Our Sun May Have Been Born With a Trouble-Making Twin Called ‘Nemesis’

A new model of how stars are made backs up the idea that most, if not all, stars have at least one sibling when they are born.

Our Sun, which is at the center of the Solar System, is probably no different. In fact, some astronomers think that the Sun’s long-lost twin might have killed off the dinosaurs.

Do all stars form as binaries?

Two researchers from UC Berkeley and the Harvard-Smithsonian Astrophysical Observatory came to the conclusion in 2017 after looking at data from a radio survey of a dust cloud in the Perseus constellation that all Sun-like stars are most likely born with a companion.

In June 2017, UC Berkeley astronomer Steven Stahler said, “We ran a series of statistical models to see if we could explain the relative numbers of young single stars and wide binaries in the Perseus molecular cloud. The only model that could explain the data was one in which all stars form first as wide binaries.”

Astronomers have been wondering for years if the many binary and triple star systems in our galaxy are made close together or if they merge after they are made.

Most people have believed in the “born together” theory, and simulations made in the last few decades have shown that almost all stars could be born as multiples that often move away from each other on their own.

There hasn’t been much real-world evidence to back up these simulations, so this new work is very exciting.

Stahler said, “Our work is a step toward understanding how binaries form and what role they play in the early evolution of stars.”

As part of the VLA nascent disk and multiplicity survey, the scientists mapped radio waves coming from a dense cocoon of dust 600 light-years away that held a nursery of young stars (VANDAM for short).

The VANDAM survey made it possible to count stars younger than half a million years old. These stars are called Class 0 stars, which is star-speak for “babies,” and stars between 500,000 and 1 million years old are called Class 1 stars.

The theoretical twin star of our Sun

Scientists found 45 single stars, 19 systems with two stars, and five systems with more than two stars by looking at the shapes of the dust clouds around them.

Even though their results said that all stars are born as binaries, they changed their conclusion to say that most stars born inside the dense cores of dust clouds are born with a partner. This is because their model had some problems.

Stahler said at the time, “I think we have the best evidence to date for making such a claim.”

When the researchers looked at how far apart the stars were, they found that all of the binaries that were more than 500 AU apart were Class 0 and lined up with the center of the egg-shaped cloud that surrounded them.

Class 1 stars, on the other hand, were usually closer together, at about 200 AU, and their axes weren’t lined up.

Sarah Sadavoy from the Harvard-Smithsonian Astrophysical Observatory said, “We don’t know exactly what it means yet, but it’s not random and must say something about how wide binaries form.”

If most stars are born with a partner, where is ours?

500 AU is about 0.008 light-years away, which is a little less than 3 light-days. To put this in perspective, Neptune is about 30 AU away, the Voyager 1 probe is about 140 AU away, and Proxima Centauri, which is the closest known star, is about 268,770 AU away.

So, if the Sun has a twin, we probably can’t see it from where we live.

But there is a theory that our Sun has a twin that likes to stop by and stir things up every once in a while.

Theoretical troublemaker Nemesis has been blamed for what seems to be a 27-million-year cycle of extinctions on Earth, including the one that killed off most dinosaurs.

Richard Muller, an astronomer at the University of California, Berkeley, suggested 23 years ago that a red dwarf star 1.5 light-years away could sometimes move through the icy outer limits of our Solar System, moving things around with its gravity and sending a few more space rocks our way.

A dim star passing by, like a brown dwarf, could also explain other strange things on the edge of our Solar System, like the dwarf planet Sedna’s wide, strange orbit.

There’s no sign of Nemesis, but our Sun could have a long-lost binary partner.

“We are saying that, yes, Nemesis probably existed a long time ago,” Stahler said.

In that case, it seems like our Sun would have gotten most of the dust and gas, leaving its twin planet dark and small.

So it’s not surprised that it’s a little mad.

This study was published in the Royal Astronomical Society’s Monthly Notices.