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MARK HARTMAN: If there were
no compact object over there,

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00:00:25,520 --> 00:00:28,760
nothing that produced
a gravitational force,

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00:00:28,760 --> 00:00:32,299
this companion star, if it
was just going this direction,

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00:00:32,299 --> 00:00:37,581
it would continue to just go up.

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00:00:37,581 --> 00:00:39,830
If there was nothing over
there and this star was just

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00:00:39,830 --> 00:00:42,630
moving through space, it
would go in a straight line.

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00:00:45,530 --> 00:00:48,306
So let's say this is
the compact object.

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00:00:48,306 --> 00:00:49,430
This is the companion star.

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00:00:49,430 --> 00:00:51,320
We're going to talk
about how do they move.

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00:00:55,580 --> 00:01:04,010
So if there was
no compact object,

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00:01:04,010 --> 00:01:06,270
the star would move
in a straight line.

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00:01:06,270 --> 00:01:07,850
If anybody's taken
physics before

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00:01:07,850 --> 00:01:14,000
and has talked about
Newton's laws of motion,

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00:01:14,000 --> 00:01:16,950
an object in motion
tends to stay in motion.

22
00:01:16,950 --> 00:01:19,250
So if there is no other
outside force that's

23
00:01:19,250 --> 00:01:20,990
acting on this object,
it's just going

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00:01:20,990 --> 00:01:23,570
to travel in a straight line.

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00:01:23,570 --> 00:01:26,660
So if no compact object,
we're going to say,

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00:01:26,660 --> 00:01:37,880
the companion star moves
in a straight line.

27
00:01:41,510 --> 00:01:46,330
So it would look like this.

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00:01:46,330 --> 00:01:54,720
This would be the velocity if
there was no compact object.

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00:01:54,720 --> 00:01:56,910
It would just move
in a straight line.

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00:01:56,910 --> 00:02:02,460
But if there is
a compact object,

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00:02:02,460 --> 00:02:21,170
if there is a compact object,
then gravitational force

32
00:02:21,170 --> 00:02:22,670
pulls the two together.

33
00:02:31,890 --> 00:02:35,740
So what would that change
about this object's motion?

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00:02:35,740 --> 00:02:37,007
Steve, you had a question.

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00:02:37,007 --> 00:02:42,392
AUDIENCE: Yes, I [INAUDIBLE]
the compact object,

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00:02:42,392 --> 00:02:45,804
like includuing the [INAUDIBLE].

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00:02:45,804 --> 00:02:47,220
MARK HARTMAN: So
that's what we're

38
00:02:47,220 --> 00:02:48,650
going to talk about right now.

39
00:02:48,650 --> 00:02:52,570
So if there is a compact
object, the gravitational force

40
00:02:52,570 --> 00:02:54,010
pulls the two together.

41
00:02:54,010 --> 00:02:59,140
So what that means is
this object feels a force.

42
00:02:59,140 --> 00:03:07,680
So we're going to say this
is gravitational force.

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00:03:07,680 --> 00:03:12,276
If it's moving upwards but
then it feels a force this way,

44
00:03:12,276 --> 00:03:14,150
which direction is it
going to start to move?

45
00:03:17,120 --> 00:03:19,610
It goes up a little bit, but
then it gets pulled that way.

46
00:03:19,610 --> 00:03:22,280
So it kind of gets
pulled over a little bit.

47
00:03:22,280 --> 00:03:25,430
But now, we know that the
gravitational force always

48
00:03:25,430 --> 00:03:27,690
acts to pull things together.

49
00:03:27,690 --> 00:03:31,790
So if we up here, now the force
is going to pull us this way.

50
00:03:31,790 --> 00:03:34,070
So then we turn a little bit
more and we move forward.

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00:03:34,070 --> 00:03:36,140
Up here, the force
on this object

52
00:03:36,140 --> 00:03:39,680
is now going to be
pulling down a little bit.

53
00:03:39,680 --> 00:03:42,470
So we're going to turn a
little bit more and keep going.

54
00:03:42,470 --> 00:03:44,690
So this gravitational
force that's

55
00:03:44,690 --> 00:03:47,360
always pulling
these two together

56
00:03:47,360 --> 00:03:55,730
ends up curving the path of this
object around the other object.

