This document discusses the origin and evolution of galaxies, stars, and planets in the universe. It describes how the universe began in a hot dense state 13.8 billion years ago and has expanded and cooled since then. Within the first few hundred million years, the first proto-galaxies formed from dense clouds of hydrogen and helium gas. These proto-galaxies eventually hosted the earliest giant stars, some hundreds to thousands of times more massive than the Sun. These short-lived early stars played a key role in producing heavier elements through supernova explosions, seeding the universe for future star and planet formation.

1. Galaxies , stars and their origin
More universes than ours ?
Earth-like planets ?
C. de Jager

2. 
The constellation Andromeda
contains the ‘nebula’ M 31

3. 
It took 2.5 million years for
these photons to reach our
eyes
When the Neanderthalers still lived here
these photons had already finished 95%
of their trip

4. 
That ‘nebula’ is our neighbouring
sister-galaxy: Messier 31

5. 
Distance 2.5 million light years
With our galaxy it is one of the two largest of
the ‘local group of galaxies’ (which contains
some 20 extragalactic systems)
Diameter about 150 000 light years
About 1012 stars
Total mass ~1.3 times that of our galaxy
Our sister-galaxy

6. 
Many more spiral-galaxies in the sky - the
whirlpool galaxy, distance 25 Mlj

7. 
M83: a barred spiral – like our
galaxy; at 15 Mlj

8. 
The sombrero galaxy – gas and dust
in the equatorial plane at 30 Mlj

9. 
Groups of galaxies: the Virgo cluster
at 53 Mlj

10. 
Part of the Coma cluster;
hundreds of galaxies at 320 Mlj

11. 
Deep space up to some 12 Glj (Giga light years) -
– more galaxies than stars on this picture

12. 
Farthest known galaxy– at 13.1 Glj

13. 
That was a rapid view of
our Universe
There were remarkable developments in the
early 20th century

14. 
 An essential question for Einstein (1915): Why does
the universe not collapse – the Earth existsed for
hundreds of millions of years if not longer; the
galaxies most probably too
 Did the universe exist that long without collapsing?
 To overcome this Einstein introduced an additional
term in his formulae – characterized by the Greek
capital Lambda. Keeping the universe in shape
Einstein’s dilemma

15. 
 Ten years after Einstein Hubble found that the
Universe is expanding
 Around 1920 - 30 that was already predicted by De
Sitter, Friedman and Lemaître
 Their suggestion: Universe is either expanding or
collapsing or (most improbable) just in balance
 Hubble could measure distances and found: it is
expanding
 Einstein: “Introducing Lambda was my biggest error”
Einstein’s ‘biggest error’

16. 
Hubble’s first diagram – 1929
(note: one parsec = 3.26 light years)

17. 
 A special type of supernovae (Supernovae type Ia) is
the most reliable standard candle
 A supernova Ia is due to the explosion of a white
dwarf star that, by collecting mass from a companion
star, exceeds its limiting mass of 1.4 solar masses
 Then it produces a radiation flux of 1010 times solar
radiation flux. Therefore visible till far in the depths
of the Universe
 All SN Ia are equally bright – that makes them a
good standard candle
Later improvements based on a
reliable standard candle

18. 

19. 
 From Hubble diagram we derive: Universe originated
13,8 Gigayears ago; must have been very small at that
time – how small?
 Lemaître (Leuven) introduced L’atome primitif: the
universe started extremely small ; elaborated by Gamov
 The hypothesis of an explosion with extremely small
origin met with much sceptisism
 Hoyle, cynically: “These fantasists with their big bang”
 Gradually – after more data and many investigations –
the conclusion became inevitable
“The day without yesterday”(Lemaître)

20. 
It was not an explosion !
Not an explosion of matter – space originated and grew
Before, there was no space; nor did time exist.
Before? That notion too had no sense

21. 
 Universe, space and time, originated from an instability
of the absolute vacuum – the Big Bang, but how?
 Perhaps the Casimir-Polder hypothesis (1948)?
 Basis: even the absolute vacuum does contain energy in
volumes as small as the Planck length – emergence and
decay of very enegetic virtual particles with positive and
negative energy explosions, and even with positive and
negative time excursions.
 Could an accumulation of energy in the sub-Planck
domain lead to an explosion followed by expansion and
decreasing temperature? Still very open question
Big Bang

