If you’re a Star Wars fan, one of the most beautiful moments in the whole movie series
was the sunset right outside of the Skywalker residence in Tatooine.
Having a curious mind like we do, surely you have thought, “Is this scenario possible?
Is it possible to stand on a planet where I would stare at a sunset with twin stars?”
Hold on to your seats as we solve this question in today’s episode!
The Skywalkers’ estate is located on a planet named Tatooine, which, according to the Star
Wars fandom wiki, belongs to the Tatoo stellar system.
This is very unique due to the characteristics of its center: it revolves around what we
call a binary star.
A binary star is a small star system orbiting about a common center of mass, or what’s
more properly called their barycenter.
If you think this is absolutely ridiculous, you would be more astonished that the recent
understanding states that there could be more than two stars revolving around a common barycenter,
which is of course surprising, especially we know stars exert gravitational force, so,
someone could easily think: “Wouldn’t the two stars affect each other gravitationally
and collide with one another eventually?”
Well, you don’t have to look far to get an answer to that.
Our very own planet orbits around the Sun but practically, we’re not colliding with
it, aren’t we?
This is due to the appropriate combination of all the factoring forces, i.e. gravity,
angular momentum, orbiting speed, that this event doesn’t happen..at least as far as
we humans are alive.
Applying this to binary star systems, the stars are in positions where in the strength
of their forces of influence towards one another is just enough to keep them in place.
Of course, theoretically speaking, collisions can still happen, but as far as the general
understanding goes, the chances of this happening is extremely small.
Back before, astronomers thought that star systems were mostly singular.
We couldn’t blame them since our very own Solar System is a single star system, so naturally,
one would think “maybe all the other stars are the same?”
Thankfully, William Herschel found out otherwise.
In the 18th century, Herschel was cataloguing as many stars as he could when he found out
that stars couldn’t just be singular, but also move in pairs, such as the binary stars.
Later on, it was established that binary -- or even multiple star systems -- are much more
prevalent in the universe than what is previously thought!
How common is a multiple star system you ask?
Recent statistics predict that the case might be that up to 85% of the stars are binary
systems.
If you put this to the perspective of human population, our universe is basically a country
where up to 8 and a half people could possibly be twins.
Talk about seeing double all the time.
To make things more strange, astronomers were also puzzled how binary stars even have planets
revolving around them.
In theory, the tug-of-war between the two star system should have a range of results
varying from eccentric orbits up to planets being ejected and quite possibly crash with
other stars.
Moreover, to convince you of how big a deal this actually is, let’s just say I would
reveal an “almost” binary star system later in this episode.
Can you guess which star it is?
Keep watching to find out!
So how do they actually form?
Well, if you recall, our Sun’s birth involved a swirling cloud of dust and gas, with an
extremely massive, and and extremely energetic center, which sooner or later settled down
to form the Solar System.
Binaries have the same story.
They, too, have started from a cloud of dust or a Nebula.
However, instead of settling to just one star, the particles coalesce to two or more.
That’s about it.
Scientists didn’t really find anything particular yet to what conditions would give birth to
specifically just binaries.
Let’s look into the types of binary stars, shall we?
The first type is the optical double stars.
These are stars that cannot be really categorically described to be binary, since in reality,
they are not.
It’s just that if we look at them hard enough, the degree of separation between the two is
really difficult to distinguish, leading to the misjudgement of taking them to be binary
stars.
One example of this is Alpha 1 and Alpha 2 from the Capricorn constellation.
Upon investigation via telescope, these two stars really appear to be very, very close
to one another.
So how do we distinguish optical doubles from actual binaries?
Earlier, we have stated that binary stars move in a common barycenter.
So, if an observed star is actually a binary, then, observing how two stars move with respect
to one another must give the information we need to verify.
A simple if-then solution but quite ingenious, isn’t it?
Okay, how about we move to the category of actual binary stars?
To have the first example, we don’t have to go so far because the closest star to earth
(after Sun, of course), Alpha Centauri , is actually a visual binary star composed of
two smaller stars called Alpha Centauri a and b.
Moreover, the Skywalkers, and practically all the residents of Tatooine, would all agree
that their star system is a visual binary.
That is of course assuming they are using the same cataloguing system as us here.
The definition of a visual binary is fairly simple.
If you can observe it via the telescope, or even by the naked eye, and you can distinguish
them as two separate stars.
then you categorize it as a binary.
But one would think, “Can’t we practically already see almost all of the stars at this
point?”
Sadly, we’re not yet there, with the current limitation of technology.
But isn’t it something awesome to look forward to?
I, for one, am very excited.
There are times when it is difficult to distinguish one star from the other, and at certain times,
one of the two may appear along our line of sight upon observation because of how far
they are from us.
So when this happens, how do we know if this star is a binary?
Well, if we are observing it from the side of its plane of orbit, and we are suspecting
the star to be binary, then, we expect to see some kind of wobbling back and forth,
if the star is actually binary.
Just to put it on a simpler perspective, let’s say for instance, you are standing on a chair
and a ceiling fan is along your line of sight.
And say, at the edge of one of the blades is a bright red tape.
When the fan is turned on, you would expect to see the red tape go left and right, wouldn’t
you?
That’s sort of the same concept applied to the observation of the wobble.
We know the stars would undergo periodic motion, so we measure the consequences of the orbital
motion.
A binary star observed using this technique is called an astrometric binary.