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00:03:55,730 --> 00:03:58,070
That's the simple,
nice, easy explanation

58
00:03:58,070 --> 00:04:02,580
of why is it that gravity
causes one thing to orbit around

59
00:04:02,580 --> 00:04:03,710
another thing.

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00:04:03,710 --> 00:04:05,960
It kind of takes this
straight-line path,

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00:04:05,960 --> 00:04:08,810
and it pulls it, and it
pulls that straight-line path

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00:04:08,810 --> 00:04:12,991
to always be around
the compact object.

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00:04:12,991 --> 00:04:13,490
Steve.

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00:04:13,490 --> 00:04:18,825
AUDIENCE: What was the
[INAUDIBLE] the other star

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00:04:18,825 --> 00:04:21,800
goes directly to the [INAUDIBLE]

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00:04:21,800 --> 00:04:24,020
MARK HARTMAN: So there are
no planets on the board.

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00:04:24,020 --> 00:04:27,800
We just have our companion star,
and we have our compact object,

68
00:04:27,800 --> 00:04:31,430
which is still a collapsed
neutron star, a black hole.

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00:04:31,430 --> 00:04:32,870
This is the simple picture.

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00:04:32,870 --> 00:04:36,962
So I'm just going to say,
if there is-- whoops.

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00:04:36,962 --> 00:04:39,800
If there is a compact
object, gravitational force

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00:04:39,800 --> 00:04:42,490
pulls the two together.

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00:04:42,490 --> 00:04:52,152
The companion orbits
the compact object.

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00:04:52,152 --> 00:04:54,610
I'm going to deal with your
question in just a second here,

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00:04:54,610 --> 00:05:00,010
Steve-- compact object.

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00:05:00,010 --> 00:05:02,590
When we say orbit, we just
mean travel in a circle around.

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00:05:05,260 --> 00:05:06,790
This is the simple version.

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00:05:11,510 --> 00:05:13,440
This is what we're
going to stick with.

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00:05:13,440 --> 00:05:16,060
And in fact, whoever does
the X-ray binary project

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00:05:16,060 --> 00:05:17,560
is going to learn
a little bit more

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00:05:17,560 --> 00:05:22,580
about how can you actually
calculate things about forces.

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00:05:22,580 --> 00:05:25,075
But, in reality,
these two objects,

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00:05:25,075 --> 00:05:26,950
it's not that this one's
just getting pulled.

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00:05:26,950 --> 00:05:30,020
This one is getting pulled too.

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00:05:30,020 --> 00:05:33,530
So gravity always acts to
pull two things together.

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00:05:33,530 --> 00:05:37,310
So the actual motion is a
little bit more complicated.

87
00:05:37,310 --> 00:05:40,827
And I think on the
very first resource

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00:05:40,827 --> 00:05:42,910
that you'll find on the
[? expert ?] project wiki,

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00:05:42,910 --> 00:05:45,130
there's a little picture.

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00:05:45,130 --> 00:05:46,810
Actually,
[? Pierre, ?] would you

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00:05:46,810 --> 00:05:49,450
mind pulling up the picture
of the binary orbit?

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00:05:49,450 --> 00:05:52,654
It's in the very first
resource on the second page

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00:05:52,654 --> 00:05:54,820
for the [? expert ?] project
under X-ray binary star

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00:05:54,820 --> 00:05:55,320
systems.

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00:06:00,590 --> 00:06:02,450
Because in reality,
they both kind of

96
00:06:02,450 --> 00:06:03,980
pull each other together.

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00:06:03,980 --> 00:06:06,600
So they really orbit
around each other.

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00:06:06,600 --> 00:06:09,360
It's not that one is
fixed at the middle.

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00:06:09,360 --> 00:06:09,860
Let's see.

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00:06:09,860 --> 00:06:11,840
Under that one, yeah.

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00:06:11,840 --> 00:06:13,040
Let's take a look here.

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00:06:13,040 --> 00:06:13,790
Go to page two.

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00:06:17,090 --> 00:06:21,047
So if you look here,
our simple model

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00:06:21,047 --> 00:06:22,630
was there was one
thing at the middle,

105
00:06:22,630 --> 00:06:24,421
and the other was going
around the outside.

