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Peter Watson, Dept. of Physics
Beeps, Flashes, Bangs and Bursts.
Peter Watson
and Chirps.
Big stars work much faster:
Live fast, Die Young!
100,000 1,000,000 100,000100,000
3 hours!
Forever
Peter Watson
•Vast majority of stars are boring: “main-sequence” (aka middle-class) changing very slowly.
•Some oscillate: e.g Cepheids
•Large bright stars change by factor 3 in brightness
Peter Watson
Change colour, size, brightness
Peter Watson
•well understood: work by blocking mechanism
•very important since period is proportional to intrinsic brightness:
•i.e. measure the apparent brightness, the period tells you the actual brightness, so you know how far away it is
Peter Watson
• we get supernovae
• 6 visible in Milky Way over last 1000 years
• SN 1006: Brightest Supernova.
• Can see remnants of the expanding shockwave
If Stars are large....
Frank Winkler (Middlebury College) et al., AURA, NOAO, NSF
Peter Watson
Remnant of a very old SN
• Part of the veil nebula in Cygnus
Sara Wager
Peter Watson
Tycho’s Supernova in X-rays
(1572)
NASA / CXC / F.J. Lu (Chinese Academy of Sciences) et al.
Peter Watson
The Crab (M1)
PW
•Recorded by Chinese astronomers
"I humbly observe that a guest star has appeared; above the star there is a feeble yellow glimmer. If one examines the divination regarding the Emperor, the interpretation [of the presence of this guest star] is the following: The fact that the star has not overrun Bi and that its brightness must represent a person of great value. I demand that the Office of Historiography is informed of this."
Peter Watson
1054: Crab• X-rays (in blue)
• + Optical
• Tangled appearance due to trapped magnetic field
Peter Watson
•Recorded by Chinese astronomers as “guest star”
•May have been recorded by Chaco Indians in New Mexico
Moon
Crab
4 a.m. Tuesday 7th May 1054Would have been as bright as the
New moon
Peter Watson
•Large star runs out of fuel
•Collapses and heats up
•Outer part explodes out,
•Core gets compressed to neutron star or black hole
What happens to a star when it goes supernova?
Peter Watson
•Shock wave blows off outer layer of star at 1/10 speed of light
Peter Watson
•Most recent close one was SN1987a
•Must have blown up earlier, leaving ring of material, now illuminated by new shock wave
Peter Watson
Surprisingly…• Most (98%) of the
energy doesn’t come out as light…
• It’s neutrinos
• As the matter falls in, the nu’s stream out!
Image credit: TeraScale Supernova Initiative.
Peter Watson
Which we can see here…
Peter Watson
•We would like to catch supernovae before they explode: here are 3 possibilities
Eta Carinae blew off a lot of material 150 years ago: probably
pre-collapse now
Credit: J. Morse (U. Colorado), K. Davidson (U. Minnesota) et al., WFPC2, HST, NASA
Peter Watson
•The Crescent Nebula is a shell of gas surrounding a very hot and unstable central star WR 136
• Should undergo a supernova explosion in next million years.
Peter Watson
•NGC 3603: can see formation of stars
•contains Sher 25 surrounded by rings: proably pre-collapse
Peter Watson
•Nova: stars that repeatedly have minor explosions
•Always a close binary •material flows from one star to companion •triggers explosion
Peter Watson
Might look like this
Mark A. Garlick (Space-art.co.uk)
Peter Watson
•V838 Monocerotis: Not a nova, since star did not lose material, instead went to M~ -7 (brightest star in galaxy) by expanding and cooling very fast
•lit up dust from previous explosions
Peter Watson
•Large star runs out of fuel
•Collapses and heats up
•Outer part explodes out,
•Core gets compressed to neutron star or black hole
What happens to a star after it goes supernova?
Peter Watson
• Pulsars
• accidentally observed (1968) by Jocelyn Bell etc.
• Very regular radio pulses
• period of 2 ms up to 4 s
• Note that height of pulse is very irregular
Peter Watson
Best known is Crab.
Known to be supernova
remnant from in 1054
Pulsar at centre has period of
~1/30 s
Peter Watson
And you can even listen to them
• This is Vela
• And this is PSR 0329+54
Period of Crab measured to be 0.03308471603 s (i.e. stable to 1 part in billion)
Peter Watson
Magnetars: Vicki Kaspi McGill
• Magnetic field is ~ 1 billion x strength of MRI magnet
Peter Watson
•This shows how the X-ray pulses move through the nebula
Peter Watson
•Double Pulsar
Peter Watson
What pulses?• Now known to be neutron star: predicted by
Oppenheimer (yes, that one) in 1935.
