The mysteries of UGC 8201: The galaxy UGC 8201, captured here by the NASA/ESA Hubble Space Telescope, is a dwarf irregular galaxy, so called because of its small size and chaotic structure. It lies just under 15 million light-years away from us in the constellation of Draco (the Dragon). As with most dwarf galaxies it is a member of a larger group of galaxies. In this case UCG 8201 is part of the M81 galaxy group; this group is one of the closest neighbours to the Local Group of galaxies, which contains our galaxy, the Milky Way. UGC 8201 is at an important phase in its evolution. It has recently finished a long period of star formation, which had significant impact on the whole galaxy. This episode lasted for several hundred million years and produced a high number of newborn bright stars. These stars can be seen in this image as the dominating light source within the galaxy. This process also changed the distribution and amount of dust and gas in between the stars in the galaxy. Such large star formation events need extensive sources of energy to trigger them. However, compared to larger galaxies, dwarf galaxies lack such sources and they do not appear to have enough gas to produce as many new stars as they do. This raises an important unanswered question in galaxy evolution: How do relatively isolated, low-mass systems such as dwarf galaxies sustain star formation for extended periods of time? Due to its relative proximity to Earth UGC 8201 is an excellent object for research and provides an opportunity to improve our understanding of how dwarf galaxies evolve and grow.

Name: UGC 8201
Type: Local Universe : Galaxy : Size : Dwarf
Category: Galaxies
Constellation: Draco
Distance: 15 million light years
Release date: 9 March 2015, 10:00
Credit: ESA/Hubble & NASA

An intriguing young-looking dwarf galaxy: The bright streak of glowing gas and stars in this NASA/ESA Hubble Space Telescope image is known as PGC 51017, or SBSG 1415+437. It is type of galaxy known as a blue compact dwarf. This particular dwarf is well studied and has an interesting star formation history. Astronomers initially thought that SBS 1415+437 was a very young galaxy currently undergoing its very first burst of star formation, but more recent studies have suggested that the galaxy is in fact a little older, containing stars over 1.3 billion years old. Starbursts are an area of ongoing research for astronomers — short-lived and intense periods of star formation, during which huge amounts of gas within a galaxy are hungrily used up to form newborn stars. They have been seen in gas-rich disc galaxies, and in some lower-mass dwarfs. However, it is still unclear whether all dwarf galaxies experience starbursts as part of their evolution. It is possible that dwarf galaxies undergo a star formation cycle, with bursts occurring repeatedly over time. SBS 1415+437 is an interesting target for another reason. Dwarf galaxies like this are thought to have formed early in the Universe, producing some of the very first stars before merging together to create more massive galaxies. Dwarf galaxies which contain very few of the heavier elements formed from having several generations of stars, like SBS 1415+437, remain some of the best places to study star-forming processes similar to those thought to occur in the early Universe. However, it seems that our nearby patch of the Universe may not contain any galaxies that are currently undergoing their first burst of star formation. A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Nick Rose.

Name: PGC 51017
Type: Local Universe : Galaxy : Size : Dwarf
Category: Galaxies
Constellation: Bootes
Distance: 45 million light years
Release date: 16 March 2015, 10:00
Credit: ESA/Hubble & NASA Acknowledgement: Alessandra Aloisi (STScI) and Nick Rose

A galaxy on the edge: This NASA/ESA Hubble Space Telescope image shows an edge-on view of the spiral galaxy NGC 5023. Due to its orientation we cannot appreciate its spiral arms, but we can admire the elegant profile of its disc. The galaxy lies over 30 million light-years away from us. NGC 5023 is part of the M51 group of galaxies. The brightest galaxy in this group is Messier 51, the Whirlpool Galaxy, which has been captured by Hubble many times. NGC 5023 is less fond of the limelight and seems rather unsociable in comparison — it is relatively isolated from the other galaxies in the group. Astronomers are particularly interested in the vertical structure of discs like these. By analysing the structure above and below the central plane of the galaxy they can make progress in understanding galaxy evolution. Astronomers are able to analyse the distribution of different types of stars within the galaxy and their properties, in particular how well evolved they are on the Hertzsprung–Russell Diagram — a scatter graph of stars that shows their evolution. NGC 5023 is one of six edge-on spiral galaxies observed as part of a study using Hubble’s Advanced Camera for Surveys. They study this vertical distribution and find a trend which suggests that heating of the disc plays an important role in producing the stars seen away from the plane of the galaxy. In fact, NGC 5023 is pretty popular when it comes to astronomers, despite its unsociable behaviour. The galaxy is also one of 14 disc galaxies that are part of the GHOSTS survey — a survey which uses Hubble data to study galaxy halos, outer discs and star clusters. It is the largest study to date of star populations in the outskirts of disc galaxies. The incredible sharp sight of Hubble has allowed scientist to count more than 30 000 individual bright stars in this image. This is only a small fraction of the several billion stars that this galaxy contains, but the others are too faint to detect individually even with Hubble.

Name: NGC 5023
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Canes Venatici
Distance: 33 million light years
Release date: 23 March 2015, 10:00
Credit: ESA/Hubble & NASA

A cosmological measuring tape: This NASA/ESA Hubble Space Telescope image shows the spiral galaxy NGC 3021 which lies about 100 million light-years away in the constellation of Leo Minor (The Little Lion). Among many other types of stars, this galaxy contains Cepheid variable stars, which can be used work out the distance to the galaxy. These stars pulsate at a rate that is closely related to their intrinsic brightness, so measurements of their rate of pulsation and their observed brightness give astronomers enough information to calculate the distance to the galaxy itself. Cepheids are also used to calibrate an even brighter distance marker, that can be used over greater distances: Type Ia supernovae. One of these bright exploding stars was observed in NGC 3021, back in 1995. In addition, the supernova in NGC 3021 was also used to refine the measurement of what is known as the Hubble constant. The value of this constant defines how fast the Universe is expanding and the more accurately we know it the more we can understand about the evolution of the Universe in the past as well as in the future. So, there is much more to this galaxy than just a pretty spiral.

Name: NGC 3021
Type: Unspecified : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Leo Minor
Distance: 100 million light years
Release date: 30 March 2015, 10:00
Credit: NASA & ESA Acknowledgement: A. Riess (STScI)