spiral arm

Glittering Frisbee Galaxy: This image from Hubble’s shows a section of a spiral galaxy located about 50 million light-years from Earth. We tend to think of spiral galaxies as massive and roughly circular celestial bodies, so this glittering oval does not immediately appear to fit the visual bill. What’s going on? Imagine a spiral galaxy as a circular frisbee spinning gently in space. When we see it face on, our observations reveal a spectacular amount of detail and structure. However, the galaxy frisbee is very nearly edge-on with respect to Earth, giving it an appearance that is more oval than circular. The spiral arms, which curve out from the galaxy’s dense core, can just about be seen.

Although spiral galaxies might appear static with their picturesque shapes frozen in space, this is very far from the truth. The stars in these dramatic spiral configurations are constantly moving as they orbit around the galaxy’s core, with those on the inside making the orbit faster than those sitting further out. This makes the formation and continued existence of a spiral galaxy’s arms something of a cosmic puzzle, because the arms wrapped around the spinning core should become wound tighter and tighter as time goes on - but this is not what we see. This is known as the winding problem.

Image credit: ESA/Hubble & NASA

For more information on this image, visit: https://go.nasa.gov/2niODGL

The beautiful Andromeda Galaxy is often imaged by planet Earth-based astronomers. Also known as M31, the nearest large spiral galaxy is a familiar sight with spiral arms traced by blue starlight. In a mosaic of well-exposed broad and narrow-band image data, faint reddish clouds of glowing ionized hydrogen gas lie in the same wide field of view. Still, the ionized hydrogen clouds likely lie in the foreground of the scene, well within our Milky Way Galaxy. They could be associated with the pervasive, dusty interstellar cirrus clouds scattered hundreds of light-years above our own galactic plane. If they were located at the 2.5 million light-year distance of the Andromeda Galaxy they would be enormous, since the Andromeda Galaxy itself is 200,000 or so light-years across.

Image Credit & Copyright: Rogelio Bernal Andreo (Deep Sky Colors)

Bright Spiral Galaxy M81 : One of the brightest galaxies in planet Earths sky is similar in size to our Milky Way Galaxy: big, beautiful M81. The grand spiral galaxy can be found toward the northern constellation of the Great Bear . This superbly detailed image reveals M81s bright yellow nucleus, blue spiral arms, tell tale pinkish star forming regions, and sweeping cosmic dust lanes with a scale comparable to the Milky Way. Hinting at a disorderly past, a remarkable dust lane actually runs straight through the disk, to the left of the galactic center, contrary to M81s other prominent spiral features. The errant dust lane may be the lingering result of a close encounter between between M81 and its smaller companion galaxy, M82. Scrutiny of variable stars in M81 has yielded one of the best determined distances for an external galaxy 11.8 million light-years. M81s dwarf companion galaxy Holmberg IX can be seen just above the large spiral. via NASA


Why do many galaxies appear as spirals? A striking example is M101, shown above, whose relatively close distance of about 27 million light years allows it to be studied in some detail. Observational evidence indicates that a close gravitational interaction with a neighboring galaxy created waves of high mass and condensed gas which continue to orbit the galaxy center. These waves compress existing gas and cause star formation. One result is that M101, also called the Pinwheel Galaxy, has several extremely bright star-forming regions (called HII regions) spread across its spiral arms. M101 is so large that its immense gravity distorts smaller nearby galaxies.

Object Names: M101, Pinwheel Galaxy

Image Type: Astronomical

Credit: Subaru Telescope (NAOJ), Hubble Space Telescope, European Southern Observatory

Procesing and Copyright: Robert Gendler

Time And Space

M33: Triangulum Galaxy : The small, northern constellation Triangulum harbors this magnificent face-on spiral galaxy, M33. Its popular names include the Pinwheel Galaxy or just the Triangulum Galaxy. M33 is over 50,000 light-years in diameter, third largest in the Local Group of galaxies after the Andromeda Galaxy , and our own Milky Way. About 3 million light-years from the Milky Way, M33 is itself thought to be a satellite of the Andromeda Galaxy and astronomers in these two galaxies would likely have spectacular views of each others grand spiral star systems. As for the view from planet Earth, this sharp composite image nicely shows off M33s blue star clusters and pinkish star forming regions along the galaxys loosely wound spiral arms. In fact, the cavernous NGC 604 is the brightest star forming region, seen here at about the 1 o'clock position from the galaxy center. Like M31, M33s population of well-measured variable stars have helped make this nearby spiral a cosmic yardstick for establishing the distance scale of the Universe. via NASA


Planetary nebula with spiral arms

The two spiral arms winding towards the bright centre might deceive you into thinking you are looking at a galaxy a bit like our Milky Way. But the object starring in this image is of a different nature: PK 329-02.2 is a ‘planetary nebula’ within our home galaxy. 

