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
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
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’
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
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
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
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
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
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