• Density ~ atomic nucleus: dime would weigh 2000,000,000 tons!
Peter Watson
•Charged particles travel along magnetic field,
• can only escape from poles of neutron star.
•Hence "lighthouse"mechanism: we only “see” pulsar when mag. pole points towards us
Peter Watson
• No, because they would have to be oriented so that they point towards us
• Neutron Star forms from supernova, Period ~1/1000 s
• spins down
• magnetic field will weaken
• Disappear after 100,000 years
Do we see all the pulsars?
Peter Watson
This is how the Fermi satellite sees the sky, in gamma-rays
Peter Watson
Gamma-rays have huge energies
• Crab?
• OK: old supernova
• Vela?
• OK: old supernova
• Geminga?
• Huh? Second brightest object in γ-rays, almost invisible as a ordinary star
• Turns out to be very old neutron star
Geminga
Crab
Peter Watson
SS433• And some things are just weird!
• A cosmic lawn sprinkler
• jets come out at 1/5 of speed of light, but are made of cold hydrogen gas!
KIC 8462852 or WTF star ("Where's The Flux?")
• Produces 20% change in output over a matter of a few days
Why?
• Huge planet?
• Alien megastructures?
• Black Hole?
• Dark Star?
• Huge cloud of comets?
Alien megastructures
Peter Watson
A Jupiter-sized planet would cause a 1% drop in light on a regular basis
Comets?
But it’s also been dimming slowly anyway
Peter Watson
Black Holes• Invented by .....?
• Einstein!!!!!!!!!
Einstein was right: Astronomers confirm key theory on black holes
Historic First Images of a Black Hole Show Einstein Was Right (Again)
Daily Express
Space.com
PW
Unfortunately Einstein predicted black holes did not exist!
PW
The essential result of this investigation is a clear understanding as to why the "Schwarzschild singularities" do not exist in physical reality. …………… The "Schwarzschild singularity" does not appear for the reason that matter cannot be concentrated arbitrarily. And this is due to the fact that otherwise the constituting particles would reach the velocity of light.
Peter Watson
Black Holes• Invented by .....?
• Einstein
• Hawking!!!!!!!!!!!
• Well, actually he didn’t: first paper he wrote was in 1971 (and first interesting paper was 1974!)
Peter Watson
Black Holes• Invented by .....?
• Einstein
• Hawking
• John Wheeler
Wheeler first used the term in a talk he gave in 1967. He understood that in
reality they would be small and dense, with the implication that they might be
observable.
Peter Watson
Black Holes• Invented by .....?
• Einstein
• Hawking
• John Wheeler
• Karl Schwarzchild?
No, but he was the first person to solve Einstein’s equations for one
Peter Watson
Black Holes
• Invented by .....?
• Einstein
• Hawking?
• John Wheeler?
• Karl Schwarzchild?
• Well, actually, John Michell, rector of Thornhill Church in Yorkshire
• geologist?philosopher? astronomer? Seismologist?
• Polymath.
• presented his ideas on “dark stars” to the Royal Society in London in 1783.
Peter Watson
•A particle will escape from the earth if it has positive energy
•At the earth's surface, “escape velocity” is 11 km/s
Peter Watson
•However we can interpret this differently: what radius would the earth have for a given escape velocity?
•In particular, if the escape velocity is the speed of light c, nothing can escape.
•If the earth was 8 mm in radius, it would be a Black hole
•This is the Schwarzchild radius: roughly the black hole radius
Peter Watson
So planets are actually moving in "straight" lines in a curved space...
• "Lenses extend unwish through curving wherewhon till unwish returns on its unself" e.e.cummings
So what is a black hole like?• It warps space (and time) round it
Peter Watson
• What is a straight line?
Did you think a laser beam was straight?
Peter Watson
•One way to see a black hole: it’s black!
•If we are really lucky....(or unlucky) as a gap in the sky
Too Close to a Black Hole Credit & Copyright: Robert Nemiroff (MTU)<
Peter Watson
•Stuff falling in will become very hot and produce X-rays
•So want binary star, one invisible but heavy, producing lots of X-rays
First candidate is Cygnus X-1
Mass of primary star ~20Mo
Mass of invisible object M~9Mo
Power output in X-rays is 10,000 x total power output by sun!
