Picture of the Week

2 November 2020: The galaxy UGCA 193, seen here by the NASA/ESA Hubble Space Telescope, is a galaxy in the constellation of Sextans (The Sextant). Looking rather like a waterfall, UGCA 193 appears to host many young stars, especially in its lower portion, creating a striking blue haze and the sense that the stars are falling from “above”. The blue colour of UGCA 193 indicates the stars that we see are hot — some with temperatures exceeding 6 times that of our Sun. We know that cooler stars appear to our eyes more red, and hotter stars appear more blue. As the mass and surface temperature of a star, and therefore its colour, are linked, heavier stars are able to “burn” at higher temperatures resulting in a blue glow from their surface.

26 October 2020: Appearing within the boundless darkness of space, the NASA/ESA Hubble Space Telescope’s snapshot of NGC 34 looks more like an otherworldly, bioluminescent creature from the deep oceans than a galaxy. Lying in the constellation Cetus (The Sea Monster), the galaxy’s outer region appears almost translucent, pinpricked with stars and strange wispy tendrils. The main cause for this galaxy’s odd appearance lies in its past. If we were able to reverse time by a few million years, we would see two beautiful spiral galaxies on a direct collision course. When these galaxies collided into one another, their intricate patterns and spiral arms were permanently disturbed. This image shows the galaxy's bright centre, a result of this merging event that has created a burst of new star formation and lit up the surrounding gas. As the galaxies continue to intertwine and become one, NGC 34’s shape will become more like that of …

19 October 2020: In this spectacular image captured by the NASA/ESA Hubble Space Telescope, the galaxy NGC 2799 (on the left) is seemingly being pulled into the centre of the galaxy NGC 2798 (on the right). Interacting galaxies, such as these, are so named because of the influence they have on each other, which may eventually result in a merger or a unique formation. Already, these two galaxies have seemingly formed a sideways waterspout, with stars from NGC 2799 appearing to fall into NGC 2798 almost like drops of water. Galactic mergers can take place over several hundred million to over a billion years. While one might think the merger of two galaxies would be catastrophic for the stellar systems within, the sheer amount of space between stars means that stellar collisions are unlikely and stars typically drift past each other.

12 October 2020: This image, taken with the NASA/ESA Hubble Space Telescope, depicts a special class of star-forming nursery known as Free-floating Evaporating Gaseous Globules, or frEGGs for short. This object is formally known as J025157.5+600606. When a massive new star starts to shine while still within the cool molecular cloud from which it formed, its energetic radiation can ionise the cloud’s hydrogen and create a large, hot bubble of ionised gas. Amazingly, located within this bubble of hot gas around a nearby massive star are the frEGGs: dark compact globules of dust and gas, some of which are giving birth to low-mass stars. The boundary between the cool, dusty frEGG and the hot gas bubble is seen as the glowing purple/blue edges in this fascinating image. In July 2020 a previous ESA/Hubble Picture of the Week, of J025027.7+600849, featured another frEEG.

5 October 2020: At around 60 million light-years from Earth, the Great Barred Spiral Galaxy NGC 1365 is captured beautifully in this image by the NASA/ESA Hubble Space Telescope. Located in the constellation of Fornax (The Furnace), the blue and fiery orange swirls show us where stars have just formed and the dusty sites of future stellar nurseries. At the outer edge of the image, enormous star-forming regions within NGC 1365 can be seen. The bright, light-blue regions indicate the presence of hundreds of baby stars that formed from coalescing gas and dust within the galaxy's outer arms. This Hubble image was captured as part of a joint survey with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. The survey will help scientists understand how the diversity of galaxy environments observed in the nearby Universe, including NGC 1365 and previous ESA/Hubble Pictures of the Week such as NGC 2835 and NGC 2775, influence …

28 September 2020: This stunning image by the NASA/ESA Hubble Space Telescope features the spiral galaxy NGC 5643 in the constellation of Lupus (The Wolf). Looking this good isn’t easy; thirty different exposures, for a total of 9 hours observation time, together with the high resolution and clarity of Hubble, were needed to produce an image of such high level of detail and of beauty. NGC 5643 is about 60 million light-years away from Earth and has been the host of a recent supernova event (not visible in this latest image). This supernova (2017cbv) was a specific type in which a white dwarf steals so much mass from a companion star that it becomes unstable and explodes. The explosion releases significant amounts of energy and lights up that part of the galaxy. The observation was proposed by Adam Riess, who was awarded a Nobel Laureate in physics 2011 for his contributions to the …

21 September 2020: Resting on the tail of the Great Bear in the constellation of Ursa Major, lies NGC 5585, a spiral galaxy that is more than it appears. The many stars, and dust and gas clouds that make up NGC 5585, shown here in this Hubble image, contribute only a small fraction of the total mass of the galaxy. As in many galaxies, this discrepancy can be explained by the abundant yet seemingly invisible presence of dark matter. The stellar disc of the galaxy extends over 35 000 light-years across. When compared with galaxies of a similar shape and size, NGC 5585 stands out by having a notably different composition: Contributing to the total mass of the galaxy, it contains a far higher proportion of dark matter. Hotspots of star formation can be seen along the galaxy’s faint spiral arms. These regions shine a brilliant blue, contrasting strikingly against the ever-black background …

