Chapter 14: The stars

The greater mass of the Sun, relative to brown dwarf stars, means that __________________________________.

- Core temperatures and pressures are much higher - Hydrogen burning proceeds at a much faster rate

Differences in the brightness of stars arise from _____________________________. The brightness of a star distinguished between a star's ________________________.

1(a). Distance - Closer is brighter 1(b). Energy output 2. Apparent brightness (the brightness it appears to have when viewed from Earth) and absolute brightness (the brightness it would have if viewed from a standard distance; the luminosity)

The intensity of solar wind can vary, and occasionally it can spike in a ____________________________________. The varying intensity of solar emissions is known as ______________________________________.

1(a). Solar flare 1(b). Coronal mass ejection - A massive burst of plasma and radiation 2. Space weather - Particles can damage sensitive electronic equipment in space, so it must have shielding

Cepheid variable

1. A Cepheid variable is a standard type of star 2. The absolute magnitude of these stars is related to the time it takes for them to go through a dimming-brightening-dimming sequence 3. By seeing what stage of the sequence the star is in, can deduce how much energy it is pouring into space 4. Compared with how much energy received on Earth 5. Estimate how far away it is

It takes _____________________________ for the energy to work its way to the photosphere but only ____________________ for photons to cover the distance between the Sun and Earth.

1. A few tens of thousands of years 2. 8 minutes

Nebular hypothesis

1. A large nebula collected in the space now occupied by our solar system 2. Under the influence of gravity, the nebula started to collapse on itself 3. The collapse caused the cloud to spin faster and faster 4. The rapid spin causes some of the material in the outer parts of the cloud began to spin out into a flat disk - Similar to a large pancake with a big lump in the middle 5. The big lump represents the material that will eventually become the Sun 6. The material in the thin, flattened disk will eventually become the planets and the rest of the solar system

Terrestrial effect of space weather

1. An intense stream of charged particles will change the shape of Earth's magnetic field 2. The field is compressed on the sunward side 3. When this distortion occurs (an event known as a geomagnetic storm), unexpected electrical currents can flow in equipment on Earth's surface - Disrupt communication systems and large-scale structures (ex: power grids and pipelines)

All main-sequence stars _________________________________.

1. Are in the hydrogen-burning phase of their lives 2. Produce energy in fusion reactions

When stars are plotted using the Hertzsprung-Russell (H-R) diagram, the majority (the ones like the Sun) fall on a _________________________________. Stars in this grouping are called __________________________________.

1. Band that stretches from the upper left to the lower right in the diagram - Trend from very hot stars emitting lots of energy, down to relatively cool stars emitting less energy 2. Main-sequence stars

The net effect of hydrogen burning is that ___________________________________. The sum of the masses of all the particles produced in this reaction amounts to ________________________ than the mass of the original four protons.

1. Four protons are converted into a helium-4 nucleus with a few extra particles thrown in 2. Less - Lost mass has been converted into energy (the nuclear energy that powers the Sun and eventually radiates out into space)

Measuring the distance of stars

1. Geometry - For short distances (up to a few hundred light-years) - Triangulation 2. Cepheid variable - For greater distances - Henrietta Leavitt

As a star forms, ___________________________________.

1. Gravity pulls the hydrogen into a dense ball that heats up 2. Electrons are torn from the hydrogen and other atoms 3. This creates a plasma made up primarily of protons (the nucleus of the hydrogen atom) and electrons 4. Normally, protons would repel each other, but as matter accumulates in the new star, the protons move faster as the temperature increases 5. Eventually, they acquire enough energy to overcome the electrical repulsion between them 6. The protons start to fuse

Satellite observatories

1. Hubble Space Telescope (HST) - Reflecting telescope 2. Chandra X-Ray Observatory - High-resolution X-ray images 3. Fermi Gamma Ray Telescope - Explore the highest energy part of the electromagnetic spectrum 4. Gaia - European Space Agency - Measures the precise location of over a billion stars in the Milky Way 5. James Webb Space Telescope - Successor to the Hubble - LaGrange point - Explores the creation of the first galaxies and the details of the formation of planetary systems 6. Kepler Observatory - Designed to search for planets circling other stars by monitoring the light from over 150,000 stars and looking for small changes in brightness as planets pass - Mechanical problems

The Sun's fuel is ____________________________, which is consumed through ____________________________.

1. Hydrogen 2. Nuclear fusion reactions

Today, the main site of telescope construction is at the ______________________________. This area is also home to the ___________________________ observatory, the _______________________ telescope, and the ______________________________ telescope.

