(via APOD: 2012 September 27 - Stars and Dust Across Corona Australis)
Stars and Dust Across Corona Australis Image Credit & Copyright: Marco Lorenzi (Glittering Lights)
Corona Australis is the Southern Crown. (Here in the northern hemisphere, we have Bootes holding Corona Borealis in the night sky. Bootes, the herdsman, is the constellation that Arcturus is in. Remember “arc to Arcturus and spike to Spica”. Spica is in Virgo.)
In any case, there’s a crown in the skies of the southern hemisphere too, and that’s where you can see this interesting collection of dust, along with a globular cluster…at least in the same line of sight.
The blue light you see in the nebulae is from the stars embedded in the dust, and is being reflected back toward us. Blue light scatters more readily in the dust of the interstellar medium, so more blue than red is being bounced off the “grains” (think something the size of soot) back at us.
The dark areas are where the dust is so thick between our point of view and the star field that we can’t see through it in visible wavelengths. An infrared image would see through it, and into it, to see what’s going on.
The cloud of dust creating this nebular complex is about 500 light-years away, but the globular cluster in the upper left of the image, while appearing close, is actually about 30,000 light-years away, far beyond the dust and stars of the nebulae. They’re very old, gravitationally bound collections of stars that orbit the galaxy, but not necessarily in the galactic plane. This one is NGC 6729.

(via APOD: 2012 September 27 - Stars and Dust Across Corona Australis)

Stars and Dust Across Corona Australis 
Image Credit & Copyright: Marco Lorenzi (Glittering Lights)

Corona Australis is the Southern Crown. (Here in the northern hemisphere, we have Bootes holding Corona Borealis in the night sky. Bootes, the herdsman, is the constellation that Arcturus is in. Remember “arc to Arcturus and spike to Spica”. Spica is in Virgo.)

In any case, there’s a crown in the skies of the southern hemisphere too, and that’s where you can see this interesting collection of dust, along with a globular cluster…at least in the same line of sight.

The blue light you see in the nebulae is from the stars embedded in the dust, and is being reflected back toward us. Blue light scatters more readily in the dust of the interstellar medium, so more blue than red is being bounced off the “grains” (think something the size of soot) back at us.

The dark areas are where the dust is so thick between our point of view and the star field that we can’t see through it in visible wavelengths. An infrared image would see through it, and into it, to see what’s going on.

The cloud of dust creating this nebular complex is about 500 light-years away, but the globular cluster in the upper left of the image, while appearing close, is actually about 30,000 light-years away, far beyond the dust and stars of the nebulae. They’re very old, gravitationally bound collections of stars that orbit the galaxy, but not necessarily in the galactic plane. This one is NGC 6729.

M4 Globular Cluster, From "A Cluster With A Secret" from the ESO:

A new image from ESO’s La Silla Observatory in Chile shows the spectacular globular star cluster Messier 4. This ball of tens of thousands of ancient stars is one of the closest and most studied of the globular clusters and recent work has revealed that one of its stars has strange and unexpected properties, apparently possessing the secret of eternal youth.
The Milky Way galaxy is orbited by more than 150 globular star clusters that date back to the distant past of the Universe (eso1141). One of the closest to the Earth is the cluster Messier 4 (also known as NGC 6121) in the constellation of Scorpius (The Scorpion). This bright object can be easily seen in binoculars, close to the bright red star Antares, and a small amateur telescope can show some of its constituent stars.
This new image of the cluster from the Wide Field Imager (WFI) on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory reveals many more of the cluster’s tens of thousands of stars and shows the cluster against the rich background of the Milky Way.
Astronomers have also studied many of the stars in the cluster individually using instruments on ESO’s Very Large Telescope. By splitting the light from the stars up into its component colours they can work out their chemical composition and ages.
New results for the stars in Messier 4 have been surprising. The stars in globular clusters are old and hence not expected to be rich in the heavier chemical elements [1]. This is what is found, but one of the stars in a recent survey was also found to have much more of the rare light element lithium than expected. The source of this lithium is mysterious. Normally this element is gradually destroyed over the billions of years of a star’s life, but this one star amongst thousands seems to have the secret of eternal youth. It has either somehow managed to retain its original lithium, or it has found a way to enrich itself with freshly made lithium.