I wish we can say that the categorization ends there, but we still have a few more to
cover!
I hope you’re still excited.
How about we take the categorization difficulty another tier higher?
Say, we have a binary star that’s myriads of kilometers away, so far that we can’t
make out by observation whether it’s wobbling or not?
What do we do then?
At times like this, we’ll rely on the nature of light being emitted by a star to help our
investigation.
For instance, let’s say we have a binary star composed of two stars named “Twinkle”
and “Shine”, that of which the former is larger than the latter.
Upon our initial observation, Shine is at the front of Twinkle, so initially, we thought
this is a solo star.
To validate whether this star system is a binary or not, we can observe its brightness.
But how exactly is that going to be useful?
When both Twinkle and Shine can be observed at the same time, we expect some amount of
measurable brightness.
We take note of this as the star’s average brightness.
Now, when Twinkle goes behind Shine, and since we know the former is bigger than the latter,
and we measure the brightness we will expect to see a great dip in its average brightness.
If the other way around occurs, where the bigger star moves behind the smaller one,
then we expect to see a great dip.
These types of binary stars are called an eclipsing binary, due to the way of how the
brightness of either the stars affect the system’s total brightness.
Just a quick clarification.
It’s not necessary that the two eclipsing stars are uneven in size.
This is just to exaggerate the example.
The important part in categorizing a star to be eclipsing is that we can observe a dip
in the brightness to supplement the data.
Algol, or Beta Persei, is an example of this kind of binary.
Okay, now that that’s been steadied into place, we move on to the next example.
Besides the brightness of a star, we can also use take advantage of the spectra of light
that it emits as it moves in its orbit.
General relativity explains that since light is a wave, a moving light source is also bound
to the Doppler effect.
Specifically speaking, in the case of stellar objects, a star moving towards the Earth tends
to have a frequency moving towards the blue spectrum, while a star moving in the opposite
manner will have a frequency moving towards the red side.
This is more commonly known as a redshift, and binary stars determined using this way
are called spectroscopic binaries.The stars Sirius and Cygnus X-1 belong to this category.
There are also stars which redshift are difficult to observe or are completely unobservable.
However, if we use spectroscopy, we are bound to see a combination of spectral change depending
on the motion of the stars in the binary.
If one star is moving away, we’re bound to observe the spectral emission to shift
closer to red, and if the other is moving towards us, it shifts towards blue.
These binaries are called Spectrum Binaries.
Human ingenuity is really awesome isn’t it?
Are you getting closer to guessing what the “almost” binary star is?
We surely hope so.
The next category is a bit controversial.
It covers what happens to binary stars once they get too close that they essentially develop
a parasitic relationship.
These stars are called contact binaries due to the fact that they are so close to one
another that they are practically “in contact”, as the name goes, all the time.
Let’s illustrate this to help us understand better.
Imagine a binary star system forms somewhere in the outer reaches of our Milky Way galaxy,
to an imaginary Nebula.
Now, both of these stars are born in the same place, but for the sake of example, let’s
say the first one evolves to be a simple, naive red dwarf, while the other takes a lot
of nutrients from the particles around that it becomes a Blue Giant.
Like all binaries, these two rotate about a common center at a constant.
Following so far?
Okay, great.
The smaller star doesn’t really do anything so exciting.
It practically just stays there and burns all its hydrogen and helium at a steady, slow
rate.
However, the bigger brother has a different story.
Since it’s bigger and more massive, and therefore, more energetic, it fuses its elements
more rapidly and as a consequence, it blows up its excessive energy and loses mass.
What happens to the mass being lost?
Well, the smaller one takes it in and now, it begins to swell up into a more massive
star, while the other one shrinks smaller and smaller!
So what happens next?
Well, there are various endings to the story of this binary star.
It could get to as simple as the process repeating all over, where the now smaller one absorbs
from the current bigger one, up to a massive and explosive supernovae or a star death.
Now, we’re done talking about the types of binary stars, are we ready for the big
reveal?
Let’s see if our guesses match, shall we?
The star that was almost a binary is, surprise, surprise, our very own Sun.
Back in the 1980’s scientists inferred the possibility of a second star that may have
formed in the same protoplanetary disc in our Solar System that they aptly named “Nemesis”.
They speculated that this might be either a brown dwarf, dim red dwarf or even a white
dwarf.
Some geologists even dared to hypothesize that this could have caused several mass extinctions
to our planet Earth.
However, the search mission still continues this very day, and the searching has been
long and difficult, and full of conflict since there are a lot of debates that've been going
on due to the true nature, or even simply the mere validity of the hypothesis.
There’s even a theory that says that the proud king of the Solar System, Jupiter, may
have been a failed star, which again, connects to the possibility of the Sun being a binary
system.
All of these theories sound really absurd, but a lot of current theories once were like
this.
Remember how Copernicus used to be the crazy one and Ptolemy’s heliocentric theory was
more revered?
Well, look at where we are now.
Maybe someday we’ll find suns’ long lost twin, and maybe even say hi.
We just have to keep looking.
Like the twin suns of Tatooine, we should also set the suns of this episode and wrap
it up with a question for you: Do you think life as we currently know it on Earth would
have survived if our Sun was a binary star?
Would life have evolved differently?
We’d love to read your answers in the comment section below!
It’s nice to see a lot of ideas come up and clash with one another.
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Thanks a lot for watching!
Stay insanely curious!