PLANETARY NEBULA

FORMATION

SARANYA V.S

Department of Space Engineering and Rocketry

STELLAR EVOLUTION- MAIN

STAGES

The Collapse of an Interstellar Cloud

Fragmentation into smaller clumps — Stars

Hydrogen Burning -Main Sequence

Helium Burning - Red Giant

Higher “nuclear” fuels (depending on mass)

Death, depending on mass:

Planetary Nebula — White Dwarf

Supernova — Neutron Star

Supernova — Black Hole

DARK NEBULA

Ninety-nine percent of the material in the Universe

is hydrogen and helium. Some of that is locked up

in stars but the vast portion floats in the spaces that

lay between them.

The distances between stellar bodies is huge, the

density of this material is exceedingly thin. some of

it is shepherded by gravity and exploding stars into

enormous nebulous clouds,

COLLAPSE OF INTERSTELLAR CLOUD

Interstellar Medium Contains Clouds.

T~10-100°K, M~10’s-1000’s of Msun

If gravitational pull exceeds gas (and B) pressure, gas

collapses.

PR

OT

OS

TA

RF

OR

MA

TIO

N

EVOLUTION OF STARS / GROSS

FEATURES:

M < 0.08 Msun – Brown Dwarf (no nuclear

burning)

0.08 Msun < M < 0.5 Msun – Central hydrogen

burning. Formation of a degenerate core. No

helium ignition –End as a He white dwarf

0.5 Msun < M < 2 Msun – Central Hydrogen

burning, Helium flash, Helium burning - End as

CO White dwarf.

2 Msun < M < 8 Msun – Central Hydrogen burning,

Helium ignites non degenerately _ End as CO

White dwarf.

8 Msun < M < 20 Msun – Numerous burning stages

after Helium burning. Type II Supernova - ends as

Neutron Star.

20 Msun < M – As above, but ends as a Black

Hole.

Note: High masses are inaccurately known due to

large wind mass loss during evolution

HYDROGEN BURNING

Brown dwarfs

Sub brown dwarfs

Red dwarfs

Super giants

HELIUM BURNING

Low mass star

becomes white dwarf after about 100 billion years

Mid size star

• red giant branch star (inert He core)

• asymptotic giant branch star (inert C core)

formation of planetary nebulae and further becomes

white or black dwarf.

Massive star

undergo supernova explosion and transforms into

neutron star or black hole

RED GIANT EXPANSION

Asymptotic Giant Branch Stars

& Planetary Nebulae

Once He is exhausted in core, core continues to

contract, He & H burn in shells, envelope

expands.

At some point, envelope becomes unstable, and

starts to pulsates, each time shedding some material.

Envelope ejected at ~ 30 km/s, and core contracts

and cools

Envelope becomes planetary nebula

Core becomes white dwarf

PLANETARY NEBULA During the red giant phase, the outer layers of the

star are expelled via pulsations and strong stellar

winds.

The exposed hot, luminous core emits ultraviolet

radiation that ionizes the ejected outer layers of the

star.

This energized shell of nebulous gas reradiates the

absorbed ultraviolet energy at visible frequencies and

appears as a planetary nebula.

Planetary nebula formation

Ring nebula

Lemon slice nebulaNecklace nebula

Crab nebula

Eskimo nebula

Helix nebula

Formation of helix nebula

Cats eye nebula

Bipolar nebulae

Formation of bipolar nebulae

ADVANCED BURNING IN MASSIVE

STARS

Shells:

SUPERNOVAE

One Iron photodisintegration takes place,

core collapses on time scale of 10’s of ms.

At “Low” masses, Neutron star is formed,

and shock appears.

As long as there is large fluxes of infalling

material, shock cannot “leave” the core.

Once shock does propagates outwards

(perhaps using n heating) it:

Heats the envelope (fast nuclear

processes take place (making Trans-

Iron isotopes).

Accelerates the envelope, and it is

ejected with speeds of order 10,000’s

km/s

Cloud Gravitationally Unstable And Starts

Collapsing. Flow Limited By Formation Of Shock

Waves

LEFT OVERS OF MASSIVE STARS

The remnant left can be

either a Neutron Star:

Or a Black Hole!

Neutron stars are held

by degeneracy pressure

of neutrons (and not

electrons)

sun

Neutron star Black hole

If the collapsing stellar core at the

center of a supernova contains

between about 1.4 and 3 solar

masses, the collapse continues until

electrons, protons neutrons are

expelled, producing a neutron star

If the collapsed stellar core is larger

than three solar masses, it collapses

completely to form a black hole: an

infinitely dense object whose gravity

is so strong that nothing can escape its

immediate proximity, not even light

CONCLUSION

Man’s inquisitiveness to know about the outer space has

led to the discovery of several secrets of space. The

formation, evolution and the death of the stars and

nebulae is discussed in this seminar. This topic has

become an interesting topic of research by the scientists

all over the world and covers a vast area of astronomy.

The outer space is limitless…….

And hence the discussion goes on……

Thank you