Hubble Photo of Globular Cluster NGC 6441, One of the Most Massive in the Milky Way

The Hubble Space Telescope has delivered another outstanding image. This one is of NGC 6441, a massive globular cluster in the constellation Scorpius. It’s one of the most massive ones in the Milky Way, and the stars in it have a combined mass of 1.6 million solar masses.

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Messier 92 – the NGC 6341 Globular Cluster

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the globular cluster known as Messier 92!

During the 18th century, famed French astronomer Charles Messier noticed the presence of several “nebulous objects” while surveying the night sky. Originally mistaking these objects for comets, he began to catalog them so that others would not make the same mistake. Today, the resulting list (known as the Messier Catalog) includes over 100 objects and is one of the most influential catalogs of Deep Space Objects.

One of these objects is Messier 92, a globular cluster located in the northern constellation of Hercules. This cluster lies at a distance of 26,700 light-years from Earth and is also approaching our galaxy at a speed of about 112 km/s (403,200 km/h; 250,500 mph) – which means it will eventually merge with our own. With an average estimated age of 14.2 billion years (± 1.2 billion years), it is almost as old as the Universe itself!

Continue reading “Messier 92 – the NGC 6341 Globular Cluster”

Messier 80 – the NGC 6093 Globular Cluster

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the globular cluster known as Messier 80!

During the 18th century, famed French astronomer Charles Messier noticed the presence of several “nebulous objects”  while surveying the night sky. Originally mistaking these objects for comets, he began to catalog them so that others would not make the same mistake. Today, the resulting list (known as the Messier Catalog) includes over 100 objects and is one of the most influential catalogs of Deep Space Objects.

One of these objects is Messier 80, a globular star cluster located about 32,600 light years from Earth in the constellation Scorpius. This cluster is one of the most densely populated in our galaxy and is located about halfway between the bright stars Antares, Alpha Scorpii, Akrab and Beta Scorpii – making it relatively easy to find.

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Messier 75 – the NGC 6864 Globular Cluster

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the globular cluster known as Messier 75!

During the 18th century, famed French astronomer Charles Messier noticed the presence of several “nebulous objects”  while surveying the night sky. Originally mistaking these objects for comets, he began to catalog them so that others would not make the same mistake. Today, the resulting list (known as the Messier Catalog) includes over 100 objects and is one of the most influential catalogs of Deep Space Objects.

One of these objects is Messier 75 (aka. NGC 6864), a globular cluster roughly 67,500 light years from Earth near the southern constellation Sagittarius. This object is also about 14,700 light years away from the Galactic Center, and on the located on the other side relative to Earth. Because of its distance and location, this object is virtually impossible to see binoculars and difficult to resolve with small telescopes. Continue reading “Messier 75 – the NGC 6864 Globular Cluster”

Messier 72 – the NGC 6981 Globular Cluster

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the globular cluster known as Messier 72.

During the 18th century, famed French astronomer Charles Messier noticed the presence of several “nebulous objects”  while surveying the night sky. Originally mistaking these objects for comets, he began to catalog them so that others would not make the same mistake. Today, the resulting list (known as the Messier Catalog) includes over 100 objects and is one of the most influential catalogs of Deep Space Objects.

One of these objects is Messier 72, a globular cluster about 54,570 light years away in the direction of the Aquarius constellation. Originally discovered by French astronomer Pierre Méchain a few years prior, Messier would go on to include this star cluster in his catalog. Located in close proximity to Messier 73, this globular cluster is one of the smaller and fainter Messier objects in the night sky. Continue reading “Messier 72 – the NGC 6981 Globular Cluster”

Messier 71 – the NGC 6838 Globular Cluster

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the unusual globular cluster known as Messier 71.

If you look up into the night sky, on a particularly clear night when there’s not a lot of bright lights nearby, you may be able to make out a series of faint objects. Similar to the Milky Way, that cloudy, ghostly band that reaches across the night sky, these small pockets of fuzzy light are in fact collections of stars located thousands of light years away.

Continue reading “Messier 71 – the NGC 6838 Globular Cluster”

Messier 70 – the NGC 6681 Globular Cluster

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the globular cluster known as Messier 70.

In the late 18th century, French astronomer Charles Messier spent much of his time looking up at the night sky in search of comets. Over time, he discovered 100 fixed, diffuse objects that resembled comets, but were something else entirely. Messier compiled a list of these objects, hoping to prevent other astronomers from making the same mistake. What resulted was the Messier Catalog, one of the influential catalogs of Deep Sky Objects.

