Authors are_:
*Mr.Rupak Bhattacharya-Bsc(cal), Msc(JU), 7/51 Purbapalli, Sodepur, Dist 24Parganas(north), Kol-110,West Bengal, India**Professor Pranab kumar Bhattacharya- MD(cal) FIC Path(Ind), Now Professor & Head, Department of Pathology [ also Convener In-charge of DCP &DLT course of WBUHS, School of Tropical Medicine, 108 C.R Avenue, Kolkata-73, W.B, India & EX Add. Professor of Pathology, Institute of Post Graduate Medical Education & Research,244 AJC Bose Road, Kolkata-20, West Bengal, India]**Miss Upasana Bhattacharya- Only daughter of Prof.P. K Bhattacharya *Mr.Ritwik Bhattacharya B.Com(cal)* Miss Rupsa Bhattacharya-Student, *Somayak Bhattacharya BHM; MSC HM PUSHA New Delhi, all Resident of 7/51 Purbapalli, Sodepur, Dist 24 parganas(north) ,Kolkata-110,West Bengal, India *** Mrs. Dalia Mukherjee BA(hons) Cal, Swamiji Road, South Habra, 24 Parganas(north), West Bengal, India*** Miss Oaindrila Mukherjee- BA (hons) Student*** Mr Debasis Mukherjee BSC(cal) ,Swamiji Road, South Habra, 24 Parganas(north), West Bengal, India***
*Mr.Rupak Bhattacharya-Bsc(cal), Msc(JU), 7/51 Purbapalli, Sodepur, Dist 24Parganas(north), Kol-110,West Bengal, India**Professor Pranab kumar Bhattacharya- MD(cal) FIC Path(Ind), Now Professor & Head, Department of Pathology [ also Convener In-charge of DCP &DLT course of WBUHS, School of Tropical Medicine, 108 C.R Avenue, Kolkata-73, W.B, India & EX Add. Professor of Pathology, Institute of Post Graduate Medical Education & Research,244 AJC Bose Road, Kolkata-20, West Bengal, India]**Miss Upasana Bhattacharya- Only daughter of Prof.P. K Bhattacharya *Mr.Ritwik Bhattacharya B.Com(cal)* Miss Rupsa Bhattacharya-Student, *Somayak Bhattacharya BHM; MSC HM PUSHA New Delhi, all Resident of 7/51 Purbapalli, Sodepur, Dist 24 parganas(north) ,Kolkata-110,West Bengal, India *** Mrs. Dalia Mukherjee BA(hons) Cal, Swamiji Road, South Habra, 24 Parganas(north), West Bengal, India*** Miss Oaindrila Mukherjee- BA (hons) Student*** Mr Debasis Mukherjee BSC(cal) ,Swamiji Road, South Habra, 24 Parganas(north), West Bengal, India***
Correspondence author Professor Pranab
kumar Bhattacharya E mail Profpkb@yahoo.co.in
Stars
last too long in this universe. For an astronomers to see any evolution of a
star or death of a star, in the course of his/their life time, unless he/they
is/are lucky enough to see one star destroying itself in a supernova or in a
nova explosion or turning towards a Red giant . My 84 years old and
in 2009 diseased father , late Mr. Bholanath Bhattacharjee of 7/51 purbapali, po-sodepur,24
parganas(north) kol-110, West Bengal, India ,used to teach our brothers and
sister in our young ages, with his built up notion like this”….. Stars are long
lived objects with ages, they are as old as our galaxy is, as old as our
universe is and they are symbol of eternity they may be 2.5 billion years – 3 billion
years old from a first generation stars explosions and are
almost perfect cosmic mile markers even
very close to Big Bang.
Today we know that looking at a supernova of a very distant star almost
at horizon of the universe, or of a Nebula, we can understand the mystery of
creation of the Universe, the Big Bang it self. They are really the symbol of
the eternity. Edington suspected, that
the nuclear reactions in the interior of the stars are primary sources of
energy for it’s luminosity and fusion of hydrogen to make Helium and that
can take place in it, in time bound scale for this ranges, from millions to
millions years. Our sun has lost it’s brightness by more then 1% from it’s
birth, due to change in it’s internal structure for past 107 years. But the
question remains how these supernovas
explode? What is the mechanism behind it?
No physics, Asronomy, probably answered it!. Here may be some
explanations by my brothers Rupak Bhattacharya and Ritwik Bhattacharya the authors
If
we consider the mode of generation of energy in the star, nuclear process
provide the only source of energy adequate to keep the stars ongoing luminous. The
nuclear fusion in which Hydrogen is built up into Helium, can function
sufficient fast at temperature, like those at central core of star (12-25
million degrees). The Helium burning process are important 1) Carbon
Nitrogen cycle at which a carbon-12 nucleus (12C) capture proton
and is converted into 13C, Nitrogen-4 and nitrogen –15. At a
final temperature, a proton leads to a fusion yielding original 12C
nucleus to a Helium nucleus .2) The Proton- Proton process, in which
protons are built direct Helium nuclei through steps, involving first in
production of a deuterium and helium3 nuclei to form Helium4
nucleus and two protons. 3) Carbon burning process where 12C
nucleus undergoes fusion reaction in the interior of a star producing neutron,
proton, and Alfa particles with huge temperature. The first reaction probably
dominates into the star, applicable to more massive stars then Sun. The
second and third reaction is applicable for Sun and in less massive stars then
Sun respectively. Thermonuclear reactions like those in a hydrogen bomb are
powering the Sun in a contained and continuous explosions converting some four
hundred millions tons (4x1014 grams) of hydrogen into helium. When
we look up in the sky in night and see the stars we see them shining because of
distant nuclear fusion in them .But hydrogen fusion can not continue for
ever. Our Sun is ~ 4.7109 years
old star. The energy produced in our ordinary star Sun in each second, is
equivalent to the destruction of 41/2 millions tons of hydrogen mass in every
second, a mere fleabite compared with the mass of the Sun which is two thousand
billion and billion tones. In the Sun or in any other stars, there is limited
so much hydrogen in it’s hot interior. Although Helium is predominating as
net fusing of Hydrogen, other elements like “carbon”, “Iron”, “L
element” “Manganese” “Chromium”, EU, yttrium, Magnesium, SR, Nickel, Osmium
are also built up in the interior of the stars. Arnett and Truran
[Arnett W.D and Truran. JW –Astrophysics.J-Vol157;P339,1969] showed
that nuclear reaction net work in the sun when 12C nuclei began to under go the fusion reaction in
the interior of sun many elements are produced such as
12C+12C---- 23Na+P+2.238mev----23Mg+
n+2.623mev------20Ne+ 27Al +4.616mev and the reaction
goes on endlessly. A large number of computed reactions are possible as the
liberated neutron and gamma particles begin reaction with all the nuclear
species generated within the hydrogen fusion. In fact Arnett and Truran
produced 99 different reactions only in 12C carbon burning net work
and 23Na,20Ne, 24Mg,27Al,29Si,
and some31P elements are also
produced. Beside these Li, Be, B ( Known as leptons)are also produced in the
stars due to hydrogen burning. Another most elementary particles are produced
in huge quantities. They are Neutrinos or ghost particles due to hydrogen
burning procedure ( Professor Pranab Bhattacharya & Mr. Rupak
Bhattacharyya). Conversion of hydrogen into helium in the center of the
stars or of the Sun, not only accounts for Sun’s brightness in photons of
visible light. It also produces a radiance of a more ghostly kind. The sun
glows faintly in neutrinos , which like
photons, weight nothing and travel at speed of light. Neutrinos emitted from
Sun carry an intrinsic angular momentum or spin while photons has no spin.
