3. STAR FORMATION
• Star formation is the process by which dense regions within
molecular clouds in interstellar space, sometimes referred to as
"stellar nurseries" or "star-forming regions", collapse and form
stars.
• These stellar nurseries or the star-forming regions are inside a
dust cloud termed as Nebula.
5. NEBULA
• A nebula, which means “cloud” or “mist” in Latin, is an interstellar cloud of
dust, hydrogen, helium and other ionized gases.
• Originally, the term was used to describe any diffuse astronomical object,
including galaxies beyond the Milky Way. The Andromeda Galaxy, for
instance, was once referred to as the Andromeda Nebula (and spiral galaxies
in general as "spiral nebulae") before the true nature of galaxies was
confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and
others.
• Although denser than the space surrounding them, most nebulae are far less
dense than any vacuum created on Earth – a nebular cloud the size of the
Earth would have a total mass of only a few kilograms.
6.
7. TYPES OF NEBULA
Nebula are classified into 4 major groups:
• Planetary Nebula
• Supernova Remnant
• H II regions, large diffused nebula containing ionised hydrogen.
• Dark Nebula
9. TYPES OF NEBULA
Nebula are classified into 4 major groups:
• Planetary Nebula
• Supernova Remnant
• H II regions, large diffused nebula containing ionised hydrogen.
• Dark Nebula
12. TYPES OF NEBULA
Nebula are classified into 4 major groups:
• Planetary Nebula
• Supernova Remnant
• H II regions, large diffused nebula containing ionised hydrogen.
• Dark Nebula
13. DIFFUSE NEBULA
• Most nebulae can be described as diffuse nebulae, which means
that they are extended and contain no well-defined boundaries.
• Diffuse nebula can be further classified into 3 sub groups, as in:
A.Emission Nebula
B.Reflection Nebula
C.Dark Nebula
• Emission Nebula is the one that emits spectral line radiation from
excited or ionised gas, mainly ionised hydrogen, they are often
called H II regions.
15. STAR FORMATION
• Stars form inside relatively dense concentrations of interstellar gas and dust
known as molecular clouds. These regions are extremely cold (temperature
about 10 to 20K, just above absolute zero). At these temperatures, gases
become molecular meaning that atoms bind together.
• CO and H2 are the most common molecules in interstellar gas clouds.
• The deep cold also causes the gas to clump to high densities. When the
density reaches a certain point, stars form.
16. • Star formation begins when the denser parts of the cloud core collapse under
their own weight/gravity.
• These cores typically have masses around 104 solar masses in the form of
gas and dust. The cores are denser than the outer cloud, so they collapse first.
• As the cores collapse they fragment into clumps around 0.1 parsecs in size and
10 to 50 solar masses in mass.
• These clumps then form into protostars and the whole process takes about 10
millions years.
STAR FORMATION
23. T-TAURI STAR
• The T-Tauri phase is when a star has:
vigorous surface activity (flares, eruptions)
strong stellar winds
variable and irregular light curves.
• A typical T-Tauri star can lose upto 50% of its mass before settling
as a main sequence star. Hence, it’s also called pre-main sequence
star.
30. WHY DO STARS DIE?
• Stars die because they end their nuclear fuel.
• The events at the end of a star’s life depend on its mass.
31. WAYS IN WHICH A STAR CAN
DIE
•MASSIVE STAR
•AVERAGE STAR
•TINIEST STAR
32. Really massive stars use up their hydrogen fuel quickly ,but are hot enough to
fuse heavier elements such as helium and carbon. Once their is no fuel left, the
star collapses and the outer layers explode as a 'supernova'. What's left over
after a supernova explosion is a ‘neutron star' - the collapsed core of the star -
or, if there's sufficient mass , a black hole.
MASSIV
E STAR
Average - sized stars will die less dramatically. As their hydrogen is used up,
they swell to become red giants , fusing helium in their cores , before shedding
their outer layers , often forming a 'planetary nebula'. The star's core remains
as a 'white dwarf' , which cools off over billions of years.
AVERAG
E STAR
The tiniest stars , known as 'red dwarfs', burn their nuclear fuel so slowly
that they might live to be 100 billion years old - much older than the current
age of the universe.
TINIEST
STAR
36. SUPERNOVA
• A supernova happens where there is a change in the core, or centre of a star. A
change can occur in two different ways, with both resulting in a supernova.
• The first type of supernova happens in binary star systems. Binary stars are two stars
that orbit the same point. One of the stars, a carbon-oxygen white dwarf, steals matter
from its companion star. Eventually, the white dwarf accumulates too much matter.
Having too much matter causes the star to explode, resulting in a supernova.
