Pacific Ocean Nettle by Bimo_SatriyoCW Chrysaora fuscescens (commonly known as the Pacific sea nettle or West Coast sea nettle) is a common free-floating scyphozoan that lives in the East Pacific Ocean from Canada to Mexico.

Sea nettles have a distinctive golden-brown bell with a reddish tint. The bell can grow to be larger than one meter (three feet) in diameter in the wild, though most are less than 50 cm across. The long, spiraling, white oral arms and the 24 undulating maroon tentacles may trail behind as far as 15 feet. For humans, its sting is often irritating, but rarely dangerous.(wikipedia)


Where is the Sun in the Milky Way?

Our Milky Way galaxy is a barred spiral galaxy, meaning there are only two major spiral arms but there are other minor arms as well. As you can see in the image, the two major arms are Perseus and Scutum-Centaurus and branching off from them are other minor arms. We are located on the minor arm Orion-Cygnus, in-between the Perseus arm and the Carina-Sagittarius arm.

This Orion Arm or Local Arm is where we reside and are currently on the outer edge of the arm. The arm was actually named after the constellation Orion and some of the well known stars and celestial objects in the constellation (Rigel, Betelgeuse, Stars in Orion’s Belt and the Orion Nebula) are well known simply because they are bright and easily visible, this is because when we look at them we are peering into our own local spiral arm.

New insights on how spiral galaxies get their arms

Spiral galaxies are some of the most beautiful and photogenic residents of the universe. Our own Milky Way is a spiral. Our solar system and Earth reside somewhere near one of its filamentous arms. And nearly 70 percent of the galaxies closest to the Milky Way are spirals.

But despite their common shape, how galaxies like ours get and maintain their characteristic arms has proved to be an enduring puzzle in astrophysics. How do the arms of spiral galaxies arise? Do they change or come and go over time?

The answers to these and other questions are now coming into focus as researchers capitalize on powerful new computer simulations to follow the motions of as many as 100 million “stellar particles” as gravity and other astrophysical forces sculpt them into familiar galactic shapes. A team of researchers from the University of Wisconsin-Madison and the Harvard-Smithsonian Center for Astrophysics reports simulations that seem to resolve long-standing questions about the origin and life history of spiral arms in disk galaxies.

“We show for the first time that stellar spiral arms are not transient features, as claimed for several decades,” says UW-Madison astrophysicist Elena D'Onghia, who led the new research along with Harvard colleagues Mark Vogelsberger and Lars Hernquist. “The spiral arms are self-perpetuating, persistent, and surprisingly long lived,” adds Vogelsberger.

The origin and fate of the emblematic spiral arms in disk galaxies have been debated by astrophysicists for decades, with two theories predominating. One holds that the arms come and go over time. A second and widely held theory is that the material that makes up the arms – stars, gas and dust – is affected by differences in gravity and jams up, like cars at rush hour, sustaining the arms for long periods.

The new results fall somewhere in between the two theories and suggest that the arms arise in the first place as a result of the influence of giant molecular clouds – star forming regions or nurseries common in galaxies. Introduced into the simulation, the clouds act as “perturbers” and are enough to not only initiate the formation of spiral arms but to sustain them indefinitely.

“We find they are forming spiral arms,” explains D'Onghia. “Past theory held the arms would go away with the perturbations removed, but we see that (once formed) the arms self-perpetuate, even when the perturbations are removed. It proves that once the arms are generated through these clouds, they can exist on their own through (the influence of) gravity, even in the extreme when the perturbations are no longer there.”

Massive Stars Show the Way:
Our Galaxy Has Four, not Two, but Four Spiral Arms
17 December 2013

On a personal note: Today I spent some time putting together an overview of the previous (2007/8) new findings - that there are only two spiral arms and not four. With stunning graphics, too. Then I see this on the Science magazine news page!  

A 12-year study of massive stars has reaffirmed that our Galaxy has four spiral arms, following years of debate sparked by images taken by NASA’s Spitzer Space Telescope that only showed two arms.

The new research, which is published online in the Monthly Notices of the Royal Astronomical Society, is part of the RMS Survey, which was launched by academics at the University of Leeds.

Read the rest of the press release from the Royal Astronomical Society …

IMAGE:  This artist’s impression shows our Galaxy, the Milky Way, as the spiral shape in the background. The massive stars referred to in the new study are indicated by red circles. The position of the Solar System is marked by a black dot and circle at the top centre. Credit: J. Urquhart et al.
Background image by Robert Hurt of the Spitzer Science Center.  (via Massive stars mark out Milky Way’s ‘missing arms’)

The new work appears in the paper “The RMS survey: galactic distribution of massive star formation”, J. S. Urquhart, et al – Monthly Notices of the Royal Astronomical Society, published by Oxford University Press.

Milky Way’s Spiral Arms Are the Product of an Intergalactic Collision Course

A dwarf galaxy named Sagittarius loaded with dark matter has careened twice through our much larger home galaxy in the past two billion years,and is lined up to do it again. As the galaxies collide, the force of the impact sends stars streaming from both in long loops. Those continue to swell with stars and are gradually tugged outward by the Milky Way’s rotation into a familiar ringed arm.

