Messier 62
A massive globular cluster with two star generations and many variables.
Messier 62 (M62), also cataloged as NGC 6266 and nicknamed the Flickering Globular Cluster, sits in the southern part of the constellation Ophiuchus. Charles Messier discovered it on June 7, 1771, and added it as the 62nd object in his catalogue eight years later.
This cluster lies about 21,500 light-years from Earth and 5,500 light-years from the Milky Way’s center. It ranks among the most massive and luminous globular clusters in our galaxy, with an estimated mass of 1.22 million solar masses and an integrated absolute V-band magnitude of –9.18, giving a mass-to-light ratio of 2.05 ± 0.04. Its projected ellipticity is just 0.01, meaning it is nearly spherical. The density profile of its stars indicates the cluster has not yet undergone core collapse. The core radius measures 1.3 light-years (0.39 parsecs), the half-mass radius is 9.6 light-years (2.95 parsecs), and the half-light radius is 6.0 light-years (1.83 parsecs). Stellar density at the core reaches 5.13 solar masses per cubic parsec, and the tidal radius extends to 59 light-years (18.0 parsecs).
M62 contains at least two distinct stellar populations, likely from two separate episodes of star formation. Among its main-sequence stars, 79% ± 1% belong to the first generation and 21% ± 1% to the second, which is enriched by elements from the first. Specifically, abundances of helium, carbon, magnesium, aluminum, and sodium differ between the two groups.
The cluster is classified as an Oosterhoff type I, or "metal-rich," system. A 2010 survey found 245 variable stars in its field: 209 RR Lyrae variables, four Type II Cepheids, 25 long-period variables, and one eclipsing binary. It may be the galaxy’s richest cluster in RR Lyrae variables. Ten binary millisecond pulsars have been identified, including one (M62B) that shows eclipsing behavior due to gas streaming off its companion, and another (M62H) with an exoplanet roughly three times Jupiter’s mass. Multiple X-ray sources exist, with 50 within the half-mass radius. Forty-seven blue straggler candidates—formed from binary star mergers—have been found, concentrated near the core.
The cluster is considered a promising place to search for an intermediate-mass black hole (IMBH).
- Discovered by
- Charles Messier
- Discovery date
- 7 June 1771
- Distance from earth
- 21.5 kly
- Distance from galactic center
- 5.5 kly
- Mass
- 1.22×10^6 M☉
- Integrated absolute magnitude v
- -9.18
- Mass to light ratio
- 2.05±0.04
- Core radius
- 1.3 ly (0.39 pc)
- Half mass radius
- 9.6 ly (2.95 pc)
- Half light radius
- 6.0 ly (1.83 pc)
Lore & Background
Messier 62 was discovered on 7 June 1771 by Charles Messier, who listed it as the 62nd entry in his catalogue published eight years later. The cluster is located in the south of Ophiuchus, about 21.5 kly from Earth and 5.5 kly from the Galactic Center. Its density profile suggests it has not yet undergone core collapse, and it is essentially spherical with a projected ellipticity of 0.01.
The cluster shows at least two distinct populations of stars, representing two separate episodes of star formation. Of the main sequence stars, 79%±1% are from the first generation and 21%±1% from the second, with the second enriched by elements released by the first. Abundances of helium, carbon, magnesium, aluminium, and sodium differ between these populations. Indications are this is an Oosterhoff type I, or 'metal-rich' system.
A 2010 study identified 245 variable stars in the cluster's field, including 209 RR Lyrae variables, four Type II Cepheids, 25 long period variables, and one eclipsing binary. The cluster may prove to be the galaxy's richest in terms of RR Lyrae variables. It has ten binary millisecond pulsars, including one (M62B) displaying eclipsing behavior from gas streaming off its companion, and one (M62H) with an orbiting exoplanet about three times the mass of Jupiter. There are multiple X-ray sources, including 50 within the half-mass radius, and 47 blue straggler candidates have been identified, preferentially concentrated near the core region.
Reader's Guide
Messier 62 is significant as one of the most massive and luminous globular clusters in the Milky Way, with an estimated mass of 1.22×10^6 M☉ and an integrated absolute magnitude of −9.18. Its mass-to-light ratio of 2.05±0.04 and core stellar density of 5.13 M☉ per cubic parsec highlight its dense, massive nature. The cluster's two distinct stellar populations, with differing abundances of helium, carbon, magnesium, aluminium, and sodium, provide evidence for multiple star formation episodes, enriching understanding of cluster evolution.
The cluster's wealth of variable stars—245 identified in a 2010 study, including 209 RR Lyrae variables—makes it a prime target for studying stellar pulsation and distance measurement. Its ten binary millisecond pulsars, including one with an eclipsing companion and one with a Jupiter-mass exoplanet, offer insights into binary evolution and planetary systems in dense environments. The presence of 50 X-ray sources within the half-mass radius and 47 blue straggler candidates near the core further underscores its dynamic activity.
M62 is also hypothesized to host an intermediate mass black hole (IMBH), though a brief study of proper motion within 17″ of the core did not require one to explain observations. Simulations cannot rule out an IMBH with a mass of a few thousand M☉, and a claim for a similar object in M15 was made by Kiselev et al. (2008) based on radial velocity measurements. This makes M62 well-suited for ongoing searches for IMBHs.
Did You Know?
- M62 is also known as the Flickering Globular Cluster.
- It contains a binary millisecond pulsar (M62H) with an exoplanet about three times the mass of Jupiter.
- The cluster has 209 RR Lyrae variables and may be the galaxy's richest in such variables.
- Its two stellar populations show differences in helium, carbon, magnesium, aluminium, and sodium abundances.
More in Messier Objects, Part 2 1-24
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