PCS 581 Lecture Notes - Lecture 5: Mount Everest, Atomic Nucleus, Accretion Disk
Lecture 5: Massive Star Remnants
Supernovae: What’s left behind
One teaspoon of Neutron Star stuff weighs as much as a mountain
What holds this up? Can’t be electron degeneracy pressure – neutron degeneracy
pressure
Could be worse…
If the core remnant was bigger than ~ 3 Sun masses, it will have more gravity than
neutron degeneracy pressure can hold back
It will collapse and collapse…. And create a black hole
Evidence: How do we know?
Older stars should contain less heavy elements than stars born recently
oConfirmed: 0,1% vs. 2-3% by mass
Can also look at the elemental abundances in the cosmos
How do we know all of this is accurate? We have seen supernova goes off and we can
prove our theory in science
Older stars contain less heavy elements because born closer to the big bang than star
composition is pure hydrogen – older star have less heavy elements
And we can use that to see how old they are by looking at the elemental abundance
Universe is still 92% H and He
Universe started off with H and He so the older stars will mostly contain H and He –
therefore modern stars will be born with more rich elements
H and He main elements of the Universe
Odd elements are rare and elements 10
Massive stars tend to make even elements so therefore less odd elements
Can even look at odd elements
Evidence: Observed Supernovae
Crab Nebula went off in A.D. 1100
oChinese records
Others: 1006, 1054, 1572. 1604
oThe first examples of imperfect, changing “heavens”
Earliest record me have of the Crab Nebula – beautiful and huge – and we know it went
off 1000 years ago
Chinese records – they’re talking about a guest star – supernova in this cause – we know
exactly when this happened thanks to their record
We have the exact day due to the records from 1000 years ago
1572 and 1602** - the fact that they observed was important because at the time
people thought the night sky did not change
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Supernovae in Other Galaxies
None in our galaxy since 1604
oBig stars are rare, death is fast, MW is obscured
2 every hundred years in other galaxies
Nearest: Supernova 1987A, in the Large Magellanic Cloud
oExploded 150,000 years ago
One about every 50 years
We have never seen a milky way supernova since 1604 – probably did happen but we
just didn’t see them - We are definitely due
Recent one was the one is magellanic cloud, in neighbouring– only visible in Southern
Hemisphere
Every telescope in the world turned to look at that
Exploded 150 000 years ago but we are just seeing it in 1987
Went off before human civilizations
After that we made a lot of observations
We are very much looking forward to the next and learn a lot more from it
10 billion stars in the Magellanic cloud
Supernova Remnant
By: Chandra X-Ray Observatory
Colours are x-ray bands
Neutron star: the hot white dot
Not visible light - X-ray photo
Very Hot gas surrounding the neutron star
X-ray observes the very hot things
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Black dwarfs put out a lot of x-ray than stars, WD much more very hot so a lot of x-ray
What’s Left Behind
Mass of 1.4-3 MSun, only 20-100 km across
Supported by neutron degeneracy pressure
As dense as an atomic nucleus
One teaspoon of Neutron Star stuff weighs as much as a mountain
Temperature 10 million K
Bigger than a white dwarf
Below 3SM but above 1.3 SM
Supported by neutron degeneracy pressure since nothing is in it – as a result - in a
neutron star it will be very dense – one giant city size atomic nucleus (element zero is
neutron (no protons) and a very heavy element)
One teaspoon of neutron star weighs as much as a mountain
Temperature very high 10 million degree – hard for x-ray to come off
Neutron Star Gravity
If you weigh 140lbs on Earth, you weigh 23lbs on the Moon, 53lbs on Mars, 331lbs “on”
Jupiter… and 19600000000000lbs on a Neutron Star
You would crush yourself into a layer of subatomic particles
Land on neutron star would be very difficult: 1. very heavy 2. you could never get there
Moon astronauts can bounce around because you weigh only 23 pounds
Your weight depends on what you land on
You Are very heavy in a neutron star
If land you wouldn’t be able to hold your weight
Crush to death with only one hair on your head
You will be crushed into a layer of subatomic particle – you won’t be atoms anymore
just protons
You will be thinner than paint – you’ll be dead
Gravity depends on the mass of the object and the size – very concentrated gravity –
may bigger and weighs more and the fact that it is
The Visiting Paperclip
A paperclip made of neutron star stuff weighs as much as Mount Everest
Bring it to Earth, it would fall through the planet like falling through air, pass out the
other side, return
Earth would “look briefly like Swiss cheese”
That material has been removed from the gravity of the Neutron star
It’s under enormous internal pressure… it’ll explode
Even worse, the half-life of neutrons is 10 min
Within a short while, they’ll decay, releasing as much energy as a trillion-megaton
nuclear bomb
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find more resources at oneclass.com
Document Summary
Can"t be electron degeneracy pressure neutron degeneracy pressure. If the core remnant was bigger than ~ 3 sun masses, it will have more gravity than neutron degeneracy pressure can hold back. Older stars should contain less heavy elements than stars born recently: confirmed: 0,1% vs. 2-3% by mass. Can also look at the elemental abundances in the cosmos. We have seen supernova goes off and we can prove our theory in science. Older stars contain less heavy elements because born closer to the big bang than star composition is pure hydrogen older star have less heavy elements. And we can use that to see how old they are by looking at the elemental abundance. Universe is still 92% h and he. Universe started off with h and he so the older stars will mostly contain h and he therefore modern stars will be born with more rich elements. H and he main elements of the universe.