M4 Globular Cluster, From "A Cluster With A Secret" from the ESO:

A new image from ESO’s La Silla Observatory in Chile shows the spectacular globular star cluster Messier 4. This ball of tens of thousands of ancient stars is one of the closest and most studied of the globular clusters and recent work has revealed that one of its stars has strange and unexpected properties, apparently possessing the secret of eternal youth.

The Milky Way galaxy is orbited by more than 150 globular star clusters that date back to the distant past of the Universe (eso1141). One of the closest to the Earth is the cluster Messier 4 (also known as NGC 6121) in the constellation of Scorpius (The Scorpion). This bright object can be easily seen in binoculars, close to the bright red star Antares, and a small amateur telescope can show some of its constituent stars.

This new image of the cluster from the Wide Field Imager (WFI) on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory reveals many more of the cluster’s tens of thousands of stars and shows the cluster against the rich background of the Milky Way.

Astronomers have also studied many of the stars in the cluster individually using instruments on ESO’s Very Large Telescope. By splitting the light from the stars up into its component colours they can work out their chemical composition and ages.

New results for the stars in Messier 4 have been surprising. The stars in globular clusters are old and hence not expected to be rich in the heavier chemical elements [1]. This is what is found, but one of the stars in a recent survey was also found to have much more of the rare light element lithium than expected. The source of this lithium is mysterious. Normally this element is gradually destroyed over the billions of years of a star’s life, but this one star amongst thousands seems to have the secret of eternal youth. It has either somehow managed to retain its original lithium, or it has found a way to enrich itself with freshly made lithium.

(via ESO - eso1141 - VISTA Finds New Globular Star Clusters)
The VISTA telescope is an optimized infrared telescope at the European Southern Observatory’s Paranal Observatory in the Atacama Desert in Chile. Being IR-optimized means that it can take wide-field images through the dust and gas that normally blocks our view of the other side of the galaxy.
What it has found in a recent survey (the Via Lactea/VVV survey) is some star clusters, two globular and one open, that we could never have seen before.
The main picture is of VVV CL001, the faint globular cluster on the left half of the frame, just above and to the right of the foreground star (with diffraction spikes). The larger, brighter globular cluster on the right has been known for some time. It is UKS 1, and the two clusters may actually be gravitationally bound to each other. While it looks quite bright in this shot, it was known previously as the dimmest globular cluster, because all the dust obscured and reddened the light. However, in IR it shines very brightly.
Not sure what I mean? Here, ESO gives you a comparison of visible light (top, from the Digitized Sky Survey II) and infrared (bottom, from VISTA):

See how much “pops out” with the infrared “bypassing” the obscuring dust?
Amazing enough already, right? Well, it turns out that there are a couple more in the VISTA survey:
VVV CL002 is the closest globular cluster to the center of the galaxy:

And finally, there’s VVV CL003, an open cluster about 15,000 light-years beyond the galactic center:

Click through to the story on the ESO’s website to get the images and even some great video (zooming in on the cluster and a transition of the view from visible to infrared).

(via ESO - eso1141 - VISTA Finds New Globular Star Clusters)

The VISTA telescope is an optimized infrared telescope at the European Southern Observatory’s Paranal Observatory in the Atacama Desert in Chile. Being IR-optimized means that it can take wide-field images through the dust and gas that normally blocks our view of the other side of the galaxy.

What it has found in a recent survey (the Via Lactea/VVV survey) is some star clusters, two globular and one open, that we could never have seen before.

The main picture is of VVV CL001, the faint globular cluster on the left half of the frame, just above and to the right of the foreground star (with diffraction spikes). The larger, brighter globular cluster on the right has been known for some time. It is UKS 1, and the two clusters may actually be gravitationally bound to each other. While it looks quite bright in this shot, it was known previously as the dimmest globular cluster, because all the dust obscured and reddened the light. However, in IR it shines very brightly.

Not sure what I mean? Here, ESO gives you a comparison of visible light (top, from the Digitized Sky Survey II) and infrared (bottom, from VISTA):

See how much “pops out” with the infrared “bypassing” the obscuring dust?

Amazing enough already, right? Well, it turns out that there are a couple more in the VISTA survey:

VVV CL002 is the closest globular cluster to the center of the galaxy:

And finally, there’s VVV CL003, an open cluster about 15,000 light-years beyond the galactic center:

Click through to the story on the ESO’s website to get the images and even some great video (zooming in on the cluster and a transition of the view from visible to infrared).