Matter is transparent to neutrinos which can pass effortlessly through the
earth and through the Sun. Only a tiny fraction of them is stopped by
intervening matter. As you look up our sun, a billions neutrinos pass through
your eye ball. They are not stopped by Retina as ordinary photons do ,but
continue unmolested through the back of your head. The curious part is that if
at night if I look down at ground, towards the place where sun would be, almost
exactly same numbers of solar neutrinos pass through my eye ball, pouring
through an interposed earth which is as transparent to neutrinos as a plane of
clear glass is to visible light. Neutrinos on very rare occasion convert
chlorine atoms into argon atoms with the same number of protons and neutrons. Davis
The
previous view regarding the “L atoms elements” was that each star makes it’s own share of these “L
atoms elements”i.e (autogenously origin). But the concept of autogenic view has
been now abandoned, because highest abundance values for stellar Li & Be
have shown to be not larger than interstellar upper limit. The formation of
each “L atoms” requires the acceleration of about 1erg fast proton. To account
auto genetically for lithium abundance in T. Tauri stars (L1/H=109),
the time integrated amount production of energy into particle acceleration must
be comparable with gravitational release, implying an unlikely high efficiency
for acceleration mechanism. So nuclear mechanism is responsible for
generation of “L atoms” in the star. It involves high-energy process
(Thermonuclear reactions). These L atoms” can be formed in two different
ways within the stellar interiors. By the collision of
incident light particles on the heavier atoms of interstellar gas
(For instance fast protons on stationary C, N, O) or the reverse (for
instance fast C, N, O on hydrogen at rest). In the first case the Products “ L
atoms are to remain in rest, while in the second case, the products are moving
at a velocity comparable with that of cosmic rays. The fate of “ L atoms” generated by fast protons on
stationary C, N, O stationary atoms and are all rapidly thermalised and become
part of ISM.
“L
atoms” generated by reverse process have a fate which depends on the initial
energy of “L atoms”. L atoms with energy E<0.2 Gev nucleon-1 will
stop in galactic gas (ISM) while L atoms with E > 0.3Gev neucleon-1
will suffer nuclear transformation of various elements in the stellar interior.
Analysis of Old stars can give us some idea that heavy
elements are produced in the interior of the stars and are subsequently ejected
into the ISM either through the supernova explosion or through stellar winds or
through cosmic rays. The total mass loss, from all stars in a
galaxy will be roughly 1MO per year. A fraction of these accumulate in the
galactic nuclei, which are center of the gravitational attraction. The halo of
our galaxy is nearly spherical region containing very old stars, which have a
smaller content of heavy elements than our sun has. It is usually assumed that
some how cloud of gas condensed to form our galaxy and that the halo stars
were formed during the collapse process and left with a nearly spherical
distribution. These stars are ultra high velocity stars. These stars show
weak spectral lines corresponding to abundance of carbon and heavier elements
[relative to hydrogen] that are lower than our Sun. Because these stars are
oldest in our galaxy quite distinct type of nuclear process have been
postulated for different groups of elements. The most abundant nuclei are 32S
and 58Fe those can be formed by silicon burning process while 16O,
20Ne,23Na 24Mg,28S may be produced
by explosive carbon burning process. When heavier elements notably Sr, Y, Zr,
Ba etc require neutron capture on slow time scale, by iron group nucleotide
already present in the star. A peculiar type of star 73 DRA has been
investigated for many a time. It is full of chromium with europium and
strontium. The star showed the presence of Cr, Eu, Sr and also Mn, Fe, Ni, in
gaseous form while osmium (z=76) is present in both neutral and ionized form.
The importance of these heavy elements is that, some of them such as Iridium,
gold, uranium are also produced in the stars in the gamma process of nucleus
synthesis [Neutron capture slow process]
So Helium, L atoms, Carbon, Iron, gold,
chromium, nickel, silicon and many other elements are built up in the stellar
interior. Although the net fusing of hydrogen into helium dominates however at
this stage. Helium builds up in the core. The supply of hydrogen fuel
diminishes and eventually becomes in sufficient to provide energy to hold up
the strain position. As the energy production decreases, the core of the
star contracts and heats up through release of gravitational energy. With a
hotter center there is a greater outward pressure and the outer layer of the
star expands, so that the star now becomes a RED GIANT. The red
giant has a radius hundred times that of a sun. Mean while in the hotter core a
new series of fusion reactions begins and with the helium as the fuel many
elements like carbon oxygen, neon, magnesium. When helium will exhaust as a
fuel, the carbon burning process will start as 12C as a fuel in the star. In
any star the internal temperature and density and therefore the rate at which
the energy is generated depend sensitively on the opacity of the stellar
material or in other words, on the ease with which the photons can escape from
the stellar core. In simple terms you can say greater the opacity harder it is
for heat to get out making core hotter. Opacities in normal star can be
calculated reliably from knowledge for the abundance of the constituent
elements and their ionization site
Suernova-: Another important
thing in our universe are the supernovas or novas. The supernovas are the
explosion of the central core or outer core of a giant massive star. These
supernovas are found in the binary star system. A star may end its life cycle
either in the form of a RED GIANT or in the form of a white dwarf or in the
form of a “ black Dwarf” or in the form of “ neutron Star” or in Black Hole” or
in the form of Supernova Explosion”. When the explosion of a star occurs in
small scale, we call it Nova. In Big bang concept, apart from hydrogen, a
little helium was produced. Every atom of every element had been built up by
the nuclear fusion reaction in the stellar pressure cooker. The elements only
could arrive in the interstellar space to mingle in the clouds of forming
protostars is through this supernovas
Novas are however quite different from supernovas. Novas occur in binary
star system and are powered by silicon or carbon fusion. Supernovas occur in single
associated with old population II stellar system such as elliptic galaxies and
in globular clusters. The classical supernovas are therefore a subset of the
cataclysmic variable class of objects, which undergoes out bursts with peak
luminiocity ~ 5x1037 to 5x 1038 ergs S-1 in
every 104 to 105 years. Around 10-5 to 10-4
MO material are ejected at velocity typically 1000 Kms-1 at each
outburst of supernova. The central system is a semi detached binary stars,
containing a white dwarf . Classical supernova out burst was observed in 1901,
where as dwarf nova out burst was first observed in 1986.
