Bars and Baby Stars: The galaxy depicted in this Picture of the Week is a barred spiral known as NGC 7541, seen here as viewed by the NASA/ESA Hubble Space Telescope, in the constellation of Pisces (The Fishes). A barred spiral is a galaxy with whirling, pinwheeling, spiral arms, and a bright centre that is intersected by a bar of gas and stars. This bar cuts directly through the galaxy’s central region, and is thought to  invigorate the region somewhat, sparking activity and fuelling myriad processes that may otherwise have never occurred or have previously ground to a halt (star formation and active galactic nuclei being key examples). We think bars exist in up to two-thirds of all spiral galaxies, including our own home, the Milky Way. NGC 7541 is actually observed to have a higher-than-usual star formation rate, adding weight to the theory that spiral bars act as stellar nurseries, corralling and funnelling inwards the material and fuel needed to create and nurture new baby stars. Along with its nearby companion NGC 7537, the galaxy makes up a pair of galaxies located about 110 million light-years away from us.

Name: NGC 7541
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Pisces
Distance: 110 million light years
Release date: 27 January 2020, 06:00
Credit: ESA/Hubble & NASA, A. Riess et al.

Nature’s Grand Design: This eye-catching galaxy is known as NGC 5364. Unmistakably a spiral, NGC 5364 is also something known as a grand design spiral galaxy — a descriptive name deserved by only one-tenth of spirals. While all spirals have a structure that is broadly similar, there is quite a bit of variation amongst individual galaxies; some have patchy, oddly-shaped arms, some have bars of stars cutting through their core, some are colossal and radiant, and others are dim and diminutive. Grand designs like NGC 5364 are in many ways the archetype of a spiral galaxy. They are characterised by their prominent, well-defined arms, which circle outwards from a clear core. Despite being classified in this way, NGC 5364 is far from perfect. Its arms are asymmetrical compared to other grand design spirals — this is thought to be due to interactions with a nearby neighbour. This neighbour and NGC 5364 are tugging on one another, warping and moving their stars and gas around and causing this misshapen appearance. This image was captured by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys and Wide Field Camera 3.

Name: NGC 5364
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Virgo
Release date: 3 February 2020, 06:00
Credit: ESA/Hubble & NASA, L. Ho, P. Erwin et al.

Open Arms: The spiral galaxy NGC 2008 sits centre stage, its ghostly spiral arms spreading out towards us, in this image captured by the NASA/ESA Hubble Space Telescope. This galaxy is located about 425 million light-years from Earth in the constellation of Pictor (The Painter’s Easel). Discovered in 1834 by astronomer John Herschel, NGC 2008 is categorised as a type Sc galaxy in the Hubble sequence, a system used to describe and classify the various morphologies of galaxies. The “S” indicates that NGC 2008 is a spiral, while the “c” means it has a relatively small central bulge and more open spiral arms. Spiral galaxies with larger central bulges tend to have more tightly wrapped arms, and are classified as Sa galaxies, while those in between are classified as type Sb. Spiral galaxies are ubiquitous across the cosmos, comprising over 70% of all observed galaxies — including our own, the Milky Way. However, their ubiquity does not detract from their beauty. These grand, spiralling collections of billions of stars are among the most wondrous sights that have been captured by telescopes such as Hubble, and are firmly embedded in astronomical iconography.

Name: NGC 2008
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Pictor
Distance: 450 million light years
Release date: 10 February 2020, 06:00
Credit: ESA/Hubble & NASA, A. Bellini