Day 28 - review for Exam 4 - part a

Day 28 - review for Exam 4 - part a

Review of stellar characteristics and the lifetime of typical stars The Hertzsprung-Russell Diagram We will plot stars on a chart which has temperature on the horizontal axis and the luminosity on the vertical axis. Named after two astronomers who

made this type of plot in the 1920s. Use units of solar luminosity and Kelvin Reminder: we need to use the HR diagram as we describe stellar evolution

Here are the main regions on the HR diagram. Stellar masses determine a stars

position along the main sequence, more than other properties do. We believe that most stars form in clusters from a single large cloud that fragments. An example of an Open Cluster is the Pleiades cluster (M45, a.k.a. the seven sisters).

H-R diagram of the Pleiades Open Cluster There are stars all along the main sequence, from blue giants

down to red dwarfs. Cluster Evolution on the HR Diagram Newborn Cluster after 10 million

years Notice that there are already some red giants from massive stars that have already run out of hydrogen fuel.

Young Cluster after 600 million years Notice that the cutoff is at Type A stars and that there are already some white dwarfs.

Globular Cluster Omega Centauri H-R diagram of Globular Cluster Omega Centauri contains no main sequence stars with mass

greater than 0.8 solar mass over 10 billion years old. Interstellar matter Gas and dust Dust grains about 10-7 m in diameter,

about the size of smoke particles Dust causes reddening of the light that passes through it, but NOT redshift. This is due to absorption of the blue components of light (more-so in UV). Light Reddening due to absorption by dust.

Interstellar gas The interstellar gas is very dilute, about ONE atom per cubic centimeter. In some places it is much denser. The distribution of gas is very uneven. It is mostly Hydrogen (90%), Helium (9%), and everything else (1%).

Molecular cloud with EGGs: Evaporating Gaseous Globules these can be

seen as pillars and egg-like objects Some properties of these nebulae: note that these are AVERAGE quantities; the nebulae are actual quite uneven in their density and

temperature. Note the huge mass (hundreds to thousands of solar masses) and sizes. Radio Emission reveals the dark dust cloud. Hydrogen 21-cm Emission (shortwave radio) In visible light, we can

see the Horsehead Nebula, a dark dust cloud. A reflection nebula is seen to the lower left of the Horsehead. This is due to scattered light from a nearby

bright star. The pink nebula is an emission nebula, due to UV illumination by a hot star. Star formation a 7 stage process

1 an interstellar cloud 2 shrinking cloud fragments 3 a fragment is the size of our solar system 4 protostar center reaches 1,000,000 K 5 protostar at ~10 solar radius, 4000K surf. 6 ignition of fusion in core, now a star 7 reaches main sequence

Orion Nebula, A closer look reveals globules or EGGs, some of which may contain protostars. Several disks

that may be protoplanetary disks are found after blowing up the Hubble photo. a.k.a. proplyds A protostar can be

plotted on the HR diagram after reaching stage 4. It is heated solely due to contraction and is fairly cool, but might be 1000 times as luminous

as our Sun, mostly in the infrared part of the spectrum. Plotting a newborn star on the HR Diagram Stage 5 T Tauri

stage has violent surface activity and may form jets Stage 6 core at 10 million K and finally get fusion, so now it is a star Stage 7 reaches

the main sequence Pre-stellar Evolutionary Tracks for stars of other masses The minimum mass needed to get

nuclear fusion and produce a real star is about 0.08 solar mass, or about 80 times the mass of Jupiter. With less mass all we get are brown dwarfs

which are failed stars. Stars with Masses between 0.08 and 0.4 times the mass of the Sun have low core temperatures,

live a long time, convect helium from the core, so it mixes uniformly, and will end up composed entirely of helium. A G-Type Star is similar

to our Sun (1 solar mass) The evolution is shown during an imaginary trek through space. At the end of the red giant stage, the core is small, the envelope huge,

and the outcome depends on the total mass of the star. Evolution of stars with more than 0.4 solar masses Solar Composition Change During stage 7

hydrogen burning causes a build-up of helium in the stars core. We will follow the evolution of a star like the Sun, with one solar mass.

Hydrogen Shell Burning occurs around an ash core, which is mostly helium, and the temperature is T = 10 million K The hydrogen shell burning causes higher pressure on the envelope, which causes the star to expand into a Red Giant.

