Principle SEQUENCE STARS, Red Giants and White Dwarfs .


92 views
Uploaded on:
Description
Vitality GENERATION . Key to all MS stars\' power: change of 4 protons (1H cores) into 1 alpha molecule (4He nucleus)with the outflow of vitality as gamma-beam photons, neutrinos, positrons (or electrons) and quick moving baryons (protons). . Stellar Mass and Fusion. The mass of a fundamental grouping star decides its center weight and temperatureStars of higher mass have higher center tempe
Transcripts
Slide 1

Principle SEQUENCE STARS, Red Giants and White Dwarfs Stars are fueled by combination responses. At the point when a fuel is depleted the star\'s structure changes drastically, creating Post-Main Sequence Evolution

Slide 2

ENERGY GENERATION Key to all MS stars\' energy: transformation of 4 protons ( 1 H cores) into 1 alpha molecule ( 4 He core) with the emanation of vitality as gamma-beam photons, neutrinos, positrons (or electrons) and quick moving baryons (protons).

Slide 3

Stellar Mass and Fusion The mass of a principle grouping star decides its center weight and temperature Stars of higher mass have higher center temperature and more quick combination, making those stars both more glowing and shorter-lived Stars of lower mass have cooler centers and slower combination rates, giving them littler radiances and longer lifetimes

Slide 4

Fusion on MS: p-p chain

Slide 5

The Proton Chains The ppI chain is predominant in lower mass stars (like the Sun) Eq 1) p + p  d + e +  Eq 2) d + p  3 He +  Eq 3) 3 He + 3 He  4 He + p + p We saw these when discussing the Sun - - so this is an audit. Be that as it may, at higher temperatures or at later circumstances, especially for stars which have less metals (mostly CNO) than the sun, and when there is: more 4 He around and less 1 H (or p) left, different responses are critical:

Slide 6

ppII chain rather than Eq (3): (4) 3 He + 4 He  7 Be +  (5) 7 Be + e -  7 Li +  (6) 7 Li + p  4 He + 4 He Net impact: 4 p  4 He This rules if T>1.6x10 7 K ppIII chain Eqs (1) (2) and (4), yet then, in lieu of (5): (7) 7 Be + p  8 B +  (8) 8 B  8 Be + e +  (this was the principal sun based neutrino recognized) (9) 8 Be  4 He + 4 He Net impact: 4 p  4 He This rules if T>2.5x10 7 K Other pp-chains: Eqns (1) & (2) dependably there

Slide 7

Balancing Nuclear Reactions Balance baryons (protons+neutrons) Balance charge (protons and positrons versus electrons) Balance lepton number (electrons and neutrinos versus positrons and hostile to neutrinos) Balance vitality and energy (with photons if just a single molecule on the correct hand side)

Slide 8

Alternative Nuclear Reactions: The CNO Bi-Cycle This is a convoluted system of responses including isotopes of Carbon, Nitrogen and Oxygen (and Fluorine) that in the end adds 4 protons to a C or O core which at long last additionally radiates an alpha molecule. Be that as it may, IT STILL YIELDS THE SAME NET REACTION: 4 protons  1 4 He core, in addition to vitality Here 12 C or 16 O acts like an impetus in substance responses The CNO bi-cycle overwhelms vitality generation in: -Pop I stars (i.e., those with creations like the Sun\'s - approximately 2% "metals") - which are likewise more gigantic than around 1.5 M  -i.e., O, B, A, F0-F5 ghostly classes.

Slide 9

CNO Cycle versus p-p Chain

Slide 10

Hydrostatic Equilibrium on MS

Slide 11

Sources of Pressure Hydrostatic harmony hangs on the MS: that is to state, weight parities gravity, basically consummately, at each point inside the star. Most stars, those up to 10 M  , are fundamentally upheld by THERMAL or GAS PRESSURE: P gas  T, with  the thickness and T the temperature. RADIATION PRESSURE is critical in the most enormous, most sweltering stars (above around 10 M  ): P rad  T 4

Slide 12

Energy Transport The interior structures of stars rely on their masses and the temperatures go up for higher mass stars. This implies distinctive vitality transport systems overwhelm in various parts of various stars. For stars < 0.5 M  (M stars) the whole star is convective. For stars like the sun (in the vicinity of 0.5 and 2 M  ) the inside is radiative and the external layer is convective. For stars in the vicinity of 2 and 5 M  there is an unpredictable structure: convective center, radiative center zone, convective envelope. Stars more huge than 5 M  are convective at the focuses and radiative in their envelopes.

Slide 13

X-beams and Mass Loss on MS Stellar chromospheres and coronae are delivered in low mass stars by the convective external layers; these can yield X-beams. Hot stars can likewise create X-beams from intense winds, driven by extremely solid radiation weight in their external layers. Stars of over 20 M  lose obvious parts of their masses amid their short life times. The winds of these monstrous stars are driven by radiation weight; winds of lower mass stars are driven by vitality from their convective external layers.