14 September 2020: The twisting patterns created by the multiple spiral arms of NGC 2835 create the illusion of an eye. This is a fitting description, as this magnificent galaxy resides near the head of the southern constellation of Hydra, the water snake. This stunning barred spiral galaxy, with a width of just over half that of the Milky Way, is brilliantly featured in this image taken by the NASA/ESA Hubble Space Telescope. Although it cannot be seen in this image, a supermassive black hole with a mass millions of times that of our Sun is known to nestle in the very centre of NGC 2835 . This galaxy was imaged as part of PHANGS-HST, a large galaxy survey with Hubble that aims to study the connections between cold gas and young stars in a variety of galaxies in the local Universe. Within NGC 2835, this cold, dense gas produces large numbers of …

7 September 2020: Many colourful stars are packed close together in this image of the globular cluster NGC 1805, taken by the NASA/ESA Hubble Space Telescope. This tight grouping of thousands of stars is located near the edge of the Large Magellanic Cloud, a satellite galaxy of our own Milky Way. The stars orbit closely to one another, like bees swarming around a hive. In the dense centre of one of these clusters, stars are 100 to 1000 times closer together than the nearest stars are to our Sun, making planetary systems around them unlikely. The striking difference in star colours is illustrated beautifully in this image, which combines two different types of light: blue stars, shining brightest in near-ultraviolet light, and red stars, illuminated in red and near-infrared. Space telescopes like Hubble can observe in the ultraviolet because they are positioned above Earth’s atmosphere, which absorbs most of this wavelength, making it …

31 August 2020: The blue and orange stars of the faint galaxy named NGC 2188 sparkle in this image taken with the NASA/ESA Hubble Space Telescope. Although NGC 2188 appears at first glance to consist solely of a narrow band of stars, it is classified by astronomers as a barred-spiral galaxy. It appears this way from our viewpoint on Earth as the centre and spiral arms of the galaxy are tilted away from us, with only the very narrow outer edge of the galaxy’s disc visible to us. Astronomers liken this occurrence to turning a dinner plate in your hands so you see only its outer edge. The true shape of the galaxy was identified by studying the distribution of the stars in the inner central bulge and outer disc and by observing the stars’ colours. NGC 2188 is estimated to be just half the size of our Milky Way, at 50 000 …

24 August 2020: While appearing as a delicate and light veil draped across the sky, this image from the NASA/ESA Hubble Space Telescope actually depicts a small section of the Cygnus supernova blast wave, located around 2400 light-years away. The name of the supernova remnant comes from its position in the northern constellation of Cygnus (The Swan), where it covers an area 36 times larger than the full moon. The original supernova explosion blasted apart a dying star about 20 times more massive than our Sun between 10 000 and 20 000 years ago. Since then, the remnant has expanded 60 light-years from its centre. The shockwave marks the outer edge of the supernova remnant and continues to expand at around 350 kilometres per second. The interaction of the ejected material and the low-density interstellar material swept up by the shockwave forms the distinctive veil-like structure seen in this image.

17 August 2020: This image from the NASA/ESA Hubble Space Telescope features the spectacular galaxy NGC 2442. This galaxy was host to a supernova explosion, known as SN2015F, that was created by a white dwarf star. The white dwarf was part of a binary star system and syphoned mass from its companion, eventually becoming too greedy and taking on more than it could handle. This unbalanced the star and triggered runaway nuclear fusion that eventually led to an intensely violent supernova explosion. SN2015F was spotted in March 2015 in the galaxy named NGC 2442, nicknamed the Meathook Galaxy owing to its extremely asymmetrical and irregular shape. The supernova shone brightly for quite some time and was easily visible from Earth through even a small telescope until later that summer.

10 August 2020: NGC 1614, captured here by the NASA/ESA Hubble Space Telescope, is an eccentrically-shaped galaxy ablaze with activity. The galaxy resides about 200 million light-years from Earth and is nestled in the southern constellation of Eridanus (The River). NGC 1614 is the result of a past galactic merger which created its peculiar appearance. The cosmic collision also drove a turbulent flow of interstellar gas from the smaller of the two galaxies involved into the nucleus of the larger one, resulting in a burst of star formation which started in the core and slowly spread outwards through the galaxy. Owing to its turbulent past and its current appearance, astronomers classify NGC 1614 as a peculiar galaxy, a starburst galaxy, and a luminous infrared galaxy. Luminous infrared galaxies are among the most luminous objects in the local Universe — and NGC 1614 is, in fact, the second most luminous galaxy within 250 million …

3 August 2020: The barred spiral galaxy known as NGC 4907 shows its best side from 270 million light-years away to anyone who can see it from the northern hemisphere.This is a new image from the NASA/ESA Hubble Space Telescope of the face-on the galaxy, displaying its beautiful spiral arms, wound loosely around its central bright bar of stars. Shining brightly below the galaxy is a star that is actually within our own Milky Way galaxy. This star appears much brighter than the many millions of stars in NGC 4907 as it is 100 000 times closer, residing only 2500 light-years away. NGC 4907 is also part of the Coma Cluster, a group of over 1000 galaxies, some of which can be seen around NGC 4907 in this image. This massive cluster of galaxies lies within the constellation of Coma Berenices, which is named for the locks of Queen Berenice II of Egypt: …

