Galaxies spiralling around Leo: Shown here is a spiral galaxy known as NGC 3455, which lies some 65 million light-years away from us in the constellation of Leo (The Lion). Galaxies are classified into different types according to their structure and appearance. This classification system is known as the Hubble Sequence, named after its creator Edwin Hubble. In this sequence, NGC 3455 is known as a type SB galaxy — a barred spiral. Barred spiral galaxies account for approximately two thirds of all spirals. Galaxies of this type appear to have a bar of stars slicing through the bulge of stars at their centre. The SB classification is further sub-divided by the appearance of a galaxy's pinwheeling spiral arms; SBa types have more tightly wound arms, whereas SBc types have looser ones. SBb types, such as NGC 3455, lie in between. NGC 3455 is part of a pair of galaxies — its partner, NGC 3454, lies out of frame. This cosmic duo belong to a group known as the NGC 3370 group, which is in turn one of the Leo II groups, a large collection of galaxies scattered some 30 million light-years to the right of the Virgo cluster. This new image is from Hubble's Advanced Camera for Surveys (ACS). A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Nick Rose.

Name: NGC 3455
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Leo
Distance: 65 million light years
Release date: 14 April 2014, 10:00
Credit: ESA/Hubble & NASA Acknowledgement: Nick Rose

Cosmic fairy lights: This sparkling jumble is Messier 5 — a globular cluster consisting of hundreds of thousands of stars bound together by their collective gravity. But Messier 5 is no normal globular cluster. At 13 billion years old it is incredibly old, dating back to close to the beginning of the Universe, which is some 13.8 billion years of age. It is also one of the biggest clusters known, and at only 24 500 light-years away, it is no wonder that Messier 5 is a popular site for astronomers to train their telescopes on. Messier 5 also presents a puzzle. Stars in globular clusters grow old and wise together. So Messier 5 should, by now, consist of old, low-mass red giants and other ancient stars. But it is actually teeming with young blue stars known as blue stragglers. These incongruous stars spring to life when stars collide, or rip material from one another.

Name: Messier 5
Type: Local Universe : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Serpens Caput
Distance: 25000 light years
Release date: 21 April 2014, 10:00
Credit: ESA/Hubble & NASA

A hungry starburst galaxy: This new Hubble picture is the sharpest ever image of the core of spiral galaxy Messier 61 and the central part of the galaxy is shown in striking detail. The image is comprised of 2003 and 2004 data from the now decommissioned High Resolution Channel (HRC) of Hubble's Advanced Camera for Surveys. Also known as NGC 4303, this galaxy is roughly 100 000 light-years across, comparable in size to our galaxy, the Milky Way. Both Messier 61 and our home galaxy belong to a group of galaxies known as the Virgo Supercluster in the constellation of Virgo (The Virgin) — a group of galaxy clusters containing up to 2000 spiral and elliptical galaxies in total. Messier 61 is a type of galaxy known as a starburst galaxy. Starburst galaxies experience an incredibly high rate of star formation, hungrily using up their reservoir of gas in a very short period of time (in astronomical terms). But this is not the only activity going on within the galaxy; deep at its heart there is thought to be a supermassive black hole that is violently spewing out radiation. Despite its inclusion in the Messier Catalogue, Messier 61 was actually discovered by Italian astronomer Barnabus Oriani in 1779. Charles Messier also noticed this galaxy on the very same day as Oriani, but mistook it for a passing comet — the comet of 1779. A version of this image was submitted to the Hubble’s Hidden Treasures image processing competition by Flickr user Det58.

Name: Messier 61
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Virgo
Distance: 55 million light years
Release date: 28 April 2014, 10:00
Credit: ESA/Hubble & NASA Acknowledgement: Det58

The scale of the Universe: This bundle of bright stars and dark dust is a dwarf spiral galaxy known as NGC 4605, located around 16 million light-years away in the constellation of Ursa Major (The Great Bear). This galaxy’s spiral structure is not obvious from this image, but NGC 4605 is classified as an SBc type galaxy — meaning that it has sprawling, loosely wound arms and a bright bar of stars cutting through its centre. NGC 4605 is a member of the Messier 81 group of galaxies, a gathering of bright galaxies including its namesake Messier 81 (heic0710), and the well-known Messier 82 (heic0604a). Galaxy groups like this usually contain around 50 galaxies, all loosely bound together by gravity. This group is famous for its unusual members, many of which formed from  collisions between galaxies. With its somewhat unusual form, NGC 4605  fits in well with the family of perturbed galaxies in the M81  group, although the origin of its abnormal features is not yet clear. The Messier 81 group is one of the nearest groups to our own, the Local Group, which houses the Milky Way and some of its well-known neighbours, including the Andromeda Galaxy and the Magellanic Clouds. Galaxy groups provide environments where galaxies can evolve through interactions like collisions and mergers. These galaxy groups are then lumped together into even larger gatherings of galaxies known as clusters and superclusters. The Local and Messier 81 groups both belong to the Virgo Supercluster, a large and massive collection of some 100 galaxy groups and clusters. With so many galaxies swarming around, NGC 4605 may seem unremarkable. However, astronomers are using this galaxy to test our knowledge of stellar evolution. The newly-formed stars in NGC 4605 are being used to investigate how interactions between galaxies affect the formation, evolution, and behaviour of the stars within, how bright stellar nurseries come together to form stellar clusters and stellar associations, and how these stars evolve over time. And that's not all — NGC 4605 is also proving to be a good testing ground for dark matter. Our theories on this hypothetical type of matter have had good success at describing how the Universe looks and behaves on a large scale — for example at the galaxy supercluster level — but when looking at individual galaxies, they have run into problems. Observations of NGC 4605 show that the way in which dark matter is spread throughout its halo is not quite as these models predict. While intriguing, observations in this area are still inconclusive, leaving astronomers to ponder over the contents of the Universe.

Name: NGC 4605
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Ursa Major
Distance: 15 million light years
Release date: 5 May 2014, 10:00
Credit: ESA/Hubble & NASAAcknowledgement: D. Calzetti (University of Massachusetts) and the LEGUS Team