Galaxies

Galaxies A galaxy is a large system of stars and interstellar matter. Stars can be classified by heavy metal concentration. Two types of star populations: Population I – hot, luminous and young stars, seeded with heavy elements Population II – older and cooler with fewer heavy elements (formed earlier than newer stars)

Types of Galaxies Galaxies can be classified in several ways. The most common is a system developed by Edwin Hubble, who discovered that the universe is filled with many galaxies beyond our own Milky Way.

Types of Galaxies Galaxies can be classified into four broad categories: 1) spiral 2) lenticular 3) elliptical 4) irregular

Types of Galaxies - Spirals Spirals are flat disks of stars with bright bulges in their centers. Spiral arms wrap around these bulges. Spiral arms probably form as the result of waves that sweep through the galactic disk. In some spirals, a wave organizes the stars in the center into a bar. The arms of barred galaxies spiral outward from the ends of the bar.

Types of Galaxies - Spirals The nucleus or bulge consists of population II stars, the disk consists of population I stars.

The Milky Way Our galaxy is a barred spiral. It has at least four spiral arms. The name was derived from Greek, then Latin.

The Milky Way – Spiral Arms Four main arms: Perseus, Norma/Cygnus, Crux/Scutum, Carina/Sagittarius The Sol system is in a spur, the Orion spur.

Andromeda

NGC 4414

NGC 1300 Barred Spiral

Very much like our Milky Way galaxy NGC 3949 Very much like our Milky Way galaxy

NGC 7331 “The Milky Way’s Twin”

A band of absorbing dust make an “evil eye”

One of my favourites; I have a summer home there M104 – Sombrero Galaxy One of my favourites; I have a summer home there

Infrared view from Spitzer telescope Sombrero Part 2 Infrared view from Spitzer telescope

Types of Galaxies – Lenticular Smooth disk galaxies. Stellar formation in these galaxies has stopped, so they are populated by population II stars.

NGC 2787

Types of Galaxies – Elliptical Like fat, fuzzy eggs or footballs. Instead of spreading out into a thin disk, as they do in spirals, the stars in ellipticals wrap completely around the galaxy's heart in all directions. Mostly population II stars

Types of Galaxies – Elliptical The largest galaxies in the universe are giant ellipticals. They can contain a trillion stars or more, and span as much as two million light-years (20 times the Milky Way). Some of them appear to contain "supermassive" black holes at their hearts —three billion times as heavy as the Sun.

M110

M32

Likely cause by a collision of two gas-rich galaxies NGC 1316 Likely cause by a collision of two gas-rich galaxies

M87 Elliptical galaxy with super massive black hole jet – one that has absorbed over 2 billion solar masses of material

Types of Galaxies – Irregular Irregulars exhibit peculiar shapes. Often distorted by gravitation by other objects .

“Baby” galaxy – the youngest galaxy found so far I Zwicky 18 “Baby” galaxy – the youngest galaxy found so far

Being pulled apart by a nearby galactic cluster NGC 1427A Being pulled apart by a nearby galactic cluster

Naming Galaxies Many conventions exist for naming galaxies. Conventions include: 1) IAU traditional names 2) Messier object names 3) New General Catalogue names

Hubble Classification Scheme Elliptical: E  elliptical #  ellipticity (0 is spherical, 7 is cigar) Spiral: S  Spiral B  Barred letter  Bulge and Arms

Hubble Classification Scheme When naming galaxies (especially ellipticals), geometry or viewing angles can play a large role. The ‘tuning fork’ is not related to galactic evolution.

Sometimes galaxies collide! Colliding Galaxies Sometimes galaxies collide!

NGC 2207 and IC 2163

NGC 4038/4039: The Antennae

NGC 4676: The Mice

Spiral galaxy sliding through a much larger galaxy NCG 1275 Spiral galaxy sliding through a much larger galaxy

Andromeda and the Milky Way In about 5 billion years, Andromeda and the Milky Way may collide resulting in an elliptical (this will take about a billion years to form)

Clusters and Superclusters Galaxies are grouped into clusters. Our cluster is known as the Local Cluster.

                                                                                                                                                                          

Clusters and Superclusters Clusters of galaxies are further grouped into superclusters. Our supercluster is known as the Virgo Supercluster, or Local Supercluster.