(via APOD: 2012 August 28 - Colorful Clouds Near Rho Ophiuchi)
Image Credit & Copyright: Tom O’Donoghue
Oooh! A lesson in the forms and varieties of nebulae all in one picture. OK, so there are three main kinds of nebulae:
Reflection
Emission
Dark
They’re produced by different processes too, so here’s what’s going on above:
Rho Ophiuchi, the bright blue star in the center of the top blue nebula is emitting regular light that is being scattered off the dust in the nebular clouds. Dust particles tend to scatter blue light more than any other wavelength of light, so the reflected light from the nebula is blue. Hence, reflection nebulae look blue.
To the lower-right, you can see Sigma Scorpii, a bright blue star in the middle of a red nebula. When the ultraviolet radiation from a star hit gas clouds, made mostly from hydrogen, they ionize the gas, stripping the electrons off the atoms. Atoms don’t stay that way forever, though, and they have a tendency to pull an electron back at some point, de-ionizing themselves. When that happens, it releases energy in the form of electromagnetic radiation, usually as red light. We see the light being emitted from the gas as it de-ionizes.
Finally, in all those spots, mostly in the middle of the picture, where you might be worried that the photographer’s camera has some sensing issues, where we’re not seeing any background starlight, or really anything at all, those are areas where there’s too much dust, in the way, making a dark spot in the sky.
Oh, a couple other things:
Big, bright, red supergiant Antares in the lower middle is so red that even it’s reflected light is yellow-red.
M4 is the globular cluster just to right of Antares, an ancient relic of the universe, as are all the globular clusters we’ve ever seen. They orbit the Milky Way and are generally around 12-13 billion years old.
Boy do I love this astronomy stuff.

(via APOD: 2012 August 28 - Colorful Clouds Near Rho Ophiuchi)

Image Credit & Copyright: Tom O’Donoghue

Oooh! A lesson in the forms and varieties of nebulae all in one picture. OK, so there are three main kinds of nebulae:

  • Reflection
  • Emission
  • Dark

They’re produced by different processes too, so here’s what’s going on above:

Rho Ophiuchi, the bright blue star in the center of the top blue nebula is emitting regular light that is being scattered off the dust in the nebular clouds. Dust particles tend to scatter blue light more than any other wavelength of light, so the reflected light from the nebula is blue. Hence, reflection nebulae look blue.

To the lower-right, you can see Sigma Scorpii, a bright blue star in the middle of a red nebula. When the ultraviolet radiation from a star hit gas clouds, made mostly from hydrogen, they ionize the gas, stripping the electrons off the atoms. Atoms don’t stay that way forever, though, and they have a tendency to pull an electron back at some point, de-ionizing themselves. When that happens, it releases energy in the form of electromagnetic radiation, usually as red light. We see the light being emitted from the gas as it de-ionizes.

Finally, in all those spots, mostly in the middle of the picture, where you might be worried that the photographer’s camera has some sensing issues, where we’re not seeing any background starlight, or really anything at all, those are areas where there’s too much dust, in the way, making a dark spot in the sky.

Oh, a couple other things:

  1. Big, bright, red supergiant Antares in the lower middle is so red that even it’s reflected light is yellow-red.
  2. M4 is the globular cluster just to right of Antares, an ancient relic of the universe, as are all the globular clusters we’ve ever seen. They orbit the Milky Way and are generally around 12-13 billion years old.

Boy do I love this astronomy stuff.

(via APOD: 2012 August 19 - M72: A Globular Cluster of Stars)
M72: A Globular Cluster of Stars Image Credit: NASA, ESA, Hubble, HPOW
Explanation via APOD:
Globular clusters once ruled the Milky Way. Back in the old days, back when our Galaxy first formed, perhaps thousands of globular clusters roamed our Galaxy. Today, there are less than 200 left. Many globular clusters were destroyed over the eons by repeated fateful encounters with each other or the Galactic center. Surviving relics are older than any Earth fossil, older than any other structures in our Galaxy, and limit the universe itself in raw age. There are few, if any, young globular clusters in our Milky Way Galaxy because conditions are not ripe for more to form. Pictured above by the Hubble Space Telescope are about 100,000 of M72's stars. M72, which spans about 50 light years and lies about 50,000 light years away, can be seen with a small telescope toward the constellation of the Water Bearer (Aquarius).