• The second type of supernova occurs at the end of a single star’s lifetime. As the star
runs out of nuclear fuel, some of its mass flows into its core. Eventually, the core is so
heavy that it cannot withstand its own gravitational force. The core collapses,
which results in the giant explosion of a supernova. The sun is a single star, but it
does not have enough mass to become a supernova.
39. RED GIANT
• Red giants are stars that have exhausted the supply of hydrogen in their cores and
have begun thermonuclear fusion of hydrogen in a shell surrounding the core.
They have radii tens to hundreds of times larger than that of the Sun. However, their
outer envelope is lower in temperature, giving them a reddish-orange hue.
• A red giant star is a dying star in the last stages of stellar evolution. In only a few
billion years, our own sun will turn into a red giant star, expand and engulf the
inner planets, possibly even Earth.
• The outer layers of the star starts to grow, cool and turn red again as it enters its
second red giant phase. Small sun-like stars move into a planetary nebula phase,
whilst stars greater than about 8 times the mass of the Sun are likely to end their
days as a supernova.
40.
41. HOW LONG DO STARS LIVE?
• A star’s life expectancy depends on its mass.
• Generally, the more massive the star, the faster it burns up its fuel
supply, and the shorter its life. The most massive stars can burn out and
explode in a supernova after only a few million years of fusion.
• A star with a mass like the Sun, on the other hand, can continue fusing
hydrogen for about 10 billion years.
• And if the star is very small, with a mass only a tenth that of the Sun, it
can keep fusing hydrogen for up to a trillion years, longer than the
current age of the universe.
42. STARS EXPLODE!
•Mild Explosions:
A.Planetary Nebula.
B.Ejection of outer layers of a red giant.
•Strong Explosions:
A.Nova
B.Eruptions in binary systems.
•Catastrophic Explosions:
A.Supernova.
B.Blasting away of the outer parts of a star.
46. WHITE DWARF
• A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed
mostly of electron-degenerate matter.
• A white dwarf is very dense: its mass is comparable to that of the Sun, while its volume
is comparable to that of Earth.
• Very low mass stars cannot fuse helium and so leave behind their helium cores.
• Intermediate mass stars may progress beyond carbon burning but not all the way to iron
– they leave can leave cores of oxygen or heavier elements.
• The material in a white dwarf no longer undergoes fusion reactions, so the star has no
source of energy. As a result, it cannot support itself by the heat generated by fusion
against gravitational collapse, but is supported only by electron degeneracy pressure,
causing it to be extremely dense.
47.
48.
49. THE CHANDRASHEKHAR
LIMIT
• For masses larger than 1.4 Msun, electron degeneracy pressure
cannot support the mass because electrons would have to move
faster than the speed of light.
• Therefore it was predicted that white dwarfs with masses larger
than this limit cannot exist.
50. LIFETIME OF A WHITE
DWARF
• The length of time it takes for a white dwarf to reach this state is
calculated to be longer than the current age of the universe
(approximately 13.8 billion years), it is thought that no black dwarfs
yet exist.
• The oldest white dwarfs still radiate at temperatures of a few
thousand kelvins.
51. SOME FACTS ABOUT WHITE
DWARF
• They can go supernova .
• Their gravity is 350,000 times that of earth.
• Many will become black dwarfs.
• A teaspoon of white dwarf matter weighs 5.5 tons.
• They have radius that’s typically around 100 times smaller around
smaller that our earth but have the mass.
• About 97% of all milky way stars will become white dwarfs.
• Almost all white dwarf star have a same mass.
• White dwarf star have atmosphere.
52. SIRIUS-B
• The first white dwarf ever observed is called "Sirius B"
and was discovered by Alvan Clark (a telescope maker)
in 1862.
55. NEUTRON STAR
• A neutron star is the collapsed core of a giant star which before
collapse had a total mass of between 10 to 29 solar masses.
• Discovered in 1967 by Jocelyn Bell and Antony Hewish by regular
radio pulses from PSR B1919+21
• Mass : 1.4 times mass of sun
• Density: 10^17 kg/m^3
• Temperature: 600000 kelvin
56.
57. FORMATION OF A NEUTRON
STAR
• Neutron stars are created when giant stars die in supernova and
their cores collapse, with protons and electrons essentially melting
into each other to form neutrons.
• Neutron stars are city-size stellar objects with a mass about 1.4
times that of the sun.
58. HOW DANGEROUS IS A NEUTRON
STAR?
• It is dangerous because of their strong fields. If a neutron star
enters our solar system , it could cause chaos , throwing off the
orbits of the planets and if it got closed enough , even raising tides
that would rip the planet apart. But the closest known neutron star
is about 500 light-years away.
63. PULSAR- A FLASHING NEUTRON
STAR
• Pulsar are spinning neutron star that emits a narrow radiation
beam . the beam is offset from pulsar’s spin axis , sweeping across
space like a lighthouse.
