The Cosmic Classroom – Binary Star Systems
Welcome back to the
Cosmic Classroom. Let’s now talk about the
life of stars that live in,live in pairs,doubles stars.
Alright,or a binary system. So what happens
to a white dwarf? It dies and then what?
You know, it becomes, it’s a white dwarf,and
then what happens to it? Do they just sit there?
Well, if the white dwarf is isolated,yes it
will just sit there,it will cool down and it will
eventually become a black dwarf that we
can not see anymore. Now, if the white
dwarf has a a companion then life
is much more interesting. And, and
more things happen. So let’s look for example
at Sirius and its white dwarf companion.
So it’s a little thing, it’s this white dwarf near
this big star, Sirius. But this white dwarf is
really important in the life of the system, right?
The companionship is really important.
So if you have a system on which one of the
stars is already a white dwarf, and then,and
there’s another star. So there is two stars.
Let’s say this is the white dwarf, and this is another
rebeller main sequence star and their orbiting is shorten
and they are happy with their lives together.
But eventually, this star here it is in main
sequence will also die. And as is dies, as all
stars die, they expand they become one big thing.
When this star starts to expand, its surface gets
close enough to the white dwarf, that the white dwarf
starts to steal material from the surface of this star.
And that’s what this drawing is showing you.
That the white dwarf companion is
stealing material and forming an external layer
of Hydrogen around it. WELL the white dwarf
is really hot, right? It’s the CORE of a star.
So as the Hydrogen heats there, and it accumulates
a little bit there, the,the star comes back to life.
It starts fusing Hydrogen into Helium again.
So the star that was dead, soon it
comes back to life. There’s fusion happening
again, the star will shine brightly again.
And it will do that a few times, as more and more
fuel is, is falling into the surface of the star.
You need to let the fuel accumulate a little bit
to be at the right density and temperature.
But every now and then the star will burst, will be luminous.
So, nova? A nova can happen
once or twice or three times as material falls
into this white dwarf. It may be that the white
dwarf steals so much material from this
companion star, that, that the degeneracy pressure
off this white dwarf cannot hold it anymore.
Cannot stop gravity anymore. The star collapses,at
once, when degeneracy pressure can’t hold that.
Collapses, and as it collapses it explodes as a supernova,
and blows everything away. What’s left from this kind
of supernova is,nothing. Not the neutron star,
not the black hole, there is just nothing there.
But let me qualify it nothing. I’m not saying that the
material disappeared. I’m just saying that it has
been, becomes dust. Alright?
It’s spread all around. When the star explode
it also affects the, the neighboring star, the one
that was its partner, it also blows that star away.
It doesn’t make that star explode.
But it blows that star away a lot of the
material from the outers, outer parts of that
star will be blown away. Right?
Because of so much energy in that explosion.
So, we call supernova, this final explosion we call
supernova,when this core collapses in the whole
thing explodes and nothing is left is called a supernova.
Now I need to tell you that this kind of supernova that
leaves no remains and that comes from a binary
system with a white dwarf, its called a Supernova Type 1.
I don’t understand why it’s called a
Supernova Type 1. Right?
If there are two stars and the supernova that
explodes when there is one big mass of star
exploding, its one big mass of star exploding,that is
called a Supernova Type 2. So if you try to use that
to memorize, do the reverse. Right?
If there is two stars it’s Supernova 1, if there is one
star is Supernova Type 2. I won’t go in the why
it has to do with the lines the way it was
classified before we knew what they were.
But that’s what it is. So I had a lot of
questions about how what, why just
binary systems? Is it possible to have three
or multiple stellar systems. And yes,we can have
multiple stellar systems. In fact there are a
lot of multiple stellar systems. In fact there are more
systems with more than one star than systems with
just one star out there. Alright?
So a star like the sun is less common than
stars that live with partners,with other stars.
So there are lots of those out there.
I have two examples here. One that you must be
very fam, that you may be very familiar with,
its Polaris, the north star. It’s not really one star,
its three as you can see. With your naked eye it’s
impossible to see because the companions are very
bright, very dimmed,and very close to the main star.
But it’s actually a system of three stars,Polaris A,
Polaris AB and Polaris B. Alright?
And here is just a drawing showing one possible
configuration out of infinite possible configurations.
There are three stars here and this little star
is orbiting this one. Almost like a moon
orbiting a planet,except that it’s, there are two
stars and those two stars are orbiting each other.
Ok? And you may have
many stars together. Alright?
When a supernova happens all the stars that are around
whether it’s 1, 2, or 3 they will just be sent away.
Most of them will be close enough to a supernova that
they won’t be able to survive, they will just be sent away.
And I hope that answers your questions and I hope it helped.
I see you next time.