Supernovas are two types Type-1(SN-I) and Type 2(SN_II) supernovas. Most astronomers must agree with us that a type 1a supernova
starts with formation of a white dwarf — an aging star that crams as much mass
as the sun into a volume no bigger than Earth. Most white dwarfs are cold and
inert. But if the star has a companion, it will siphon mass off the neighbor
star until tipping the scales at about 1.4 solar masses. At that mass, the
white dwarf becomes dense and hot enough to initiate an explosion. mass
accreting white dwarfs, A far
more exciting end awaited a white dwarf that is part of a binary star system,
which is fairly common in our universe. In this case, the white dwarf’s strong
gravity robs the companion star of its gas. However, when the white dwarf grew to 1.4 our solar masses, it no longer manages to hold
together. When this happens, the interior of the dwarf becomes sufficiently hot
for runaway fusion reactions to start, and the star gets ripped apart in
seconds. The nuclear fusion products emit strong radiation that increases
rapidly during the first weeks after the explosion, only to decrease over the
following months. So there is a rush to find supernovae – their violent
explosions are brief. Across the visible Universe, about ten type Ia supernovae
occur every minute in our universe. But the Universe is huge. In a typical
galaxy only one or two supernova explosions occur in a thousand years. In
September 2011, we were lucky to observe one such supernova in a galaxy close
to the Big Dipper, visible just through a pair of regular binoculars. But most
supernovae are much farther away and thus dimmer. So where and when would you
look in the canopy of the sky. We
knew they had to comb the heavens for distant supernovae. The trick was to compare
two images of the same small piece of the sky, corresponding to a thumbnail at
arm’s length. The first image has to be taken just after the new moon and the
second three weeks later, before the moonlight swamps out starlight. Then the
two images was compared in the hope of discovering a small dot of light – a
pixel among others in the CCD image – that could be a sign of a supernova in a
galaxy far far away. Only supernovae
farther than a third of the way across the visible Universe were used, in order
to eliminate local distortions. The researchers had many other problems to deal
with. Type Ia
The
remnants of the Exploding stars or supernovas are called Supernova remnants.
They are easily identified by radio astronomers up to millions years after
their explosion. The optical ultra violets and X-rays continue are produced
by the supernova explosion and interaction of the resting debris (Supernova
remnants), with dense Circumstellar gas shell, previously formed by the stellar
wind of the progenitor supernova. L. Stavely Smith , in 1992 showed the
birth of the radio noise supernova remnants SNR1987A, following radio outbursts
of Supernova 1987A[ Nature Vol-355 1992]. In the mid 1990, about 1200
earthen days after the supernova radio emission was detected at frequencies 843
MHZ and 8.6 GHG and this radio emission was within 0.5 arsc of the optical
supernovas
Although both young and old star can give rise to
supernovas, the massive stars, none of which is thought to live more than
several million years, are also thought to end their life in this way.
Supernovas can occur in conjunction with their satellite planet or binary
stars. One of You among readers of our thesis may obviously ask me that in what
conditions could a star or a planet can survive such a nearby explosion?
Several simplifying assumption can be made to answer this question.
1) The time of mass ejection will be small compared
with the orbiting period
2) The mass of the second star or planet will be smaller than that of
the pre- supernova star. The first
simplification was based on that the ejection velocity of major fraction of the
matter from a supernova will be comparable with or larger than its initial
escape velocity from the pre- supernova star. Because the binary number is
necessarily at larger radius, its orbital velocity will be less than the
average ejection velocity. If the combined mass is reduced to less than a half
by the supernova, in the limit, where the mass ejection is sudden and where the
mass of the secondary is small, the system will un-banned regardless of the
effects of the collision of the ejected matter within the satellite of the
planet.
The fractional mass ejection by supernova is
known for the thermonuclear supernova model. No remnant of star remain on the
other hand models of neutron star supernova, predicts various fractional mass
ejection depending on mass and structure of the initial star. But all the
models, be it thermonuclear or neutron star or cataclysmic variables predicts a
small fractional mass ejection, for the models slightly more massive mass than
C.S. Limit, and are self consistent, in that the mass of the remnant neutron
star does not exceed current stability limit. A star of initial mass 1.5MO leaves a remnant neutron star of mass 1MO.
The link between supernova explosion and formation of a neutron star has to be
rather established even if Type II supernovas are expected to leave to a
stellar component. Only five example of Pulsar
Supernova remnant association are known on our galaxy and in large
Megallenic cloud.
Previously as we the authors told, that mass
accreting white dwarf in close binary system can be considered to be Type-1
supernovas progenitors. Low mass (Mtot≈5MO) binary X ray sources( Known as type
II supernovas) appear to be descendents of cataclysmic variables and thus they
have been produced by collapse of a mass
accreting white dwarf. The fashionable model of explaining the out burst
involves central deflagration of a white dwarf in close binary system living no
remnant. But this model implies a unique configuration and do allow for
variation. Slow supernovas show higher peak of luminosity, higher velocity in
their ejecta and slower decline in their light curve. Fast Supernovas are
dimmer velocities of expanding material are low and light curve decay is
faster.
Super
humps_: They are periodic increase in Brightness (up to 40%) that are
observed during occasional super out bursts lasting about 12 days, that are
additional to normal outbursts of a subclass of white dwarf Nova. Dwarf Nova’s
are characterized by two distinct class of out bursts. Normal outbursts of duration ~2 days and less frequent
super outbursts which lasts for ~12 days. During super outbursts, super hemps
are observed which modulate the visible light by≤40% with a period 3-7% longer
than biniary period.
Mechanism
of Explosion in Supernova-a mechanism by Professor Pranab Kumar
Bhattacharya Mr, Rupak Bhattacharya_: What is
the mechanism of a supernova explosion in a star? It is not Known and yet
explained very well. Possibly one of
the standard mechanisms of a supernova is the collapse& out going shock
due to collapse, leaving behind a neutron star, is the collapse of the iron
core of a massive star. During the initial phase of the collapse, a sizable
portion of the star transfers into neutrinos with emissions of ve energy≤10Mev.[Rupak
Bhattacharya and professor Pranab Kumar Bhattacharya’s theory] The collapse
phase lasts until the infiltrating matter becomes opaque to neutrinos. A few~1056 ve neutrinos are emitted
during this phase. As the collapsed core reaches nuclear matter densities, an
out going shock develop. When the shock reaches the dense layer that are still
transparent to neutrinos, another ~1056V
mostly Ve are expected to be emitted. The second one of the bursts , produce
neutrinos with an average energy~10Mev5~10.
