(ORDO NEWS) — Using the MeerKAT radio telescope, an international team of astronomers studied the globular cluster known as NGC 6440.
As a result, two new millisecond pulsars were discovered in this cluster, which received the designations NGC 6440G and NGC 6440H. The discovery was described in an article published April 1 on the arXiv preprint server.
Pulsars are highly magnetized, spinning neutron stars that emit a beam of electromagnetic radiation. They are usually detected as short bursts of radio emission, but some of them are also observed with optical, X-ray and gamma-ray telescopes.
The fastest rotating pulsars, with a rotation period of less than 30 milliseconds, are known as millisecond pulsars (MSPs). The researchers suggest that they are formed in binary systems, when the initially more massive component turns into a neutron star, which then spins up due to the accretion of matter from the secondary star.
The class of extreme binary pulsars with half-corrupted companion stars is called “spider pulsars”. These objects are also classified as “black widows” if the companion has an extremely low mass (less than 0.1 solar mass), and are called “red spins” if the secondary star is heavier.
Now, a team of astronomers led by Laila Vlishauer from the University of Manchester, UK, are reporting the discovery of two new MSPs, namely NGC 6440G and NGC 6440H.
These two pulsars were discovered in NGC 6440, a massive and dense globular cluster (GC) located about 27,000 light-years away in the constellation Sagittarius. The discovery was the result of 33 observations using the L-band (856-1712 MHz) receivers of the MeerKAT telescope (with a center frequency of 1284 MHz).
According to the article, NGC 6440G (also known as PSR J1748-2021G) is an isolated MSP with a rotation period of about 5.22 milliseconds. The dispersion of the pulsar is about 219.6 pc/cm3.
NGC 6440H (or PSR J1748-2021H) is a binary MSP with a rotation period of 2.85 milliseconds. The pulsar has a very low-mass companion (with a minimum mass of about 0.006 solar masses) orbiting it every 0.36 days, indicating its “black widow”. The dispersion of this MSP was estimated at 222.6 pc/cm3.
The discovery by the Wleschauer team expands the list of known pulsars in NGC 6440 to eight (four isolated and four binary pulsars). The researchers noted that NGC 6440H has the lightest mass of any known pulsar in globular clusters.
“Companion NGC 6440H is also the lightest pulsar companion, with a minimum mass of 0.006 M. These two new additions support the previously observed equal ratio of isolated to binary pulsars in NGC6440 (now 4:4) and contribute to MeerKAT’s discovery of pulsars in the GC,” – concluded the astronomers.
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