The star follows the yellow curve on the HR diagram. Stage 8 is the subgiant branch and the radius is about 3 times the solar radius.

An example is the star Arcturus, M = 1.5 Msolar and R = 23 Rsolar, the luminosity is about 100 times solar. Stage 10 follows the Helium Flash,

which is like a huge nuclear explosion of helium flashing or burning quickly into carbon at 108 K Fusion of 3 He-4 nuclei produces a

C-12 nucleus plus other products Then there is the Horizontal Branch Helium Shell Burning on the Horizontal Branch

Reascending the Giant Branch occurs in a way similar to the original move up to a giant. Burning in the H and He shells is even faster than before,

so the star expands even more on this asymptotic branch Planetary Nebulae form when the core cant reach 600 million K, the minimum needed for carbon burning. All but the core of the star blows off to form a

Planetary Nebula . A white dwarf remains. A Planetary Nebula with the shape of a ring, 0.5 pc across, called the Ring Nebula. White Dwarf formation on the HR Diagram

Some heavier elements are formed in the last years of the burning in the shells surrounding the carbon core. H, He, C, O, and some Ne and Mg are expelled from

the star as a planetary nebula High-Mass stellar evolutionary tracks are quite different from the low-mass stellar evolution

tracks. Notice that the core can heat up so fast that the envelope of the star tends to lag behind. Carbon fusion can start before the red giant phase.

Heavy Element Fusion - shells like an onion A Type II Supernova is a core collapse and occurs when the core is finally pure iron, which cannot be fused to other elements. The core collapses to a big ball of neutrons, which causes a

shock wave to bounce back outward, which blows off the entire envelope of the red giant, to form a supernova remnant. M1 the Crab Nebula is from a supernova

seen in year A.D. 1054 The remnant is 1800 pc away and the diameter is currently 2 pc.

Supernova Light Curves fall into two types Sirius Binary System: Sirius B is a white dwarf Sirius B has a high mass for a white dwarf, and probably came from a mass 4 Msolar star. White dwarfs are about the size of the Earth.

Recently Viewed Presentations

  • AHEPA ONLINE MEMBERSHIP TUTORIAL Presented by Rosalind N ...

    AHEPA ONLINE MEMBERSHIP TUTORIAL Presented by Rosalind N ...

    Once email has been updated in the system, you will receive an email to re-activate your account by going to the Sign-in home page - see below screen shot, click the 'Forgot my password' link (follow instruction as provided on...
  • Reactions of Alkanes -

    Reactions of Alkanes -

    Reactions of Alkanes IB Combustion of alkanes Alkanes are unreactive as a family because of the strong C-C and C-H bonds as well as them being nonpolar compounds. At room temperature alkanes do not react with acids, bases, or strong...


    XAMPP. free and open source cross-platform web server solution stack package, consisting mainly of the Apache HTTP Server, MySQL database, and interpreters for scripts written in the PHP and Perl programming languages.
  • As news of data security breaches at high-profile

    As news of data security breaches at high-profile

    "As news of data security breaches at high-profile companies keeps coming, so too does the need for security planning and management skills. IT security is one of the top 10 skills that will become "newly important" to companies in the...


    The Renaissance Outcome: The Renaissance in Italy The Renaissance The Middle Ages Ends Europe is starting to take shape with England, France, and regions in Italy all evolving Revival of culture Return to cities The Church was still powerful Writers...
  • Patient Safety Alert

    Patient Safety Alert

    2. The Sterile Processing Manager will conduct 5 random audits each month beginning January 2008 to ensure that instruments have received scheduled maintenance. It is expected that audits will show 90% compliance in Jan and Feb and 100% compliance beginning...
  • Diapositiva 1 - UB

    Diapositiva 1 - UB

    Revisió de dades per part del CRAI Ingesta en el Repositori per SWORD SWORD des del CRAI (Molt aviat ) SWORD actual des de BioMed (autors UB) Models de documents associats al DD Autoritzacions per crear col·leccions Col·leccions en general...
  • Circular Motion - Midland Independent School District

    Circular Motion - Midland Independent School District

    Circular Motion = the movement of an object at constant speed around a circle with fixed radius Axis - straight line around which rotation takes place Rotation - object turns around an internal axis Ex. Ice skater Revolution - object...