The Black Hole

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The Black Hole
0310354 ??? 0310358 ??
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1.Introduction to black holes 2.Photo
Gallery 3.Observational evidence for black
holes 4.Black holes and critical
phenomena 5.(P.S.)Universe look pale green
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What is a black hole? A black hole is a region of
spacetime from which nothing can escape, even
light. To see why this happens, imagine throwing
a tennis ball into the air. The harder you throw
the tennis ball, the faster it is travelling when
it leaves your hand and the higher the ball will
go before turning back. If you throw it hard
enough it will never return, the gravitational
attraction will not be able to pull it back down.
The velocity the ball must have to escape is
known as the escape velocity and for the earth is
about 7 miles a second.
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As a body is crushed into a smaller and smaller
volume, the gravitational attraction increases,
and hence the escape velocity gets bigger. Things
have to be thrown harder and harder to escape.
Eventually a point is reached when even light,
which travels at 186 thousand miles a second, is
not travelling fast enough to escape. At this
point, nothing can get out as nothing can travel
faster than light. This is a black hole.
Crush vt.??, ??, ??, ?? ,(?)??
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Do they really exist? It is impossible to see a
black hole directly because no light can escape
from them they are black. But there are good
reasons to think they exist. When a large star
has burnt all its fuel it explodes into a
supernova. The stuff that is left collapses down
to an extremely dense object known as a neutron
star. We know that these objects exist because
several have been found using radio telescopes.
Supernova n.???? collapse n.??, ?? dense
adj.???, ??? neutron starn. ???
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If the neutron star is too large, the
gravitational forces overwhelm the pressure
gradients and collapse cannot be halted. The
neutron star continues to shrink until it finally
becomes a black hole. This mass limit is only a
couple of solar masses, that is about twice the
mass of our sun, and so we should expect at least
a few neutron stars to have this mass. (Our sun
is not particularly large in fact it is quite
small.)
Overwhelm vt.??, ??, ?? gradient adj.???n.??,
??? Shrink v.??, (?)??, ?? solar adj.???, ???
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A supernova occurs in our galaxy once every 300
years, and in neighbouring galaxies about 500
neutron stars have been identified. Therefore we
are quite confident that there should also be
some black holes.
supernovan. ????
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Back
Forget this, I want to see some pictures To see
some observational evidence for black holes from
the Hubble space telescope see the next page.
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Black Hole Jet
The plasma in a galactic jet is propelled outward
by a galaxy's central, supermassive black
hole.NASA / GSFC
plasma?????,???? Supermassive adj.??????
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This illustration shows a possible view of a
binary system between a black hole and a massive
star. The star ejects gas in the form of a
stellar wind. Much of this gas is collected in a
disk around the black hole. When it is funnelled
and accelerated into the disk, the gas releases a
large amount of energy from gamma rays to visible
and infrared light. However, the remaining gas
surrounding the black hole forms a thick cloud
which blocks most of the radiation. Only the very
energetic gamma rays can escape and be
detected.European Space Agency
Hidden Black Hole
Binary adj. ??? eject vt. ?? Funnelled
adj.????infraredadj.????
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Intermediate Black Hole
Jet v.?? perpendicular adj.???, ???
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Sagittarius A in X Rays
The supermassive black hole at the center of our
galaxy is believed to reside in the brightest
part of the x-ray cloud at the center of this
Chandra X-ray Observatory image. The two
red-colored clouds to the upper right and lower
left are huge lobes of 20-million-degree-Celsius
gas which suggest enormous explosions from the
galaxy's center occurred numerous times in the
past. The Chandra observations also show two
thousand other x-ray sources in addition to
Sagittarius A, making this one of the richest
fields ever studied.NASA / CXC / MIT / F.K.
Baganoff et al.
Observatory adj.??? Celsius adj.???
Sagittariuslt?gt???
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Sagittarius A
Sagittarius A, the black hole at the center of
the galaxy, is located about 26,000 light-years
from Earth.NASA / CXC / SAO
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Black Hole Binary System
While black holes cannot be seen, astronomers
spot them by identifying material being pulled
into the black hole as well as some material
propelled outward in blowtorch-like jets.ESA /
NASA / F. Mirabel (French Atomic Energy
Commission /Institute for Astronomy and Space
Physics)
Propel vt.??, ?? Blowtorch n.??, ??
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SS 433 Illustration
stripvt.?, ?? Jettison n.?? Gaseous adj.
??? Wobble ????, ? ?, ???,
?? precess?vi.???? vt.?????
