Stellar Explosions and the Universe

Flashcards covering key concepts related to stellar explosions, the evolution of high mass stars, star clusters, black holes, and cosmology.

Novae

occurs when a white dwarf in a binary star system accretes material from its companion star, leading to a thermonuclear explosion on the surface

Chandrasekhar limit

The maximum mass (approximately 1.4 solar masses) a white dwarf can have before collapsing into a neutron star or black hole.

Type 1a Supernova

A supernova resulting from a white dwarf in a binary system accreting enough matter to exceed the Chandrasekhar limit.

CNO cycle

A nuclear fusion process in high-mass stars where hydrogen is converted to helium using carbon, nitrogen, and oxygen as catalysts.

Carbon burning

The fusion of carbon atoms at core temperatures of around 600 million K, producing heavier elements.

Onion-like core structure

The layered structure of a star's core where different fusion processes occur at varying temperatures.

Iron (Fe) uniqueness

Iron is the heaviest element that can be fused in a star's core without consuming energy.

Neutron core

The extremely dense core of a neutron star composed almost entirely of neutrons, formed after a supernova.

Type II Supernova

A supernova that occurs when a massive star exhausts its nuclear fuel and its core collapses.

Nucleosynthesis during supernovae

The formation of elements heavier than iron, including gold and uranium, in supernova events.

Supernova remnants

The expanding cloud of gas and dust left behind after a supernova explosion.

Neutron stars

Extremely dense remnants of massive stars, with masses between 1.4 and 3 solar masses, mainly composed of neutrons.

Pulsars

Rapidly rotating neutron stars that emit beams of radiation at regular intervals.

Black hole formation

when a star's core collapses under gravity, with a mass greater than 3 solar masses.

Open clusters

Young, loosely bound groups of stars typically found in the disk of a galaxy.

Globular clusters

Older, tightly bound groups of stars found in the halo of a galaxy.

Escape speed

The minimum speed required for an object to break free from the gravitational pull of a massive object.

Schwarzschild radius

The radius of the event horizon of a black hole, the boundary beyond which nothing can escape.

General relativity

Einstein’s theory of gravity that describes the curvature of space and time caused by mass and energy.

Local Group

A collection of galaxies, including the Milky Way and Andromeda, gravitationally bound together.

Hubble’s Law

The principle stating that the velocity of a galaxy's recession is directly proportional to its distance from us.

Dark matter

An unseen form of matter that does not emit light or energy, inferred from its gravitational effects on visible matter.

Cosmic Microwave Background (CMB)

The radiation left over from the Big Bang, currently at a temperature of about 2.725 K.

Degeneracy Pressure:

no two electrons/neutrons.protons can exist in the same quantum state at the same time so this creates a resistance to compression, even without heat or regular gas pressure.

the universe is what percent “normal matter” (stars, galaxies, people)

5%

the universe is what percent “dark matter”  (invisible mass detected via gravitational effects)

27%

the universe is what percent “dark energy”

68%

critical density

The density at which the universe would expand forever, slowing down but never halting, becoming flat.

Large Scale Structure

• Galaxies are not evenly distributed—they cluster into groups, clusters, superclusters, and filaments, leaving behind vast empty voids.

Big Bang Theory

The prevailing cosmological model that describes the universe as originating from an extremely hot, dense state ~13.7 billion years ago and expanding ever since.

Cosmological Principle

On large scales, the universe is homogeneous (the same everywhere) and isotropic (the same in all directions).

Redshift (z)

A shift in the wavelength of light toward longer (redder) wavelengths, caused by the expansion of the universe.

Hubble’s Law

• This law implies that the universe is expanding—galaxies are moving away from us, with speed proportional to their distance.

Cepheid Variables:

• Pulsating stars with a well-known relation between their pulsation period and luminosity.

Accretion Disk

A rotating disk of gas and dust spiraling into a black hole. The material becomes extremely hot and emits radiation across the electromagnetic spectrum.

Quasar (Quasi-Stellar Object)

• Appears star-like in images but has a spectrum with large redshifts.

• Among the most luminous and energetic objects in the universe.

• Can emit more energy than hundreds of galaxies combined.

