Survey of the Universe Tom Burbine [e-mail]

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Survey of the UniverseTom Burbinetburbine_at_mtho
lyoke.edu
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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

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• 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

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Type Ia Supernova Lightcurve
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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

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• Last Type Ia supernovas that occurred in our
  galaxy were observed by Tycho Brahe (1572) and
  Johannes Kepler (1604)

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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

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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

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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

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Fate of Massive Stars
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Light Curves of supernovae of stars undergoing
core collapse
Dashed red line is Type Ia supernova
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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

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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

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Initially

• Gravity keeps on pulling the core together
• The core keeps on shrinking
• Electron degeneracy keeps the core together for
  awhile

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Then

• The iron core becomes too massive and collapses
• The iron core becomes neutrons when protons and
  electrons fuse together

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• 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

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Type Ia Supernova
Type II Supernova
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http//www.ifa.hawaii.edu/barnes/ast110_06/tooe/1
314a.jpg
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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 http//en.wikipedia.o
rg/wiki/FileSN1987a_debris_evolution_animation.gi
f
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Type II Supernova remnants of different ages
Cassiopeia A 300 years old
Crab Nebula 1,000 years old
Supernova Several thousand years old
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Type II Supernova explosion
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Hypernova explosion - Hypothetical supernova
explosion of a star so massive that its core
collapses directly into a black hole
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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

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How do you make a neutron star?

• Remnant of a Supernova

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How do we know there are neutron stars?

• The identification of Pulsars
• Pulsars give out pulses of radio waves at precise
  intervals

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Pulsars

• Pulsars were found at the center of supernovae
  remnants
• Fastest pulsars are called millisecond pulsars

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Pulsars

• Pulsars were interpreted as rotating neutron
  stars
• Only neutron stars could rotate that fast
• Strong magnetic fields can beam radiation out

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Conservation of Angular Momentum (M x V x R) If
Radius shrinks, Rotation Velocity must increase
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• X-ray pulsars generate pulses of X-ray
  radiation
• Magnetars neutron stars with extremely intense
  magnetic fields that generate intense bursts of
  X-ray and gamma-ray radiation

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Black Hole

• A black hole is a region where nothing can
  escape, even light.

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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

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http//www.astronomynotes.com/evolutn/remnants.gif
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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

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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)

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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

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Anything with mass curves space
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Can you see a Black Hole?
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No

• Black Holes do not emit any light
• So you must see them indirectly
• You need to see the effects of their gravity

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Accretion disk flat disk of gas or other
material held in orbit around a body before it
falls onto the body
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Evidence

• The white area is the core of a Galaxy
• Inside the core there is a brown spiral-shaped
  disk.
• It weighs a hundred thousand times as much as our
  Sun.

http//helios.augustana.edu/dr/img/ngc4261.jpg
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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.

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• http//documentaryheaven.com/whos-afraid-of-a-big-
  black-hole/

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Any Questions?