The whole process lasts much less than a second. The remainder of the
gravitational energy (~2x1053ergs)
is emitted in the form of vv pairs of all flavors. Although the neutron star
contain vv pairs of very high energy (100Mev), the only low energy one is
eliminated, because the neutrinos mean the free path, is strongly energy
dependent. The energy is larger for µ, e R neutrinos (Rupak neutrinos). There
are dozen of neutrinos particles of 7-35 mev mass in that energy. There charges
is smaller than about 10-17
times the charge of electron. [Such a neutrinos is R particles or R neutrinos-a
near zero mass, conceptualized by Rupak Bhattacharya and hence nomenclatured
according to his name]
What is the Key thermonuclear feature of an
expanding star that will end it in supernovas? The ignition of helium in
the hydrogen as soon as exhausted, in core of a low mass star, in the presence
of a degenerate electron gas which is providing the bulk of the pressure
support of the star, the expansion of the star core starts. Because pressure of
such a gas does not increase ,substantially when temperature rises, where as
the rates of thermonuclear reaction increase dramatically with increasing
temperature, a brief run away in thermonuclear activity ensues. After this the
star in there core quickly expands. After only a small degree of nuclear
burning to an adjusted configuration, where burning can proceed in hydrostatic
equilibrium with subsequent discovery of very effective cooling of stellar
interior due to neutrinos emission, it has become apparent that intrinsically
more explosive nuclear fuel namely 12C
and16O may also ignite in
a very degenerate electron gas and that in that case, the run away in nuclear
reaction may be great enough completely to disrupt the star via a thermonuclear
explosion. The high temperature of the explosion which lasts only a fraction
of second produces such a high degree nuclear processing that expelled
thermonuclear product are vastly different than the composition of the mass
zone of the star, before the explosion. The key thermonuclear feature of
explosive burning is that several fuel combust at temperature considerably
higher than those at which same fuel burn in an object in hydrostatic
equilibrium with considerable effect in abundances of ejected matter. The over
heating may result either from the fact that the fuels first ignite in a
degenerate electron gas for the non central mass zones from the compression
heating, produced as a strong pressure and have propagation outward fro an expanding
core. In either case large amount of thermal energy are liberated in a time
short compared with star’s ability to compensate hydro dynamically, with the
result that the entire star may be given with positive energy sufficient to
disrupt it in explosion.
Before
the explosion, the gas is virtually half and consisted of 12C and 16O.
The first indication of importance of dynamics of the explosion of the final
nuclear product came in a study of carbon burning phenomenon of Arnet, who
established a numerical scheme for solving the nuclear reaction net work that
result when12C nuclear reaction began to undergo the fusion reaction
in the interior of the star before supernova[ Arnet W.D & Truran J.W
Astrophysics Jpurnal V157;P339;1969]
12C+12C 23Na+P+2.238mev 23Mg+tn -2.623mev 20 Net+α+4.616Mev
A
large numbers of computed reactions are thus possible, as the fusion reaction liberated proton, neutron,
neutrinos and alpha particles and began to react with all of the nuclear species
generated within the gas. Before the explosion, the gas is virtually half and
half of the 12C and 16O as produced in previous epoch on
helium burning plus 2% of 18O which is the result of earlier
conversion, within the same star, of all of the original CNO nuclei in to 18O
by hydrogen burning and helium burning in turn. Carbon burn furiously for about
1/10th of second at which
time reactions are frozen by falling temperature, associated with vigerous
expansion of gas. Most of the carbon and virtually all of the initial oxygen
remain unburned, so that the final ratio of 12C/24Mg
matches the solar ratio. More subsequently the nuclei 2One,23Na, 24Mg,
26Mg,27Al, 29Si and 3O and some
time 31P are produced. So today whatever elementary nucluie we
know in our earth or in earth’s atmosphere is the fusion-burning product of a
supernova explosion in a dying star.
1987
A Supernova-: and Recently detected
Supernovas[ Picture by
In
our galaxy there were evidences of eight supernovas. They are in the years
185,393,1006 AD and in 1054,1181,1572,1604,and very recently one is 1987.Only
supernovas 1006,1572,1604 were observed by European Astronomers. The
supernova of 1054 was as a cloudy patch, and remains still as Crab nebulae as
the legs of a crab. It is the remnant of that supernova. It is at a
distance of 4500 light years away and is left over gases that has a diameter of
about 6 miles.[Mitra A.K- Space Light first year 2nd quarter1997
P10]. Supernova 1987A occurred in the large Megaloionic Cloud (MLC).It was a
supernova of a giant star SK69202 that exploded. The star was the star of
multiple star systems instead of a binary star system. SN 1987a
was 18 solar mass blue giant Sanduleak -69° 202a, a mere 0.000168 billion
light-years distant. This star had lost
a considerable mass of M20O due to the explosion. The other members
of this giant multiple system is now visible as supernova remnant. The SK
69202 was probably a red super giant 104—105 years ago.
The outer envelop, blue star giant progenitor star is preserved during the
rapid supersonic un turbulence outflow of the supernova. The huge amount of R-
neutrinos (Rupak Particles) are now emitted by this 1987A supernova proposes
the formation of a neutron star, inside this supernova some have reported
that central region of this supernova was a central pulsar. However the
history of this supernova 1987A is today 23 years old. In the supernova 1987A
there is evidence of presence of H3+ in the envelope or in the shell
of it. The infrared L window spectrum of supernova 1987A is between 2.95-4.15um
were obtained by hydrogen re combination line ( Mcikle.W. PS Not.R. Astr
Society V283;P193-223;1989). But from 110 days onward there were an evidence
of hydrogen recombination line between spectrum 3.41-3.53um. These were
possibilities in wave length at which H3+ announces most strongly presence of a
planet like Jupiter (Okata.T etal- Astrophysics J-Vol351;P253-56;1990).When
the first explosion of supernova 1987A happened there were a brief initial
outburst of radio emissions that lasted for more than a few days. The expanding
Nebulae were set into motion by the ejection and cooling of ejected material
and its interaction with circumstellar material that surrounded the
progenitor& was then non visible at the available radio frequencies.
Evolution of radio-supernova remnant over the last years provided us the
information about the progress of the expanding supernova remnant. The nature
of its unusual progenitor star which was first a red
giant and then a blue giant, before it exploded. In the red giant phase, the
star threw off a dense slow moving wind which was succeeded by a more tenuous
but faster wind from the blue giant. The circumstellar material of the
progenitor at the moment of the explosion there fore consisted of a hot thin
gas- cocooned inside a cooler thicker shell with a supersonic shock wave
created at the boundary, as the blue
giant wind ran into red giant wind. The first brief flash of radio
emission was a very minor part of the initial supernova outbursts and was
probably attributable to the propagation of shock wave from explosion through
the thin material immediately surrounding what had been progenitor star.
Supernova are now routinely observed in other
galaxies . During the life time of a galaxy about 10 billion years, a hundred
millions of stars exploded. Amongst them, David Helfend and Knoxlong reported
an extremely intense burst of hard X-ray and gamma rays which was also recorded
by nine interplanetary space crafts and which was also probably Supernova N49
remnant in large Megellanic Cloud [ MLC is a small satellite galaxy of Milky
Way 18,0000 light year distant)[ Nature march5,1979 & decemb6 1979]. The
recent nova which had been detected in Cygx-1 galaxy. It was Nova V404 cygni-
Low mass x ray binary emits x ray and x ray behavior is similar to black hole
system. In April 6,1947 discovered a supernova in a satellite of famous
whirlpool galaxy M51- A star suddenly had maximum brightness and had then
overlooked. On 9th January 2008, while viewing of galaxy NGC 2770 an unexpected
transient burst of Xray was detected in one of the galaxies spiral arm. Further
observation showed that the burst was a first sighting of new type of Ibc
supernova duly was named as SN200D. Most distant Supernovae are super bright,
and that makes them easy to see from far away. Very far away. 11 Billion Light
years to be exact from earth. almost at time of birth of first generation stars
and galaxy.
