A fascinating core: This NASA/ESA Hubble Space Telescope image captures the galaxy Messier 84 — also known as NGC 4374 — an object from the Messier catalogue, published in its final version in 1781 by Charles Messier. This elliptical galaxy was discovered in March 1781 and lies about 60 million light-years away from Earth in the constellation of Virgo (The Virgin). The galaxy is part of the very heavily populated centre of the Virgo Cluster, a cluster which consists of more than 1000 galaxies. This image does not show the whole galaxy but only its very interesting centre, and is likely to be the best image of the region ever captured. Previous observations using Hubble’s Space Telescope Imaging Spectrograph (STIS) revealed a supermassive black hole in the centre of Messier 84. Astronomers found the supermassive black hole by mapping the motion of the gas and the stars which are caught in its grip. Next to its interesting centre Messier 84 is also known for its supernovae. Two supernovae have been observed within the galaxy. The first, SN1957 was discovered in 1957 and another, called SN1991bg, was discovered in 1991.

Name: M 84
Type: Local Universe : Galaxy : Type : Elliptical
Category: Nebulae
Constellation: Virgo
Distance: 60 million light years
Release date: 1 June 2015, 10:00
Credit: ESA/Hubble & NASA

Meeting the neighbours: There are many galaxies in the Universe and although there is plenty of room, they tend to stick together. The Milky Way, for example, is part of a large gathering of over fifty galaxies known as the Local Group. Galaxy groups like this come together to form even larger groups called clusters which can congregate further still to create mammoth superclusters. The sphere of space surrounding our galaxy is known as the Local Volume, a region some 35 million light-years in diameter and home to several hundred known galaxies. The subject of this new NASA/ESA Hubble Space Telescope image, a beautiful dwarf irregular galaxy known as PGC 18431, is one of these galaxies. This image shows PGC 18431 smudged across the sky, but it wasn’t imaged purely for its looks. These Hubble observations were gathered in order to probe how Local Volume galaxies cluster together and move around. Hubble’s high resolution allows astronomers to explore star populations within these moderately distant galaxies — specifically, stars known as tip of the red-giant branch stars — in order to get an idea of the galaxy’s composition and, crucially, its distance from us. Knowing galactic distances enables us to accurately map a galaxy sample in three dimensions, a method key to understanding more about our cosmic neighbours, and to dismiss perspective and line-of-sight illusions.

Name: PGC 18431
Type: Local Universe : Galaxy : Type : Irregular
Category: Galaxies
Constellation: Columba
Distance: 35 million light years
Release date: 8 June 2015, 10:00
Credit: ESA/Hubble & NASA

True blue: This NASA/ESA Hubble Space Telescope image shows a galaxy known as UGC 11411. It is a galaxy type known as an irregular blue compact dwarf (BCD) galaxy. BCD galaxies are about a tenth of the size of a typical spiral galaxy such as the Milky Way, and are made up of large clusters of hot, massive stars that ionise the surrounding gas with their intense radiation. Because these stars are so hot they glow brightly with a blue hue, giving galaxies like UGC 11411 their characteristic blue tint. With these massive stars being less than 10 million years old, they are very young compared to stellar standards. They were created during a starburst, a galaxy-wide episode of furious star formation. UGC 11411 in particular has an extremely high star formation rate, even for a BCD galaxy. Unusually for galaxies with such intense star-forming regions, BCDs don’t contain either a lot of dust, or the heavy elements that are typically found as trace elements in recently formed stars, making their composition very similar to that of the material from which the first stars formed in the early Universe. Because of this astronomers consider BCD galaxies to be good objects to study to improve our understanding of primordial star-forming processes. The bright stars in the image are foreground stars in our own Milky Way galaxy.

Name: UGC 11411
Type: Local Universe : Galaxy : Size : Dwarf
Category: Galaxies
Constellation: Draco
Distance: 15 million light years
Release date: 15 June 2015, 10:00
Credit: ESA/Hubble & NASA

A nitrogen-rich nebula: This NASA/ESA Hubble Space Telescope image shows a planetary nebula named NGC 6153, located about 4000 light-years away in the southern constellation of Scorpius (The Scorpion). The faint blue haze across the frame shows what remains of a star like the Sun after it has depleted most of its fuel. When this happens, the outer layers of the star are ejected, and get excited and ionised by the energetic ultraviolet light emitted by the bright hot core of the star, forming the nebula. NGC 6153 is a planetary nebula that is elliptical in shape, with an extremely rich network of loops and filaments, shown clearly in this Hubble image. However, this is not what makes this planetary nebula so interesting for astronomers. Measurements show that NGC 6153 contains large amounts of neon, argon, oxygen, carbon and chlorine — up to three times more than can be found in the Solar System. The nebula contains a whopping five times more nitrogen than the Sun! Although it may be that the star developed higher levels of these elements as it grew and evolved, it is more likely that the star originally formed from a cloud of material that already contained lots more of these elements. A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Matej Novak.

Name: NGC 6153
Type: Milky Way : Nebula : Type : Planetary
Category: Nebulae
Constellation: Scorpius
Distance: 4000 light years
Release date: 22 June 2015, 10:00
Credit: ESA/Hubble & NASA Acknowledgement: Matej Novak

Intense and short-lived: This NASA/ESA Hubble Space Telescope picture shows a galaxy named SBS 1415+437 or SDSS CGB 12067.1, located about 45 million light-years from Earth. SBS 1415+437 is a Wolf–Rayet galaxy, a type of starbursting galaxy with an unusually high number of extremely hot and massive stars known as Wolf–Rayet stars. These stars can be around 20 times as massive as the Sun, but seem to be on a mission to shed surplus mass as quickly as possible — they blast substantial winds of particles out into space, causing them to dwindle at a rapid rate. A typical star of this type can lose a mass equal to that of our Sun in just 100 000 years! These massive stars are also incredibly hot, with surface temperatures some 10 to 40 times that of the Sun, and very luminous, glowing at tens of thousands to several million times the brightness of the Sun. Many of the brightest and most massive stars in the Milky Way are Wolf–Rayet stars. Because these stars are so intense they do not last very long, burning up their fuel and blasting their bulk out into the cosmos on very short timescale ‒ only a few hundred thousand years. Because of this it is unusual to find more than a few of these stars per galaxy — except in Wolf–Rayet  galaxies, like the one in this image.

Name: SBS1415+437
Type: Unspecified : Galaxy : Activity : Starburst
Category: Galaxies
Constellation: Bootes
Distance: 45 million light years
Release date: 29 June 2015, 10:00
Credit: ESA/Hubble & NASA