Radio Galaxy

A type of galaxy that emits strong radio waves, often containing active supermassive black holes at their centers. They are characterized by their radio jets and lobes that extend far beyond the galaxy itself.

Active Galactic Nucleus (AGN)

A central region in an active galaxy thought to contain a supermassive black hole, emitting extraordinary amounts of energy due to accretion of material.

Hubble’s Tuning Fork Classification

A morphological classification system for galaxies developed by Edwin Hubble, categorizing them into three main types: elliptical, spiral, and irregular galaxies.

the future of the milky way

is expected to involve a collision with the Andromeda galaxy in about 4.5 billion years, leading to the formation of a larger elliptical galaxy.

The Galactic Center

is the rotational center of the Milky Way galaxy, containing a supermassive black hole known as Sagittarius A*.

Dark Matter

is a form of matter that does not emit, absorb, or reflect light and is thought to make up about 27% of the universe's total mass and energy. Its existence is inferred from gravitational effects on visible matter.

Mass Estimation

is the process of determining the total mass of astronomical objects, often inferred from their gravitational effects on other objects and light. It involves using various methods such as dynamics, lensing, and stellar population analysis.

Disk stars

young, found in the disk, loosely bound, have circular orbits

Halo stars:

old, found in the halo, generally more metal-poor than disk stars, and have elliptical orbits.

Open Clusters

groups of young stars that are loosely bound by mutual gravitational attraction, typically containing a few dozen to a few thousand stars.

globular clusters

spherical collections of older stars that are densely packed and gravitationally bound, typically containing thousands to millions of stars.

Structure of the Milky Way: disk

region containing young stars, gas, and dust, characterized by a flattened shape and spiral arm structure.

Structure of the Milky Way: bulge

dense, older populations of stars

Structure of the Milky Way: halo

a roughly spherical region surrounding the Milky Way, containing older stars, globular clusters, and dark matter.

Schwarzschild Radius (Event Horizon)

The radius at which the escape velocity = speed of light (c)

Inside this radius, nothing escapes, not even light.

High-Mass Stars

are stars with masses greater than about 8 solar masses, which undergo rapid nuclear fusion and end their lives in supernova explosions.

how do high mass stars evolve?

faster than low-mass stars due to higher pressure and temperature.

CNO cycle

A stellar nuclear fusion process in which carbon, nitrogen, and oxygen isotopes act as catalysts to convert hydrogen into helium, releasing energy faster in high-mass stars.

Stellar Core Fusion Sequence

As fuel runs out in the core, fusion shifts to outer shells, producing an "onion shell" structure

The Hubble Ultra Deep Field

A very deep image of a small region of space taken by the Hubble Space Telescope. It contains thousands of galaxies, providing a view of the early universe.

Virgo cluster

A massive cluster of galaxies located in the Virgo constellation, containing over 1,300 member galaxies and serving as one of the closest large clusters to Earth.

Local Supercluster

The supercluster that contains the Local Group, including the Milky Way and Andromeda galaxies, as well as others.

Coma cluster

A large, dense cluster of galaxies located about 320 million light-years away. It contains thousands of galaxies

Superclusters*

are massive groupings of galaxies that are bound together by gravity, often containing several clusters and groups of galaxies.

Galaxies arranged in filamentary structures and voids

are part of the large-scale structure of the universe, known as the cosmic web.

What does dark energy do?

Dark energy is the mysterious force driving the accelerated expansion of the universe. It counteracts gravity and causes galaxies to move apart at increasing speeds.

4 main pieces of evidence for the Big Bang theory: cosmic microwave background

radiation, which is the faint afterglow of the Big Bang.

4 main pieces of evidence for the Big Bang theory: *expansion of the universe

redshift of distant galaxies showing they are moving away from us.

4 main pieces of evidence for the Big Bang theory: abundance of light elements

refers to the observed quantities of hydrogen, helium, and lithium, which align with predictions from Big Bang nucleosynthesis.

4 main pieces of evidence for the Big Bang theory: Large-scale structure

refers to the distribution and pattern of galaxies and galaxy clusters in the universe, which supports the predictions of the Big Bang model.