ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars - - PowerPoint PPT Presentation

ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies

• Homework #4

Homework #4 on Mastering Astronomy,

• n Mastering Astronomy,

due on Thursday due on Thursday this week, 10/08, by 5pm this week, 10/08, by 5pm

• Next Extra Credit Observing Night:

–Thursday, 10/08 at Sommers-Bausch

• Sequence of expansion/contraction

repeats as higher and higher elements begin to fuse

• Each heavier element requires

higher core temperatures to fuse

High-Mass Stars High-Mass Stars

• Core structure

keeps on building successive shell

• Like an onion
• Lighter elements
• n the outside,

heavier ones on the inside

No significant changes in luminosity Star travels back and forth

• n the HR diagram

In the most massive stars, changes happen so quickly that the outer layers do not have time to respond

High-Mass Stars: High-Mass Stars:

Outer layers subject to strong winds

Massive Massive red giant red giant

• r
• r supergiant

supergiant: : Fierce hot Fierce hot winds and winds and pulsed pulsed ejecta ejecta

Hubble Hubble

Wildest of all ! Wildest of all ! ETA CARINAE ETA CARINAE Supermassive Supermassive star (150 M star (150 MSUN

SUN )

) late in life, late in life, giant outburst giant outburst 160 yr ago 160 yr ago Violent bipolar Violent bipolar ejecta ejecta + disk + disk at equator at equator

Question: Question: why do we see the glowing gas surrounding the star to grow in time?

Note: the star emitted a pulse of radiation some time ago.

Star V838 Star V838 Monocerotis Monocerotis HST-ACS HST-ACS

`Light Echo `Light Echo’ ’ from pulse from pulse Red Giant Red Giant with with intense intense brightening brightening

• Most elements are formed via Helium Capture

Helium Capture

– A helium (2 protons) nucleus is absorbed, energy is released

• The elements are created going up the periodic

table in steps of 2

Other Reactions Other Reactions

Carbon (6), Oxygen (8), Neon (10) Carbon (6), Oxygen (8), Neon (10) Magnesium (12) Magnesium (12)… …. .

E ARE STAR STUFF!!

• Carl
• Carl Sagan

Sagan

“ “We are all star-stuff We are all star-stuff” ”

• Carl
• Carl Sagan

Sagan

• All

All heavy elements are created and dispersed through the galaxy by stars

• Without high mass stars, very little

very little heavier than carbon

• Our atoms were once parts of stars

parts of stars that died more than 4.6 billion years ago, whose remains were swept up into the solar system when the Sun formed

What is the heaviest element that can be What is the heaviest element that can be created through fusion? created through fusion?

• A. Carbon
• B. Silicon
• C. Iron
• D. Uranium

Clicker Question Clicker Question

What is the heaviest element that can be What is the heaviest element that can be created through fusion? created through fusion?

• A. Carbon
• B. Silicon
• C. Iron
• D. Uranium

Clicker Question Clicker Question

HIGH mass stars keep creating HIGH mass stars keep creating elements up the periodic table UNTIL elements up the periodic table UNTIL… …. . IRON IRON (Fe, 26 protons ) (Fe, 26 protons )

• Iron does not

release energy through fusion or fission

– – Remember: Remember: All energy created by the loss of mass from the fusion (E=mc E=mc2

2)

• The core of a high

mass star accumulates accumulates iron iron as the layers above it fuse

• Without any outward

pressure, the core

• nce again starts to

contract contract.

• Electron degeneracy

pressure supports the core for awhile until the mass of iron gets too too heavy heavy (how heavy?)

(how heavy?)

• When mass is too large

(>1.4Msun), core collapses and iron atoms get compressed into pure neutrons

• protons + electrons neutrons

+ neutrinos

– – This takes less than 0.01 seconds This takes less than 0.01 seconds

• Electron degeneracy pressure -

GONE!

– Core collapses completely

• Eventually neutron degeneracy pressure stops the

collapse abruptly

• Infalling atmosphere impacts

impacts on the core.

• Time for a demo…

Basketball & Super ball Demo Basketball & Super ball Demo

• What do you think will happen?

A.