Slide 14

On the MS Things Change SLOWLY Fusion drains H and expands He, essentially in the center Only slight conformities in temperature, thickness and weight are required to hold hydrostatic harmony for millions, billions or trillions of years

Slide 15

Hydrostatic Equilibrium at Different Times: Pressure & Gravity Adjust

Slide 16

STELLAR LIFETIMES The measure of fuel is corresponding to the star\'s mass, so you may think more monstrous stars live more. In any case, the rate at which it is singed is corresponding to the star\'s radiance. What\'s more, more monstrous stars are more blazing in the center, which means their atomic responses go significantly speedier and they are more radiant . This clarifies the MASS-LUMINOSITY connection for MS stars. Particularly we have, as you will RECALL: L  M 3.5 - on the MS (as it were). So the lifetime, t  (measure of fuel/consume rate) Main Sequence Lifetime Applet

Slide 17

Lifetimes in Math That\'s  the proportionality. As a condition  Example: you know the Sun lives 1.0x10 10 yr, so to what extent does a 5 M  star live? So a 5M  star lives under 200 million years!

Slide 18

POST-MAIN SEQUENCE EVOLUTION THE END OF THE MAIN SEQUENCE A star leaves the MS when it debilitates H at the center. Amid the MS, there is a brilliant harmony amongst P and gravity: HYDROSTATIC EQUILIBRIUM When H is gone, the center is basically all He and (at in the vicinity of 6 and 40 million K), extremely cool to begin atomic combination of He. The structure must rearrange since the H combination, which had given the vitality and weight, at the inside.

Slide 19

SUBGIANT PHASE All H gone in center: He "ash" is excessively chilly, making it impossible to "burn" Pressure gave by vitality from combination in the center vanishes. The He center contracts - gravity wins over weight once more. Compression warms the center. The greater part of this warmth is caught, so center T rises. Rising thickness and T suggest center P rises really quick, so there is a constriction, NOT a crumple.

Slide 20

Hydrogen Burning Shell (Subgiant)

Slide 21

Thought Question What happens when a star can no longer circuit hydrogen to helium in its center? A. Center chills B. Center psychologists and warms up C. Center grows and warms up D. Helium combination quickly starts

Slide 22

Thought Question What happens when a star can no longer wire hydrogen to helium in its center? A. Center chills B. Center therapists and warms up C. Center grows and warms up D. Helium combination promptly starts

Slide 23

Subgiant , 2 Increased center T diffuses into the H BURNING SHELL - the layer of H sufficiently hot to meld outside the inactive He center. This higher T causes a sensational increment in L from that shell (both pp chains and CNO cycle combination rates are VERY SENSITIVE to T) Higher L in shell makes the inactive H envelope grow. Work is done in delivering this extension, so the star\'s surface T decays (an extending billow of gas cools similarly as a hazy contracting one warms). This compares to the star moving to one side and up on the H-R chart and it enters the SUBGIANT stage.

Slide 24

Life Track after Main Sequence Observations of star groups demonstrate that a star gets to be distinctly bigger, redder, and more iridescent after its time on the principle succession is over

Slide 25

RED-GIANT PHASE As the center keeps on contracting and warmth up, T = 10 8 K is at long last achieved; Then higher electric shock of Helium cores can be overcome AND He CAN FUSE INTO CARBON: 3 4 He  12 C +  (the TRIPLE-ALPHA REACTION ). Truly, 4 He + 4 He  8 Be yet Be-8 is unsteady, so 3 He-4\'s are expected to meet up about all the while. This creates more vitality, and both L and T in center increments.

Slide 26

Helium Flash For M < 2 M  this happens while the He center is worsen; (more about this later when we talk about White Dwarfs) As P doesn\'t ascend with T for deteriorate matter, the "indoor regulator" is broken So he center temperature rises quick when He combination starts: and the Luminosity from He goes up significantly quicker: HELIUM FLASH until warm weight is huge again and extends center once more, again dropping the center temperature This causes a quick extension of the star\'s envelope, and a further cooling of its surface, yielding a RED GIANT (with size 100\'s of that of Sun on MS however bring down T s ).

Slide 27

Life Track after Helium Flash Models demonstrate that a red goliath ought to contract and turn out to be less radiant after helium combination starts in the center

Slide 28

Pop Quiz Print your name (1) 1) Complete, and clarify the adjusting of, the accompanying atomic response (5): 15 N + 1 H  12 C + ___ 2) Sketch, on a marked H-R chart, the way of a 1 M  star from the season of accumulation as a protostar to the red mammoth stage. (5)

Slide 29

THE HORIZONTAL BRANCH He Flash finishes rapidly, once center weight has developed, making the center range rise, thus, yielding a decrease in T c to pretty much 10 8 K. Presently He consumes easily in the center - delivering the He BURNING MAIN SEQUENCE - which is obvious on a H-R graph as the HORIZONTAL BRANCH (bring down L yet higher T s than amid the He streak). Stars are again in HYDROSTATIC EQUILIBRIUM all through: the indoor regulator works again These are still RGs, and on HB the higher masses are to one side some portion of the HB. Most

Recommended
View more...