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MARK HARTMAN: So what are the
parameters of this system?

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If over there, the parameters
for our lighthouses

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were like the number of balls
and maybe the luminosity

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of the bulbs, what are our
parameters for this system?

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OK, it could be the
gravitational force

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that the companion star feels.

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Where does that gravitational
force come from?

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AUDIENCE: The compact object.

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MARK HARTMAN: OK.

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What about the compact
object allows it

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to have a gravitational force?

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AUDIENCE: That is
gravitational force maker.

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MARK HARTMAN: It's a
gravitational force

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maker, which we call mass.

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AUDIENCE: Yeah.

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MARK HARTMAN:
Anything that has mass

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produces gravitational force,
so one of the parameters

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is the mass of the
compact object.

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What's another parameter
of this whole system?

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And remember when
we say system, we're

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just meaning a bunch of
parts, maybe different things,

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that kind of work together.

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AUDIENCE: The mass
of the other object.

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PROFESSOR: OK, the
mass of the companion.

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All right.

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Because if the mass of the
companion is different,

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we're going to have a different
gravitational force that's

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pulling them, and that
could change something

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about how that companion orbits.

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Chris?

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AUDIENCE: The size
of the companion.

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PROFESSOR: The size of
the companion, right?

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Let's think about maybe the
radius of the companion.

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How big is that?

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I mean, we talked
about its mass.

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We could also talk
about its size.

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So I'll put down, here,
radius of companion.

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What else?

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Steve?

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AUDIENCE: Luminosity.

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PROFESSOR: OK, the luminosity.

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And it could be X-ray
luminosity of which one?

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AUDIENCE: Luminosity of
the [? companion star. ?]

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PROFESSOR: OK, we know that
only the compact object produces

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X-ray, we think.

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AUDIENCE: [INAUDIBLE]

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PROFESSOR: What else?

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We have the radius of
the companion here.

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What else could we say?

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AUDIENCE: The radius
of the compact object.

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PROFESSOR: Radius of
companion and then

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also of a compact object.

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AUDIENCE: The linear size.

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PROFESSOR: OK, so the
linear size of what?

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AUDIENCE: Of the compact object.

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PROFESSOR: OK, if we knew the
radius of the compact object,

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that's kind of like saying that
is the linear radius, right?

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But that's a good point.

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00:03:22,250 --> 00:03:23,480
I mean, we could say--

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00:03:23,480 --> 00:03:25,010
yeah, the radius
of the companion,

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00:03:25,010 --> 00:03:28,860
the diameter of the companion,
the volume of the companion.

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But if we know the
radius, we can figure out

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those other ones.

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00:03:31,850 --> 00:03:33,350
So we want to think
about it as what

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are the most important
parameters of this model?

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Anything else?

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[? Island? ?]

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AUDIENCE: Accretion?

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MARK HARTMAN: OK,
accretion because remember

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we left this out--

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so what about accretion?

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AUDIENCE: [INAUDIBLE]

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MARK HARTMAN: OK, so if
we're talking about there's

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this accretion
stream, we could maybe

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00:03:53,390 --> 00:04:03,940
say the mass that is
accreted, and that

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00:04:03,940 --> 00:04:06,340
could be either a total
amount of mass or maybe--

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00:04:06,340 --> 00:04:10,450
astronomers actually use
the amount of mass per year

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00:04:10,450 --> 00:04:15,010
that is transferred from
one object to the other.

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00:04:15,010 --> 00:04:22,130
So the mass that is accreted,
or maybe its rate of accretion.

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00:04:22,130 --> 00:04:24,100
As it turns out, the
rate of the accretion

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is actually directly related to
the luminosity of the object,

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00:04:28,002 --> 00:04:28,960
so that's a good point.

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00:04:28,960 --> 00:04:30,836
We left that out, so
now we put that back in.

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00:04:30,836 --> 00:04:32,501
Bianca, were you going
to say something?

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00:04:32,501 --> 00:04:33,674
AUDIENCE: Distance, maybe?

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00:04:33,674 --> 00:04:34,840
MARK HARTMAN: What distance?

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00:04:34,840 --> 00:04:37,500
AUDIENCE: Between the compact
object and the companion star.

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00:04:37,500 --> 00:04:39,160
MARK HARTMAN: OK,
so the distance

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00:04:39,160 --> 00:04:45,240
between the compact object
and the companion star, that

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00:04:45,240 --> 00:04:51,840
is a distance, but it's also
the radius of the orbit.

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00:04:51,840 --> 00:04:55,980
So we could say
radius of the orbit.

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00:04:59,500 --> 00:05:02,044
That's a lot of parameters.

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00:05:02,044 --> 00:05:03,390
AUDIENCE: That's too many.

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00:05:03,390 --> 00:05:05,460
PROFESSOR: It's too many?

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00:05:05,460 --> 00:05:06,600
Chris is right.

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00:05:06,600 --> 00:05:11,130
There are too many, because
I can use this same drawing.

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00:05:11,130 --> 00:05:13,060
I could change any one of those.

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00:05:13,060 --> 00:05:16,500
I could change all of
those, and the predictions

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00:05:16,500 --> 00:05:19,710
for things that I would
expect from this system

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00:05:19,710 --> 00:05:20,580
would be different.

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00:05:23,620 --> 00:05:25,589
We have a model for
an X-ray binary star,

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00:05:25,589 --> 00:05:27,130
but if we really
wanted to figure out

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00:05:27,130 --> 00:05:29,470
for our specific
situation, we would

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have to figure out each
one of these things

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00:05:32,440 --> 00:05:35,650
to be able to specify what's
really going on there.

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00:05:35,650 --> 00:05:37,930
The X-ray binary
project is going

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00:05:37,930 --> 00:05:39,855
to go through and do this.

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00:05:39,855 --> 00:05:41,980
You're going to either have
assumptions or actually

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00:05:41,980 --> 00:05:45,540
make predictions of
what all of these are.