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XTE J1550-564 Jets
The gravitational pull from this stellar-mass
black hole is so great that it strips material
off its companion star. This material forms a
disk. Periodically, parts of this disk collapse
and trigger runaway nuclear reactions. When this
happens the entire system brightens, and
high-energy electrons light up jets that stream
off the poles of the black hole. The series of
boxes to the left show changes in XTE J1550-564's
jets. The central x-ray source reveals the black
hole's position.x-ray NASA / CXC illustration
CXC / M. Weiss
periodicallyadv.????, ???? trigger vt.??, ??, ??
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Illustrations of XTE J1118480 and Its Orbit
Back
The black hole known as XTE J1118480 is
currently about 6,000 light-years away in the
galaxy's halo.I. Rodrigues / I.F. Mirabel /
STScI / NRAO / AUI / NSF
Halo n.(?????)??, ??, ??
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Observational Evidence for Black Holes Dust disk
around a black hole
This Hubble Space Telescope image contains three
main features. The outer white area is the core
or centre of the galazy. Inside the core there
is a brown spiral-shaped disk. It weighs on
hundred thousand times as much as our sun.
Spiral adj.????
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Because it is rotating we can measure the radii
and speed of its constituents, and hence weigh
the object at its centre. This object is about as
large as our solar system, but weighs
1,200,000,000 times as much as our sun.

This means that gravity is about one million
times as strong as on the sun. Almost certainly
this object is a black hole.
Constituent n. ??
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                   M87 is an active galaxy, one
in which we see interesting objects. Near its
core (or centre) there is a spiral-shpaed disc of
hot gas. The first picture places it in context.
The second superposes spectra from opposite
sides. This allows us to determine the speed of
rotation of the disk and its size. From this we
can weigh the size of the invisible object at the
centre
Black hole in M87
Spectra n.??, ??
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Back
Although the object is no bigger than our solar
system it weighs three billion times as much as
the sun. This means that gravity is so strong
that light cannot escape. We have a black hole.
In the first figure, there is a diagonal line.
This is believed to be the passage out of those
fortunate particles which escape along the axis
of rotation and avoid being swallowed by the
black hole.
Diagonal adj.??, ???, ????
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Black Holes and Critical Phenomena A scalar field
is a simple form of matter which feels two forces
only, gravity produced by itself, and its own
pressure. If you try to build a ball in which the
field is initially weak, pressure wins and the
ball expands away leaving nothing behind. If the
field is initially strong gravity wins and the
ball collapses to form a black hole
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There is a special critical initial strength such
that the field cannot decide whether to evaporate
away or collapse to form a black hole. Instead it
oscillates increasingly rapidly, performing an
infinite number of oscillations in a finite time.
The two animations show first an evolution which
doesn't form a black hole, and second an
evolution which does. The initial strengths
differ only by one in the fifteenth decimal
place. Each frame shows the scalar field as a
function of position. The gravitational field
changes the frequency of the field and so the
colour indicates what a distant observer would
see.
Back
Evaporate v.(?)??, ?? oscillatev.??
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Universe looks pale green Red giants?White
drarfs?Blue heaven?No,it turns out the universe
is pale green.Not plain green ,though according
to Ivan Baldry,an astronomer who worked to
findthe average colour of all the light in the
universe. Its pale turquoises,Baldry said
last Thursday.Baldry and his colleaguesworked
with data of more then 200,0000 galaxies at a
distance of 2 billion to 3billion light years
from Earth.By given a numeric value to the
colours of thedifferent galaxies,adding them
together and then averaging them,they came up
with light green colour.
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Blue to green to red That colour lies near the
midpoint of a cosmic spectrum,the
researchercreated.This spectrum shows the
universe beginning with a blue period,movingthroug
h green and eventrually getting red.As there are
no new young star formed,the universe will get
redder.Baldrysaid.It started out blue as the
light dominated by hot stars.So far itsenvolved
to a greenish colour.Because young stars are hot
and blue,they dominatethe light,he said,and
its only when the young stars decline that you
aregoing to change colours.
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The cosmic green colour is what scientists
believe the human eye would see if thelight
wasnt broken up into its component parts.But
there is no way that any human could see
this.The only way to see it is if you saw the
universe from the same distance away and it
wasnt moving ,Baldry said.Baldry and his
co-author,Karl Glazebrook,have both joked about
possible marketingopportunities for the new
colour,such as the colour-of-universe T-shirts or
coffeemugs.But Baldry added,I dont know if you
can patent a colour,thats not ourbusiness.We
havent actually been to a paint shop yet to see
if they have any fancy names for this colour. 
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"the mostincomprehensible thing about the
universe is that it is comprehensible
- A. Einstein.