Despite the name, this isn’t a planet either. Planetary nebula is a misnomer that came about because of how much nebulas resembled giant, gaseous planets when looked through a telescope in the 1700s. Rather, what we see in this image is the last breath of a dying star. 

When stars like the Sun are nearing the end of their lives, they let go of their gaseous outermost layers. As these clouds of stellar material move away from the central star they can acquire irregular and complex shapes. This complexity is evident in the faint scattered gas you see at the centre of the image. But there is also beautiful symmetry in PK 329-02.2, as the two bright blue spiral arms perfectly align with the two stars at the centre of the nebula. 

It may look like the spiral arms are connected, but it is the stars that are companions. They are part of a visual binary, though only the one at the upper right gave rise to the nebula. While the stars will continue to orbit each other for millions or billions of years, the nebula – and its spiral arms – will spread out from the centre and eventually fade away over the next few thousands of years.

Credit: ESA/Hubble & NASA; Acknowledgement: Serge Meunier

The Andromeda constellation is one of the 88 modern constellations and should not be confused with our neighboring Andromeda Galaxy. The Andromeda constellation is home to the pictured galaxy known as NGC 7640.

Many different classifications are used to identify galaxies by shape and structure — NGC 7640 is a barred spiral type. These are recognizable by their spiral arms, which fan out not from a circular core, but from an elongated bar cutting through the galaxy’s center. Our home galaxy, the Milky Way, is also a barred spiral galaxy. NGC 7640 might not look much like a spiral in this image, but this is due to the orientation of the galaxy with respect to Earth — or to Hubble, which acted as photographer in this case! We often do not see galaxies face on, which can make features such as spiral arms less obvious.

There is evidence that NGC 7640 has experienced some kind of interaction in its past. Galaxies contain vast amounts of mass, and therefore affect one another via gravity. Sometimes these interactions can be mild, and sometimes hugely dramatic, with two or more colliding and merging into a new, bigger galaxy. Understanding the history of a galaxy, and what interactions it has experienced, helps astronomers to improve their understanding of how galaxies — and the stars within them — form.

Image credit: ESA/Hubble & NASA

Text credit: European Space Agency

Time And Space

The Hydrogen Clouds of M33 : Gorgeous spiral galaxy M33 seems to have more than its fair share of glowing hydrogen gas. A prominent member of the local group of galaxies, M33 is also known as the Triangulum Galaxy and lies about 3 million light-years distant. The galaxy’s inner 30,000 light-years or so are shown in this telescopic portrait that enhances its reddish ionized hydrogen clouds or HII regions. Sprawling along loose spiral arms that wind toward the core, M33’s giant HII regions are some of the largest known stellar nurseries, sites of the formation of short-lived but very massive stars. Intense ultraviolet radiation from the luminous, massive stars ionizes the surrounding hydrogen gas and ultimately produces the characteristic red glow. To enhance this image, broadband data was used to produce a color view of the galaxy and combined with narrowband data recorded through a hydrogen-alpha filter. That filter transmits the light of the strongest visible hydrogen emission line. via NASA


Seagull to Sirius 

This broad, beautiful mosaic spans almost 20 degrees across planet Earth’s sky. The nebula-rich region lies near the edge of the Orion-Eridanus superbubble, filled with looping, expanding shells of gas and dust embedded in molecular clouds near the plane of the Milky Way Galaxy. Recognizable at the left is the expansive Seagull Nebula, composed of emission nebula NGC 2327, seen as the seagull’s head, with the more diffuse IC 2177 as the wings and body. Some 3,800 light-years away, the wings of the Seagull Nebula spread about 240 light-years, still within our local spiral arm.

The bluish light of Sirius, alpha star of Canis Major and brightest star in the night, easily dominates the scene at right but shines from a distance of only 8.6 light-years. Study the big picture and you should also be rewarded with star cluster Messier 41, also known as NGC 2287, not to mention the mighty Thor’s Helmet.

A mere 20,000 light-years from the Sun lies NGC 3603, a resident of the nearby Carina spiral arm of our Milky Way Galaxy. NGC 3603 is well known to astronomers as one of the Milky Way’s largest star-forming regions. The central open star cluster contains thousands of stars more massive than our Sun, stars that likely formed only one or two million years ago in a single burst of star formation. In fact, nearby NGC 3603 is thought to contain a convenient example of the massive star clusters that populate much more distant starburst galaxies.Surrounding the cluster are natal clouds of glowing interstellar gas and obscuring dust, sculpted by energetic stellar radiation and winds. 

