NGC 6652
From Wikipedia, the free encyclopedia
NGC 6652 is a globular cluster in Sagittarius. It is located about 6,500 light years from the Galactic Center and about 30,000 light years away from Earth.[3] The cluster was discovered on September 3, 1826 by James Dunlop.[4]
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| NGC 6652 | |
|---|---|
NGC 6652 seen by the Hubble Space Telescope | |
| Observation data | |
| Constellation | Sagittarius |
| Right ascension | 18h 35m 45.63s[1] |
| Declination | −32° 59′ 26.6″[1][2] |
| Distance | ~30,000 |
| Apparent magnitude (V) | 9.75 |
| Apparent dimensions (V) | 5.1' x 5.1' |
| Physical characteristics | |
| Estimated age | 13.6 billion years |
| Other designations | NGC 6652, GCl 98, RX J1835.7-3259, 4FGL J1835.7-3258[1] |
Observations
According to a study published in 2011 by J. Boyles and his colleagues, the metallicity of the globular cluster NGC 6652 is -0.81 and its mass is 109,000 M☉.[5] In the same study, the distance to the cluster is also estimated at approximately 10.0 kpc (∼32,600 ly). The study published by Forbes and Bridges indicates a metallicity of -0.70.[6]
Stars
As of November 2022, 267 pulsars had been discovered in 36 globular clusters of the Milky Way.[7] Out of 267 pulsars, two millisecond binary pulsars are located in NGC 6652.[7] The first pulsar in this globular cluster was discovered using the Green Bank Telescope and is known as PSR J1835-3259A. Its period is 3.9 ms[8] and it has an elliptical orbit with eccentricity of 0.95 and a period of 9.25 days. Assuming a mass of 1.4 M☉ the mass of its companion would be 0.74 M☉.[8] The second is PSR J1835−3259B, a millisecond pulsar with a period of 1.83 ms. It is in a nearly circular orbit around a companion with an estimated mass of about 0.2 M☉, probably a white dwarf.[9] This pulsar is probably the source of the gamma radiation from NGC 6652.[10]
Finally, a third candidate was discovered in this cluster based on simultaneous observations from the Chandra X-ray Observatory and the Karl G. Jansky Very Large Array. It was given the name NGC 6652B and is possibly a transitional millisecond pulsar (tMSP), that is, a pulsar that switches between a rotationally powered state and an accretion-powered state.[11] Other hypotheses must also be considered to explain the behavior of NGC 6625B, although less likely than the tMSP. Confirmation that it is indeed a tMSP will come from a direct observation of its state change.[11]
Observations made with the Chandra X-ray Observatory have detected eleven X-ray sources, six of which were already known and five of which are new. Source A is a low-mass X-ray binary (LMXB). Source B suggests the presence of a neutron star in an LMXB system, but with unusual variability.[12] The spectrum of source C suggests it is a cataclysmic variable. The spectrum of source D suggests the presence of a neutron star in an LMXB system, which would make it the third LMXB source of NGC 6652.[12] Finally, sources E and F show spectra located relatively in the hard X-ray region, suggesting the presence of high-energy plasma.[12]
