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91
Figure 3.1.
The Hubble Ultra-Deep Field, taken from the Hubble Space Telescope in a
second
exposure. The red ‘smudges’, circled in these images (several blow-ups shown on right) are among
times as bright
the most distant galaxies ever observed optically. The faintest objects are as what can be observed with the naked eye. These galaxies, or rather ‘galaxy precursors’, are seen
as they were at a time when the Universe was only 5% of its current age. These galaxies are much
smaller than the giant systems we see today and suggest that today’s galaxies are formed by smaller
systems building up into larger ones. Credit: NASA, ESA, R. Windhorst (Arizona State University),
and H. Yan (Spitzer Science Center, Caltech)
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MATTER IN THE UNIVERSE
Figure 3.2.
Temperature map of the Cosmic Microwave Background (CMB) radiation as measured
by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, launched in 2001. The CMB
is remnant black body radiation (see Sect. ??) from a time 380,000 after the Big Bang when the
temperature of the Universe cooled enough for electrons and protons to combine and form neutral
atomic hydrogen. The mean observed temperature of the CMB is 2.73 K, but tiny fluctuations in
K (red) to
K (dark blue) (Ref. [8]).
temperature can be seen in this image of order
The fluctuations are caused by sound waves. The angular scale over which perturbations can be
seen provide information that constrains the cosmological parameters of our Universe. Credit: The
WMAP team and NASA.
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93
Figure 3.3.
Estimates of the components of the energy density (which includes matter) of the
Universe, from a variety of sources (Sect. 3.2) are shown here. The dark energy/matter proportion
is thought to be known to within a few percentage points The uncertainty on what fraction of the
baryonic matter is considered to have been detected is larger.
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MATTER IN THE UNIVERSE
Figure 3.4.
The P-P chain of nuclear reactions, illustrated here, powers all stars less than about
1.5 M . Note that the intermediate elements created are used up again so the only product is He.
Two branching arrows indicate that two possible reactions can occur with the probabilities noted.
However, the reaction in the PPI branch
occurs more quickly than the precursor step to PPII and PPIII
so, for the Sun, the production of He ends via the PPI branch 86% of the time. Note that the first
two reactions need to occur
twice
in order to drive the PPI reaction. In the Sun, the PPI chain can be
summarized as 4H He + 2e + 2 plus
26 MeV of thermal energy. Of the non-nuclear photons
or particles, represents a -ray photon, e is a positron and is an electron neutrino. The neutrino
in the PPIII chain has historically been an important player in the so-called solar neutrino problem
in which fewer electron neutrinos from the Sun were observed than predicted by the above steps.
This problem was solved in the year 2002 with the definitive detection of different ‘flavours’ (types)
of neutrino by the Sudbury Neutrino Observatory (Fig. I.3.a), showing that neutrinos can undergo
oscillations and change favour en-route to the Earth (Ref. [34]). redraw so not copy of text. Get rid
of lower numbers on each atom. Change position of start of arrow so they originate from the
correct end point of previous equation.
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Figure 3.5.
Evolution track of a 1
analogue). permission requested
95
star in the HR diagram (see Fig. 1.13. for an observational
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MATTER IN THE UNIVERSE
Figure 3.6.
Examples of planetary nebulae, the end result of the evolution of low mass stars
like our Sun. The planetary nebula on the left is NGC 6751 and on the right is NGC 6543. The
nebula itself represents the outer atmospheric layers of the star after they have been expelled and the
now exposed degenerate remnant at the center, originally the core of the star, is called a white dwarf
star. The complex nebular morphologies are not completely understood but seem to be related to
different phases of stellar winds and mass loss. Circumstellar disks, magnetic fields and the presence
of companions may also play a role (Ref. [28]). permission requested
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97
Figure 3.7.
The galaxy, M 51, before (left) and after (right) a Type II supernova went off in its
disk. The supernova, named SN 2005cs, was discovered in June, 2005 by Wolfgang Kloehr using an
8-inch telescope, and can be seen directly below the nucleus in the spiral arm closest to the nucleus. A
supernova explosion takes only a fraction of a second but maximum light is achieved 2 to 3 weeks later.
The brightness of a Type II may then plateau or decline in brightness over
about 80 days followed by
a continuing slow decline thereafter. This galaxy is 9.6 Mpc ( ly) distant so the supernova
we see now actually occurred 3.3 Myr ago. Credit: R. Jay GaBany (with permission).
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MATTER IN THE UNIVERSE
14
12
lo g (a b u n d a n c e ) + 1 2
10
8
6
4
2
0
1
4
7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91
-2
Atomic Number
Figure 3.8.
Logarithmic plot of elemental abundances in the Solar System as a function of
atomic number. Black boxes represent values for the Sun’s photosphere and clear box values are for
meteorites. In several places there are no data, for example a measurement for H in meteorites or
for short-lived radioactive elements. All abundances have been normalized to hydrogen which has a
value of 12 in this plot. For example, a value of 6 on the graph corresponds to an abundance of with respect to hydrogen. Abundances refer to the numbers of particles, rather than their weights.
Data from Ref. [47].
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99
IMF
–1
Disk
–2
dn/dx = 4.4E-2 M^(-1.3)
M > 1.0 M_sun
dn/dx = 0.158 exp{-(1/2)[(x+1.10)/0.69]^2}
log(dn/dx)
M < 1.0 M_sun
–3
Halo
–4
–5
dn/dx = 3.6E-4 exp{-(1/2)[(x+0.66)/0.33]^2}
M < 0.7 M_sun
–6
dn/dx = 7.1E-5 M^(-1.3)
M > 0.7 M_sun
–7 –1
–0.5
0
0.5
1
1.5
2
x = log(M)
Figure 3.9.
The initial mass function (IMF) for disk and stellar halo of the Milky Way. Masses are
. The IMF, given by dn/d[log(M)] (pc [log(M )] ) represents the number density
in units of
of stars per logarithmic mass interval that have formed over the history of the region being studied.
It is determined by counting the number density of stars in a given luminosity interval, applying
corrections for observational biases, converting to the number density of stars in a given mass range,
and then applying corrections for the number of stars that have evolved, i.e. that are no longer on the
main sequence. The functional expressions are labelled on the plot. There are some significant error
bars associated with the fitted parameters that are not shown, but the plot provides a good idea as to
how many stars of different masses form in the Milky Way. There are clearly many more stars per
unit volume in the disk than in the halo and many more low mass stars in comparison to high mass
stars. Star formation via gravity alone cannot reproduce the details of these plots and it is likely that
turbulence plays an important role. From Ref. [13].