Pulsar formation is generally attributed to
supernova events and two pulsars are till associated with known supernova
events. They are Crab Nebulae pulsar NP0532 and Vela. Other pulsars are close
enough to supernova remnants to suggest an association but only if they are
moving away from the remnants at velocities of order 103 Km/second.
Fowler KA and Hogel F in 1963 suggested that supernova core may well be too
massive to form a gravitationally stable
object(neutron Star) and gravitationally Collapsing Object(black Hole too).
They suggested that systemic ejection of Radio luminous material from galaxy
could be caused by symmetrical process occurring in the collapse of very
massive objects, thus the more massive core could fission into several less
massive objects. The same process can be applied to supernova events where core
fragments into some distribution of neutron stars” Black holes’ and general
debris[ Fowler WA, Hoyel F Nature 197; 533;1963]. There is a pulsar PSR 1509-58
located near the center of radio supernova remnant MSH 15-52, a supernova
remnant of supernova AD1054. This pulsar is young only about 1700 years. The
near coincidence of this age with that of supernova of AD 185 strongly suggest
that PSR1509-58 was born in AD1054 supernova explosion.
Why Supernova is So important
before physicists?
Supernova means accelerating
expansion of the universe! The discovery of
the accelerating expansion of the universe was a real milestone for cosmology, ultra high Physics as significant as the
discovery of the minute temperature variations in the Cosmic Microwave
Background (CMB) radiation with the COBE satellite (Nobel Prize in Physics 2006, won & Received by John Mather{ See the link at Nobel
prize org face book ask a question to Jhon Mather at
http://www.facebook.com/note.php?note_id=163524746719} and prof. George Smoot NL. By studying the CMB, we can learn about the early history of our Universe and the origins of all structures we see around us, whereas the expansion history of the universe gives us insights into its evolution and possibly its ultimate fate{ It was predicted in Mayan calendar & by some shallow knowledgeable people & Physicists that our world will see its end in 2012 December either through a collision with a giant planet approaching towards us or through strong solar storms}. The expansion of the universe was originally discovered by Vesto Slipher, Carl Wirtz, Knut Lundmark, Georges Lemaître himself and Edwin Hubble in the 1920’s[ I wonder often why George Lemaitre was not awarded Nobel prize for his BIG Bang theory!]. The expansion rate depends on the energy content – a universe containing only matter should eventually slow down due to the attractive force of gravity. However, observations of type Ia supernovae ( often it is designated as “SNe”) at distances of about 6 billion light years by two independent research groups, led by Saul Perlmutter and by Brian Schmidt and Adam Riess respectively, revealed that presently the expansion rate instead is accelerating rapidly . Within the framework of the standard Big Bang cosmological model, the acceleration is generally believed to be caused by the vacuum energy (sometimes we call it as ”Dark energy”) which is again – based on concordant data from the SNe, the observations of the anisotropies in the CMB and surveys of the clustering of galaxies – accounts for about 73% of the total energy density of our universe. Of the remainder, about 23% is due to an unknown form of matter ( we call it ”dark matter”). Only about 4% of the energy density corresponds to ordinary matter like atoms. Is that not so strange!
http://www.facebook.com/note.php?note_id=163524746719} and prof. George Smoot NL. By studying the CMB, we can learn about the early history of our Universe and the origins of all structures we see around us, whereas the expansion history of the universe gives us insights into its evolution and possibly its ultimate fate{ It was predicted in Mayan calendar & by some shallow knowledgeable people & Physicists that our world will see its end in 2012 December either through a collision with a giant planet approaching towards us or through strong solar storms}. The expansion of the universe was originally discovered by Vesto Slipher, Carl Wirtz, Knut Lundmark, Georges Lemaître himself and Edwin Hubble in the 1920’s[ I wonder often why George Lemaitre was not awarded Nobel prize for his BIG Bang theory!]. The expansion rate depends on the energy content – a universe containing only matter should eventually slow down due to the attractive force of gravity. However, observations of type Ia supernovae ( often it is designated as “SNe”) at distances of about 6 billion light years by two independent research groups, led by Saul Perlmutter and by Brian Schmidt and Adam Riess respectively, revealed that presently the expansion rate instead is accelerating rapidly . Within the framework of the standard Big Bang cosmological model, the acceleration is generally believed to be caused by the vacuum energy (sometimes we call it as ”Dark energy”) which is again – based on concordant data from the SNe, the observations of the anisotropies in the CMB and surveys of the clustering of galaxies – accounts for about 73% of the total energy density of our universe. Of the remainder, about 23% is due to an unknown form of matter ( we call it ”dark matter”). Only about 4% of the energy density corresponds to ordinary matter like atoms. Is that not so strange!
In our everyday life, the effects of the vacuum energy are so tiny,
but measurable – observed
for instance in the form of shifts of the energy levels of the
hydrogen atom, the Lamb
shift ( Lamb won Nobel Prize in Physics 1955). The evolution of the universe
was also described by Einstein’s theory
of general relativity- the essence of that theory was that. In relativistic
field theories, the vacuum energy contribution is given by an expression mathematically
similar to the famous “cosmological constant “in Einstein’s theory.
The question of whether the vacuum energy term is truly time independent like
the cosmological constant, or varies with time, is currently a very hot
research topic.
General Relativity and the our Universe!
The stars in the night sky always fascinated human beings( males and
females), Poets Literature, Dramatists, scientists, lovers and in worlds top
Romantics. Why Stars in dark space time of night? We can only guess what the
people of ancient times speculated about when they saw the stars return every
night to the same spots in the sky! We know of Greek philosophers who proposed a
heliocentric astronomical model with the Sun in the middle and the planets
circulating around it as early as the 3rd century B.C., but it was in fact
Nicolaus Copernicus, who in the 16th century developed the first modern version
of a model. It took Galileo Galilei’s genius in the beginning of the next
century to really observe and understand the underlying facts, building one of
the first telescopes for astronomy and hence laying the ground for modern
astronomy. For the next three hundred years, astronomers collected ever more
impressive tables of observations of the visible stars. In the Copernican system,
the stars were assumed to be fixed to a distant sphere and nothing in the observations
indicated anything to the contrary. In 1718, Edmund Halley discovered that
stars actually could move in the sky, but it was believed that this happened in
a static, fixed universe. Throughout the 18th and 19th century, the study of
celestial bodies was placed on an ever-firmer footing with the famous laws of
Kepler and Newton
In 1917, Einstein applied the GR equations to the entire Universe ,
making the
implicit assumption that the universe is homogenous isotropic ; if
we consider cosmological
scales large enough such that local clusters of matter are evened
out. He argued that this
assumption fited well with his theory and he was not bothered by
the fact that the
observations at the time did not really substantiate his
conjecture. Remarkably, the
solutions of the equations indicated that the universe could not be
stable. This was
contrary to all the thinking of the time and bothered much Einstein.