1. Las Campanas Observatory in the Andes Mountains in northern Chile - Very high - Very dry (not effected by water vapor) 2. Atacama Large Millimeter Array (ALMA) - Measures radiation in the microwave and infrared range - 1st international telescope 3. Giant Magellan Telescope 4. European Extremely Large Telescope (E-ELT) - European Space Agency - Will be world's largest

Solar neutrino problem

1. Nuclear fusion reactions in the Sun's core produce neutrinos 2. Most of these neutrinos escape from the Sun without being absorbed or changed, and they arrive at Earth unchanged 3. When measurements were taken, scientists saw only about one-third to one-half of the number of neutrinos they had expected to see 4. This is because there are actually three different types of neutrinos 5. If one type of neutrino is produced in nuclear reactions in the Sun, by the time those original neutrinos get to Earth some will have changed identity 6. Only a third will still be of the type produced in the Sun

Two additional clumpings of stars that appear in the H-R diagram are ________________________________.

1. Red giants 2. White dwarfs

The interaction of the solar wind with the outer reaches of Earth's atmosphere gives rise to _____________________________. Solar radiation is the __________________________. The energy in sunlight also heats ____________________________.

1. The aurora borealis or northern lights 2. Primary source of energy for most living things on the planet 3. The air at the equator - Drives Earth's weather patterns

The larger a telescope is, _____________________________________.

1. The more light it will gather 2. The more detailed the data it will produce

The chromosphere and the corona

1. The sun gradually becomes thinner and thinner farther away from the surface 2. These gaseous layers are not usually visible from Earth 3. Visible during a total eclipse of the Sun - Halo

Four measurements of photons from space

1. Wavelength - Measured by spectroscopy 2. Intensity - Measured by a device like a light meter 3. Direction 4. Variations of wavelengths, intensities, and positions with time

Final stage in the life of a star (size of the Sun)

1. When the core consumes all of its nuclear fuel, the hydrogen-burning shells surrounding the central region will be pulled in 2. This temporary collapse will increase the amount of energy generated by fusion 3. The increased energy will cause the surface of the Sun to balloon out 4. The solar wind will also increase - Mass will drop - Gravitational force will decrease - Nearby planets will move outward 5. Will emit almost much more energy, but it will do so through a much larger surface - Surface will appear to be very cool (red giant) 6. Helium in the core will undergo nuclear fusion reactions to produce an inner core primarily of carbon 7. Core starts to collapse 8. Electrons will be compressed into a smaller and smaller volume 9. Electrons will reach the pointwhere they can no longer be pushed together 10. Pauli principle will take over, and the collapse will stop 11. A permanent outward force will be exerted on every element in the star to balance the inward force of gravity - Small - Very hot, but no longer generating energy (white dwarf) 12. Most of the carbon that is the end product of helium burning will remain locked in the white dwarf

The core of the Sun is estimated to take up what percent of the Sun's total volume?

10%

Supernovas probably happen within the Milky Way galaxy about every _________________________________.

30 years

Red giants

A clumping in the upper-right corner of an H-R diagram - Emit a lot of energy - Surfaces are very cool - Very large (many times the size of the Sun) - Appear reddish

Telescope

A device that focuses and concentrates radiation from distant objects; used by astronomers to collect and analyze radio waves, microwaves, light, and other radiation

White dwarfs

A grouping in the lower-left corner of the H-R diagram - Very low emission of energy - Very high surface temperatures - Very small (Earth-sized)

The classic reflecting telescope has ______________________________.

A large mirror that reflects and focuses light to produce an image of the object being studied

Ernie

A neutrino with 1140.8 trillion electron volts - The most energetic neutrino ever - Discovered by IceCube

Pulsar

A neutron star in which fast-moving particles speed out along the intense magnetic field lines of the rotating star, giving off electromagnetic radiation that we detect as a series of pulses of radio waves - Discovered by Jocelyn Bell

LaGrange point

A point between Earth and the Sun, where the gravitational forces create a point of stability for objects in orbit

Hertzsprung-Russell (H-R) diagram

A simple graphical technique widely used in astronomy 1. On a graph's vertical axis, plot the amount of energy given off by a star - Measured by estimating the star's distance and brightness 2. On the graph's horizontal axis, plot the star's surface temperature - Determined by its color (spectrum) 3. Each star has its own characteristic combination of energy and temperature - Appears as a single point

Brown dwarf

A small star (with perhaps only 10% of the Sun's mass) - Less hydrogen in its core - Lower surface temperatures - Nuclear fusion occurs slowly (glow steadily for a hundred billion years without any significant change in size, temperature, or energy output)

Solar wind

A stream of charged particles emitted constantly by the Sun into the space around it - Mainly ions of hydrogen, helium, and electrons

Supernova

A stupendous explosion of a star, which increases its brightness hundreds of millions of times in a few days; results from the implosion of the core of a massive star at the end of its life

All elements beyond iron are created in ___________________________.