106
00:06:24,421 --> 00:06:26,530
Ooh, there we go.

107
00:06:26,530 --> 00:06:29,770
But in this case, it's
that each of these objects

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00:06:29,770 --> 00:06:31,150
pull on each other.

109
00:06:31,150 --> 00:06:34,660
So they're kind of
orbiting around each other.

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00:06:34,660 --> 00:06:36,160
It's a little bit
more complicated,

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00:06:36,160 --> 00:06:38,320
but you can see that
this object still

112
00:06:38,320 --> 00:06:40,315
goes in a circle,
or something close.

113
00:06:40,315 --> 00:06:43,390
It could be an ellipse,
kind of an elongated oval.

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00:06:43,390 --> 00:06:46,840
And this one also
goes in a circle.

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00:06:46,840 --> 00:06:50,350
It just depends on how
massive each one of those is.

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00:06:50,350 --> 00:06:52,730
If you've got a very massive
object in the middle,

117
00:06:52,730 --> 00:06:55,780
it's not going to move around
a lot as the other one moves

118
00:06:55,780 --> 00:06:56,770
around.

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00:06:56,770 --> 00:06:58,690
If you have objects
that have the same mass,

120
00:06:58,690 --> 00:07:01,984
they're actually going
to both move a lot.

121
00:07:01,984 --> 00:07:03,400
But the simple
picture and the one

122
00:07:03,400 --> 00:07:07,270
that we're going to keep in
mind is this one over here.

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00:07:07,270 --> 00:07:10,210
We're going to assume
that our compact object is

124
00:07:10,210 --> 00:07:14,440
nice and heavy,
has a lot of mass.

125
00:07:14,440 --> 00:07:16,600
And then this star is
going to be the one that

126
00:07:16,600 --> 00:07:18,132
actually goes around it.

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00:07:18,132 --> 00:07:19,840
It's going to make it
a little bit easier

128
00:07:19,840 --> 00:07:21,070
for us to think about.

129
00:07:21,070 --> 00:07:24,580
This also helps us to think
about accretion, right,

130
00:07:24,580 --> 00:07:26,890
because we said accretion
is when mass is transferred

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00:07:26,890 --> 00:07:29,960
from one object to another.

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00:07:29,960 --> 00:07:34,810
Well, if this star is over here
the, outer layers of this star

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00:07:34,810 --> 00:07:39,020
are held together by the
gravity of that object.

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00:07:39,020 --> 00:07:43,960
If this star gets close
to the compact object,

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00:07:43,960 --> 00:07:46,450
the gravitational force
between two objects

136
00:07:46,450 --> 00:07:48,550
depends on how close they are.

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00:07:48,550 --> 00:07:50,540
If you have a big
object and a big object,

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00:07:50,540 --> 00:07:52,630
there's going to
be lots of force.

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00:07:52,630 --> 00:07:55,150
If you have a big
object and a big object

140
00:07:55,150 --> 00:07:57,604
and a small
distance, what do you

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00:07:57,604 --> 00:07:59,770
think is going to happen
to the amount of force that

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00:07:59,770 --> 00:08:04,440
pulls them together if you
bring two things close?

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00:08:04,440 --> 00:08:06,790
AUDIENCE: They're
going to combine.

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00:08:06,790 --> 00:08:09,110
MARK HARTMAN: OK.

145
00:08:09,110 --> 00:08:12,120
If you bring two things
really close together,

146
00:08:12,120 --> 00:08:13,850
the force actually
gets stronger.

147
00:08:13,850 --> 00:08:16,290
If you've ever done kind of a
similar thing with magnets--

148
00:08:16,290 --> 00:08:18,226
if you take magnets
and they're far apart,

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00:08:18,226 --> 00:08:20,100
it's kind of easy to
pull them further apart.

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00:08:20,100 --> 00:08:23,000
But as you get them closer
and closer together,

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00:08:23,000 --> 00:08:26,360
you have to hold them back
harder and harder and harder

152
00:08:26,360 --> 00:08:28,740
because the magnetic
force between the two

153
00:08:28,740 --> 00:08:31,115
gets stronger and stronger as
your distance gets smaller.

