Planetary Nebulae The Ring Nebula Planetary Nebulae discovered by Herschel Planetary Nebulae are Shells that Look Like Rings despite the name they have nothing to do with planets ID: 575787
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Slide1
White Dwarfs Exposed:Planetary Nebulae
Slide2
The ‘Ring’ Nebula Slide3
‘Planetary’ Nebulae discovered by HerschelSlide4
Planetary Nebulae are Shells that Look Like Rings
despite the name, they have
nothing to do with planetsSlide5
Soap BubbleShells Can Also Look
Like Rings
!
note the very
prominent edges
Slide6
Some Examples[thousands are known]Slide7
The Shell is ‘Puffed Off’Gently
In total, a considerable fraction of
the
star’s mass comes off
gently,
at
speeds of perhaps 30 km/
sec.
Only part of the original stellar mass is left behind.
Note that
the material in the nebula
is
raw star stuff
– not the products of the nuclear reactions deep within the core
! It is almost pure H + He.
The
escaping material
eventually
merges into the interstellar
medium, and is available to
be used in other stars that may
form later. Slide8
This Process Leaves BehindIncandescently Hot Dense CoresSlide9
The Cores…These intensely hot, luminous cores are new
white
dwarf
stars
that will
never
succumb to gravity
.
Thanks to their extreme heat, they emit an enormous amount of
ultraviolet light
. That energetic radiation causes the gas in the planetary nebula to glow by
fluorescence,
like a celestial
neon lamp.
The nebula disappears after some tens of thousands of years as (
i
) the gas dissipates and (ii) the central star cools down and becomes fainter.Slide10
Some Real Examples Slide11
Found EverywhereCold carbon clinkers – ‘diamonds in the sky’
[although not like any diamond you ever encountered!
– a million times the density of water, held up by electron
degeneracy – but nevertheless full of Carbon nuclei]
There are literally
tens of millions
of such stars in our galaxy.Slide12
“Like a Diamond…” (sort of!) Slide13
White Dwarfs in Plenty!Here, in the core of the globular cluster M4Slide14
The ‘Cooling Track’The prominent sequence to the right is the main sequence. All the brighter hotter stars (to the upper left) have evolved away; the bright red giants lie to the upper right of this figure, off the plot. The star shown in yellow has been there for billions of years, essentially unchanging.
The
red
spot to the left is a
recently-formed white dwarf
– still relatively hot and bright.
It will
cool off and get fainter,
moving down along the
cooling
track.
Many other white dwarfshave already done so.Slide15
The Sun’s Life In Summary