He soon found a solution, however. His theory of 1915 was not the most general
one consistent with the
Equivalence Principle. He
could also introduce a cosmological constant, a constant
energy density component of the Universe. With this Einstein could
balance the
Universe to make it static. In the beginning of the 1920s, the Russian mathematician and
physicist Alexander Friedmann NL studied the problem of the dynamics of the universe
using essentially the same assumptions as Einstein, and found in 1922 that
Einstein’s steady state solution was really unstable [4]. Any small
perturbation would make the universe non-static. At first Einstein did not
believe Friedmann’s results and submitted his criticism to
Zeitschrift für Physik, where
Friedmann’s paper had been published first. However, a year
later Einstein found that he had made a mistake and submitted a
new letter to the journal
acknowledging this fact. Even so, Einstein did not like the concept of an expanding
Universe and is said to have found the idea “abominable”. In 1924, Friedmann
presented his full equations , but after he died in 1925 his work
remained essentially
neglected or mostly unknown, even though it had been published in
a prestigious journal. We
have to remember that a true revolution was going on in physics
during these years with
the advent of the new quantum mechanics, and most physicists were
busy with this
process. In 1927, the Belgian priest and
physicist Georges Lemaître working
independently from Friedmann performed similar calculations based on
GR and arrived
at the same results [6]. Very Unfortunately, Lemaître’s
paper was published in a local Belgian
journal and again the results did not spread far, even though Einstein knew of them and
discussed them with Lemaître. In the beginning of the 20th century
it was generally believed that the entire universe only consisted of our
galaxy, the Milky Way. The many nebulae which had been found in the sky were
thought to be merely gas clouds in distant parts of the Milky Way. In1912,
Vesto Slipher [7], while working at the Lowell Observatory, pioneered
measurements of the shifts towards red of the light from the
brightest of these spiral
nebulae. The red shift of an object depends on its velocity radially away from us, and
Slipher found that the nebulae seemed to move faster than the
Milky Way escape
velocity. In the following years, the nature of the spiral nebulae
was intensely debated. Could there be more than one galaxy? This question was
finally settled in the 1920s with
Edwin Hubble as a key figure. Using the new 100-inch telescope at
Mt Wilson, Hubble
was able to resolve individual stars in the Andromeda nebula and
some other spiral
nebulae, discovering that some of these stars were Cepheids,
dimming and brightening
with a regular period [8].
The Cepheids are pulsating giants with a characteristic relation
between luminosity and
the time interval between peaks in brightness, discovered by the
American astronomer
Henrietta Leavitt in 1912. This luminosity-period relation,
calibrated with nearby
Cepheids whose distances are known from parallax measurements,
allows the
determination of a Cepheid’s true luminosity from its time
variation – and hence its
distance (within ~10%) from the inverse square law. Hubble used
Leavitt’s relation to estimate the distance to the spiral nebulae, concluding that
they were much too distant to be part of the Milky Way and hence must be
galaxies of their own. Combining his own measurements and those of other
astronomers he was able to plot the distances to 46 galaxies and found a rough
proportionality of an object’s distance with its red shift. In 1929, he
published what is today known as ‘Hubble’s law’: a galaxy’s distance is
proportional to its radial recession velocity [9]. Even though Hubble’s data were
quite rough and not as precise as the modern ones, the law became generally
accepted, and Einstein had to admit that the universe is indeed expanding. It is
said, that he called the introduction of the cosmological constant his “greatest
mistake” (Eselei in German). From this time on, the
importance of the
cosmological constant faded, although it reappeared from time to
time.4 (17)
It should be noted for the historic records that Lemaître in his
1927 paper correctly
derived the equations for an expanding Universe obtaining a
relation similar to Hubble’s and found essentially the same proportionality
constant (the “Hubble constant”) as Hubble did two years later. After Hubble’s
result had spread, Arthur Eddington had Lemaître’s paper translated into English
in 1931, without the sections about Hubble’s law. In a reply to Eddington, Lemaître [10] also pointed out a logical consequence
of an expanding Universe: The Universe must have existed for a finite time
only, and must have emerged from an initial single quantum (in his words). In this sense,
he paved the way for the concept of the Big Bang (a name
coined much later by Fred Hoyle). It should also be noted that Carl Wirtz in
1924 [11] and Knut Lundmark in 1925 [12] had found that nebulae farther away
recede faster than closer ones.
Hubble’s and others’ results from 1926 to 1934, even though not
very precise, were
encouraging indications of a homogeneous Universe and most
scientists were quick to
accept the notion. The concept of a homogeneous and isotropic universe
is called the
Cosmological Principle. This
goes back to Copernicus, who stated that the Earth is in
no special, favored place in the Universe. In modern language it
is assumed that the
Universe looks the same on cosmological scales to all observers,
independent of their
location and independent of in which direction they look in. The
assumption of the
Cosmological Principle was inherent in the work of Friedmann and
Lemaître but
virtually unknown in large parts of the scientific society. Thanks
to the work of Howard
Robertson in 1935-1936 [13] and Arthur Walker in 1936 [14] it
became well known.
Robertson and Walker constructed the general metric of space time consistent with the
Cosmological Principle and showed that it was not tied
specifically to Einstein’s
equations, as had been assumed by Friedmann and Lemaître. Since
the 1930s, the
evidence for the validity of the Cosmological Principle has grown
stronger and stronger,
and with the 1964 discovery of the CMB radiation by Arno Penzias and Robert Wilson
(Nobel Prize in Physics 1978), the
question was finally settled [15]. The recent
observations of the CMB show that the largest temperature
anisotropies (on the order of
10-3) arise due to the motion of the Milky Way through space. Subtracting this dipole
component, the residual anisotropies are a hundred times smaller.
Einstein’s Equations for a
Homogeneous and Isotropic Universe
In Einstein’s theory [1], gravity was described by the space time
metric guv , where the
indices run over the time and the three space coordinates, and
where the metric varies in
space time. The infinitesimal, invariant, line element dτ is given bydτ2 = gμν (x)dxμ dxν . (1)
There are then ten(10) gravity fields over the four space time
coordinates. However, the
symmetries of the theory stemming from the “Equivalence Principle”
reduce that to two
independent degrees of freedom.
Professor Albert Einstein himself used the mathematical theory of
differential geometry
to find out the relevant tensors
quadratic in space time derivatives of the metric field, the Ricci tensor
particle Rμν and the curvature scalar R, to derive the dynamical equations
for the metric tensor. In the modified form with a cosmological constant Λ, the equations were R μν − Rg μν + Λ gμν = π GT μν…… (2) where G
was Newton
where a(t) is a scale factor and k is a constant
that depends on the curvature of space time. The constant k has been
normalized to the values -1, 0 or 1 describing
either an open, flat or closed type Universe. The
variables r, θ and ϕ are so called co-moving coordinates, in which a typical galaxy had
fixed values. The physical cosmological distance for galaxies separated by r
at a given time t (in the case of k = 0) is a(t)r, which
grows with time as the scale factor a(t) in an rapidly expanding Universe. In order to solve
Einstein’s equations for this metric one also must assume a form for the matter
density. The Cosmological Principle implies that the energy-momentum tensor
particle has a form similar to that of the energy-momentum tensor in
relativistic hydrodynamic, for a totally homogeneous and isotropic fluid with
density ρ and pressure p (which both may depend on time). It is, in
the rest frame of the fluid, a diagonal tensor with the diagonal elements (ρ, p, p, p). If we will insert the metric
above and the energy-momentum tensor into the equations (2) , we get then two independent.