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00:08:33,890 --> 00:08:38,150
We can actually write, and
some of you may have seen--

155
00:08:38,150 --> 00:08:40,669
the expression or the
equation for how much

156
00:08:40,669 --> 00:08:44,000
force this gets
pulled together with

157
00:08:44,000 --> 00:08:48,920
is going to be the force is
equal to this number g, which

158
00:08:48,920 --> 00:08:54,530
is a constant, times
the mass of one object--

159
00:08:54,530 --> 00:08:58,670
this is going to be the
mass of the other object--

160
00:08:58,670 --> 00:09:01,709
divided by the distance
between them squared.

161
00:09:01,709 --> 00:09:02,750
And this is the distance.

162
00:09:07,230 --> 00:09:09,800
So that means if one of
these objects gets bigger,

163
00:09:09,800 --> 00:09:11,150
the force gets bigger.

164
00:09:11,150 --> 00:09:14,150
If the other object gets
bigger, the force gets bigger.

165
00:09:14,150 --> 00:09:18,380
If the distance between
them gets smaller,

166
00:09:18,380 --> 00:09:19,800
this number gets smaller.

167
00:09:19,800 --> 00:09:22,670
So if you take something
divided by a smaller number,

168
00:09:22,670 --> 00:09:24,590
you get a bigger number.

169
00:09:24,590 --> 00:09:25,980
That makes sense.

170
00:09:25,980 --> 00:09:29,970
And in fact, let's look at what
[? Island ?] wrote over here.

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00:09:29,970 --> 00:09:33,080
She said, "the faster
the orbital speeds,

172
00:09:33,080 --> 00:09:35,180
the stronger the
gravitational force

173
00:09:35,180 --> 00:09:40,750
gets, which enables gas and
stars to be held in the orbit."

174
00:09:40,750 --> 00:09:42,600
Let's think about that.

175
00:09:42,600 --> 00:09:47,300
If we were orbiting out
here, we could go slow,

176
00:09:47,300 --> 00:09:51,240
and the force would be
enough to hold us together.

177
00:09:51,240 --> 00:09:55,580
But if we were in here,
orbits happen faster when

178
00:09:55,580 --> 00:09:58,800
you're closer to the object.

179
00:09:58,800 --> 00:10:01,340
And if you have a
faster orbital speed--

180
00:10:01,340 --> 00:10:04,820
there's actually a subtle detail
here that isn't quite right.

181
00:10:04,820 --> 00:10:07,580
It's not that the faster
you go, the stronger

182
00:10:07,580 --> 00:10:10,310
the gravitational force gets.

183
00:10:10,310 --> 00:10:12,710
It's the faster you
go, the stronger

184
00:10:12,710 --> 00:10:19,490
the gravitational force
you need to enable the gas

185
00:10:19,490 --> 00:10:22,910
and stars to be
held in their orbit.

186
00:10:22,910 --> 00:10:24,650
So remember, if we
look at this equation,

187
00:10:24,650 --> 00:10:27,560
force has nothing to do
with how fast it's going.

188
00:10:27,560 --> 00:10:30,300
It just has to do with
how far away it is.

189
00:10:30,300 --> 00:10:32,690
And if the object's
really close,

190
00:10:32,690 --> 00:10:35,330
that force is going
to be really strong.

191
00:10:35,330 --> 00:10:39,350
So you can go really
fast and not fly away.

192
00:10:39,350 --> 00:10:41,690
So we don't really need to
know all of these details.

193
00:10:41,690 --> 00:10:44,160
But if you're interested
in exactly how this works,

194
00:10:44,160 --> 00:10:47,600
this is what you'll work on
with the X-ray binary project.

195
00:10:47,600 --> 00:10:50,120
For right now, though, what
I want you to think about

196
00:10:50,120 --> 00:10:52,040
is we've got our compact
object at the center.

197
00:10:52,040 --> 00:10:55,090
We have our companion star
going around the outside.

198
00:10:55,090 --> 00:11:01,220
And a simple way to think about,
well, OK, what does all this

199
00:11:01,220 --> 00:11:02,930
have to do with flux--

200
00:11:02,930 --> 00:11:05,890
what does all this have to
do with the brightness--

201
00:11:05,890 --> 00:11:13,315
we are going to look at
both the X-ray luminosity,

202
00:11:13,315 --> 00:11:19,670
and we're going to look at
the visible light luminosity.

