Messier 57 – The Ring Nebula

Welcome back to Messier Monday! We continue our tribute to our dear friend, Tammy Plotner, by looking at the the Big Ring itself, the planetary nebula known as Messier 57. Enjoy!

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list – known as the Messier Catalog – would go on to serve a more important function.

One of these objects is known as Messier 57, a planetary nebula that is also known as the Ring Nebula. This object is located about 2,300 light years from Earth in the direction of the Lyra constellation. Because of its proximity to Vega, the brightest star in Lyra and one of the stars that form the Summer Triangle, the nebula is relatively easy to find using binoculars or a small telescope.

What You Are Looking At:

Here you see the remainders of a sun-like star… At one time in its life, it may have had twice the mass of Sol, but now all that’s left is a white dwarf that burns over 100,000 degrees kelvin. Surrounding it is an envelope about 2 to 3 light years in size of what once was its outer layers – blown away in a cylindrical shape some 6000 to 8000 years ago. Like looking down the barrel of a smoking gun, we’re looking back in time at the end of a Mira-like star’s evolutionary phase.

It’s called a planetary nebula, because once upon a time before telescopes could resolve them, they appeared almost planet-like. But, as for M57, the central star itself is no larger than a terrestrial planet! The tiny white dwarf star, although it could be as much as 2300 light years away, has an intrinsic brightness of about 50 to 100 times that of our Sun.

One of the most beautiful features of M57 is the structure in the ring itself, sometimes called braiding – but scientifically known as “knots” in the gaseous structure. As C.R. O’Dell (et al) indicated in their 2003 study:

“We have studied the closest bright planetary nebulae with the Hubble Space Telescope’s WFPC2 in order to characterize the dense knots already known to exist in NGC 7293. We find knots in all of the objects, arguing that knots are common, simply not always observed because of distance. The knots appear to form early in the life cycle of the nebula, probably being formed by an instability mechanism operating at the nebula’s ionization front. As the front passes through the knots they are exposed to the photoionizing radiation field of the central star, causing them to be modified in their appearance. This would then explain as evolution the difference of appearance like the lacy filaments seen only in extinction in IC 4406 on the one extreme and the highly symmetric “cometary” knots seen in NGC 7293. The intermediate form knots seen in NGC 2392, NGC 6720, and NGC 6853 would then represent intermediate phases of this evolution.”

However, examining things like planetaries nebulae in different wavelengths of light can tell us so much more about them. Behold the beauty when see through the Spitzer Space Telescope! As M.M. Roth explained in a 2007 study:

“Emission nebulae like H II regions, Planetary Nebulae, Novae, Herbig Haro objects etc. are found as extended objects in the Milky Way, but also as point sources in other galaxies, where they are sometimes observable out to very large distances due to the high contrast provided by some prominent emission lines. It is shown how 3D spectroscopy can be used as a powerful tool for observations of both large resolved emission nebulae and distant extragalactic objects, with special emphasis on faint detection limits.”

History of Observation:

This deep space object was first discovered in early January 1779 by Antoine Darquier who wrote in his notes:

“This nebula, to my knowledge, has not yet been noticed by any astronomer. One can only see it with a very good telescope, it is not resembling any of those [nebula] already known; it has the apparent dimension of Jupiter, is perfectly round and sharply limited; its dull glow resembles the dark part of the Moon before the first and after the last quarter. Meanwhile, the center appears a bit less pale than the remaining part of its surface.”

Although Darquier did not post a date, it is believed his observation preceded Messier’s independent recovery made on January 31, 1779 when he states that Darquier picked it up before him:

“A cluster of light between Gamma and Beta Lyrae, discovered when looking for the Comet of 1779, which has passed it very close: it seems that this patch of light, which is round, must be composed of very small stars: with the best telescopes it is impossible to distinguish them; there stays only a suspicion that they are there. M. Messier reported this patch of light on the Chart of the Comet of 1779. M. Darquier, at Toulouse, discovered it when observing the same comet, and he reports: ‘Nebula between gamma and beta Lyrae; it is very dull, but perfectly outlined; it is as large as Jupiter and resembles a planet which is fading’.”