A supernova explosion 1. Shock waves raise temperature enough to form all of the chemical elements in the periodic table 2. Some of the nuclei up to iron that have been created by the successive fusion reactions soak up neutrons and undergo beta decay 3. Form nuclei up to uranium and beyond

Neutron star

A very dense, very small star, usually with a high rate of rotation and a strong magnetic field; the core of neutrons that was created in a supernova - Maybe 10 miles across - Give off very little light

Energy inside a star is brought from the core to the surface in a stepwise process, first by ___________________, then by __________________________.

A. Collisions B. Convection 1. Nuclear reactions occur in the stellar core 2. Energy transfer takes place largely through collisions of high-energy particles that are generated by the core's nuclear reactions - Gamma rays and X-rays - Conversion of mass to energy 3. Energy generated in the core streams out from the center 4. Energy-transfer mechanism changes about four-fifths of the way out - Convection zone 5. Here, the hydrogen-rich material in the Sun begins to undergo large-scale convection

The flattening of the nebula into a disk also explains the fact that ____________________________.

All planetary orbits lie near the same plane

Many modern light-gathering telescopes have _____________________________.

An array of small, independently controlled, lightweight mirrors that, taken together, produce an image - Ex: Keck Telescope in Hawaii

Hydrogen burning nuclear reactions (are/are not) ___________________ the same as the chemical reactions that we commonly call burning

Are not

How is the direction of photons from space measured?

By recording two angles 1. Altitude - Up from the horizon 2. Azimuth - Around from north

Where would a supernova be found on an H-R diagram?

Center

Stellar core

Center of a star in which pressure and temperature are high enough for fusion to occur - About 10% of the Sun's total volume

The region of the Sun's interior that conducts energy between the innermost portion and the outermost portion is the ______________________________.

Convection zone

From the inside out, the layers of our Sun are _______________________________.

Core, convection zone, photosopshere, chromososphere, corona

Nebulae

Dust and gas clouds, common throughout the Milky Way galaxy - Typically contain more than 99% hydrogen and helium, with lesser amounts of all the other naturally occurring elements

The fact that you can see the stars means that they are _____________________________.

Emitting electromagnetic radiation in the form of photons - Travels through space - Energy radiates out in every direction from the star - Primary source of data on distant stars

Two consequences of a star's depleted hydrogen

First 1. The temperature in the region immediately surrounding the core will begin to rise 2. Any remaining hydrogen in that region, which had not been consumed because it had been at too low a temperature, will begin to undergo nuclear fusion reactions 3. A hydrogen-burning shell will begin to form around the extinguished core Second 1. The temperature in the core will rise until helium, the "ash" of hydrogen burning, will begin to undergo nuclear fusion reactions - Helium burning 2. Star will resemble an onion - Helium-burning core surrounded by a layer where hydrogen is being fused 3. Star will begin to move off of the Herzsprung-Russell main sequence

Black hole

Formed at the death of a very large star, an object so dense, with a mass so concentrated, that nothing—not even light—can escape from its surface - Perhaps 50 or more times as massive as the Sun - Stellar (smaller) or galactic (larger)

One way to look at the life of a star like the Sun is to think of it as a continual battle against the force of ____________________________.

Gravity - Forces particles inward toward collapse 1. Hydrogen burning occurs in the core 2. The increase in temperature in the center raises the pressure in the star's interior 3. Balances the inward pull of gravity 4. When hydrogen fuel in the core is depleted, the amount of energy generated in the core will decrease 5. Gravity will begin to take over 6. The star will begin to contract and heat up

Helium burning

Helium in the core undergoes nuclear fusion reactions to make carbon - Final energy-producing stage

The most abundant element in the universe is ________________________________.

Hydrogen

All stars begin their lives in the ____________________________ stage.

Hydrogen-burning

The world's premier neutrino detector is called ____________________________

IceCube - Located at the South Pole How it works 1. Hot water is used to create a mile-deep hole in the ice 2. A cable with detectors attached is lowered into the hole 3. The ice is allowed to freeze up around it 4. Detects light emitted from particles with which the passing neutrinos have interacted 5. These neutrinos come through the entire Earth before interacting with atoms in the rocks underneath the ice cap (or with the ice cap itself)

Stars more than 10 times as massive as the Sun end their lives __________________________.