(via APOD: 2012 August 19 - M72: A Globular Cluster of Stars)

M72: A Globular Cluster of Stars 
Image Credit: NASAESAHubbleHPOW

Explanation via APOD:

Globular clusters once ruled the Milky Way. Back in the old days, back when our Galaxy first formed, perhaps thousands of globular clusters roamed our Galaxy. Today, there are less than 200 left. Many globular clusters were destroyed over the eons by repeated fateful encounters with each other or the Galactic center. Surviving relics are older than any Earth fossil, older than any other structures in our Galaxy, and limit the universe itself in raw age. There are few, if any, young globular clusters in our Milky Way Galaxy because conditions are not ripe for more to form. Pictured above by the Hubble Space Telescope are about 100,000 of M72's stars. M72, which spans about 50 light years and lies about 50,000 light years away, can be seen with a small telescope toward the constellation of the Water Bearer (Aquarius).
(via APOD: 2012 August 3 - Messier 5)
Image Credit & Copyright: Adam Block, Mt. Lemmon SkyCenter, University of Arizona
Messier discovered this “nebula” between Libra and Serpens as the 5th non-comet object in his sky survey. M5 is a globular cluster, dense collections of stars that orbit the halo of the Milky Way galaxy. They are very old in general, but M5 is about 13 billion years old, making it one of the oldest. You can see the red and blue giants, even near the core, standing out quite well.

(via APOD: 2012 August 3 - Messier 5)

Image Credit & Copyright: Adam BlockMt. Lemmon SkyCenterUniversity of Arizona

Messier discovered this “nebula” between Libra and Serpens as the 5th non-comet object in his sky survey. M5 is a globular cluster, dense collections of stars that orbit the halo of the Milky Way galaxy. They are very old in general, but M5 is about 13 billion years old, making it one of the oldest. You can see the red and blue giants, even near the core, standing out quite well.

(via APOD: 2012 June 14 - M13: The Great Globular Cluster in Hercules)
You could actually see M13 in a dark, moonless sky. I mean really dark, no light pollution at all. It would just be a smear, but if you put a telescope on this smear in the constellation of Hercules, you’ll find an amazingly bright globular cluster. At the center of the cluster, the stars have a density of 100 per cubic parsec (~3 light-years in a parsec). For reference, as the APOD editors point out, the next closest star to our Sun, Proxima Centauri - of the Alpha Cen binary - is 4 light-years away.
While most of a globular cluster is all stars about the same age, that density of stars creates occasional collisions and mergers and the like, so that you can sometimes end up with red or blue giants that seem “out of sequence”.
Image Credit & Copyright: Martin Pugh

(via APOD: 2012 June 14 - M13: The Great Globular Cluster in Hercules)

You could actually see M13 in a dark, moonless sky. I mean really dark, no light pollution at all. It would just be a smear, but if you put a telescope on this smear in the constellation of Hercules, you’ll find an amazingly bright globular cluster. At the center of the cluster, the stars have a density of 100 per cubic parsec (~3 light-years in a parsec). For reference, as the APOD editors point out, the next closest star to our Sun, Proxima Centauri - of the Alpha Cen binary - is 4 light-years away.

While most of a globular cluster is all stars about the same age, that density of stars creates occasional collisions and mergers and the like, so that you can sometimes end up with red or blue giants that seem “out of sequence”.

Image Credit & Copyright: Martin Pugh

(via APOD: 2012 April 17 - Antares and Clouds)
Antares, the red supergiant on the left, throws off gas, which is then lit up by Al Niyat, its companion blue star, quite bright in this image.
Antares is the heart of Scorpio, an easily visible red star in the night sky (like Betelgeuse and Mars, it really is quite red) with 850 times the diameter of the Sun, 15 times the mass and 10,000 times the true luminosity. (Distance is a real beast for apparent luminosity, with the difference increasing as the square of the amount of intervening space.)
As an added bonus, M4, the globular cluster of stars, appears in this shot, looking like it sits between Antares and Al Niyat, but, in fact, it is far behind the two stars.
Image Credit & Copyright: Ivan Eder

(via APOD: 2012 April 17 - Antares and Clouds)

Antares, the red supergiant on the left, throws off gas, which is then lit up by Al Niyat, its companion blue star, quite bright in this image.