203
00:11:23,130 --> 00:11:26,190
What do we mean when we say
X-ray luminosity and visible

204
00:11:26,190 --> 00:11:27,708
light luminosity?

205
00:11:31,920 --> 00:11:34,160
What do you think?

206
00:11:34,160 --> 00:11:35,090
What is luminosity?

207
00:11:35,090 --> 00:11:36,890
Steve.

208
00:11:36,890 --> 00:11:39,830
AUDIENCE: When you talk
about X-ray luminosity,

209
00:11:39,830 --> 00:11:42,770
you mean the X-ray--
like, an object that

210
00:11:42,770 --> 00:11:48,160
produces X-ray [INAUDIBLE]
flux of the object, and then

211
00:11:48,160 --> 00:11:50,915
[INAUDIBLE] flux of
the X-ray [INAUDIBLE]..

212
00:11:50,915 --> 00:11:57,947
And then visible light, you
mean the [INAUDIBLE] flux

213
00:11:57,947 --> 00:11:59,650
of the object.

214
00:11:59,650 --> 00:12:00,520
MARK HARTMAN: OK.

215
00:12:00,520 --> 00:12:01,260
[? Ezeke, ?] you want to--

216
00:12:01,260 --> 00:12:02,160
AUDIENCE: So luminosity--

217
00:12:02,160 --> 00:12:03,326
MARK HARTMAN: Nice and loud.

218
00:12:03,326 --> 00:12:06,150
AUDIENCE: Luminosity is the
light given by the source.

219
00:12:06,150 --> 00:12:08,180
Flux is what we receive.

220
00:12:08,180 --> 00:12:11,130
MARK HARTMAN: OK, luminosity is
the light given by the source.

221
00:12:11,130 --> 00:12:13,100
So if I say X-ray luminosity--

222
00:12:13,100 --> 00:12:16,394
AUDIENCE: It's [INAUDIBLE]
that's given off by the source.

223
00:12:16,394 --> 00:12:17,810
MARK HARTMAN: How
much energy does

224
00:12:17,810 --> 00:12:21,860
that object put
out as X-ray light,

225
00:12:21,860 --> 00:12:26,000
versus visible light luminosity,
how much light does that object

226
00:12:26,000 --> 00:12:28,737
put out invisible light photons.

227
00:12:28,737 --> 00:12:30,320
Because remember,
our detector is only

228
00:12:30,320 --> 00:12:31,700
sensitive to one or the other.

229
00:12:31,700 --> 00:12:33,970
It's not both.

230
00:12:33,970 --> 00:12:36,650
So what we have here--

231
00:12:36,650 --> 00:12:41,840
the X-ray luminosity
for our compact object,

232
00:12:41,840 --> 00:12:46,642
which one of these objects is
going to produce more X-rays?

233
00:12:46,642 --> 00:12:48,016
AUDIENCE: The bigger one.

234
00:12:48,016 --> 00:12:49,390
AUDIENCE: The compact.

235
00:12:49,390 --> 00:12:50,580
MARK HARTMAN: The what?

236
00:12:50,580 --> 00:12:53,160
AUDIENCE: I said the one
in the middle, the compact.

237
00:12:53,160 --> 00:12:54,826
MARK HARTMAN: OK,
you're saying compact.

238
00:12:54,826 --> 00:12:56,314
You're saying the bigger one.

239
00:12:56,314 --> 00:12:58,612
AUDIENCE: [INAUDIBLE]

240
00:12:58,612 --> 00:12:59,320
MARK HARTMAN: OK.

241
00:12:59,320 --> 00:13:00,670
So be careful when
you say bigger.

242
00:13:00,670 --> 00:13:01,670
Do you mean bigger mass?

243
00:13:01,670 --> 00:13:03,740
Do you mean bigger in size?

244
00:13:03,740 --> 00:13:04,840
What do you mean?

245
00:13:04,840 --> 00:13:09,700
So this compact object, the
neutron star or the black hole,

246
00:13:09,700 --> 00:13:12,670
the X-ray luminosity is high.

247
00:13:12,670 --> 00:13:16,010
It's putting out lots
of light in X-rays.