One of the objects he catalogued is Messier 70 (aka.  NGC 6681), a globular cluster located 29,300 light years away from Earth and close to the Galactic Center. It’s location within the asterism known as the “Tea Pot” (which is part of the northern Sagittarius constellation). It is also in close proximity to both the M54 and M69 globular clusters. Continue reading “Messier 70 – the NGC 6681 Globular Cluster”

Messier 69 – the NGC 6637 Globular Cluster

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the globular cluster known as Messier 69.

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects he initially mistook for comets. In time, he would come to compile a list of approximately 100 of these objects, hoping to prevent other astronomers from making the same mistake. This list – known as the Messier Catalog – would go on to become one of the most influential catalogs of Deep Sky Objects.

One of these objects is known as Messier 69 (NGC 6637), a globular cluster located in the constellation Sagittarius. Located about about 29,700 light-years away from Earth, this cluster lies close to Messier 70 (both of which were discovered Charles Messier on August 31st, 1780). Both objects lie close to the galactic center, and M69 is one of the most metal-rich globular clusters known. Continue reading “Messier 69 – the NGC 6637 Globular Cluster”

Messier 62 – the NGC 6266 Globular Cluster

Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the globular cluster known as Messier 62.

In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects he initially mistook for comets. In time, he would come to compile a list of approximately 100 of these objects, hoping to prevent other astronomers from making the same mistake. This list – known as the Messier Catalog – would go on to become one of the most influential catalogs of Deep Sky Objects.

One of these objects is the globular cluster known as Messier 62, which spans about 100 light-years in diameter and is approximately 22,200 light years from Earth. Located in the southern constellation of Ophiuchus, this cluster is easy to find because of its proximity to Antares – the brightest star in Scorpius constellation – and is easily viewed suing binoculars and small telescopes.

Description:

Positioned about 22,500 light years away from Earth, this glorious gravitationally bound ball of stars could span as much as 100 light years of space. Captured within its confines are 89 known variable stars – most of them RR Lyrae types. M62 has a very dense core… One which may have experienced core collapse during its long history. An ordinary globular cluster? Not hardly. It’s one that holds some optical surprises.

The globular cluster Messier 62 in the constellation Ophiuchus. Credit: Wikipedia Commons/Hewholooks

As G. Cocozza (et al) indicated in their 2008 study:

“We report on the optical identification of the companion to the eclipsing millisecond pulsar PSR J1701-3006B in the globular cluster NGC 6266. A relatively bright star with an anomalous red color and an optical variability (~0.2 mag) that nicely correlates with the orbital period of the pulsar (~0.144 days) has been found nearly coincident with the pulsar nominal position. This star is also found to lie within the error box position of an X-ray source detected by Chandra observations, thus supporting the hypothesis that some interaction is occurring between the pulsar wind and the gas streaming off the companion. Although the shape of the optical light curve is suggestive of a tidally deformed star which has nearly completely filled its Roche lobe, the luminosity (~1.9 Lsolar) and the surface temperature (~6000 K) of the star, deduced from the observed magnitude and colors, would imply a stellar radius significantly larger than the Roche lobe radius.”

Is it possible that this is the smoking gun for intermediate mass black holes in globular clusters? Julio Chaname seems to think so. As he explained in his 2009 study:

“The existence of intermediate-mass black holes [IMBHs] in star clusters has been predicted by a variety of theoretical arguments and, more recently, by several large, realistic sets of collisional N-body simulations. Establishing their presence or absence at the centers of globular clusters would profoundly impact our understanding of problems ranging from the formation and long-term dynamical evolution of stellar systems, to the nature of the seeds and the growth mechanisms of the supermassive black holes {BHs} that inhabit the centers of most large, luminous galaxies. Observationally, the unambiguous signature of a massive central BH would be the discovery of central, unresolved X-ray or radio emission that is not consistent with more common stellar-mass accreting objects or pulsars. Yet, due to the largely uncertain details of accretion modeling, a precise mass determination of a central BH must necessarily come from stellar dynamics. This goal has not been achieved to date at the centers of Galactic globular clusters because of lack of adequate data as well as the use of too simplified methods of analysis. This situation can be overcome today through the combination of HST proper-motion measurements and state-of-the-art dynamical models specifically designed to take full advantage of this type of dataset. In this project, we will use two HST orbits to obtain another epoch of observations of NGC 6266. This cluster has photometric and structural properties that are consistent with current theoretical expectations for a cluster harboring an IMBH. Even more importantly, it is the only Galactic globular cluster for which there exists a detection of radio emission coincident with the cluster’s core, and with a flux density that appears to rule out a stellar or binary origin. The goal of our project is to obtain proper motion measurements to either confirm an IMBH in this cluster and measure its mass, or to set limits to its mass and existence.”

