* Astronomy

Blobrana · L

RE: Terzan 5

Blobrana · L

Cosmic "Dig" Reveals Vestiges of the Milky Way's Building Blocks
Peering through the thick dust clouds of our galaxy's "bulge" (the myriads of stars surrounding its centre), and revealing an amazing amount of detail, a team of astronomers has unveiled an unusual mix of stars in the stellar grouping known as Terzan 5. Never observed anywhere in the bulge before, this peculiar "****tail" of stars suggests that Terzan 5 is in fact one of the bulge's primordial building blocks, most likely the relic of a proto-galaxy that merged with the Milky Way during its very early days.

"The history of the Milky Way is encoded in its oldest fragments, globular clusters and other systems of stars that have witnessed the entire evolution of our galaxy. Our study opens a new window on yet another piece of our galactic past" - Francesco Ferraro from the University of Bologna, lead author of a paper appearing in this week's issue of the journal Nature.

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Blobrana · L

Title: Eight New Millisecond Pulsars in NGC 6440 and NGC 6441
Authors: Paulo C. C. Freire, Scott M. Ransom, Steve Begin, Ingrid H. Stairs, Jason W. T. Hessels, Lucille H. Frey, Fernando Camilo

Motivated by the recent discovery of 30 new millisecond pulsars in Terzan 5, made using the Green Bank Telescope's S-band receiver and the Pulsar Spigot spectrometer, we have set out to use the same observing system in a systematic search for pulsars in other globular clusters. Here we report on the discovery of five new pulsars in NGC 6440 and three in NGC 6441; each cluster previously had one known pulsar. Using the most recent distance estimates to these clusters, we conclude that there are as many potentially observable pulsars in NGC 6440 and NGC 6441 as in Terzan 5. We present timing solutions for all of the pulsars in these globular clusters. Four of the new discoveries are in binary systems; one of them, PSR J1748-2021B (NGC 6440B), has a wide (P_b = 20.5 d) and eccentric (e = 0.57) orbit. This allowed a measurement of its rate of advance of periastron: 0.00391(18) degrees per year. If due to the effects of general relativity, the total mass of this binary system is 2.92 ± 0.20 solar masses (1 sigma), implying a median pulsar mass of 2.74 ± 0.21 solar masses. There is a 1 % probability that the inclination is low enough that pulsar mass is below 2 solar masses, and 0.10 % probability that it is between 1.20 and 1.44 solar masses. If confirmed, this anomalously large mass would strongly constrain the equation of state for dense matter. The other highly eccentric binary, PSR J1750-37A, has e = 0.71, and periastron advance of 0.0055(3) degrees per year, implying a total system mass of 1.97 ±0.15 solar masses and, along with the mass function, maximum and median pulsar masses of 1.65 and 1.26 solar masses respectively.

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