A few years later, Sir William Herschel would also observe Messier Object 57 with his superior telescope and in his private notes he writes:

“Among the curiosities of the heavens should be placed a nebula, that has a regular, concentric, dark spot in the middle, and is probably a Ring of stars. It is of an oval shape, the shorter axis being to the longer as about 83 to 100; so that, if the stars form a circle, its inclination to a line drawn from the sun to the center of this nebula must be about 56 degrees. The light is of the resolvable kind [i.e., mottled], and in the northern side three very faint stars may be seen, as also one or two in the southern part. The vertices of the longer axis seem less bright and not so well defined as the rest. There are several small stars very bear, but none seems to belong to it.”

Admiral Smyth would go on in later years to add his own detailed observations to history’s records:

“This annular nebula, between Beta and Gamma on the cross-piece of the Lyre, forms the apex of a triangle which it makes with two stars of the 9th magnitude; and its form is that of an elliptic ring, the major axis of which trends sp to nf [SW to NE]. This wonderful object seems to have been noted by Darquier, in 1779; but neither he nor his contemporaries, Messier and Méchain, discerned its real form, seeing in this aureola of glory only “a mass of light in the form of a planetary disc, very dingy in colour.”

“Sir W. Herschel called it a perforated resolvable nebula, and justly ranked it among the curiosities of the heavens. He considered the vertices of the longer axis less bright and not so well defined as the rest; and he afterwards added: ‘By the observations of the 20-feet telescope, the profundity of the stars, of which it probably consists, must be of a higher than the 900th order, perhaps 950.'”

“This is a vast view of the ample and inconceivable dimensions of the spaces of the Universe; and if the oft-cited cannon-ball, flying with the uniform velocity of 500 miles an hour, would require millions of years to reach Sirius, what an incomprehensible time it would require to pass so overwhelming an interval as 950 times the distance! And yet, could we arrive there, by all analogy, no boundary would meet the eye, but thousands and ten thousands of other remote and crowded systems would still bewilder the imagination.

“In my refractor this nebula has a most singular appearance, the central vacuity being black, so as to countenance the trite remark of its having a hole through it. Under favourable circumstances, when the instrument obeys the smooth motion of the equatorial clock, it offers the curious phenomenon of a solid ring of light in the profundity of space. The annexed sketch affords a notion of it. Sir John Herschel, however, with the superior light of his instrument, found that the interior is far from absolutely dark. “It is filled,’ he says, ‘with a feeble but very evident nebulous light, which I do not remember to have been noticed by former observers.'”

Since Sir John’s observation, the powerful telescope of Lord Rosse has been directed to this subject, and under powers 600, 800, and 1000, it displayed very evident symptoms of resolvability at its minor axis. The fainter nebulous matter which fills it, was found to be irregularly distributed, having several stripes or wisps in it, and the regularity of the outline was broken by appendages branching into space, of which prolongations the brightest was in the direction of the major axis.

Locating Messier 57:

M57 is a breeze to locate because it is positioned between Beta and Gamma Lyrae (the westernmost pair of the lyre’s stars), at about one-third the distance from Beta to Gamma. While it is easily seen in binoculars, it is a little difficult to identify because of its small size, so binoculars must be very steady to distinguish it from the surrounding star field.

In even a small telescope at minimum power, you’ll quickly notice a very small, but perfect ring structure which takes very well to magnification. Despite low visual brightness, M57 actually takes well to urban lighting conditions and can even be spied during fairly well moonlit nights. Larger aperture telescopes will easily see braiding in the nebula structure and often glimpse the central star. May you also see the many faces of the “Ring”!

The location of Messier 57 in the Lyra Constellation. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

And here are the quick facts on Messier 57 to help you get started:

Object Name: Messier 57
Alternative Designations: M57, NGC 6720, the “Ring Nebula”
Object Type: Planetary Nebula
Constellation: Lyra
Right Ascension: 18 : 53.6 (h:m)
Declination: +33 : 02 (deg:m)
Distance: 2.3 (kly)
Visual Brightness: 8.8 (mag)
Apparent Dimension: 1.4×1.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier ObjectsM1 – The Crab Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Nebulae: What Are They And Where Do They Come From?

