, and simulations developed in recent decades have revealed that almost all stars could be born as multiples that often spin away on their own.
Unfortunately, empirical evidence supporting these simulations has been limited, making this new work very exciting.
“Our work is a step forward in understanding both how binaries form and also the role that binaries play in early stellar evolution,” said Stahler.
The researchers mapped radio waves leaking out of a dense cocoon of dust about 600 light-years away that contained a nursery of young stars as part of the VLA nascent disk and multiplicity survey (VANDAM for short).
The VANDAM survey allowed for a census of stars younger than half a million years old, known as Class 0 stars – “babies” in star terms – and stars a little older, between 500,000 and 1 million years old, known as Class 1.
The theoretical twin star of our Sun.
Using data on the shapes of the surrounding cloud of dust, the scientists discovered 45 lonely stars, 19 binary star systems, and five systems with more than two stars.
While their results predicted all stars were born as binaries, they amended their conclusion to take into account limitations in their model by saying most stars formed inside the dense cores of dust clouds are born with a partner.
“I think we have the strongest evidence to date for such an assertion,” said Stahler at the time.
When the researchers examined the distances between the stars, they discovered that all binaries separated by 500 AU or more were Class 0 and aligned with the axis of the egg-shaped cloud that surrounded them.
Class 1 stars, on the other hand, tended to be closer together at around 200 AU and weren’t aligned with their ‘egg’s’ axis.
“We don’t yet know quite what it means, but it isn’t random and must say something about the way wide binaries form,” said Sarah Sadavoy from the Harvard-Smithsonian Astrophysical Observatory.
If most stars are born with a partner, where is ours?
A distance of 500 AU is approximately 0.008 light-years, or slightly less than 3 light-days. To put this in context, Neptune is approximately 30 AU away, the Voyager 1 probe is currently approximately 140 AU away, and the nearest known star, Proxima Centauri, is 268,770 AU away.
So, if the Sun has a twin, it’s almost certainly not visible in our neighborhood.
But there is an hypothesis that our Sun has a twin that likes to swing by every now and then, and stir things up.
This theoretical troublemaker, dubbed Nemesis, has been proposed as the cause of an apparent 27-million-year cycle of extinctions on Earth, including the one that wiped out the majority of the dinosaurs.
An astronomer from the University of California Berkeley named Richard Muller proposed 23 years ago that a red dwarf star 1.5 light-years away could periodically travel through the icy outer limits of our Solar System, stirring up material with its gravity, knocking a few more space boulders our way.
A dim passing star, such as a brown dwarf, could also explain other anomalies on the outskirts of our Solar System, such as the dwarf planet Sedna’s unusual, wide orbit.
There’s no sign of Nemesis, but a long-lost binary partner for our Sun could fit the bill.
“We are saying, yes, there probably was a Nemesis, a long time ago,” said Stahler.
In that case, it appears that our Sun would have gathered the lion’s share of dust and gas, leaving its twin dark and stunted.
No wonder it’s a little pissed off.
This study was published in the Royal Astronomical Society’s Monthly Notices.
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