Click on the image for a full resolution version
M4 or Messier 4 is a rather small sized globular cluster. It has about 30,000 stars (this deep, high resolution image shows more than 17,000 stars…), what compared with monster clusters like Omega Centauri (with about 10,000,000 stars) or NGC 104 (47 Tuc, with about 1,000,000 stars) makes it just a humble version of them. We see it as one of the (angularly) big clusters, due to its closeness. It is the second known globular cluster to us (7,200 ly). This globular cluster shows several unusual characteristics. When seen telescopically, it shows a distinct central bar made of 11-magnitude stars (see image with lower exposure below):
This globular has also an unusually high number of Blue Stragglers, 21 of them, (Blue Stragglers are main sequence stars that are bluer and more luminous than their main sequence counter parts at the turn-off point of the cluster. They are usually originated by igniting, at a higher total mass, the gas absorbed from lower mass close companions in the cluster. Blue Stragglers are frequent in globulars, but the number detected in M4 is high for such a small cluster. In July 2003, an exoplanet was discovered orbiting a binary “star” system (a white dwarf and a pulsar) in M4. This 2.5 Jupiter-mass planet is believed to be more than 12.5 billion years old and was, therefore, dubbed Methuselah…
Lower exposure time images were taken to provide a better resolution in the bright core.
Additional Information
Object
Name(s): M4, Messier 4, NGC 6121
Type: Globular Cluster
RA: 16h 23m 34s
Dec: -26º 31’ 25”
Constellation: Scorpius
Size (arcmin): 26 arcmin
Magnitude: +5.6
Distance: 7,200 ly
Image
Date: 2018-04-28 to 2018-05-18
Location: iTelescope.net, SSO near Coonabarabran, NSW Australia
Size (arcmin): 36×36 arcmin
Telescope: Planewave CDK 20” f/6.8
Camera: SBIG STX16803 (4096x4096pix)
Guiding: Astrodon MonsterMOAG off-axis guider
Total exposure: 7 hours (L: 15x10min + 16x2min; RGB 8x10min each)
Processing: CCDStack, Photoshop CC 2018