The Fairy of Eagle Nebula

A nebula is a truly wondrous thing to behold. Named after the Latin word for “cloud”, nebulae are not only massive clouds of dust, hydrogen and helium gas, and plasma; they are also often “stellar nurseries” – i.e. the place where stars are born. And for centuries, distant galaxies were often mistaken for these massive clouds.

Alas, such descriptions barely scratch the surface of what nebulae are and what there significance is. Between their formation process, their role in stellar and planetary formation, and their diversity, nebulae have provided humanity with endless intrigue and discovery.

Continue reading “Nebulae: What Are They And Where Do They Come From?”

Amateur Images of the Ring Nebula Rival Views from Space Telescopes

The Ring Nebula is a planetary nebula about 2,000 light-years from Earth and measures roughly 1 light-year across. It is located in the constellation Lyra, and is a popular target for amateur astronomers.

But this new image, done as a collaboration between amateur astronomers Terry Hancock of Michigan and Fred Herrmann of Alabama, is amazing, with detail usually only seen from large ground-based observatories or space telescopes, particularly the detail of the gaseous outer shell of the nebula.

With over 25 hours of total exposure time, this is a remarkably deep exposure which explores the looping filaments of glowing gas. The collaborative effort combined data from two different telescopes, and both Hancock and Herrmann used Astro-Tech 12″ Ritchey-Chrétien astrographs.

Below is another view, a wide field version:

Image of M 57 (Ring Nebula), a collaboration by amateur astronomers Terry Hancock of Michigan and Fred Herrmann of Alabama who both used Astro-Tech 12 inch Ritchey-Chrétien astrographs.
Image of M 57 (Ring Nebula), a collaboration by amateur astronomers Terry Hancock of Michigan and Fred Herrmann of Alabama who both used Astro-Tech 12 inch Ritchey-Chrétien astrographs.

Hancock’s data is from 2012 and 2013 using a QHY9 monochrome CCD and Herrmann’s data is from an SBIG STT-8300 monochrome CCD. Data was collected over 14 nights and six one hour narrow-band hydrogen alpha exposures were taken in order to show the dimmer outer shell.

Hancock explained on G+ that the lighter hydrogen forms the outer reddish envelope while the heavier blue-green oxygen remains about the core. “The gases in the expanding shell are illuminated by the radiation of the central white dwarf, and the glow is still 200 times brighter than our Sun,” he said.

Also visible in the images is the barred spiral galaxy IC 1296.

Recent views from the Hubble Space Telescope of the Ring Nebula showed how the ‘ring’ is really more similar to a football-shaped jelly donut, and Hancock and Herrmann’s view shows that shape as well.

Awesome work!

The Ring Nebula is Really a Football-Shaped Jelly Donut

Sometimes the popular names given to an astronomical object hit the mark of describing its features. Other times…. not so much. Case in point, the Ring Nebula. While the distinctive loop shape and colorful beauty have made it one of the most famous celestial discs, it is not really a classic “ring.” And this recent image from the Hubble Space Telescope shows an amazing new level of detail in this iconic nebula.

“The nebula is not like a bagel, but rather, it’s like a jelly doughnut, because it’s filled with material in the middle,” said C. Robert O’Dell of Vanderbilt University, who led a research team that used Hubble and several ground-based telescopes to obtain the best view yet of the Ring nebula. The images show a more complex structure than astronomers once thought and have allowed them to construct the most precise 3-D model of the nebula.

“With Hubble’s detail, we see a completely different shape than what’s been thought about historically for this classic nebula,” O’Dell said. “The new Hubble observations show the nebula in much clearer detail, and we see things are not as simple as we previously thought.”

The Ring Nebula is about 2,000 light-years from Earth and measures roughly 1 light-year across. Located in the constellation Lyra, the nebula is a popular target for amateur astronomers.

Previous observations by several telescopes had detected the gaseous material in the ring’s central region. But the new view by Hubble’s Wide Field Camera 3 shows the nebula’s structure in more detail. O’Dell’s team suggests the ring wraps around a blue, football-shaped structure. Each end of the structure protrudes out of opposite sides of the ring.