• As the pulsar rotates , the beam may sweep across the earth,
appearing to astronomers as a flashing object. If the beam does not
point in the direction of earth, it cannot be seen.
• All pulsars are neutron stars , but not all neutron stars are pulsars
66. MAGNETAR- A MAGNETIC
MONSTER
• A magnetar is a type of neutron star with an extremely powerful
magnetic field. The magnetic field decay powers the emission of
high-energy electromagnetic radiation, particularly X-rays and
gamma rays.
• Starquakes caused by fracturing of the magnetar’s surface can
cause huge radiation bursts to be released , which are powerful
enough to be detected on earth , tens of thousands of light years
away.
68. SOME FACTS ABOUT NEUTRON
STAR
• In just the first few seconds after a star begins its transformation into a
neutron star, the energy leaving in neutrinos is equal to the total amount of
light emitted by all of the stars in absolute universe.
• Its been speculated that if there were life on neutrinos stars , it would be 2
dimensional.
• The fastest known spinning neutron star rotates about 700 times each
second.
• The wrong kind of neutron star would wreak havoc on earth.
• Despites the extremes of neutron stars , researchers still have ways to
study them.
69. DEATH OF A NEUTRON STAR
Neutron star dies when pressure on its core become so
great that the quarks collapse and lose their angular
momentum. They turn in cluster singularities orbited by
strings of energy as forming dark matter or black hole.
72. WHAT IS A BLACK HOLE?
• Everyone always talks about black holes and how things go in and never come
out .But what is black hole exactly? Black holes are extremely massive objects
with immense gravity that don’t allow anything to escape, not even light.
• The strong gravity occurs because matter has been pressed into a tiny space.
This compression can take place at the end of a star’s life. Black holes are a
result of dying stars.
• Because no light can escape, black holes are invisible. However, space
telescope with special instruments can help find black holes.
• They can observe the behaviour of material and stars that are very close to
black holes.
73.
74. DISCOVERY OF A BLACK
HOLE
• The first time the idea of a black hole
was suggested was in the late 1790’s
by John Michell of England and
Pierre-Simon Lapace of France.
• They both proposed the idea of the
existence of an “ invisible star” by
applying the first Newton Law. They
calculate its mass and size, which is
now called the “ event horizon” that an
object would need in order to be faster
than even the speed of light.
75.
76. TYPES OF BLACK HOLES
There are three types of Black Holes:
1. Primordial
2. Stellar
3. Supermassive
77. FORMATION OF BLACK
HOLES
• Primordial black holes are thought to have formed in the early
universe, soon after the big bang.
• Stellar black holes form when the centre of a very massive star
collapses in upon itself. This collapse also causes a supernova,
or an exploding star, that blasts part of the star into space.
• Scientists think supermassive black holes formed at the sae
time as the galaxy they are in. The size of the supermassive
black hole is related to the size and mass of the galaxy it is in.
79. • There are two basic parts to a black hole:
A. The singularity.
B. Event Horizon.
• The event horizon is the “point of no return” around the black hole. It is not a physical
surface, but a sphere surrounding the black hole that marks where the escape velocity
is equal to the speed of light. Its radius is the Schwarzschild radius mentioned
earlier.
• This point is called the singularity. It is vanishingly small, so it has essentially an
infinite density. It’s likely that the laws of physics break down at the singularity. Scientists
are actively engaged in research to better understand what happens at these
singularities, as well as how to develop a full theory that better describes what happens
at the centre of a black hole.
STRUCTURE OF A BLACK
HOLE
80.
81. DEATH OF A BLACK HOLE
• Yes, black holes do die, and they do so when the theories of the
extremely large come together with the theories of the very small.
• They do so slowly , and then all at once.
82. • Framed English physicist Stephen Hawking theorised that
something different happens around a black hole. The idea is that
particles and antiparticles may not be able to automatically cancel
each other out because the black hole’s gravity pulls the negative
antiparticle into black hole-oblivion.
• This process leaves the positive particle then, are emitted from the
black hole. The phenomenon is called Hawking Radiation.
DEATH OF A BLACK HOLE
83.
84. • But that’s not the end. After a long time, the black hole would lose
mass due to gradual addition of antiparticles. As Hawking says, the
black holes would evaporate. During evaporation, the black hole emits
energy in the form of the positive particles that escape.
• The more massive the black hole, the more energy would be released.
Over time, the black hole would eventually lose so much mass that it
would become small and unstable. This is the dramatic end. The black
hole would then lose the rest of its mass in a short amount of time as
abrupt explosions as gamma rays bursts. The end.
DEATH OF A BLACK HOLE