The Messier 62 globular cluster, as imaged by the Hubble Space Telescope. Credit: NASA, ESA

History of Observation:

While Charles Messier first discovered this globular cluster on June 7, 1771 – he didn’t accurately record its position until June 4, 1779.

“”Very beautiful nebula, discovered in Scorpio, it resembles a little Comet, the center is brilliant and surrounded by a faint glow. Its position determined, by comparing it with the star Tau of Scorpius. M. Messier had already seen this nebula on June 7, 1771, without having determined the position where it is close to. Seen again on March 22, 1781.”

Sir William Herschel would resolve it two years after Messier cataloged it, but it was Admiral Smyth who gave it a little more historic significance when he writes in his notes:

“A fine large resolvable nebula, at the root of the creature’s [Scorpion’s] tail, and in the preceding part of the Galaxy [Milky Way band]. It is an aggregated mass of small stars running up to a blaze in the centre, which renders the differentiating comparatively easy and satisfactory; and in this instance it was referred to its neighbor, 26 Ophiuchi, which is 5deg distant to the north: and it lies only about 7deg from Antares, on the south-east. This was registered in 1779, and Messier described it as “a very pretty nebula, resembling a little comet, the centre bright, and surrounded by a faint light.” Sir William Herschel, who first resolved it, pronounced it a miniature of Messier’s No. 3, and adds, “By the 20-foot telescope, which at the time of these observations was of the Newtonian construction, the profundity of this cluster is of the 734th order.” To my annoyance, it was started as a comet a few years ago, by a gentleman who ought to have known better.”

Locating Messier 62:

M62 is easily located about 5 degrees (3 finger widths) southeast of Antares – but because it is small, it can easily be overlooked in binoculars. Take your time, because it is only just a little more than an average binocular field away from an easy marker star and bright enough to be seen even with smaller instruments under not so good skies.

The locations of Messier 62 in the Ophiuchus constellation. Credit: IAU/Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

In the finderscope of a telescope, begin with Antares in the center and shift southwest. At 5X magnification, it will show as a faint haze. In a small telescope, you may get some resolution – but expect this globular cluster to appear more comet-like. Larger telescopes can expect a wonderful explosion of stars!

Enjoy your observations! And as always, here are the quick facts on this Messier Object to help you get started:

Object Name: Messier 62
Alternative Designations: M62, NGC 6266
Object Type: Class IV Globular Cluster
Constellation: Ophiuchus
Right Ascension: 17 : 01.2 (h:m)
Declination: -30 : 07 (deg:m)
Distance: 22.5 (kly)
Visual Brightness: 6.5 (mag)
Apparent Dimension: 15.0 (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:

Messier 55 – the NGC 6809 Globular Star Cluster

Welcome back to Messier Monday! We continue our tribute to our dear friend, Tammy Plotner, by looking at the “Summer Rose Star”, other known as the globular star cluster of Messier 55. 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 Messier 55, a globular star cluster located in the Sagittarius Constellation. Also known as the “Summer Rose Star”, this cluster is located 17,600 light-years from Earth and spans about 100 light-years in diameter. While it can be seen with binocular, resolving its individual stars can only be done with a small telescope and finderscope.

Description:

Located some 17,300 light years from planet Earth and spanning nearly 100 light years in diameter, this loose appearing ball of stellar points may not seem concentrated – but its home to tens of thousands stars. Does anyone really take the time to count them? You bet. M.J. Irwin and V. Trimble did just that during their 1984 study of Messier 55:

“We report star counts, as a function of position and apparent magnitude, in the rich, relatively open southern globular cluster NGC 6809 (M55). Three AAO 150arcsec plates were scanned by the Automatic Plate Measuring System (APM) at the Institute of Astronomy, Cambridge, and 20825 images were counted by its associated software. Previously known features of rich globular clusters which appear in the raw counts include a flattening of the luminosity function, increased central concentration of bright stars relative to faint ones (normally interpreted as mass segregation), and mild deviations in radial profile from King models. Crowding of the field, which causes the counting procedure to miss faint stars preferentially near the cluster center, contributes to all of these, and may be responsible for all of the apparent mass segregation, but not for all of the other two effects.”