This video zooms into the constellation Lyra to the location of the Ring Nebula and the new image from the Hubble Space Telescope and the Large Binocular Telescope:

In the analysis, the research team also obtained images from the Large Binocular Telescope at the Mount Graham International Observatory in Arizona and spectroscopic data from the San Pedro Martir Observatory in Baja California, Mexico.

The nebula is tilted toward Earth so that astronomers see the ring face-on. In the Hubble image, the blue structure is the glow of helium. Radiation from the white dwarf star, the white dot in the center of the ring, is exciting the helium to glow. The white dwarf is the stellar remnant of a sun-like star that has exhausted its hydrogen fuel and has shed its outer layers of gas to gravitationally collapse to a compact object.

O’Dell’s team was surprised at the detailed Hubble views of the dark, irregular knots of dense gas embedded along the inner rim of the ring, which look like spokes in a bicycle wheel. These gaseous tentacles formed when expanding hot gas pushed into cool gas ejected previously by the doomed star. The knots are more resistant to erosion by the wave of ultraviolet light unleashed by the star. The Hubble images have allowed the team to match up the knots with the spikes of light around the bright, main ring, which are a shadow effect. Astronomers have found similar knots in other planetary nebulae.

This illustration depicts a sideways view of the Ring Nebula, as deduced by astronomers using new Hubble observations. Credit: NASA, ESA, and A. Feild (STScI)
This illustration depicts a sideways view of the Ring Nebula, as deduced by astronomers using new Hubble observations. Credit: NASA, ESA, and A. Feild (STScI)

All of this gas was expelled by the central star about 4,000 years ago. The original star was several times more massive than our sun. After billions of years converting hydrogen to helium in its core, the star began to run out of fuel. It then ballooned in size, becoming a red giant. During this phase, the star shed its outer gaseous layers into space and began to collapse as fusion reactions began to die out. A gusher of ultraviolet light from the dying star energized the gas, making it glow.

The outer rings were formed when faster-moving gas slammed into slower-moving material. The nebula is expanding at more than 43,000 miles an hour, but the center is moving faster than the expansion of the main ring. O’Dell’s team measured the nebula’s expansion by comparing the new Hubble observations with Hubble studies made in 1998.

The Ring Nebula will continue to expand for another 10,000 years, a short phase in the lifetime of the star. The nebula will become fainter and fainter until it merges with the interstellar medium.

Studying the Ring Nebula’s fate will provide insight into the sun’s demise in another 6 billion years. The sun is less massive than the Ring Nebula’s progenitor star, so it will not have an opulent ending.

“When the sun becomes a white dwarf, it will heat more slowly after it ejects its outer gaseous layers,” O’Dell said. “The material will be farther away once it becomes hot enough to illuminate the gas. This larger distance means the sun’s nebula will be fainter because it is more extended.”

Source: HubbleSite

Weekly SkyWatcher’s Forecast: September 3-9, 2012

Greetings, fellow SkyWatchers! With the change in seasons becoming quickly apparent, it’s time to put some early hours dark skies to good use and enjoy some favorite nebulae. If you’ve enjoyed the Mars-mania, then you’ll also enjoy the return of Mars in the pre-dawn hours. Speaking of early mornings, be sure to watch as the Moon and Jupiter head for a splendid conjunction this coming Saturday. When you’re ready, grab your binoculars and set up your telescopes… It’s time to dance!

Monday, September 3 – Tonight it’s time for us to head directly between the two lower stars in the constellations of Lyra and grab the “Ring”.

First discovered by French astronomer, Antoine Darquier in 1779, the “Ring” was cataloged later that year by Charles Messier as M57 (Right Ascension: 18 : 53.6 – Declination: +33 : 02). In binoculars the “Ring” will appear as slightly larger than a star, yet it cannot be focused to a sharp point. To a modest telescope at even low power, the M57 turns into a glowing donut against a wonderfully stellar backdrop. The average accepted distance to this unusual structure is believed to be around 1,400 light years and how you see the “Ring” on any given night is highly attributable to conditions. As aperture and power increase, so do details and it is not impossible to see braiding in the nebula structure with scopes as small as eight inches on a fine night, or to pick up the star caught on the edge in even smaller apertures.

