The Cosmic Classroom - Binary Star Systems


Uploaded by vmargoniner on 30.10.2009

Transcript:
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.