While we may be used to the eight solar system planets orbiting just one sun, having a single
star isn’t the norm for the rest of the universe.
Binary star systems, where two stars orbit a common point – or barycenter – are actually
incredibly common… leading some scientists to wonder why it is that our sun is off on
its own, or whether we might actually have miscounted?
This is Unveiled, and today we’re answering the extraordinary question; could the solar
system have another star?
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It may sound dangerous and unstable to have two or more stars in such close proximity
to each other… but many systems do boast numerous stars and are appropriately called
“multiple star systems”.
Similarly, we also have binary black hole systems in the universe, with two (sometimes
supermassive) black holes also orbiting a common point, thought to be as a result of
galactic mergers long ago.
With something like our sun, though, there’s some research to suggest that perhaps all
stars form in pairs.
A 2017 study into the Perseus molecular cloud, which is home to lots of new stars less than
four million years old, appears to show just that - that every single star (or, at least,
most of them) once had a partner.
Naturally, then, if it exists, there’s some debate over where, exactly, our sun’s twin
is.
There are a few potential answers, too… but none are stranger than what’s been dubbed
the “Nemesis Hypothesis”.
In 1984, two teams of physicists independently published academic papers about the perceived
periodic mass extinctions on Earth.
At the time, there was an assumption that those extinctions were all caused by comets
arriving at apparent intervals of 26 million years… and that there must have been something
that was responsible for this.
That something, according to the theory in ‘84, was the Nemesis star; a second star
orbiting the sun at a distance of 1.5 lightyears, which every twenty-six million years or so
disturbed distant objects in the Oort Cloud and sent them hurtling towards Earth.
In 1988, Richard Muller (one of the physicists working on the theory) even wrote a book on
the subject, called “Nemesis: The Death Star”.
The idea was that the Nemesis star would have to be a red or brown dwarf, both of which
are only visible using infrared technology and spectrographs which didn’t exist in
the 1980s.
Muller conceded that improving technology would either prove – or disprove – the
theory but, when the first papers were written, there was no way to assess it.
For those who believe in it, it is the gravitational influence of the Nemesis Star which alters
the paths of asteroids and causes mass extinctions.
Today, the Nemesis Theory doesn’t quite capture attention as it once did, and quickly
begins to fall apart once it’s examined.
First, the claim toward a twenty-six-million-year cycle of mass extinctions is controversial
enough in its own right, and has never been conclusively proven.
After all, what’s generally considered the last great extinction, which heralded the
end of the dinosaurs, happened sixty-six million years ago.
Second, though the extinction of the dinosaurs has been widely connected to a comet strike,
some of the others before it haven’t.
And then there’s the fact that researchers disagree on exactly how many mass extinctions
there have even been.
The so-called “big five”, however, the extinctions that are almost universally accepted,
definitely didn’t occur at twenty-six-million-year intervals and weren’t all necessarily triggered
by an asteroid strike.
When we look at the Oort Cloud itself, the science behind the Nemesis Star appears to
get even shakier.
The Oort Cloud is the most distant region of the solar system; anything beyond is too
far away to be affected by the sun’s gravity.
It’s currently a theoretical construct because it hasn’t been directly observed, but scientists
and astronomers are generally confident that it does exist, stretching from between 2,000
Astronomical Units away from the sun to 200,000 - which is 3.2 lightyears away at its furthest.
The Nemesis Star is speculated to lie 1.5 lightyears away, so it would be in the perfect
spot to interfere with the icy comets and planetoids orbiting in the Oort Cloud.
But is the Oort Cloud really so easily influenced?
Perhaps not.
70,000 years ago, a binary star system called Scholz’s Star, made up of a red dwarf and
a brown dwarf, came gliding through the solar system just 0.82 lightyears away from the
sun, much closer than Nemesis is said to be.
Scholz’s Star is also definitely, verifiably real, and is currently twenty-two lightyears
away from us.
But the effect it had on comets when it visited our star system is thought to be negligible.
While it could take millions of years for a displaced Oort Cloud comet to reach us (giving
us lots of time), we haven’t actually spotted any comets that appear to be making this journey
so far, with any apparent “peaks” in comet distribution usually explained away as the
normal effects of what’s called the “Galactic tide”.
If the Scholz’s Star flyby, then, hasn’t doomed us all, it seems unlikely that the
Nemesis Star could ever be influential enough to regularly, every twenty-six million years,
send Oort Cloud comets on a collision course with Earth through so much empty space.
Space is rarely as reliable or predictable as all that!
Of course, it isn’t Muller’s fault that the theory doesn’t hold much water all these
years later – lots of scientific theories get disproven.
We now have the benefit of infrared surveys, which use specialist telescopes capable of
seeing beyond the visible light spectrum - they’re effectively purpose-built to find things like
red and brown dwarfs.
Between 1997 and 2001, the Two Micron All-Sky Survey, otherwise known as 2MASS, discovered
all sorts of new objects that up until then we’d had no idea about – but it didn’t
find the Nemesis Star.
NASA’s Wide-field Infrared Survey Explorer, or WISE, launched in 2009 and has been collecting
data ever since.
Again though, the proposed red dwarf star about 1.5 lightyears away hasn’t been spotted.
What’s more, WISE did discover Luhman 16, comprised of the closet known brown dwarfs
to us, a whole 6.5 lightyears away.
It makes sense, then, that if we can observe Luhman 16 with our current telescopes, we
should also be able to observe the ever-elusive Nemesis… but, no luck.
For most scientists, this is all the proof needed to definitively state that the Nemesis
Star doesn’t exist… but we are still left with its unexplained absence.
Say the idea that stars form in pairs holds true (which it may or may not), then even
if Nemesis isn’t real, there has to be something, somewhere.
But the simplest explanation is often the best, and now there are increasing scientists
and cosmologists of the opinion that the sun did form with a companion star a long time
ago, but that that companion has long since left.
The same stars in the Perseus molecular cloud that show us how stars form in binaries have
also shown that it’s possible for these stellar pairs to break apart and drift away
from one another - which could have easily happened at any point in the last 4.5 billion
years since the sun formed.
With that in mind, the sun’s twin (if it exists) also need not be the malign, ominous
force that the Nemesis Hypothesis suggests it would be, leading some to argue that it
deserves a friendlier name.
Finally, though, the Nemesis star is rarely talked about on its own.
It’s usually connected to another mysterious, celestial, solar system body that supposedly
influences distant comets: Planet Nine.
Those who believe in one often believe in both… with one of the most far-out theories
being that Planet Nine, which also has very little by way of evidence for its existence,
is actually orbiting Nemesis in an evil copy of the entire solar system.
Another popular topic where both of these hypothetical objects are concerned is Sedna,
a distant planetoid with an extremely unusual, elongated orbit.
For some Nemesis and Planet Nine advocates, the general strangeness of Sedna could be
explained if it’s only being pulled so far from the sun because there’s another star
out there, with at least one other planet under its control.
There are, of course, other theories as to why Sedna’s orbit is so unusual - including
that it was actually redirected long ago by an ancient, rogue planet.
But for as long as there’s an element of the unknown, there’s at least a sniff of
possibility for second star theorists.
For now, though, the science does stack against the Nemesis Star existing.
If it were real, it should’ve been picked up by numerous infrared surveys over the last
few decades.
Still, it is an exciting thought that our sun could well have once had a twin… and
that that twin could now be anywhere else in the Milky Way galaxy, or perhaps even further
afield.
The universe never fails to astound.
What do you think?
Is there anything we missed?
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