Like all planetary nebula, seeing the central star is considered the ultimate of viewing. The central itself is a peculiar bluish dwarf which gives off a continuous spectrum and might very well be a variable. At times, this shy, near 15th magnitude star can be seen with ease with a 12.5? telescope, yet be elusive to 31? in aperture weeks later. No matter what details you may see, reach for the “Ring” tonight. You’ll be glad you did.

Tuesday, September 4 – Of course, studying some of the summer’s finest means that we’d be very remiss if we didn’t look at another cosmic curiosity – “The Blinking Planetary”.

Located a couple of degrees east of visible star Theta Cygnii, and in the same lower power field as 16 Cygnii, the NGC 6826 (Right Ascension: 19 : 44.8 – Declination: +50 : 31) is often referred to as the “Blinking Planetary” nebula. Viewable in even small telescopes at mid to high power, you’ll learn very quickly how it came about its name. When you look directly at it, you can only see the central 9th magnitude star. Now, look away. Focus your attention on visual double 16 Cygnii. See that? When you avert, the nebula itself is visible. This is actually a trick of the eye. The central portion of our vision is more sensitive to detail and will only see the central star. At the edge of our vision, we are more likely to see dim light, and the planetary nebula appears. Located around 2,000 light years from our solar system, it doesn’t matter if the “Blinking Planetary” is a trick of the eye or not… Because it’s cool!

Wednesday, September 5 – If you’re up before dawn, maybe you’ve noticed the return of Mars? It’s been on the move and this universal date marks its official change in position from the constellation of Virgo into the constellation of Libra.

Don’t put away your binoculars tonight just because you think this next study is beyond you… Just lift your sights three degrees higher than the “Omega” and tonight we’ll return again to fly with the “Eagle” – M16 (Right Ascension: 18 : 18.8 – Declination: -13 : 47)

Small binoculars will have no trouble distinguishing the cluster of stars discovered by de Cheseaux in 1746, but larger binoculars and small telescopes from a dark sky site will also see a faint nebulosity to the region that was reported by Messier in 1764. This “faint light” will remind you highly of the reflection that is seen within the Pleiades, or “Rosette” nebula. While the most outstanding views of the “Eagle” nebula are in photographs, larger telescopes will have no problem picking out a vague cloud of nebula, encased stars and an unusual dark obscuration in the center which has always reminded this author as a “Klingon Bird of Prey”. While all of this is very grand, what’s really interesting is the little notch on the northeast edge of the nebula. This is easily seen under good conditions with scopes as small as 8? and is undeniable in larger aperture. This tiny “notch” rocketed to worldwide fame when viewed through the eyes of the Hubble. It’s name? “The Pillars of Creation”.

Thursday, September 6 – Today celebrates the founding of the Astronomical and Astrophysical Society of America. Started in 1899, it is now known as the American Astronomical Society.

Tonight let’s relax a little bit and have a look at a superb open cluster that stays superb no matter if you use small binoculars or a big telescope. Of whom do I speak so highly? M34 (Right Ascension: 2 : 42.0 – Declination: +42 : 47)…

Easily found on Perseus west border by scanning between Beta Perseii (Algol) and Gamma Andromeda (Almach), the M34 was discovered by Messier in 1764. Containing around 80 members, the central knot of stars is what truly makes it beautiful. At around 1400 light years away, this stellar collection is believed to be around 10 million years old. While binocular users are going to be very happy with this object, scopists are going to appreciate the fact that there is a double right in the heart of M34. This fixed pair is around magnitude 8 and separated by about 20?.

Friday, September 7 – Tonight we are going to take a journey once again toward an area which has intrigued this author since I first laid eyes on it with a telescope. Some think it difficult to find, but there is a very simple trick. Look for the primary stars of Sagitta just to the west of bright Albireo. Make note of the distance between the two brightest and look exactly that distance north of the “tip of the arrow” and you’ll find the M27 (Right Ascension: 19 : 59.6 – Declination: +22 : 43).