In explosions of unimaginable power 1. Pressure exerted by gravity is extremely high 2. Helium in the core burns to carbon 3. Carbon can also undergo fusion reactions to produce oxygen, magnesium, silicon, and other larger nuclei 4. Nuclear burning goes on until iron is produced - Impossible to extract energy from iron by any kind of nuclear reaction (most tightly-bound nucleus) 5. Incredible pressures and temperatures at the center of the star combine the electrons with protons inside the iron nuclei, forming neutrons - Exact opposite of radioactive beta decay 6. All of the protons in the iron nuclei are turned into neutrons, and all of the electrons disappear 7. Core of the star begins a catastrophic collapse 8. Core collapses so fast that it falls inward beyond the point where the degeneracy pressure of the neutrons can balance gravity 9. Star's falling matter first bounces inward and then rebounds as the neutrons exert a counterpressure 10. Outer gaseous envelope of the star begins a free-fall toward the interior of the star 11. When the collapsing envelope of dense gas meets the rebounding core of neutrons, intense shock waves are set up in the sta 12. The entire outer part of the star literally explodes - Supernova

________________________ is an Earth-based telescope.

Keck telescope

Because the particles of solar wind are charged, they affect the _________________________________.

Magnetic fields of the planets 1. Compresses the fields on the "upstream" side 2. Drags the fields out on the "downstream" side

Stars

Objects such as our Sun that form from giant clouds of interstellar dust and generate energy by nuclear fusion reactions - Mostly hydrogen and helium - Held together by gravity - Complex and dynamic interior structure that is constantly changing and evolving

The outer layer of the Sun that radiates energy into space is the ____________________________.

Photosphere

The modern theory of star and planet formation was first put forward by ___________________________.

Pierre Simon Laplace - Nebular hypothesis

Which region of the electromagnetic spectrum can easily reach a telescope on the Earth's surface?

Radio waves

Large stars have a ___________________________ lifetime than smaller stars

Shorter

Of all the possible waves in the electromagnetic spectrum, the human eye can detect only the ________________________________________.

Small interval of wavelengths between red and violet Reasons 1. Earth's atmosphere is transparent to these wavelengths, so it is possible for the waves to travel long distances through the air 2. The Sun's peak output of energy is in the middle of the visible spectrum

The Cepheid variable scale is an example of a ________________________________.

Standard candle 1. See how much energy an object is giving off 2. Compare that with how much energy you are actually receiving 3. Can figure out how far away the object is

Differently colored stars are at different _____________________________.

Temperatures - Blue is hotter (high-energy photons) - Orange/red is cooler (low-energy photons)

Lightyear

The distance light travels in one year; 10 trillion kilometers

Photosphere

The outer part of the Sun - Part that actually emits most of the light we see

The hydrogen-burning process is generally confined to _______________________.

The stellar core - Only the hydrogen in the stellar core is measured when estimating how long the Sun can consume hydrogen at its present rate

Luminosity

The total energy emitted by a star

The nuclear fusion process in the Sun's core

Three-step fusion process is called hydrogen burning 1. Two protons (P) come together to form a deuterium nucleus (D, the isotope hydrogen-2, made up of one proton and one neutron), a positron (e⁺), and a neutrino Equation: P + P → D +e ⁺ + neutrino + energy 2. Another proton collides with the deuterium produced in the first step to form the isotope helium-3, which has two protons and one neutron in its nucleus - A photon in the form of an energetic gamma ray is also produced Equation: D + P → ³He + photon + energy 3. Two helium-3 nuclei collide to form helium-4, two protons, and a photon (another gamma ray) Equation: ³He + ³He → ⁴He + 2 protons + photon + energy

The ultimate fate of any given star depends on the ___________________________.

Total mass of hydrogen and helium

Except for ___________________________, Earth's atmosphere is largely opaque to the electromagnetic spectrum.

Visible light and radio waves - Most infrared and all ultraviolet radiation, short-wavelength microwaves, X-rays, and gamma rays entering the top of the atmosphere are absorbed long before they can reach instruments at the surface - Necessitates use of satellite observatories

When are electromagnetic waves from a pulsar detected on Earth?

When one of the magnetic poles is pointed toward our planet

Basic life cycle of stars

main sequence → red giant → white dwarf