“ dead ” stars

Charles HakesFort Lewis College 1


“Dead” Stars


Outline

• Test 3 Friday• Lab Notes• Dead (?) Stars• Review (?)


Test 3

• Review Spectroscopy (Wein, Stefan) and Doppler Shift

• The Sun (structure, fusion)• Magnitude• Parallax• Interstellar Medium• Stellar Evolution• Dead Stars


Lab Notes

• Constellation presentation this week• Telescope lab• Star identification lab?• Observatory Field Trip?• Parallax


More Precisely 12-1The Cycle of Stellar Evolution


Supernovae

• On-line images• Supernova in M 74 http://www.rochesterastronomy.org/sn2003/n628s2.jpg• Supernova in NGC 1448

http://members.optushome.com.au/edobosz/images/1448_sn.jpg • Supernova in NGC 3169

http://www.astrooptik.com/Bildergalerie/PolluxGallery/NGC3169.htm• Supernova in NGC 3190

http://www.astrooptik.com/Bildergalerie/PolluxGallery/NGC3190.htm • Supernova in NGC 5965 http://www.nordita.dk/~dahle/ngc5965_sub.gif• Supernova in NGC 918 http://antwrp.gsfc.nasa.gov/apod/ap091112.html

http://www.rochesterastronomy.org/sn2003/n628s2.jpg

http://members.optushome.com.au/edobosz/images/1448_sn.jpg

http://www.astrooptik.com/Bildergalerie/PolluxGallery/NGC3169.htm

http://www.astrooptik.com/Bildergalerie/PolluxGallery/NGC3190.htm

http://www.nordita.dk/~dahle/ngc5965_sub.gif

http://antwrp.gsfc.nasa.gov/apod/ap091112.html


Chapter 13

• What is left after a Supernova?


Figure 12.21Supernova Remnants


Figure 13.1Neutron Star - from a type II Supernova

• typically ~20 km diameter

• mass > Msun

• thimbleful would weigh 108 tons

• rotate very quickly• have very strong

magnetic fields.


Figure 13.2Pulsar Radiation

• The first observed neutron star was a pulsar

• Neutron stars rotate VERY quickly.


Figure 13.3Pulsar Model

lighthouse model - if the beam sweeps past the Earth, we see a pulse.


At a distance of 1 A.U., which would have the greatest gravitational force?

A) A 1 solar mass main sequence starB) A 1 solar mass white dwarf C) A 1 solar mass neutron starD) They all have the same force.


At a distance of 1 A.U., which would have the greatest gravitational force?



At the surface of the object, which would have the greatest gravitational force?



• A neutron star cannot be more than 3 Msun.


• A neutron star cannot be more than 3 Msun.• Surface gravity will become so great that

not even light can escape. (Escape velocity > c)


• A neutron star cannot be more than 3 Msun.• Surface gravity will become so great that

not even light can escape. (Escape velocity > c)

• Stars that began with > 25 Msun will probably become black holes.


Black Holes

• Can black holes be made of things other than neutron stars?• Any object of any mass has a radius that

if it is compressed below that radius, light cannot escape.

• This is called the Schwarzschild radius.

• rS = 3km x M(solar masses)


Black Holes

• Example Schwarzschild radii :• Sun = 3km• 3MsolarCore = 9km• Jupiter = 3m


Black Holes

• Exercise - calculate the size required to compress a 70 kg person to make a black hole.

• recall:rS = 3km x M(solar masses)


Black Holes

• Example Schwarzschild radii :• Sun = 3km• 3MsolarCore = 9km• Jupiter = 3m• Earth = ~1cm• Person = ~1x10-25 m• Mobservable universe = ~robservable universe


If the Sun were suddenly replaced by a one solar mass black hole:

A) we would immediately escape into deep space, driven out by its radiation.

B) our clocks would all stop.C) life here would be unchanged.D) we would still orbit it in a period of one year.E) all terrestrial planets would fall in immediately.


Practice Problem

• You observe a binary star system where the two stars are exactly the same temperature. The diameter of one star is 1.2 times the diameter of the second star. How many times more energy is emitted by the brighter star?


Practice Problem

• You observe a binary star system where the two stars are exactly the same temperature. The diameter of one star is 1.2 times the diameter of the second star. How many times more energy is emitted by the brighter star?

A. 1.095x B. 1.2x C. 1.44x D. 2x


Practice Problem

• You observe a binary star system where the two stars are exactly the same size. One star is 5500 K. The other star is 6100 K. How many times more energy is emitted by the brighter star?


Practice Problem

• You observe a binary star system where the two stars are exactly the same size. One star is 5500 K. The other star is 6100 K. How many times more energy is emitted by the brighter star?

A. 1.11x B. 1.23x C. 1.51x D. 600x


Review Questions


An ordinary star becomes a Red Giant when:

A) A white dwarf companion star goes novaB) There is no Hydrogen remaining in the starC) Nutrino oscillations drive the outer layersD) The core becomes almost entirely Helium


A main sequence star of 19 solar masses will eventually be a:

A) A brown dwarfB) A white dwarfC) A type I supernovaD) A type II supernova


A supernova is observed with very little H in the spectrum. It is most likely a:

A) type IB) type IIC) type IIID) not enough information


A source of light is approaching us at 3,000 km/s. All its waves are:

A) Red shifted by 1%B) Blue shifted by 1%C) Not affected, as c is constant in all reference

frames.D) Red shifted out of the visible into the infraredE) Blue shifted out of the visible into the ultraviolet


How could you determine the temperature of the photosphere of the Sun?

A) only direct spacecraft measurementB) Newton’s LawC) Stefan’s LawD) Wein’s law


If a star has a parallax of 0.05”, then its distance must be

A) 5 light years.B) 5 parsecsC) 20 light years.D) 20 parsecs.E) 200 parsecs


Assume your naked eye limiting magnitude is 4. With a 70mm diameter telescope (100x

area of your pupil) which object would be barely visible?

A) Seventh magnitude Titan, Saturn’s largest moon.B) Eighth magnitude Uranus.C) Ninth magnitude Barnard’s StarD) Eleventh magnitude Tethys, another Saturn moonE) Thirteenth magnitude Pluto


On the H-R diagram, red supergiants like Betelguese lie:

A) top rightB) top leftC) about the middleD) lower leftE) on the coolest portion of the main sequence


From inside out, which is the correct order?

A) core, convective zone, radiative zoneB) photosphere, radiative zone, coronaC) radiative zone, convective zone, chromosphereD) core, chromosphere, photosphereE) convective zone, radiative zone, granulation


If Vega is apparent magnitude zero, and Deneb first magnitude, then

A) Vega is about 100x brighter than Deneb..B) Deneb is one magnitude brighter than Vega.C) Vega appears 2.5x brighter than Deneb.D) Deneb must be a main sequence star, and Vega a giant.E) Vega must be 2.5x more luminous than Deneb.


Three Minute Paper• Write 1-3 sentences.• What was the most important thing

you learned today?• What questions do you still have

about today’s topics?

“ dead ” stars

Documents

solar mass neutron stard

solar mass white dwarf

solar mass main sequence

observed neutron star

greatest gravitational

surface gravity

escape velocity cstars

pulsarneutron stars