Globular cluster Messier 55 (M55, or NGC 6809) in the constellation Sagittarius, as imaged by the ESO 3.6-metre telescope on La Silla. Release date: 3 December 2009. Credit: ESO

But just want good does counting the stars do? Well, knowing how many stars are within a given area helps astronomers compute other things as well, like chemical abundances. Said Carlos Alvarez and Eric Sandquist in their 2004 study:

“We have compiled the asymptotic giant, horizontal, and upper red giant branch (AGB, HB, and RGB) stars in the globular cluster M55 (NGC 6809). Using the star counts and the R-parameter we compute the initial helium abundance. The ratio is unusually high for a globular cluster, being almost 2 away from the predicted values, and the highest recorded for a massive globular cluster. We argue that M55’s particular HB morphology and metallicity have produced long-lived HB stars that are not too blue to avoid producing AGB stars. This result hints that we are able to map evolutionary effects on the HB. Finally, although we find no evidence of variations in HB morphology with distance from the center of the cluster, the red HB stars are significantly less concentrated than the majority of HB stars, and the bluest HB stars are more centrally concentrated.”

Studying globular clusters photometrically also gives astronomers the advantage of comparing them to others, to see how each evolves. As P. Richter (et al) indicated in their 1999 study:

“We present Stroemgren CCD photometry for the two galactic globular clusters M55 (NGC 6809) and M22 (NGC 6656). The difference between M55 and M22 may resemble the difference in integral CN band strength between M31 globular clusters and the galactic system. The colour-magnitude diagram of M55 shows the presence of a population of 56 blue-straggler stars that are more centrally concentrated than the red giant-branch stars.”

And viewing globular clusters like Messier 55 in a different wavelength of light other than optical reveals even more stunning details – like the vision of the XMM-Newton. As N.A. Webb (et al) said in their 2006 study:

“Using the new generation of X-ray observatories, we are now beginning to identify populations of close binaries in globular clusters, previously elusive in the optical domain because of the high stellar density. These binaries are thought to be, at least in part, responsible for delaying the inevitable core collapse of globular clusters and their identification is therefore essential in understanding the evolution of globular clusters, as well as being valuable in the study of the binaries themselves. Here, we present observations made with XMM-Newton of globular clusters, in which we have identified neutron star low mass X-ray binaries and their descendants (millisecond pulsars), cataclysmic variables and other types of binaries. We discuss not only the characteristics of these binaries, but also their formation and evolution in globular clusters and their use in tracing the dynamical history of these clusters.”

History of Observation:

M55 was originally discovered by Abbe Lacaille on June 16th, 1752, when he was observing in South Africa. In his notes, he wrote: “It resembles an obscure nucleus of a big comet.” Of course, our own comet hunter, Charles Messier, would search for a good many years before he recovered it to add to his own catalog. By July 24th, 1778, he found the object and recorded it as follows in his notes:

“A nebula which is a whitish spot, of about 6′ extension, its light is even and does not appear to contain any star. Its position has been determined from zeta Sagittarii, with the use of an intermediate star of 7th magnitude. This nebula has been discovered by M. l’Abbe de LaCaille, see Mem. Acad. 1755, p. 194. M. Messier has looked for it in vain on July 29, 1764, as reported in his memoir.”

Messier 55 in Sagittarius. Credit: Hewholooks/Wikipedia Commons

Johann Elert Bode, Dunlop and Caroline Herschel would follow, but it would be Sir William Herschel who would be first to glimpse the resolvability of this great globular cluster. In his private notes he writes:

“A rich cluster of very compressed stars, irregularly round, about 8 minutes long. By the observation of the small 20 feet telescope, which could reach stars 38.99 times as far as the eye, the profundity of this cluster cannot be much less than of the 467th order: I have taken it to be of the 400th order.”

Locating Messier 55:

M55 is by no means easy to find. One of the best ways to locate it is to begin at Theta 1 and Theta 2 Sagittarius, where you’ll find it approximately two finger widths northwest of this pair approximately four degrees. Both Thetas are on the dim side for the unaided eye – about magnitude 4 and 5 respectively, but you’ll recognize them when you find two stars separated by less than half a degree and oriented north/south.

For average binoculars, this will put M55 about a binocular field away to the northwest. For average image correct finderscopes, place the Thetas in the 8:00 position at the edge of the finderscope field and go to the eyepiece with the lowest possible magnification to locate it.

Messier 55 location. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

Although it has a high visual brightness, M55 has low surface brightness so it isn’t suitable to urban or light polluted skies. With dark sky conditions, binoculars will see it as a round hazy patch – like a diffuse comet, while small telescopes can begin to resolve individual stars. Larger aperture telescopes will pick out the fine grain of low magnitude stars quite easily!

Enjoy your own resolvability of this great globular cluster!

And as always, here are the quick facts on this Messier Object:

Object Name: Messier 55
Alternative Designations: M55, NGC 6809
Object Type: Class XI Globular Cluster
Constellation: Sagittarius
Right Ascension: 19 : 40.0 (h:m)
Declination: -30 : 58 (deg:m)
Distance: 17.3 (kly)
Visual Brightness: 6.3 (mag)
Apparent Dimension: 19.0 (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: