Come a little closer: This Picture of the Week stars Messier 90, a beautiful spiral galaxy located roughly 60 million light-years from the Milky Way in the constellation of Virgo (The Virgin). The galaxy is part of the Virgo Cluster, a gathering of galaxies that is over 1200 strong. This image combines infrared, ultraviolet, and visible light gathered by the Wide Field and Planetary Camera 2 on the NASA/ESA Hubble Space Telescope. This camera was operational between 1994 and 2010, producing images with an unusual staircase-like shape as seen here. This is because the camera was made up of four light detectors with overlapping fields of view, one of which gave a higher magnification than the other three. When the four images are combined together in one picture, the high magnification image needs to be reduced in size in order for the image to align properly. This produces an image with a layout that looks like three steps. Messier 90 is remarkable; it is one of the few galaxies seen to be travelling toward the Milky Way, not away from it. The galaxy’s light reveals this incoming motion in that it is blueshifted. In simple terms, the galaxy is compressing the wavelength of its light as it moves towards us, like a slinky being squashed when you push on one end. This increases the frequency of the light and shifts it towards the blue end of the spectrum. As our Universe is expanding, almost all of the galaxies we see in the Universe are moving away from us, and we therefore see their light as redshifted, but Messier 90 appears to be a rare exception. Astronomers think that this blueshift is likely caused by the cluster’s colossal mass accelerating its members to high velocities on bizarre and peculiar orbits, sending them whirling around on odd paths that take them both towards and away from us over time. While the cluster itself is moving away from us, some of its constituent galaxies, such as Messier 90, are moving faster than the cluster as a whole, making it so that from Earth we see the galaxy heading towards us. However, some are also moving in the opposite direction within the cluster, and thus seem to be streaking away from us at very high velocity.

Name: Messier 90
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Virgo
Distance: 60 million light years
Release date: 20 May 2019, 06:00
Credit: ESA/Hubble & NASA, W. Sargent et al.

Bucking the trend: This luminous orb is the galaxy NGC 4621, better known as Messier 59. As this latter moniker indicates, the galaxy was listed in the famous catalogue of deep-sky objects compiled by French comet-hunter Charles Messier in 1779. However, German astronomer Johann Gottfried Koehler is credited with discovering the galaxy just days before Messier added it to his collection. Modern observations show that Messier 59 is an elliptical galaxy, one of the three main kinds of galaxies along with spirals and irregulars. Ellipticals tend to be the most evolved of the trio, full of old, red stars and exhibiting little or no new star formation. Messier 59, however, bucks this trend somewhat; the galaxy does show signs of star formation, with some newborn stars residing within a disc near the core. Located in the 2000-strong Virgo Cluster of galaxies within the constellation of Virgo (The Virgin), Messier 59 lies approximately 50 million light-years away from us. This image was taken by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys.

Name: NGC 4621
Type: Local Universe : Galaxy : Type : Elliptical
Category: Galaxies
Constellation: Virgo
Release date: 27 May 2019, 06:00
Credit: ESA/Hubble & NASA, P. Cote

Galactic maturity: This striking image was taken by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3, a powerful instrument installed on the telescope in 2009. WFC3 is responsible for many of Hubble’s most breathtaking and iconic photographs, including Pictures of the Week. Shown here, NGC 7773 is a beautiful example of a barred spiral galaxy. A luminous bar-shaped structure cuts prominently through the galaxy's bright core, extending to the inner boundary of NGC 7773's sweeping, pinwheel-like spiral arms. Astronomers think that these bar structures emerge later in the lifetime of a galaxy, as star-forming material makes its way towards the galactic centre — younger spirals do not feature barred structures as often as older spirals do, suggesting that bars are a sign of galactic maturity. They are also thought to act as stellar nurseries, as they gleam brightly with copious numbers of youthful stars. Our galaxy, the Milky Way, is thought to be a barred spiral like NGC 7773. By studying galactic specimens such as NGC 7773 throughout the Universe, researchers hope to learn more about the processes that have shaped — and continue to shape — our cosmic home.

Name: NGC 7773
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Pegasus
Release date: 3 June 2019, 06:00
Credit: ESA/Hubble & NASA, J. Walsh

An explosive galaxy: When massive stars die at the end of their short lives, they light up the cosmos with bright, explosive bursts of light and material known as supernovae. A supernova event is incredibly energetic and intensely luminous — so much so that it forms what looks like an especially bright new star that slowly fades away over time. These exploding stars glow so incredibly brightly when they first form that they can be spotted from afar using telescopes such as the NASA/ESA Hubble Space Telescope. The subject of this image, a spiral galaxy named NGC 4051 — about 45 million light-years from Earth — has hosted multiple supernovae in past years. The first was spotted in 1983 (SN 1983I), the second in 2003 (SN 2003ie), and the most recent in 2010 (SN 2010br). These explosive events were seen scattered throughout the centre and spiral arms of NGC 4051. The SN 1983I and SN 2010br were both categorised as supernovae of type Ic. This type of supernova is produced by the core collapse of a massive star that has lost its outer layer of hydrogen and helium, either via winds or by mass transfer to a companion. Because of this, type Ic — and also type Ib — supernovae are sometimes referred to as stripped core-collapse supernovae. NGC 4501 sits in the southern part of a cluster of galaxies known as the Ursa Major I Cluster; this cluster is especially rich in spirals such as NGC 4051, and is a subset of the larger Virgo Supercluster, which also houses the Milky Way.

Name: NGC 4051
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Ursa Major
Distance: 45 million light years
Release date: 10 June 2019, 06:00
Credit: ESA/Hubble & NASA, D. Crenshaw and O. Fox