Recorded by the Hubble Space Telescope, the image spans about 17 light-years.

Image Credit: NASA, ESA, Hubble Heritage(STScI/AURA)-ESA/ Hubble Collaboration; 

Acknowledgment: J. Maiz Apellaniz (Inst. Astrofisica Andalucia) et al., & Davide de Martin (skyfactory.org)

Time And Space

The Whirlpool Galaxy and Beyond : Follow the handle of the Big Dipper away from the dippers bowl, until you get to the handles last bright star. Then, just slide your telescope a little south and west and you might find this stunning pair of interacting galaxies, the 51st entry in Charles Messiers famous catalog. Perhaps the original spiral nebula, the large galaxy with well defined spiral structure is also cataloged as NGC 5194. Its spiral arms and dust lanes clearly sweep in front of its companion galaxy , NGC 5195. The pair are about 31 million light-years distant and officially lie within the angular boundaries of the small constellation Canes Venatici. Though M51 looks faint and fuzzy to the human eye, the above long-exposure, deep-field image taken earlier this year shows much of the faint complexity that actually surrounds the smaller galaxy. Thousands of the faint dots in background of the featured image are actually galaxies far across the universe. via NASA


The beautiful Andromeda Galaxy is often imaged by planet Earth-based astronomers. Also known as M31, the nearest large spiral galaxy is a familiar sight with dark dust lanes, bright yellowish core, and spiral arms traced by blue starlight. A mosaic of well-exposed broad and narrow-band image data, this colorful, premier portrait of our neighboring island universe offers strikingly unfamiliar features though, faint reddish clouds of glowing ionized hydrogen gas in the same wide field of view. Still, the ionized hydrogen clouds likely lie in the foreground of the scene, well within our Milky Way Galaxy. They could be associated with the pervasive, dusty interstellar cirrus clouds scattered hundreds of light-years above our own galactic plane. If they were located at the 2.5 million light-year distance of the Andromeda Galaxy they would be enormous, since the Andromeda Galaxy itself is 200,000 or so light-years across.

Image Credit &Copyright:Rogelio BernalAndreo(Deep Sky Colors)

Time And Space

Barred spiral galaxy NGC 2903 is only some 20 million light-years distant. Popular among amateur astronomers, it shines in the northern spring constellation Leo, near the top of the lion’s head. That part of the constellation is sometimes seen as a reversed question mark or sickle. One of the brighter galaxies visible from the northern hemisphere, NGC 2903 is surprisingly missing from Charles Messier’s catalog of lustrous celestial sights. This colorful image from a small ground-based telescope shows off the galaxy’s gorgeous spiral arms traced by young, blue star clusters and pinkish star forming regions. Included are intriguing details of NGC 2903’s bright core, a remarkable mix of old and young clusters with immense dust and gas clouds. In fact, NGC 2903 exhibits an exceptional rate of star formation activitynear its center, also bright in radio, infrared, ultraviolet, and x-ray bands. Just a little smaller than our own Milky Way, NGC 2903 is about 80,000 light-years across.

Image Credit & Copyright: Tony Hallas

Time And Space

Hubble catches a transformation in the Virgo constellation

The constellation of Virgo (The Virgin) is especially rich in galaxies, due in part to the presence of a massive and gravitationally-bound collection of over 1300 galaxies called the Virgo Cluster. One particular member of this cosmic community, NGC 4388, is captured in this image, as seen by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3).

Located some 60 million light-years away, NGC 4388 is experiencing some of the less desirable effects that come with belonging to such a massive galaxy cluster. It is undergoing a transformation, and has taken on a somewhat confused identity.

While the galaxy’s outskirts appear smooth and featureless, a classic feature of an elliptical galaxy, its center displays remarkable dust lanes constrained within two symmetric spiral arms, which emerge from the galaxy’s glowing core – one of the obvious features of a spiral galaxy. Within the arms, speckles of bright blue mark the locations of young stars, indicating that NGC 4388 has hosted recent bursts of star formation.

Despite the mixed messages, NGC 4388 is classified as a spiral galaxy. Its unusual combination of features are thought to have been caused by interactions between NGC 4388 and other galaxies in the Virgo Cluster. Gravitational interactions – from glancing blows to head-on collisions, tidal influencing, mergers, and galactic cannibalism – can be devastating to galaxies. While some may be lucky enough to simply suffer a distorted spiral arm or newly-triggered wave of star formation, others see their structure and contents completely and irrevocably altered.