The NGC and its modern counterpart: Some astronomical objects have endearing or quirky nicknames, inspired by mythology or their own appearance. Take, for example, the constellation of Orion (The Hunter), the Sombrero Galaxy, the Horsehead Nebula, or even the Milky Way. However, the vast majority of cosmic objects appear in astronomical catalogues, and are given rather less poetic names based on the order of their discovery. Two galaxies are clearly visible in this Hubble image, the larger of which is NGC 4424. This galaxy is catalogued in the New General Catalogue of Nebulae and lusters of Stars (NGC), which was compiled in 1888. The NGC is one of the largest astronomical catalogues, which is why so many Hubble Pictures of the Week feature NGC objects. In total there are 7840 entries in the catalogue and they are also generally the larger, brighter, and more eye-catching objects in the night sky, and hence the ones more easily spotted by early stargazers. The smaller, flatter, bright galaxy sitting just below NGC 4424 is named LEDA 213994. The Lyon-Meudon Extragalactic Database (LEDA) is far more modern than the NGC. Created in 1983 at the Lyon Observatory it contains millions of objects. However, many NGC objects still go by their initial names simply because they were christened within the NGC first. No astronomer can resist a good acronym, and “LEDA” is more appealing than “the LMED”, perhaps thanks to the old astronomical affinity with mythology when it comes to naming things: Leda was a princess in Ancient Greek mythology.

Name: LEDA 213994, NGC 4424
Type: Local Universe : Galaxy
Category: Galaxies
Constellation: Virgo
Distance: 30 million light years
Release date: 27 March 2017, 06:00
Credit: ESA/Hubble & NASA

Starbursts in Virgo: Despite all efforts galaxy formation and evolution are still far from being fully understood. Fortunately, the conditions we see within certain galaxies — such as so-called starburst galaxies — can tell us a lot about how they have evolved over time. Starburst galaxies contain a region (or many regions) where stars are forming at such a breakneck rate that the galaxy is eating up its gas supply faster than it can be replenished! NGC 4536 is such a galaxy, captured here in beautiful detail by the Hubble’s Wide Field Camera 3 (WFC3). Located roughly 50 million light-years away in the constellation of Virgo (The Virgin), it is a hub of extreme star formation. There are several different factors that can lead to such an ideal environment in which stars can form at such a rapid rate. Crucially, there has to be a sufficiently massive supply of gas. This might be acquired in a number of ways — for example by passing very close to another galaxy, in a full-blown galactic collision, or as a result of some event that forces lots of gas into a relatively small space.

Name: NGC 4536
Type: Local Universe : Galaxy : Type : SpiralLocal Universe : Galaxy : Activity : Starburst
Category: Galaxies
Constellation: Virgo
Distance: 50 million light years
Release date: 10 April 2017, 06:00
Credit: ESA/Hubble & NASA

Blowing cosmic bubbles: This entrancing image shows a few of the tenuous threads that comprise Sh2-308, a faint and wispy shell of gas located 5200 light-years away in the constellation of Canis Major (The Great Dog). Sh2-308 is a large bubble-like structure wrapped around an extremely large, bright type of star known as a Wolf-Rayet Star — this particular star is called EZ Canis Majoris. These type of stars are among the brightest and most massive stars in the Universe, tens of times more massive than our own Sun, and they represent the extremes of stellar evolution. Thick winds continually poured off the progenitors of  such stars, flooding their surroundings and draining the outer layers of  the Wolf-Rayet stars. The fast wind of a Wolf-Rayet star therefore sweeps up the  surrounding material to form bubbles of gas. EZ Canis Majoris is responsible for creating the bubble of Sh2-308 — the star threw off its outer layers to create the strands visible here. The intense and ongoing radiation from the star pushes the bubble out further and further, blowing it bigger and bigger. Currently the edges of Sh2-308 are some 60 light-years apart! Beautiful as these cosmic bubbles are, they are fleeting. The same stars that form them will also cause their death, eclipsing and subsuming them in violent supernova explosions.

Name: EZ Canis Majoris, Sh2-308
Type: Milky Way : Star : Type : Wolf-Rayet
Category: Nebulae
Constellation: Canis Major
Distance: 5000 light years
Release date: 17 April 2017, 06:00
Credit: ESA/Hubble & NASA

A matter of distance: In space, being outshone is an occupational hazard. This NASA/ESA Hubble Space Telescope image captures a galaxy named NGC 7250. Despite being remarkable in its own right — it has bright bursts of star formation and recorded supernova explosions — it blends into the background somewhat thanks to the gloriously bright star hogging the limelight next to it. 
This bright object is a single and little-studied star named TYC 3203-450-1, located in the constellation of Lacerta (The Lizard), much closer than the much more distant galaxy. Only this way a normal star can outshine an entire galaxy, consisting of billions of stars. Astronomers studying distant objects call these stars “foreground stars” and they are often not very happy about them, as their bright light is contaminating the faint light from the more distant and interesting objects they actually want to study.
In this case TYC 3203-450-1 million times closer than NGC 7250 which lies over 45 million light-years away from us. Would the star be the same distance as NGC 7250, it would hardly be visible in this image.

Name: NGC 7250, TYC 3203-450-1
Type: Local Universe : StarLocal Universe : Galaxy
Category: GalaxiesStars
Constellation: Lacerta
Release date: 24 April 2017, 06:00
Credit: ESA/Hubble & NASA

A cosmic conversation: This image from Hubble’s Wide Field Camera 3 (WFC3) shows a spiral galaxy NGC 5917, perhaps best known for its intriguing interactions with its neighbouring galaxy MCG-01-39-003 (not visible here, but located off the bottom right of the frame — as seen here). Mass is often confused with weight, but they are very different things. Mass is the very substance of an object and is something one always has, no matter the location. If you fly to the Moon and experience low-gravity conditions, your mass has not changed at all. What has actually changed is your weight, because weight is a force caused by the gravitational attraction of another massive body. Gravity is how objects with mass “talk” to one another. People do weigh less on the Moon, but not because they have lost any body mass — the mass of the Moon is less than that of the Earth, so it exerts a smaller gravitational pull on them. Understanding mass is vital when it comes to understanding why objects behave the way they do in space. Without mass “talking” via gravity, the planets would not orbit the Sun, and galaxies would not interact as NGC 5917 does with its neighbour. Galaxy interactions can lead to very interesting effects; the galaxies can steal mass — in form of stars, dust and gas — from one another, distort and warp one another’s shape, or trigger immense waves of new star formation. Sometimes, a galactic duo interact so strongly that they end up colliding and merging completely. Unfortunately, if NGC 5917 is destined to merge with its celestial neighbour, it will happen much too far into the future for us to enjoy the spectacle.

Name: NGC 5917
Type: Local Universe : Galaxy : Type : Interacting
Category: Galaxies
Constellation: Libra
Release date: 1 May 2017, 06:00
Credit: ESA/Hubble & NASA