Download - Beyond the Solar System

Beyond the Solar System

Terms

• Quark– Subatomic particle– Makes up protons and neutrons

• Degenerate matter– Compressed atoms– Electrons pushed close to nucleus

Terms

• Interstellar– “Between the stars”– Any part of the universe not within a solar system

• Parsec (pc): 3.26 light-years

• Kiloparsec (Kpc): 1000 parsecs

• Megaparsec (Mpc): 1 million parsecs

Terms

• Magnitude– Brightness of a celestial object– Higher number = dimmer object

Beyond the Solar System

• Introduction to the Universe

• Interstellar Matter

• Classifying Stars

• Stellar Evolution

• Stellar Remnants

PSCI 131: Beyond the Solar System

Introduction to the Universe


How the Universe is Organized

• Galactic clusters– Galaxies

• Stars/solar systems

• Where are we?

• Local Group galactic cluster– Milky Way galaxy

• Our solar system

PSCI 131: Beyond the Solar System – Intro to the Universe

Map of the Local Group. pc: parsec. Mpc: megaparsec.

Size of the Known Universe

• 100s of billions of galaxies

• Nearest large galaxy: 2.5 million ly (light-yrs)

• Furthest object observed: 13 billion ly


From: nasa.gov

Hubble Telescope “Deep Field” image. Most objects are distant galaxies.

History of the Universe• Age: about 13.7 billion years


From: tandempost.com

The Big Bang and the evolution of the universe. Matter has cooled and “clumped” over time to form galaxies and stars.

Interstellar Matter


Interstellar Matter• Matter that occupies space between solar systems

• Mostly dispersed hydrogen and helium atoms (99%)

• Rest is atom-sized dust of other elements

• Nebula: localized concentration of gas and dust into a cloud


Role of Nebulae• Birth of stars and solar systems

PSCI 131: Beyond the Solar System: Interstellar Matter

Types of Nebulae• Bright

– Emission– Reflection– Planetary

• Dark


Bright Nebulae: Emission• Emit their own

radiation

• Glowing gases


The Lagoon Nebula, 1,250 parsecs from Earth.

Bright Nebulae: Reflection

• Reflect radiation from other sources


The Merope Nebula, in the Pleiades star cluster.

From: thinkquest.org

Bright Nebulae: Planetary

• Envelope of gases ejected from a dying medium-mass star

• Gases glow (emit their own radiation)


The Helix Nebula, remnant of a dead Sun-like star.

From: thinkquest.org

Dark Nebulae

•Not hot enough to glow

•Not close enough to light sources to reflect


The Horsehead Nebula. From: nasa.gov

Classifying Stars


Luminosity

•Brightness relative to the Sun (Sun=1)

•Expresses “true” brightness of an object– Distance from Earth is factored out

PSCI 131: Beyond the Solar System: Classifying Stars

The Herzsprung-Russell DiagramPSCI 131: Beyond the Solar System: Classifying Stars

Lum

inos

ity

Surface temperature

Brightest

Dimmest

Hottest Coolest

Stellar Evolution


Two Key Forces Within Stars

• Gravity– Promotes contraction

• Gas pressure– Outward movement of gas and energy from star’s core– Promotes expansion

• Stellar evolution is a balance between them

PSCI 131: Beyond the Solar System: Stellar Evolution

Steps in a Star’s Life Cycle

• Birth• Protostar• Main-sequence• Red Giant*• Death

*Medium- and high-mass stars

only


Stellar evolution of a medium-mass star, plotted on the H-R diagram.

Stellar Birth• Contraction and heating of nebular gases (mostly hydrogen)


Protostar• Contracting nebula becomes hot enough to glow


Main Sequence• Nuclear fusion

begins

• Gas pressure balances gravity

• Star becomes stable

• Longest part of cycle


Red Giant

• Hydrogen fuel in core runs out

• Star expands, cools


Red Giant

• Core– Hydrogen fuel depleted, nuclear fusion stops

– Core collapses and heats up

– Heat radiates into outer shell


Red Giant

• Outer shell– Nuclear fusion continues

– Accelerated by heat from core

– More gas pressure, so outer shell expands and cools


Red Giant

• Outer shell– Gravity balances gas pressure– Expansion stops– Size of star becomes stable

• Core – Still contracting and heating: 2 million degrees F– Starts to fuse helium, forming carbon


Stellar Death: Low-mass stars

• Stars with less than one-half of Sun’s mass

• No red giant stage– Not enough heat from gravitational collapse

• Contract into a white dwarf star when hydrogen depleted


Stellar Death: Medium-mass stars

• Stars one-half to eight times Sun’s mass

• Core contracts into a white dwarf when helium gone

• Outer shell ejected into space: planetary nebula


Stellar Death: High-mass stars• Stars more than eight times Sun’s mass

• Core collapses– Heat causes outer shell to explode in a supernova

• Brightness increases by millions of times• Generates heavier elements (gold, lead, uranium, etc.)

– Collapsed core becomes a neutron star or black hole, depending on star’s mass


Stellar Remnants


Types of Stellar Remnants

• White dwarf– Low- and medium-mass stars

• Neutron star– High-mass stars

• Black hole


White Dwarf• About Earth-sized, but mass is similar to Sun’s

• Degenerate matter– Extremely dense

• A handful would weigh many tons

PSCI 131: Beyond the Solar System: Stellar Remnants

Neutron Star• Denser than white dwarf

• Electrons pushed into nucleus

• A handful would weigh millions of tons


Hypothesized cross-section of a neutron star. Note mass and diameter.

Black Holes• Densest known objects

• Remnants of highest-mass stars (more than 25 times Sun’s mass)

• Radiation (light) can’t escape gravity


Black HolesPSCI 131: Beyond the Solar System: Stellar Remnants

Artist’s conception of a black hole. Matter being pulled in gives off energy as it is compressed, creating detectable signals from around the black hole itself. Inset shows jet of electrons from a black hole in galaxy M87 (bright area).

End of Chapter

Download - Beyond the Solar System

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