Antares is the heart of Scorpio, an easily visible red star in the night sky (like Betelgeuse and Mars, it really is quite red) with 850 times the diameter of the Sun, 15 times the mass and 10,000 times the true luminosity. (Distance is a real beast for apparent luminosity, with the difference increasing as the square of the amount of intervening space.)

As an added bonus, M4, the globular cluster of stars, appears in this shot, looking like it sits between Antares and Al Niyat, but, in fact, it is far behind the two stars.

Image Credit & CopyrightIvan Eder

(via APOD: 2012 April 9 - Blue Straggler Stars in Globular Cluster M53)
More Hubble globular cluster fun. This time, M53 is our raison d’etre. (I’m not typing the accents, I know. Shoot me. Actually, you know what, the French might for that kind of thing.)
Aaaaanyway, we’re back with M53 for those fun little blue stragglers again. Blue stragglers, you’ll recall, are idiosyncratically younger stars in a globular cluster. I say idiosyncratic because all the stars in a globular cluster form at once, while the blue stragglers “look” younger. It turns out that they are the result of interactions between dying older stars in the cluster that give “new life” to a star, usually in a binary pair collapsing or collisions between older stars.
They may help to more precisely give the age of the cluster, and get better ideas of the age of the universe, since globular clusters are, in general, really old, even on an astronomical timescale, so any age differences that the blue stragglers give evidence of can indicate how long the cluster has been able to “recombine” its stars, giving a more detailed view of history of the cluster.
Image Credit: ESA/Hubble, NASA

(via APOD: 2012 April 9 - Blue Straggler Stars in Globular Cluster M53)

More Hubble globular cluster fun. This time, M53 is our raison d’etre. (I’m not typing the accents, I know. Shoot me. Actually, you know what, the French might for that kind of thing.)

Aaaaanyway, we’re back with M53 for those fun little blue stragglers again. Blue stragglers, you’ll recall, are idiosyncratically younger stars in a globular cluster. I say idiosyncratic because all the stars in a globular cluster form at once, while the blue stragglers “look” younger. It turns out that they are the result of interactions between dying older stars in the cluster that give “new life” to a star, usually in a binary pair collapsing or collisions between older stars.

They may help to more precisely give the age of the cluster, and get better ideas of the age of the universe, since globular clusters are, in general, really old, even on an astronomical timescale, so any age differences that the blue stragglers give evidence of can indicate how long the cluster has been able to “recombine” its stars, giving a more detailed view of history of the cluster.

Image Credit: ESA/HubbleNASA

(via Desktop Project Part 3: The massive massiveness of M54 | Bad Astronomy | Discover Magazine)
Sometimes you worry that all these globular clusters look too much the same - M9, M54, NGC 7006, etc. - but there’s no good reason to pass up an amazing HST shot of a massive globular cluster.
Especially when it also houses an intermediate mass black hole.
What?
You know stellar-mass black holes?
Yeah, around the mass of very large stars or a little more.
You know supermassive black holes?
Yeah, millions or billions times the mass of the Sun, at the centers of galaxies, especially active galactic nuclei.
The black hole in M54 is about 9400 times the mass of the Sun, not supermassive, but definitely larger than your average stellar-mass black hole.
Also, this globular cluster might be part of the Sagittarius Dwarf Elliptical, which the Milky Way is in the process of absorbing…which makes M54 an extragalactic cluster…for now…discovered by Charles Messier (that’s why it’s an “M” object) in 1778.
Image credit: ESA/Hubble & NASA

(via Desktop Project Part 3: The massive massiveness of M54 | Bad Astronomy | Discover Magazine)

Sometimes you worry that all these globular clusters look too much the same - M9, M54, NGC 7006, etc. - but there’s no good reason to pass up an amazing HST shot of a massive globular cluster.

Especially when it also houses an intermediate mass black hole.

What?

You know stellar-mass black holes?

Yeah, around the mass of very large stars or a little more.

You know supermassive black holes?

Yeah, millions or billions times the mass of the Sun, at the centers of galaxies, especially active galactic nuclei.

The black hole in M54 is about 9400 times the mass of the Sun, not supermassive, but definitely larger than your average stellar-mass black hole.

Also, this globular cluster might be part of the Sagittarius Dwarf Elliptical, which the Milky Way is in the process of absorbing…which makes M54 an extragalactic cluster…for now…discovered by Charles Messier (that’s why it’s an “M” object) in 1778.

Image credit: ESA/Hubble & NASA