Friedmann equations H 2Ξ(a/a ) 2=8 πGρ/3- k/ a2+ a/3 And ä/a=−
4π G/3( ρ+3 p) + Λ /3……………(4) where a
dot means a time derivative and H is the expansion rate of our Universe,
called the Hubble parameter, or the Hubble
constant, with its present value H0. It is seen to depend on both the energy
density of the universe as well as its curvature and a possible cosmological
constant. When k and Λ set to zero, one defines the
critical density as ρc=3 H2/8 πG………(5) In 1934, Lemaître [16] himself
had already pointed out that the cosmological constant could be considered
as a vacuum energy and hence a contribution to the energy density of the form
ρΛ=Λ/8 π G. We will then assume that the Universe is
composed of a set of components i, each having a fraction, Ωi , of the critical density, Ωi= ρi/ ρc. The two Friedmann equations were not enough
to fully solve for the energy density, the pressure and the scale
factor. We also then needed an equation of state, ρ = f(p), which could usually be
written as wi = pi / ρi. For
example, wi takes the value 0 for normal, non-relativistic, matter and 1/3 for photons. Since we now consider the
cosmological constant as a part of the energy-momentum tensor we can
compare the expression for the energy-momentum tensor for a perfect
fluid in the rest frame, with diagonal elements (ρ, p, p, p), to the cosmological term ρΛ gμν, with diagonal elements ρΛ (1, -1,
-1, -1). We concluded that pΛ = -ρΛ, i.e., = −1 Λ w . The cosmological constant can hence be
seen as a fluid with negative pressure. From Eq. (5), it was clear that a static universe cannot be
stable. Eq. (5) determines the deceleration or acceleration of the
Universe. Since the expansion of the Universe was (wrongly) assumed to
be slowing down (i.e., a negative sign of the acceleration), a parameter
q0, called the deceleration parameter, was defined by
q0=− ä a/ ä2=− ä/ aH0 2……………………..(6)
From Eq:s (4) and (5) it then follows that q0=1/2 ΣiΩi(1+ 3 w i )……………….(6)
When we measured the light coming from a long distant object, we can obtain two pieces
of information apart from the direction to the object. We can measure the red
shift and the apparent luminosity of the object: It is straightforward to
measure the wavelength of light (e.g. from a given atomic spectral line) that a
distant object emits. From Eq. (3) one can easily compute the relation between
the wavelength an object emits, λ1 at time t1
and the wavelength observed here λ0 at time t0 λ0/ λ1= a(t0)/ a(t1)-
This is conventionally
expressed in terms of a red shift parameter z as z= λ0−λ1/ λ1= a(t0 )/ a(t1 )- 1.
For small z, we can then interpret the red shift z was
the radial velocity of the object (it would correspond to a Doppler effect),
and we find again Hubble’s law. For cosmological distances, the interpretation
is less simple. Once we find standard candles luminous enough, however,
measurements of red shift are relatively straightforward.
Measuring a cosmological distance in the universe is not
straightforward. We must use a light signal that is emitted at a certain time
and detected at another. During this time the universe has expanded. There are
different distance measures introduced, but the one used for standard candles, i.e.,
objects with known intrinsic luminosity is the luminosity distance dL,
defined by dL = (L/4πl)1/2 , where L
is the absolute luminosity of the standard candle and l is the apparent luminosity.
Luminosity distance can be computed in terms of the parameters in which we are interested,
and for small z we can expand it as
dL=1/ H0 [ z
+1/2(1−q0)z2)+ ... .] Again, to
be completely clear, dL is not an unambiguous measure of the
distance to the standard candle, but it is a measure sensitive to the
parameters we want to determine. In order to use it we need to know of
celestial objects with known absolute luminosity.
From Eq. , we can see that in the nearby universe, the luminosity
distances scale linearly with red shift, with 1/H0 as the constant of
proportionality. In the more distant Universe, dL depends to
first order on the rate of deceleration, or equivalently on the amount and
types of matter that make up the Universe. The general expression has to be written
in terms of an integral over the redshift” z’ of the propagating photon
as it travels from redshift z to us, at z = 0. In the case that
relates to 2011 Nobel Prize in Physics, we may assume a flat Universe, k = 0
(as indicated to good accuracy by CMB measurements), and since radiation
gives only a tiny contribution today, we may as approximation keep only the
matter contribution ΩM and that
of dark energy ΩΛ. The expression for the luminosity distance then becomes
If we could measure dL accurately for low z as
well as for higher red shifts, we could
both measure the Hubble constant and determine the energy
components of our Universe, in particular the value of ΩΛ [17]. It
may be noted from the expression under the square root in Eq. (8) that when one
measures very high redshift objects, the influence of the cosmological constant
is reduced, and the optimal range is roughly for 0.3 < z < 2.
The Standard Candles in
Astronomy
A well-known class of standard candles, as mentioned above, is the
Cepheid variable
stars, which nowadays can be identified out to distances of about
10 Mpc. To obtain a
record of the expansion history of the Universe, one needs,
however, standard candles
that can be identified over distances at least 100 times larger. Already in 1938, Walter
Baade [18], working closely with Fritz Zwicky at the Mt Wilson Observatory,
suggested that supernovae are promising as distance indicators: they are extremely bright and can, over a few weeks, outshine an
entire galaxy. Therefore, they would be visible over a considerable redshift
interval. The SNe that have been discussed over the past decades as standard
candles [19] are designated type Ia (SNe
Ia
e.g., by Chinese astronomers in 1054 and by Tycho Brahe in 1572. The supernova
1987A (not of type Ia) in the
nearby galaxy the Large Magellanic Cloud, at a distance of160 000 light years,
was observed both in light and in neutrinos (Nobel Prize in Physics 2002). For a review of supernova Ia properties, and their use as
standard candles, see,e.g., the review by David
Branch and Gustav Tammann [21].SNe Ia are identified
through their spectral signatures: The absence of hydrogen features and the
presence of a silicon absorption line. Their spectra and light curves are amazingly
uniform, indicating a common origin and a common intrinsic luminosity. The small deviations from
uniformity can be investigated and corrected. Observations of how the brightness of these SNe varies with red shift,
therefore, allow studies of the expansion history of the Universe. And because – according to theory –the expansion rate is
determined by the energy-momentum density of the Universe andthe curvature of
spacetime, discovery of the ultimate fate of the Universe appearspossible.