Discovered in 1764 by Messier in a three and a half foot telescope, I discovered this 48,000 year old planetary nebula for the first time in a 4.5? telescope. I was hooked immediately. Here before my eager eyes was a glowing green “apple core” which had a quality about it that I did not understand. It somehow moved… It pulsated. It appeared “living”.

For many years I quested to understand the 850 light year distant M27, but no one could answer my questions. I researched and learned it was made up of doubly ionized oxygen. I had hoped that perhaps there was a spectral reason to what I viewed year after year – but still no answer. Like all amateurs, I became the victim of “aperture fever” and I continued to study the M27 with a 12.5? telescope, never realizing the answer was right there – I just hadn’t powered up enough.

Several years later while studying at the Observatory, I was viewing through a friend’s identical 12.5? telescope and as chance would have it, he was using about twice the magnification that I normally used on the “Dumbbell”. Imagine my total astonishment as I realized for the very first time that the faint central star had an even fainter companion that made it seem to wink! At smaller apertures or low power, this was not revealed. Still, the eye could “see” a movement within the nebula – the central, radiating star and its companion.

Do not sell the “Dumbbell” short. It can be seen as a small, unresolved area in common binoculars, easily picked out with larger binoculars as an irregular planetary nebula, and turns astounding with even the smallest of telescopes. In the words of Burnham, “The observer who spends a few moments in quiet contemplation of this nebula will be made aware of direct contact with cosmic things; even the radiation reaching us from the celestial depths is of a type unknown on Earth…”

Saturday, September 8 – Heads up for early risers! This morning is a beautiful conjunction of Jupiter and the Moon. For viewers in the western regions of Southern America, this is an occultation event, so be sure to check for times in your area!

Today in 1966, a legend was born as the television program Star Trek premiered. Created by Gene Roddenberry, its enduring legacy inspired several generations to an interest in space, astronomy, and technology. Its five-year mission still airs – along with numerous movie and series sequels. May Star Trek continue to “live long and prosper!”

Tonight a great opportunity to have another look at all the things we’ve studied this week. However, I would encourage those of you with larger binoculars and telescopes to head for a dark sky location, because tonight we are going on a quest… The quest for the holy “Veil”.

By no means is the Veil Nebula Complex an easy one. The brightest portion, NGC 6992 (Right Ascension: 20 : 56.4 – Declination: +31 : 43), can be spotted in large binoculars and you can find it just slightly south of a central point between Epsilon and Zeta Cygnii. The NGC 6992 is much better in a 6-8? scope however, and low power is essential to see the long ghostly filaments which span more than a degree of sky. About two and a half degrees west/southwest, and incorporating star 52 is another long narrow ribbon of what may be classified as a supernova remnant. When aperture reaches the 12? range, so does the true breadth of this fascinating complex. It is possible to trace these long filaments across several fields of view. They sometimes dim and at other times widen, but like a surreal solar flare, you will not be able to tear your eyes away from this area. Another undesignated area lies between the two NGCs, and the whole 1,500 light year distant area spans over two and a half degrees. Sometimes known as the “Cygnus Loop”, it’s definitely one of the summer’s finest objects.

Sunday, September 9 – On this day in 1839, John Herschel froze time by making the very first glass plate photograph – and we’re glad he did. His photo was of his father William’s famous 40-foot telescope in Slough, England. The scope had not been used in decades and was disassembled shortly after the photograph was taken. Later in 1892, on this same day, Edward Emerson Barnard was busy at Lick Observatory discovering Jupiter’s innermost moon – Amalthea.

Do I always save the best for last? You bet. And tonight it’s my favorite galaxy structure – edge-on.

The NGC 7814 (Right Ascension: 0 : 03.3 – Declination: +16 : 09) is easy enough to find. Just head towards Gamma Pegasi and look in your finderscope for a star that is around 3 degrees to the northwest. At low power you will see the galaxy to the southeast of this star as a scratch of light. Up the power in both aperture and magnification and enjoy! This galaxy has a deeply concentrated nucleus and a very prominent dissecting dark dustlane. By the way… It’s Caldwell 43.

Until next week? Wishing you clear skies!

Four views of M57 – Credit: NOAO/AURA/NSF