248
00:13:16,010 --> 00:13:17,025
Why?

249
00:13:17,025 --> 00:13:18,400
And again, this
is where you guys

250
00:13:18,400 --> 00:13:19,691
should write these things down.

251
00:13:19,691 --> 00:13:22,360
Over here on this board that
[? Shekeeb ?] is currently

252
00:13:22,360 --> 00:13:23,680
taking pictures of--

253
00:13:23,680 --> 00:13:24,990
no, go ahead.

254
00:13:24,990 --> 00:13:26,669
In the bottom, it says--

255
00:13:26,669 --> 00:13:28,210
and this one also
got a lot of stars,

256
00:13:28,210 --> 00:13:29,626
so you should write
this down too.

257
00:13:29,626 --> 00:13:35,260
The heat of accretion
produces X-rays.

258
00:13:35,260 --> 00:13:40,090
From this star, we
have material that's

259
00:13:40,090 --> 00:13:42,130
kind of being pulled off.

260
00:13:45,330 --> 00:13:47,990
Sorry, this diagram's
getting a little bit messy.

261
00:13:47,990 --> 00:13:52,250
But you've got material
that's being pulled off

262
00:13:52,250 --> 00:14:01,320
here and formed into an
accretion disk, which

263
00:14:01,320 --> 00:14:05,730
is the thing that's swirling
around that compact object.

264
00:14:05,730 --> 00:14:12,770
If you look in your
pictures, here again,

265
00:14:12,770 --> 00:14:14,480
we have this
swirling stuff that's

266
00:14:14,480 --> 00:14:17,190
swirling around
the compact object.

267
00:14:17,190 --> 00:14:21,140
So the accretion
disk gives off X-rays

268
00:14:21,140 --> 00:14:22,595
because it's very, very hot.

269
00:14:25,730 --> 00:14:28,520
It's because all of that
gas, as it's swirling around

270
00:14:28,520 --> 00:14:32,390
in the accretion disk, is
rubbing against each other.

271
00:14:32,390 --> 00:14:34,760
The inner parts of
the gas orbit fast.

272
00:14:34,760 --> 00:14:37,670
The outer parts orbit
slower, and so they rub past

273
00:14:37,670 --> 00:14:38,436
each other.

274
00:14:38,436 --> 00:14:40,310
And since they're spinning
around and rubbing

275
00:14:40,310 --> 00:14:45,350
past each other so hard,
it heats things up.

276
00:14:45,350 --> 00:14:53,720
So our accretion disk gives
off lots of X-ray luminosity

277
00:14:53,720 --> 00:14:57,080
because the heat of
accretion produces X-rays.

278
00:14:57,080 --> 00:15:01,310
If this was less hot, it
wouldn't give off X-rays.

279
00:15:01,310 --> 00:15:02,810
What kind of a
spectrum do you think

280
00:15:02,810 --> 00:15:05,555
we should try to fit if we were
looking at an accretion disk?

281
00:15:09,330 --> 00:15:09,830
Any ideas?

282
00:15:13,480 --> 00:15:15,990
If something is giving off
light because it's hot--

283
00:15:21,834 --> 00:15:23,790
AUDIENCE: A black body?

284
00:15:23,790 --> 00:15:26,920
MARK HARTMAN: So Chris
says is a black body.

285
00:15:26,920 --> 00:15:29,680
If this accretion
disk is thick, which

286
00:15:29,680 --> 00:15:32,380
means that you can't
see through it,

287
00:15:32,380 --> 00:15:36,135
then it would give off
a black-body spectrum.

288
00:15:36,135 --> 00:15:37,510
So try and make
those connections

289
00:15:37,510 --> 00:15:38,885
back and forth
through the things

290
00:15:38,885 --> 00:15:40,090
that we looked at before.

291
00:15:40,090 --> 00:15:41,070
Let's finish filling
in this table,

292
00:15:41,070 --> 00:15:42,236
and then we'll take a break.

293
00:15:42,236 --> 00:15:44,830
So we've got the compact
object, neutron star/black hole,

294
00:15:44,830 --> 00:15:47,010
has high X-ray luminosity.

295
00:15:47,010 --> 00:15:50,510
Would something that is this hot
give off lots of visible light?