PW
Note Stephen Hawking’s main claim to fame
• He bet Kip Thorne a year’s subscription to Penthouse that Cyg X-1 was NOT a BH Supernova-
Black Hole formation animation from Chandra
Why Einstein was wrong: BH’s are formed explosively
Peter Watson
•Then moving BH’s will produce a wave in space
•
Peter Watson
•Black Hole merger: The Caltech/Cornell SXS Collaboration
Peter Watson
•and these will radiate gravitational waves
Peter Watson
•And this is maybe where it is happening now:
•Two galaxies have collided and the black holes seem to be coalescing
3C75 X-rays from Chandra
U of R
One of the first attempts
• Giorgio Pappini at University of Regina
• Build cold quartz-crystal detector
Peter Watson
•Which we might be able to pick up on earth as gravitational waves
•This is LIGO: twin detectors in Louisiana and Washington
Peter Watson Peter Watson
Peter Watson
and they found a second one!
• Which you can listen to!
Peter Watson
Rainer Weiss Barry BarishKip Thorne
2017
Nobel Prize in Physics
Peter Watson
Found accidentally by Vela satellite (designed to look for γ's from nuclear explosions).
Gamma-ray bursters
Peter Watson
•Vary short (often less than 1/100 s!) intense bursts of γ-rays.
•Don’t repeat, don’t come from any known object
Seem to be massive explosions
in very distant galaxies
PW
• Common (about 1/week)
• Extremely energetic (energy ~ all stars in known universe concentrated into few seconds)
• No two the same!
PW
Scattered all over the sky
If they were local they would map out the Milky Way
Wikipedia
All the Gold you dreamed of….
But where did it c
ome
from????
????
PW
A long story……
PW
Mostly science has no dramatic moments: e.g. DNA
• isolated (Friderich Miescher) ~1885
• nucleotides identified Phoebus Levene ~ 1919
• "giant hereditary molecule" (Koltsov) ~ 1927
• Genetic material in T2 Phage (Hershey) ~1953
• X-ray diffraction show helix (Wilkins & Franklin) ~ 1953
PW
• DNA is two interlocked coils of amino-acids
====> Central Dogma: Watson & Crick 1953
Peter Watson
•Lived in Pisa
GALILEO (1564-1642)
Peter Watson
• Exploited (but didn’t invent) telescope
Peter Watson
• Moons of Jupiter: Jan 7/8th 1608
PW
Galileo shows BOTH Prolemy and Copernicus are • The earth is not the centre of the universe,
but more things than the sun can be the centre of orbits
• Need Newton to understand this
Peter Watson
This is his original notebook
Where does everything come from?
PW
To make heavy nuclei, just add protons & neutrons
PW
To start with, fusing light nuclei to make heavier nuclei GIVES us energy
• But after Iron, we need to add energy to create new nuclei
Peter Watson
•Type 1a Supernova
•Very rare (1/galaxy/century), very bright and they are all the same
•This is one in Centaurus A
Long straight bit of light curve is decay
of Co56 to Iron
Created in Big BangSmall Stars
Large stars & supernova
????????????????????????????
Where does everything come from? Cassiopeia A Supernova remnant from about 350 years ago
silicon red, sulphur yellowcalcium green iron purpleX-rays blue
Image Credit: NASA, CXC, SAO
neutron star
PW
Confused? An executive summary
• We don’t know where the heavy elements come from
• We don’t know what gamma-ray bursters (GRB’s) are
• We don’t know if gravitational waves travel at the speed of light
• We’ve never seen two stars collide!
PW
August 17, 2017, 12∶41:04 UTC• Gravitational Wave Signal seen
It all comes
together!
PW
1.7 s later,
Gamma-ray pulse
PW
Where is it?
Email your friends…
GW+EM Observatories MapApproximately 70 light-based observatories that detected the gravitational-wave event called GW170817. PW
Dark-Energy Camera in Chile finds it first!
NGC 4993: The Galactic Home of an Historic Explosion
Image Credit: NASA & ESA
In Hydra
PW
And that’s how the gold in your wedding ring was made!
Jastrow, Wikimedia
Approximately 10 Earth Masses of Gold and Platinum!
~10,000,000,000,000,000, 000,000,000 tonnes
Wedding ring, Byzantium, 7th c. AD, nielloed gold
NASA
What it looked like..
So in one day… 6000 people round the world
• Verified Einstein (gravitational waves exist and travel at the speed of light)
• Explained GRB’s as colliding neutron stars
• Observed a “kilonova” for the first time
• Showed us how elements are made
• A good day for al
l of us!