It’s the weighty dark matter from Sagittarius that provided the initial push. The smaller galaxy pays a steep price though – sucked inward repeatedly by the Milky Way’s mightier gravity, it’s being ripped apart by the blows, sending huge amounts of its stars and dark matter reeling into the new arms.

When all that dark matter first smacked into the Milky Way, 80% to 90% of it was stripped off. That first impact triggered instabilities that were amplified, and quickly formed spiral arms and associated ring-like structures in the outskirts of our galaxy.

The Sagittarius galaxy is due to strike the southern face of the Milky Way disk fairly soon, Purcell said – in another 10 million years or so.

Image: Computer model of the Milky Way and its smaller neighbor, the Sagittarius dwarf galaxy. The flat disk is the Milky Way, and the looping stream of material is made of stars torn from Sagittarius as a result of the strong gravity of our galaxy. The spiral arms began to emerge about two billion years ago, when the Sagittarius galaxy first collided with the Milky Way disk.

Massive Nearby Spiral Galaxy NGC 2841

It is one of the more massive galaxies known. A mere 46 million light-years distant, spiral galaxy NGC 2841 can be found in the northern constellation of Ursa Major. This sharp view of the gorgeous island universe shows off a striking yellow nucleus and galactic disk. Dust lanes, small, pink star-forming regions, and young blue star clusters are embedded in the patchy, tightly wound spiral arms. In contrast, many other spirals exhibit grand, sweeping arms with large star-forming regions. NGC 2841 has a diameter of over 150,000 light-years, even larger than our own Milky Way and captured by this composite image merging exposures from the orbiting 2.4-meter Hubble Space Telescope and the ground-based 8.2-meter Subaru Telescope. X-ray images suggest that resulting winds and stellar explosions create plumes of hot gas extending into a halo around NGC 2841.

Image Credit: Hubble, Subaru; Composition & Copyright: Roberto Colombari

Spiral Galaxy NGC 1232 - The central region contains older stars of a reddish color, while the spiral arms are populated by young, blue stars and star-forming regions.


From Nasa’s Hubble Telescope Page

The NASA/ESA Hubble Space Telescope has provided us with another outstanding image of a nearby galaxy. This week, we highlight the galaxy NGC 4183, seen here with a beautiful backdrop of distant galaxies and nearby stars.

Located about 55 million light-years from the sun and spanning about eighty thousand light-years, NGC 4183 is a little smaller than the Milky Way. This galaxy, which belongs to the Ursa Major Group, lies in the northern constellation of Canes Venatici (The Hunting Dogs).

NGC 4183 is a spiral galaxy with a faint core and an open spiral structure. Unfortunately, this galaxy is viewed edge-on from the Earth, and we cannot fully appreciate its spiral arms. But we can admire its galactic disk.

The disks of galaxies are mainly composed of gas, dust and stars. There is evidence of dust over the galactic plane, visible as dark intricate filaments that block the visible light from the core of the galaxy. In addition, recent studies suggest that this galaxy may have a bar structure.

Galactic bars are thought to act as a mechanism that channels gas from the spiral arms to the center, enhancing star formation, which is typically more pronounced in the spiral arms than in the bulge of the galaxy.

British astronomer William Herschel first observed NGC 4183 on 14 January 1778.

ESO 498-G5

The NASA/ESA Hubble Space Telescope captured this image of the spiral galaxy known as ESO 498-G5. One interesting feature of this galaxy is that its spiral arms wind all the way into the centre, so that ESO 498-G5’s core looks like a bit like a miniature spiral galaxy. This sort of structure is in contrast to the elliptical star-filled centres (or bulges) of many other spiral galaxies, which instead appear as glowing masses, as in the case of NGC 6384.

Credit: ESA/Hubble & NASA

NASA Astronomy Picture of the Day 2015 May 2

M51: The Whirlpool Galaxy

Follow the handle of the Big Dipper away from the dipper’s bowl until you get to the handle’s 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 Messier 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 (right), 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 eye, deep images like this one can reveal striking colors and the faint tidal debris around the smaller galaxy

One-Armed Spiral Galaxy NGC 4725 : While most spiral galaxies, including our own Milky Way, have two or more spiral arms, NGC 4725 has only one. In this sharp color composite image, the solo spira mirabilis seems to wind from a prominent ring of bluish, newborn star clusters and red tinted star forming regions. The odd galaxy also sports obscuring dust lanes a yellowish central bar structure composed of an older population of stars. NGC 4725 is over 100 thousand light-years across and lies 41 million light-years away in the well-groomed constellation Coma Berenices. Computer simulations of the formation of single spiral arms suggest that they can be either leading or trailing arms with respect to a galaxy’s overall rotation. Also included in the frame, sporting a noticably more traditional spiral galaxy look, is a more distant background galaxy. via NASA


NGC 2903: A Missing Jewel in Leo : 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 activity near 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. via NASA

Disks Don't Need Planets to Make Patterns, NASA Study Shows

Disks Don’t Need Planets to Make Patterns, NASA Study Shows


Many young stars known to host planets also possess disks containing dust and icy grains, particles produced by collisions among asteroids and comets also orbiting the star. These debris disks often show sharply defined rings or spiral patterns, features that could signal the presence of…

Many young stars known…

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