296
00:15:55,300 --> 00:15:56,258
AUDIENCE: Kind of.

297
00:15:56,258 --> 00:15:57,220
Sort of.

298
00:15:57,220 --> 00:15:58,136
MARK HARTMAN: Kind of?

299
00:15:58,136 --> 00:15:59,410
Sort of?

300
00:15:59,410 --> 00:16:02,110
We're going to say, for
these compact objects,

301
00:16:02,110 --> 00:16:06,360
most of the light comes
out as X-ray luminosity.

302
00:16:06,360 --> 00:16:07,269
AUDIENCE: Most.

303
00:16:07,269 --> 00:16:08,060
MARK HARTMAN: Most.

304
00:16:08,060 --> 00:16:10,630
So we're going to say the
visible light luminosity

305
00:16:10,630 --> 00:16:11,530
is low.

306
00:16:11,530 --> 00:16:13,750
Over here, for the
companion star,

307
00:16:13,750 --> 00:16:16,120
if this is just a
regular star, it's

308
00:16:16,120 --> 00:16:18,310
not hot enough to
produce X-rays.

309
00:16:18,310 --> 00:16:21,980
We saw that regular stars
produce mostly visible light.

310
00:16:21,980 --> 00:16:25,000
So the X-ray luminosity
here is going

311
00:16:25,000 --> 00:16:27,280
to be low for our
companion star.

312
00:16:27,280 --> 00:16:29,050
So I want everybody
to put that in.

313
00:16:29,050 --> 00:16:34,300
And then the visible light,
it's going to give off

314
00:16:34,300 --> 00:16:35,590
a higher luminosity.

315
00:16:35,590 --> 00:16:39,190
We'll expect to see this
star in visible light,

316
00:16:39,190 --> 00:16:43,550
but not in X-ray light.

317
00:16:43,550 --> 00:16:45,850
So let's take a look at this.

318
00:16:45,850 --> 00:16:46,900
We are going to--

319
00:16:49,630 --> 00:16:50,380
here's an example.

320
00:16:53,190 --> 00:16:56,170
Here, I'm going to say
this is my compact object,

321
00:16:56,170 --> 00:16:57,965
my X-ray-emitting object.

322
00:16:57,965 --> 00:16:59,840
Because we still never
answered the question,

323
00:16:59,840 --> 00:17:01,779
what does this have
to do with flux?

324
00:17:01,779 --> 00:17:03,820
Most of you guys already
have this model up here,

325
00:17:03,820 --> 00:17:05,750
so I hope this makes sense.

326
00:17:05,750 --> 00:17:08,260
If we had a low-mass
X-ray binary

327
00:17:08,260 --> 00:17:11,140
system which has a
neutron star, we're

328
00:17:11,140 --> 00:17:14,859
going to say that this light
coming out is X-ray light.

329
00:17:14,859 --> 00:17:17,410
So this is our
compact object, which

330
00:17:17,410 --> 00:17:18,790
has a high X-ray luminosity.

331
00:17:18,790 --> 00:17:20,640
AUDIENCE: [INAUDIBLE]

332
00:17:20,640 --> 00:17:21,700
MARK HARTMAN: Yeah.

333
00:17:21,700 --> 00:17:25,260
And then this is
our companion star.

334
00:17:25,260 --> 00:17:26,950
Now, in this case,
if you look, it

335
00:17:26,950 --> 00:17:30,310
says this could be
a white dwarf star.

336
00:17:30,310 --> 00:17:36,960
If I have my white dwarf star
and I orbit around this star--

337
00:17:36,960 --> 00:17:38,820
let me put this down
at your eye level.

338
00:17:38,820 --> 00:17:41,640
I want you to tell me
what happens to the flux

339
00:17:41,640 --> 00:17:46,590
that your eye receives
from this X-ray object

340
00:17:46,590 --> 00:17:48,345
if I make this go
around in a circle.

341
00:17:54,930 --> 00:17:57,150
So it might help if
you close one eye.

342
00:18:03,066 --> 00:18:05,531
AUDIENCE: [LAUGHS]

343
00:18:06,517 --> 00:18:07,781
[INAUDIBLE]

344
00:18:07,781 --> 00:18:08,489
MARK HARTMAN: OK.