27 July 2020: Looking its best ever is the star cluster NGC 2203, here imaged by the NASA/ESA Hubble Space Telescope. Aside from its dazzling good looks, this cluster of stars contains lots of astronomical treats that have helped astronomers puzzle together the lifetimes of stars. A main sequence star, like our Sun, is the term applied to a star during the longest period of its life, when it burns fuel steadily. Our Sun’s fuel will run out in approximately 6 billion years, and it will then move on to the next stage of its life when it will turn into a red giant. Astronomers studying NGC 2203, which contains stars that are roughly twice as massive as our Sun, found that their rotation might be a factor as to why some of the stars stay longer than usual in this main-sequence phase of their life. This is the best resolution obtained of …

20 July 2020: A notable feature of most spiral galaxies is the multitude of arching spiral arms that seemingly spin out from the galaxy’s centre. In this image, taken with the NASA/ESA Hubble Space Telescope, the stunning silvery-blue spiral arms of the galaxy NGC 4848 are observed in immense detail. Not only do we see the inner section of the spiral arms containing hundreds of thousands of young, bright, blue stars, but Hubble has also captured the extremely faint wispy tails of the outer spiral arms. This wispy barred spiral galaxy was first discovered in 1865 by the German astronomer Heinrich Louis d’Arrest. In his career, Heinrich also notably discovered the asteroid 76 Freia and many other galaxies and he also contributed to the discovery of Neptune. If you are situated in the Northern Hemisphere with a large telescope, you might just be able to observe the ghost-like appearance of this faint galaxy …

13 July 2020: Galaxies are well known as the birthplaces of stars and planets thanks to the overwhelmingly large amount of dust and gas within them. Over time, cold gas coalesces into molecular clouds, leading to the further emergence of star-forming regions. This image taken with the NASA/ESA Hubble Space Telescope depicts a fantastic new class of star-forming nursery, known as Free-floating Evaporating Gaseous Globules, or frEGGs for short. This object, known as J025027.7+600849, is located in the constellation of Cassiopeia. When a massive new star (or stars) starts to shine while still within the cool molecular cloud from which it formed, its energetic radiation can ionise the cloud’s hydrogen and create a large, hot bubble of ionised gas. Amazingly, located within this bubble of hot gas around a nearby massive star are the frEGGs: dark compact globules of dust and gas, some of which are also giving birth to low-mass stars. The …

6 July 2020: Captured by the NASA/ESA Hubble Space Telescope, this image shows NGC 7513, a barred spiral galaxy. Located approximately 60 million light-years away, NGC 7513 lies within the Sculptor constellation in the southern hemisphere. This galaxy is moving at the astounding speed of 1564 kilometres per second, and it is heading away from us. For context, the Earth orbits the Sun at about 30 kilometres per second. Though NGC 7513’s apparent movement away from the Milky Way might seem strange, it is not that unusual. While some galaxies, like the Milky Way and the Andromeda galaxy, are caught in each other’s gravitational pull and will eventually merge together, the vast majority of galaxies in our Universe appear to be moving away from each other. This phenomenon is due to the expansion of the Universe, and it is the space between galaxies that is stretching, rather than the galaxies themselves moving.

29 June 2020: The spiral pattern shown by the galaxy in this image from the NASA/ESA Hubble Space Telescope is striking because of its delicate, feathery nature. These "flocculent" spiral arms indicate that the recent history of star formation of the galaxy, known as NGC 2775, has been relatively quiet. There is virtually no star formation in the central part of the galaxy, which is dominated by an unusually large and relatively empty galactic bulge, where all the gas was converted into stars long ago. NGC 2275 is classified as a flocculent spiral galaxy, located 67 million light-years away in the constellation of Cancer. Millions of bright, young, blue stars shine in the complex, feather-like spiral arms, interlaced with dark lanes of dust. Complexes of these hot, blue stars are thought to trigger star formation in nearby gas clouds. The overall feather-like spiral patterns of the arms are then formed by shearing of …

22 June 2020: The galaxy known as NGC 5907 stretches wide across this image. Appearing as an elongated line of stars and dark dust, the galaxy is categorised as a spiral galaxy just like our own Milky Way. In this new image from the NASA/ESA Hubble Space Telescope, we don’t see the beautiful spiral arms because we are viewing it edge-on, like looking at the rim of a plate. It is for this reason that NGC 5907 is also known as the Knife Edge Galaxy. The Knife Edge Galaxy is about 50 million light-years from Earth, lying in the northern constellation of Draco. Although not visible in this image, ghostly streams of stars on large arching loops extend into space, circling around the galaxy; they are believed to be remnants of a small dwarf galaxy, torn apart by the Knife Edge Galaxy and merged with it over four billion years ago.