Editing Millisecond pulsar (section)

==Origins==
Millisecond pulsars are thought to be related to [[low-mass X-ray binary]] systems. It is thought that the X-rays in these systems are emitted by the [[accretion disk]] of a [[neutron star]] produced by the outer layers of a companion star that has overflowed its [[Roche lobe]]. The transfer of [[angular momentum]] from this accretion event can increase the rotation rate of the pulsar to hundreds of times per second, as is observed in millisecond pulsars.

There has been recent evidence that the standard evolutionary model fails to explain the evolution of all millisecond pulsars, especially young millisecond pulsars with relatively high magnetic fields, e.g. [[PSR B1937+21]]. [[Bülent Kiziltan]] and [[S. E. Thorsett]] ([[University of California, Santa Cruz|UCSC]]) showed that different millisecond pulsars must form by at least two distinct processes.<ref>{{cite journal |last1=Kızıltan |first1=Bülent |title=Constraints on Pulsar Evolution: The Joint Period-Spin-down Distribution of Millisecond Pulsars |year=2009 |last2=Thorsett |first2=S. E. |periodical=[[The Astrophysical Journal Letters]] |volume=693 |issue=2 |pages=L109–L112 |doi=10.1088/0004-637X/693/2/L109 |bibcode = 2009ApJ...693L.109K |arxiv = 0902.0604 |s2cid=2156395 }}</ref> But the nature of the other process remains a mystery.<ref>{{Cite news |last=Naeye |first=Robert |year=2009 |title=Surprising Trove of Gamma-Ray Pulsars |periodical=[[Sky & Telescope]] |url=http://www.skyandtelescope.com/astronomy-news/surprising-trove-of-gamma-ray-pulsars }}</ref>

Many millisecond pulsars are found in [[globular cluster]]s. This is consistent with the spin-up hypothesis of their formation, as the extremely high stellar density of these clusters implies a much higher likelihood of a pulsar having (or capturing) a giant companion star.  Currently there are approximately 130 millisecond pulsars known in globular clusters.<ref>{{cite web
  | last = Freire
  | first = Paulo
  | title = Pulsars in globular clusters
  | publisher = [[Arecibo Observatory]]
  | url = http://www2.naic.edu/~pfreire/GCpsr.html
  | access-date =2007-01-18 }}</ref> The globular cluster [[Terzan 5]] contains 37 of these, followed by [[47 Tucanae]] with 22 and [[Messier 28|M28]] and [[Messier 15|M15]] with 8 pulsars each.