345
00:18:11,470 --> 00:18:16,140
Now if instead of that, I
had a massive X-ray binary,

346
00:18:16,140 --> 00:18:18,190
I have a bigger star here.

347
00:18:18,190 --> 00:18:20,230
It's still orbiting around.

348
00:18:20,230 --> 00:18:24,250
But now, this is a
slightly bigger size.

349
00:18:24,250 --> 00:18:27,640
If I put this one and I
move it around, again,

350
00:18:27,640 --> 00:18:29,545
what happens to the
flux that you receive?

351
00:18:32,560 --> 00:18:34,080
What happens?

352
00:18:34,080 --> 00:18:36,310
Somebody describe it.

353
00:18:36,310 --> 00:18:37,472
[INAUDIBLE]

354
00:18:37,472 --> 00:18:40,410
AUDIENCE: It's smaller
when you orbit it

355
00:18:40,410 --> 00:18:44,010
around the light source.

356
00:18:44,010 --> 00:18:46,740
It didn't block out
that much light.

357
00:18:46,740 --> 00:18:49,255
If you do this, it blocks
out light for a longer

358
00:18:49,255 --> 00:18:51,449
time if the object's massive.

359
00:18:51,449 --> 00:18:52,990
MARK HARTMAN: If
the object is, well,

360
00:18:52,990 --> 00:18:54,440
not necessarily massive,
but in this case,

361
00:18:54,440 --> 00:18:55,690
it has to do with the size.

362
00:18:55,690 --> 00:19:00,850
If the object is bigger,
it blocks off the light

363
00:19:00,850 --> 00:19:05,230
from getting to you for
a longer amount of time.

364
00:19:05,230 --> 00:19:08,200
So when we're talking
about X-ray binary systems

365
00:19:08,200 --> 00:19:12,610
as an explanation for changing
flux, what we really mean

366
00:19:12,610 --> 00:19:16,456
is this idea, that we block
some of the flux as we go by.

367
00:19:16,456 --> 00:19:17,830
But let me ask
you one more quick

368
00:19:17,830 --> 00:19:19,600
question before we take a break.

369
00:19:19,600 --> 00:19:22,720
What if I did it this way?

370
00:19:22,720 --> 00:19:24,110
Let me do it like this.

371
00:19:24,110 --> 00:19:27,340
If I went like this and
made this orbit around--

372
00:19:27,340 --> 00:19:30,232
actually, [? Shekeeb, ?] can
you come and hold this for me?

373
00:19:30,232 --> 00:19:31,140
AUDIENCE: Like this?

374
00:19:31,140 --> 00:19:34,790
MARK HARTMAN: Yeah, just
like that, just like that.

375
00:19:34,790 --> 00:19:36,170
Good.

376
00:19:36,170 --> 00:19:41,663
Now if I do this, what
do you see, Steve?

377
00:19:41,663 --> 00:19:42,704
AUDIENCE: The same thing.

378
00:19:42,704 --> 00:19:44,392
I see the same flux.

379
00:19:44,392 --> 00:19:45,100
MARK HARTMAN: OK.

380
00:19:45,100 --> 00:19:46,993
And Bianca, what do you see?

381
00:19:46,993 --> 00:19:50,304
AUDIENCE: When the star passes
in front [? on ?] this side,

382
00:19:50,304 --> 00:19:53,150
it's blocked out [INAUDIBLE].

383
00:19:53,150 --> 00:19:54,200
MARK HARTMAN: OK.

384
00:19:54,200 --> 00:19:57,530
So you don't always
get a change in flux

385
00:19:57,530 --> 00:19:59,850
when you have an
X-ray binary system.

386
00:19:59,850 --> 00:20:02,180
It depends on what angle
you're looking at it from,

387
00:20:02,180 --> 00:20:07,070
because Juan is also going to
see that flux get blocked--

388
00:20:07,070 --> 00:20:07,690
well, kind of.

389
00:20:07,690 --> 00:20:09,710
Maybe it's getting
blocked by his hand.

390
00:20:09,710 --> 00:20:12,590
But then Steve and Chris
are still not going

391
00:20:12,590 --> 00:20:14,830
to see this thing get blocked.