Download April 15th

Survey of the Universe
Tom Burbine
[email protected]
Next Quiz
• This Wednesday
• Quiz includes material covered up to and
including April 8th
• Cumulative
• You can bring in one 8 ½ by 11 inch piece of
paper with anything written on it
• If you are unhappy with any of your grades:
• You can write a 10 page paper on an astronomical
subject to replace it
• 12 point font
• Times New Roman font
• Double space
• No figures or plots
• Due by May 1st
Type Ia Supernova Lightcurve
Type Ia Supernova are consistent with
coming from exploding white dwarfs
• No signs of hydrogen in their spectra, consistent a
star that have lost their outer atmospheres of
hydrogen in a stellar wind
• Lightcurve matches theoretical predictions of
exploding white dwarfs
• Last Type Ia supernovas that occurred in our
galaxy were observed by Tycho Brahe (1572) and
Johannes Kepler (1604)
Standard Candles
• Type Ia supernovas make excellent standard
candles because they have identical maximum
luminosities
• Their collapse and explosion occur the same way
each time
Products
• Type Ia Supernovas are rich in elements such as
carbon, oxygen, silicon, and iron
• Magnetic fields in the expanding remnant can
accelerate atomic nuclei to speed close to the
speed of light, which are called cosmic rays
Massive Stars
• Greater than 8 Solar Masses
• Begins life on main sequence as Blue Star
• Follows the same path as a low mass star but
everything occurs faster
Fate of Massive Stars
Light Curves of
supernovae of stars
undergoing
core collapse
Dashed red line is
Type Ia supernova
How do you get a
Core-Collapse Supernova?
• A high-mass star keeps on fusing elements into
ones with larger atomic masses
• Is now a Red Supergiant
• Energy keeps on being released since the mass of
the new nucleus is less than the original ones
This stops with Iron
• Fusion of Iron with another element does not
release energy
• Fission of Iron with another element does not
release energy
• So you keep on making Iron
Initially
• Gravity keeps on pulling the core together
• The core keeps on shrinking
• Electron degeneracy keeps the core together for
awhile
Then
• The iron core becomes too massive and collapses
• The iron core becomes neutrons when protons and
electrons fuse together
• Type I are classified based on the lack of
hydrogen lines in their spectra
– Type Ia are due to collapsing white dwarfs
– Type Ib and Ic are due to collapsing cores of stars that
have lost their hydrogen atmospheres
• Type II have hydrogen lines in their spectra
– Due to collapsing cores
Type Ia Supernova
Type II Supernova
http://www.ifa.hawaii.edu/~barnes/ast110_06/tooe/1314a.jpg
Supernova 1987A that exploded
in Large Magellanic Cloud
(a small, nearby galaxy)
168,000 light-years away
Could be seen with naked eye
peak magnitude +2.9
Type II Supernova remnants of different ages
Cassiopeia A
300 years old
Crab Nebula
1,000 years old
Supernova
Several thousand
years old
Type II Supernova explosion
Hypernova explosion Hypothetical supernova explosion of a star so
massive that its core collapses directly into a black hole
Neutron Star
•
•
•
•
Neutron stars are usually ~10 kilometers across
But more massive than the Sun
Made almost entirely of neutrons
Electrons and protons have fused together
How do you make a neutron star?
• Remnant of a Supernova
How do we know there are neutron stars?
• The identification of Pulsars
• Pulsars give out pulses of radio waves at precise
intervals
Pulsars
• Pulsars were found at the center of supernovae
remnants
• Fastest pulsars are called millisecond pulsars
Pulsars
• Pulsars were interpreted as rotating neutron stars
• Only neutron stars could rotate that fast
• Strong magnetic fields can beam radiation out
Conservation of Angular Momentum (M x V x R)
If Radius shrinks, Rotation Velocity must increase
• X-ray pulsars – generate pulses of X-ray radiation
• Magnetars – neutron stars with extremely intense
magnetic fields that generate intense bursts of Xray and gamma-ray radiation
Black Hole
• A black hole is a region where nothing can
escape, even light.
Black Hole
• After a supernova if all the outer mass of the star
is not blown off
• The mass falls back on the neutron star
• The gravity causes the neutron star to keep
contracting
http://www.astronomynotes.com/evolutn/remnants.gif
Event Horizon
• Event Horizon is the boundary between the inside
and outside of the Black Hole
• Within the Event Horizon, the escape velocity is
greater than the speed of light
• Nothing can escape once it enters the Event
Horizon
How do calculate the
radius of the Event Horizon?
•
•
•
•
It is called the Schwarzschild Radius
Radius = 2GM/c2
This is a variation of the escape velocity formula
Escape velocity = square root (2GMplanet/Rplanet)
Black Hole Sizes
• A Black Hole with the mass of the Earth would
have a radius of ~0.009 meters
• A Black Hole with the mass of the Sun would
have a radius of ~3 kilometers
Anything with mass curves space
Can you see a Black Hole?
No
• Black Holes do not emit any light
• So you must see them indirectly
• You need to see the effects of their gravity
Accretion disk – flat disk of gas or other material
held in orbit around a body before it falls onto the body
Evidence
• The white area is
the core of a Galaxy
• Inside the core there
is a brown spiralshaped disk.
• It weighs a hundred
thousand times as
much as our Sun.
http://helios.augustana.edu/~dr/img/ngc4261.jpg
Evidence
• Because it is rotating we can measure its
radii and speed, and hence determine its
mass.
• This object is about as large as our solar
system, but weighs 1,200,000,000 times as
much as our sun.
• Gravity is about one million times as strong
as on the sun.
• Almost certainly this object is a black hole.
• http://documentaryheaven.com/whos-afraid-of-abig-black-hole/
Any Questions?