Detection of Type Ia
The homogeneity of SNe
Ia
candidates. Because the peak luminosity occurs after only a short
time, a supernova
must be observed early on after the explosion in order to
determine the peak magnitude
with high precision. There is also another catch: SNe Ia
couple of times per millennium in any given galaxy. However, to
get a statistically
significant determination of cosmological parameters, a large
observational sample is needed, including SNe at fairly high red shifts (z
> 0.3).The first systematic search for SNe Ia at high red shifts was
made during the late 1980s by a Danish-British collaboration [22] working at
the 1.5 m Danish telescope at La Silla, Chile. Two years of observations
resulted in the discovery of two distant SNe –one of them of Type Ia USA ,
with the aim of measuring the presumed deceleration of the Universe - using SNe Ia Chile ,
Hawaii and La Palma Australia
experts, backed by the renowned scientist Robert Kirshner – the
High-z Supernova
Search Team (HZT). Over the following years the two collaborations
independently
searched for supernovae, often but not always at the same
telescopes. Like SCP, HZT
could successfully demonstrate the validity of the chosen
strategy, finding batches of
SNe at or close to maximum light that then could be followed up by
spectroscopic
observations.In the beginning of 1998, both groups published scientific papers
and gave talks at conferences, cautiously pointing out that their observations
seemed consistent with a
low matter density Universe.The two breakthrough papers [27, 28] implying that the expansion
of the Universe doesnot slow down but actually accelerates, were submitted for publication
later that year.
The HZT article is based on observations of 16 SNe Ia mainly
analyzed by Adam Riess,
then a postdoctoral researcher at University
of California at Berkeley
paper, with Perlmutter as the driving force, includes 42 Type Ia
SNe.
The fact that both groups independently presented similar - albeit
extraordinary - results
was a crucial aspect for their acceptance within the physics and
astronomy community.
The Observations
The larger the magnitude, the fainter is the object. On the red
shift scale, z = 1
corresponds to a light travel time of almost 8 billion light
years. The data was compared to
a number of cosmological scenarios with and without vacuum energy
(or cosmological
constant). The data at z < 0.1 is from [26]. At redshifts
z > 0.1 (i.e., distances greater
than about a billion light years), the cosmological predictions
started to diverge.
Compared to an unrealistic empty Universe (ΩM = ΩΛ = 0)
with a constant expansion
rate, the SNe for a given high red shift are observed to be about
10 - 15% fainter. If the
Universe were matter dominated (ΩM = 1), the high-z supernovae should
have been
about 25% brighter than what is actually observed. The conclusion
was that the
deceleration parameter q0 is negative, and that the
expansion at the present epoch
unexpectedly accelerates. The result of the analyses of the
twocollaborations, showing that ΩΛ = 0 is excluded with high
significance, and that the expansion
of the Universe accelerates,.
Could the dimness of the distant supernovae be the effect of
intervening dust? Or might
the SNe Ia in the early Universe have had different properties
from the nearby, recent
ones?Such questions have been extensively addressed by both
collaborations, indicating that dust is not a major problem and that the
spectral properties of near and distant SNe arevery similar. Although not as
evident at the time of the discovery, later studies of SNe
beyond z = 1 [29], from the time when the Universe was much
denser and ΩM
dominated, indicate that at that early epoch, gravity did slow
down the expansion as
predicted by cosmological models. Repulsion only set in when the
Universe was about
half its present age.
What is Dark Energy?
The driving force behind the acceleration is however yet unknown,
but the current belief is that the cause of the expansion is vacuum energy (in
this context called dark energy) – as it was suggested by Lemaître
already in 1934 [16]. The SN results emerged at a time when some cosmologists,
for many different reasons, argued that the universe might be
vacuum dominated. Others were, however, reluctant to accept such a
claim implying a
non-zero cosmological constant. The SN observations were the crucial
link in support of
vacuum dominance, directly testing models with Λ > 0. The currently accepted
cosmological standard model – the Concordance Model or the Λ CDM model – includes
both a cosmological constant Λ and Cold
(i.e. non-relativistic) Dark Matter. The SNe
results combined with the CMB data and interpreted in terms of the
Concordance Model
allow a precise determination of ΩM and ΩΛ . The predictions of the Concordance Model agree, within the
experimental uncertainties, with all the presently available data. None of the
alternative models proposed to explain the SN observations, based on
inhomogeneities of the Universe at large scales, extra dimensions or
modifications of general relativity, seem to convincingly account for all observations.
The very successful Standard Model for Particle Physics, which
describes nature at the
smallest scales where we can measure, has two inherent sources for
vacuum energy,
quantum fluctuations and spontaneous symmetry breaking. In
relativistic quantum
physics the vacuum is not empty but filled with quantum
fluctuations, allowed by
Heisenberg’s uncertainty principle (Nobel Prize in Physics 1932).
A naïve estimate of
the size of the vacuum energy density, using the gravity constant G,
Planck’s constant and the velocity
of light, c, would imply a contribution to the energy density ρΛ of the
order of
3
2
~
P
P
l
M c
Λ ρ ,
where MP is the Planck mass (~ 1019 GeV/c2) and lP is
the Planck length (~ 10-33 cm),
i.e., about 10118 GeV/cm3. This is to be compared to the
present-day critical density of ~
0.5·10-5 GeV/cm3. Since the energy density of the Universe
according to measurements
seems very close to critical, the naïve estimate is wrong by 122
orders of magnitude.
Prior to the discovery of the accelerated expansion of the
Universe, particle physicists
believed, that there must be a symmetry principle forbidding a
cosmological constant.
There is, however, another mechanism in the Standard Model that
generates vacuum
energy. In order to explain how the Universe can be so homogeneous
with different
parts that seemingly cannot have been in causal contact with each
other, the idea of an
inflationary phase in the early Universe was put forward [30]. It
states that at a very
early stage, the Universe went through a phase transition,
breaking certain symmetries,
spontaneously generating a time-dependent, huge vacuum energy
density that during a
very short time made the Universe expand enormously. A similar
effect may still be at
work, leading to the vacuum energy that we see today. This
so-called quintessence may
perhaps be detectable, as such a vacuum energy would have a weak
time dependence
(see [31], and references therein).
Other important but yet unanswered questions are why ΩΛ has its measured value – and
why ΩΛ and ΩM at the present epoch in the history of the
Universe are of the same order
of magnitude. At present we have no theoretical understanding of
the value of ΩΛ.
Conclusion
The study of distant supernovae specially Type Ia
References
1]”
Did our universe started in a Big Bang gospel or Just Be?” Authors: Professor
Pranab Kumar Bhattacharya, Mr. Rupak Bhattacharya, Mr. Ritwik Bhattacharya Mrs. Dalia Mukherjee & Miss Upasana
Bhattacharya in the chapter” Fate of a Star” published at www.unipathos.com as E book in July 2004
[2] K. Schwarzschild, “Über das Gravitationsfeld eines
Massenpunktes nach der
Einsteinschen Theorie”, Sitzungsber. Preuss. Akad. Wiss.
Berlin, 1916: 189-196,
(1916),
[3] A. Einstein, “Kosmologische Betrachtungen zur
allgemeinen Relativitätstheorie”,
Sitzungsber. Preuss. Akad. Wiss. Berlin, 1917:
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32] Scientific Background on the Nobel
Prize in Physics 2011THE aCCELERATING UNIVERSEcompiled by the Class for Physics
of the Royal Swedish Academy
http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/advanced-physicsprize2011.pdf
http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/advanced-physicsprize2011.pdf
Links to see the Publication
http://phys.org/news162651549.html at Physics org
http://www.sciencenews.org/view/generic/id/46298 At Science News
Ask a Nobel Laureate on Facebook, David Gross, Nobel Prize in Physics 2004by Nobelprize.org on Monday, May 31, 2010 at 12:21am
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