• A. The two balls will bounce up together

The two balls will bounce up together B.

• B. The little ball will bounce higher than the

The little ball will bounce higher than the basketball but no higher than when the basketball but no higher than when the little ball little ball is dropped alone is dropped alone C.

• C. The little ball will bounce much higher than the

The little ball will bounce much higher than the basketball basketball

Clicker Question Clicker Question

Supernova! Supernova!

• The lightweight atmosphere impacts on

the heavy core and is “ “bounced bounced” ” off in a huge explosion

• Plus huge energy release from

neutrinos!

e sta e sta former surface zooms outwar former surface zooms outwar i a veloci of 10,000 km/s! i a veloci of 10,000 km/s!

“ “Massive Star SUPERNOVA Massive Star SUPERNOVA” ”

• Exploding remnant

Exploding remnant

• f
• f

massive star massive star disperses disperses heavy heavy elements elements through through the galaxy the galaxy

• Inside may be a

Inside may be a neutron star neutron star – – a a remnant core of remnant core of pure neutrons! pure neutrons!

Crab Nebula (M1), Crab Nebula (M1), first seen as SUPERNOVA first seen as SUPERNOVA

• n 4 July 1054 from China -- visible in daytime
• n 4 July 1054 from China -- visible in daytime

Was Crab SN recorded in Chaco? Was Crab SN recorded in Chaco?

• Petroglyph from

Chaco Canyon (New Mexico):

– Correct configuration relative to the new moon for the Crab Supernovae – Of course it could also just be Venus with the moon!

• Chinese records also

report a “guest star” in the sky in 1054 A.D.

Observing Supernovae Observing Supernovae

• About 1 per century per galaxy

(none in Milky Way since (none in Milky Way since 1604) 1604)

• Bright explosions visible for

weeks/months weeks/months

– some visible in daytime!

• Remnant visible for 100’s of

thousands of years as huge bubbles and “veils”

Supernovae in Other Galaxies Supernovae in Other Galaxies

• Bright enough to be seen

as a sudden, bright point in other galaxies

• Scores of amateur and

pro astronomers monitor nearby galaxies nightly to catch them

– (1 per 100 years per galaxy means that monitoring 100 galaxies will get you 1 supernova per year)

SN 1987A: Nearest One Since 1604 SN 1987A: Nearest One Since 1604

• Exploded in the Large

Magellanic Cloud (companion dwarf galaxy to MW, 150,000 ly away)

• Seen only from southern

hemisphere

– But neutrino detectors in Ohio, Japan, and Russia detected neutrinos from the explosion!

• Ring structure: illuminated

remnants of an earlier stellar wind or gas left

• ver from star’s formation

Betelgeuse (In Orion) Is Currently Betelgeuse (In Orion) Is Currently In Its Red In Its Red Supergiant Supergiant Phase Phase

might be next…

• nly 1500 ly

away.. would be

very dramatic…

The ultimate fate of a The ultimate fate of a massive star massive star

Core burns to Core burns to Fe, Fe, leading to a core collapse leading to a core collapse SUPERNOVA SUPERNOVA

What happens to the Fe core? What happens to the Fe core? Neutron Star Neutron Star - for star masses < 30-40 Msun Black Hole Black Hole - for star masses > 30-40 Msun

The Stellar Graveyard The Stellar Graveyard

What What’ ’s In The Stellar Graveyard? s In The Stellar Graveyard?

• Low mass stars white dwarfs

white dwarfs

– Gravity vs. electron degeneracy pressure

• High mass stars neutron stars

neutron stars

– Gravity vs. neutron degeneracy pressure

• Even more massive stars black holes

black holes

– Gravity wins

When a high-mass star (M>8M When a high-mass star (M>8Msun

sun)ends its

)ends its life, what does it leave behind? life, what does it leave behind?

• A. A neutron star or black hole
• B. A white dwarf
• C. A black hole
• D. A neutrino ball
• E. A red supergiant

Clicker Question Clicker Question

When a high-mass star (M>8M When a high-mass star (M>8Msun

sun)ends its

)ends its life, what does it leave behind? life, what does it leave behind?