22. 
 In times shorter that Planck time (1.35 x !0-43sec) and space
smaller than Planck length (4.05 x 10-35 meter) notions
time and space lose their meaning. Virtual particle can
originate and decay.
 Formation involves positive and negative energy of order
of Planck energy (2x 109 Joule) and associated pressures
 Corresponding temperature is 3.55x 032 K
 Could such an explosion have given rise to the Universe?
 And: why then only one universe ? A multiverse?
The Planck era and the Multiverse

23. 
 After its formation the universe expanded and cooled
 Basic constituents of chemcal elememts originated:
 Quark–gluon liquid after ~ 10-6 s; T = 1013 K
 Thereafter protons and neutrons formed and then the
simplest atomic nuclei (H, He, Li)
 After 300 seconds: T has decreased to ~ 109 K, universe
consisted of positive ions of Hydrogen, Deuterium,
Helium-3, Helium-4, Lithium and many electrons
 After 370 000 years: T smaller than 4000 K; recombination
of protons and electrons: universe became transparent
After Planck era: formation of first
chemical elements

24. 
This was the standard
picture
It was accepted till end of last century.
Recent new developments

25. 
 (a) Study of motions in (groups of) galaxies shows
there must exist more matter than what is visible
 Initial estimates: there is about five to ten times more
invisible than visible matter. What is it?
 Dark matter – nice name but explains nothing
 (b) But additionally it was found that expansion of
universe is accelerating (Einstein’s Lambda returns!)
 Enormous energy needed for this acceleration
 Dark energy – nice name but explains nothing
Dark matter and dark energy

26. 
 The relation between velocity of expansion and distance
is not linear – the expansion accelerates!
 Acceleration by some form of energy. How much?
 We tranform energy into mass with E = m.c2
 Best agremeent is found for 30% mass (visible and
invisible) and 70% mass corresponding with dark
energy
 See next graph
More about the acceleration

27. 

28. 
A closer look at the
developing universe
After the first few minutes, the Universe, while
continuing to cool down, still consisted only of
atoms of Hydrogen and Helium.

29. 
 By recombination of electrons and protons the first
hydrogen atoms formed. The universe became practically
transparent (apart from absorption by He atoms)
 This happened after some 370 000 years . At that time T
had decreased till below 4000 K – but by exansion of
universe we see T = 2.7 K
 Do stars and galaxies originate at that time? Can we see
that ?
 WMAP and Planck satellites, observing at mm
wavelengths gave image of the universe at that time
 Result was disappointing: practically smooth universe
After 370 000 years

30. 
Planck satellite observing at many mm wavelengths

31. 
The universe, 370 000 years old;
very smooth; most fluctuations ~ 0.2 mK

32. 
Power spectrum

33. 
 Total relative mass of visible matter (baryons and
electrons) is 0.0486 ± 0.0007
 Total relative mass of dark matter is 0.273 ± 0.006
 Total relative mass correspoding with dark energy is
0.68 ± 0.02
 Expansion velocity increases wit 67.3 ± 1.2
km/sec/megaparsec (Hubble constant); age of
univere 13.8 Giga-years
 Hence: visible matter: 5%; dark matter: one-fourth;
dark energy: two-thirds
Results of analysis

34. 
Birth of galaxies, stars
and planets
At that time: only Hydrogen-Helium bodies
Heavier atoms did not exist
Hence: no rocky planets possible
Life was neither possible

35. 
 With the given densities and radiation flux only
fairly small individual clouds of gas can form
 Mass of order 10 000 solar masses.
 This happened after 300 to 500 million years
 Gradually H2 molecules form, a fraction of 0.001 to
0.000 1 produces sufficient cooling allowing for more
mass accretion; thus these clouds grew
 After about 600 million year the mass has increased
to 1 – 10 million solar masses; not yet a galaxy.
 We call these objecs: proto-galaxies
Proto-galaxies

36. 
 Small density fluctuations in the proto-galaxies can lead
to fragmentation followed by further contraction – thus
the first stars form
 Size is limited by the absorption in the atmospheres – if
this is large enough, atmophere expands and escapes.
This limits the size of the star
 Present most massive stars contain enough absorbing
matter to keep their mass below 60 – 80 solar; their
radiation flux is one million times the solar value.
 In contrary: the earliest stars of the universe could reach
masses up to a thousand solar masses
The first stars - gigantic objects