• A. A neutron star or black hole
• B. A white dwarf
• C. A black hole
• D. A neutrino ball
• E. A red supergiant

Clicker Question Clicker Question

Binary Systems: The Binary Systems: The Algol Algol Paradox Paradox

• Algol

Algol is a is a binary system binary system consisting of a 3.7 consisting of a 3.7 solar mass solar mass main sequence star main sequence star and a 0.8 and a 0.8 solar mass solar mass red giant red giant. . Why is this strange? Why is this strange?

• A.
• A. A 3.7 MSun star should have become a red giant

before a 0.8 MSun star

• B.
• B. Binary stars usually have the same mass
• C.
• C. 0.8 MSun stars usually never become red giants

Clicker Question Clicker Question

Binary Systems: The Binary Systems: The Algol Algol Paradox Paradox

• Algol

Algol is a is a binary system binary system consisting of a 3.7 consisting of a 3.7 solar mass solar mass main sequence star main sequence star and a 0.8 and a 0.8 solar mass solar mass red giant red giant. . Why is this strange? Why is this strange?

• A.
• A. A 3.7 MSun star should have become a red giant

before a 0.8 MSun star

• B.
• B. Binary stars usually have the same mass
• C.
• C. 0.8 MSun stars usually never become red giants

Clicker Question Clicker Question

Algol Algol Binary System Binary System

• Binary stars can

Binary stars can have different have different masses but usually masses but usually ARE ARE formed at the formed at the same time. same time.

• More massive star

More massive star should have had a should have had a shorter shorter main main sequence lifetime sequence lifetime

What happened? What happened?

• The 0.8 solar mass star once

The 0.8 solar mass star once was more massive (3.0), with was more massive (3.0), with a 1.5 mass companion a 1.5 mass companion

• As it became a

As it became a red giant red giant, , it it swelled and poured material swelled and poured material

• nto its companion (lost 2.2)
• nto its companion (lost 2.2)
• The

The red giant red giant (0.8) is now (0.8) is now less massive than its less massive than its companion (3.7) companion (3.7)

• Future

Future: when the other star : when the other star becomes becomes red giant red giant, it may , it may pour gas back pour gas back… …? ?

Binary Mass Exchange Binary Mass Exchange

3.0 3.0 1.5 1.5

• 2.2
• 2.2

0.8 0.8 3.7 3.7

early MS early MS now now

Moral of the story: Choose your companions wisely, for they may determine your fate

White Dwarfs: summary White Dwarfs: summary

• For <8 MSun star = a hot core of carbon

(can also be oxygen for higher mass stars) Size ~ Earth !! Density – 1 cm3 is about 5 tons Held up by electron degeneracy pressure Cool from white-blue through red red to black black Maximum mass = 1.4 Msun

White Dwarfs in Binary White Dwarfs in Binary Systems Systems

• Mass transfer from a

companion red giant spirals into an accretion disk accretion disk

• Inner parts become

Inner parts become VERY hot; VERY hot; glow in UV (mostly), X-rays

Novae Novae (not Supernovae!) (not Supernovae!)

• Accretion of hydrogen

gas onto the white dwarf can heat and fuse for while (only on surface)

• Star becomes much

brighter nova nova (new star)

– Dimmer than supernova but still impressive!

White Dwarf Supernovae White Dwarf Supernovae

• If enough mass is

accreted, electron degeneracy is

• vercome

– Limit = 1.4 Solar masses (recall the Chandrasekhar Limit)

• Star then collapses,

carbon fusion begins in its core (explosively)

– – Bye bye white dwarf! Bye bye white dwarf!

• Dr. Chandrasekhar says:

“Do not weigh more than 1.4 solar masses or you will collapse!”

Comparing The Comparing The Two Types of Two Types of Supernovae Supernovae

• Massive star SN (collapse of massive star)

Massive star SN (collapse of massive star)

– Found in young star formation regions – Make neutron stars or black holes

• White dwarf SN (flash burning of WD)

White dwarf SN (flash burning of WD) – Binary systems only – Occurs in older star populations – Nothing left inside

We We’ ’ll be looking at these again as ll be looking at these again as distance measurement tools! distance measurement tools!