37. 
 The early H-He stars had high central pressure and
temperature. Intense nuclear radiation and hence intense
radiation flux ( ~108 to 109 times solar value)
 Hence shortlived star
 Compare: sun is expected to live for 10 Gigayears; star of
100 solar masses lives only 1 – 3 million years
 Star of 1000 solar masses is expected to live not longer
than 30.000 years; ; they radiate few 100 million times
more intense than the sun
 Explosion at end of life – hypernova
 Remaining core becomes black hole of ~ 100 solar masses
Short living objects; hypernovae

38. 
 At the end of the life of a star heavier than ~ 10 solar
masses it explodes
 Core remains and becomes neutron star or black hole
 This proces is called a supernova. Atomic nuclei up
to Fe, Ni … etc. .. are formed during explosion
 The explosion of the initial very large stars of many
hundres of solar masses are called hypernovae
 During their explosions large numbers of high-mass
atomic nuclei are formed and spread over space
Compare super- and hypernovae

39. 
An ordinary supernova and its galaxy
SN1994D

40. 
Remnants of a supernova expand
with 5000 – 10.000 km/sec

41. 
GammaRay Burst 030329; may 2003
(compare brightness of burst with that of neighbour galaxy!) Star
was 40 solar; new elements up to Ni formed

42. 
Gamma ray burst associated with hypernova
16-09-2008

43. 
Source distance : 12.2 Gigalightyears

44. 
 Universe exists for 13.8 Gigayears
 0.37 million years: universe becomes transparent
 400 million years: first matter accumulated
 600 million years: protogalaxies; first hypergiant
stars, hundreds to thousand times larger than sun
 800 million years: first present-days galaxies; smaller
stars
 After 1 to 2 Gigayears: first sunlike stars
Summarizing (all data are aproximative)

45. 
We exist
You and me: We exist thanks to the
supergiant stars and to the super-
and hypernovae

46. 
 Sun-like stars can only exist if they contain enough
absorbing matter, which is atoms heavier than He
 In cores of massive stars (20 – 80 times sun) elements such
as O, Ne, Mg, Si are formed
 In ‘ordinary’ supernovae (mass above 10 solar, and up to
~ 80 solar) chemical elements up to atomic numbers
around Fe and Ni are formed during their explosion
 In hypernovae (more massive stars) formation of still
much massive chemical elements
 Thanks to such stars rocky planets and life can exist
We exist thanks to massive stars

47. 
Back to earth
Earth-like planets could therefore exist in
the universe
But how about life?

48. 
First extrasolar planets discovered in 1992 and
1995. Presently some 1800 known and 3000
candidates; various discovery methods

49. 
Limited habitable area

50. 
Planets in habitable area
star: Gliese 667C

51. 
 Only big planets can yet be discovered
 Only those that revolve close to the parent star
 Thus ‘hot Jupiters’ are frequently found
 The Earth reflecting only fraction 10 -10 of the sun’s
light, occulting some 10-4 part of the sun and
revolving around the sun in a time as long as one
year, would be very difficult to discover
 But Jupiter too would be a difficult object in spite of
its big mass, because of its long revolution time
Limitations to discoveries

52. 
A new approach: starlight being eliminated by
interferometry; three planets found

53. 
 Set of four spacecrafts, pointing same direction
 Mutual relative distances and distance to fifth
spacecraft to be controlled with extreme precission
 Light sent from the four to the central spacecraft
 By interferometry light of star is eliminated; light of
planet(s) remains
 Residual light inspected spectroscopically –search for
molecules that relate to life
 This is a proposal to ESA – not yet accepted
A fascinating proposal: the
Darwin mission

54. 
Darwin spacecraft cluster

55. 
IR spectra of Earth, Venus, Mars:
note O2 , H2O , CO2

56. Containing at least one small rocky
planet, surrounded by a thin layer of
water and much thinner layer of gas.
A good Universe to live in

57. Go to page: presentations ; there to Universe
See also: oerknal
Eerste melkwegstelsels
Eerste sterren
Hete reuzenplaneten