_s_Io ______NEWSAND VIEWS------N_A_T_u_R_E_v_o_L._3_37_9_F_E_B_Ru_A_R_Y_.:_I9.::..:...89

Pulsar astronomy explosion would be similar to those involved in the formation of the cele­ brated Hulse-Taylor system containing Spin-up more apparent than real the binary pulsar PSR1913+ 16 and another neutron star'. In this case, the Andrew Lyne binary system survived the supernova explosion in which the first neutron star GLOBU LAR clusters of stars have recently 5 x w-s m s-' is, on the other hand, rather was formed . The companion subsequently been found to be a rich source of milli­ large for either of these explanations; the evolved, and overflowed its Roche lobe 3 second pulsars'- • In a search for such pulsar needs to be improbably close to its (beyond which its gravity fails to hold back objects, Wolszczan et at. , who report on nearest neighbour or the core must be material) , so spinning up the neutron star, page 531 of this issue\ have discovered a substantially more massive than we believe. before it underwent a supernova explo­ pulsar, PSR2127+11 , near the centre of Precise timing measurements over the sion itself. In the case ofPSR1913+ 16, the the globular cluster M15 , one of the most next few years and the determination of binary system was not quite disrupted and dense clusters in the northern skies. What the second period derivative could allow the old pulsar with a period of 59 ms was makes this pulsar interesting is that, not the distinction to be made between these left in a very eccentric orbit around the only does it have a relatively long spin two rather uncomfortable possibilities. new neutron star formed by the exploded period, but it is solitary and, unlike any Although not a millisecond pulsar, companion. other known radio pulsar, its rotation rate PSR2127+11, with a period of 110 ms, is The solitary pulsar PSR2127 + 11 could seems to be increasing. The authors spinning rapidly compared with normal have been formed in circumstances only conjecture that this apparent spin-up may old pulsars. Together with the seemingly slightly different: the second supernova be an illusion due to the acceleration small value of intrinsic spin down rate, this could have disrupted the binary system towards us of the object in the gravita­ suggests that the pulsar is an old one which and, provided it was not ejected from the tional field of the collapsed core of the was rejuvenated somewhat by accretion in cluster, PSR2127+11 would have been cluster. There seem to be two mysteries a binary system. This leaves the question left in its intermediate-period spin state. If which need to be explained: why is the as to what has happened to the donor this was the case, it must have happened a acceleration so large and why is the pulsar companion star. Wolszczan et at.' suggest long time ago when the cluster was young solitary? two possible explanations. First, the com­ and there were still young, massive stars Globular clusters are gravitationally panion star has been ablated by radiation which could suffer supernova collapse. D bound swarms of 10'-10' old stars found in from the pulsar, a mechanism proposed' I. Lyne, A.G. et a/. Nature 328,399-401 (1987). our Galaxy. The central stellar density is to explain the recently discovered eclips­ 2. Lync , A .G., Biggs , J.D .. Brinklow. A .. Ashworth. M. & often as high as 104-10' stars per cubic ing binary pulsar PSR1957+20. However, McKenn a, J. Nature 332, 45-47 ( 1988). 3 3. Ables. J .G. et a/. lA U Circ. No.4602 (1988). parsec compared with less than 1 pc- in they argue that it is unlikely that this 4. Wolszczan, A. eta/. Nature337, 531-533 (1989) . the solar neighbourhood. This relatively pulsar was ever spinning rapidly enough to 5. Van de n Heuvel, E.P.J. in The Origin and Evolution of Newton IAU Symposium No.l25 (eds Helford. D.J. & large density probably causes many stellar have the required energy output to Huang . J .H.)393-406 (Reidel , Dordrecht , 1987). interactions, resulting in a high incidence achieve this. Second, perhaps the binary 6. Fruchter, A .S. . Stinebring, D .R. & T ay lor, J.H . Nature of low-mass X-ray binary systems in which system was disrupted by an encounter 333, 237- 239 (1988). 7. Rappaport , S .. Putney. A. & Verbunt . F. Astrophys. J. we see compact objects, probably neutron with a third star'. (submitted). stars, being spun up by accretion of There is a third possibility that should 8. Hulse , R.A . & Taylor, J .H . Astrophys. J. 195, L5 t (1 975). material from less evolved companions. be considered: the disruption ofthe binary Andrew Lyne is at the Universily of Manchester We detect many of these systems by the system by the supernova explosion of the Nuffield Radio Aslronomy Laboralories, copious X-rays emitted by the hot accret­ companion. The circumstances of the Jodrell Bank, Macclesfield SKI I 9DL, UK. ing gas. This is the process by which it is believed old long-period radio pulsars are Photosynthesis given the rapid rotation rates which we subsequently see in millisecond pulsars after the accretion has ceased (see ref. 5). Giant revelations to come Hence the success of the searches for such pulsars in globular clusters carried out Bob Ford recently. The new pulsar has a period P of 110 ms CoNsiDER a huge, membrane-located As a source for their reaction centre, so that it is not a true millisecond pulsar protein complex that is so complex that Witt et al. use one of the most thermo­ and the absence of varying Doppler about a quarter of its mass consists of philic photosynthetic organisms known , effects indicates that it is not in a short­ tightly bound pigment molecules. Imagine the vivid blue cyanobacterium Synecho­ period binary system. But although all this protein assembly also contains an coccus, found in a Japanese hot spring at other known pulsars spin down as they intricate electron pathway which, using temperatures of around 70 oc. The reac­ lose rotational kinetic energy through light energy, produces stable reduced tion centre crystallizes as a trimeric com­ their radiation, PSR2127 + 11 is observed components at redox potentials around plex which has a total relative molecular to be spinning up slightly. This cannot be minus 500 mY. This is no fictitious giant, mass of about 800 ,000. Each of the three due to any accretion process as it has no but one of the two light-energy-utilizing reaction centres contains about 60 chloro­ companion and so it sc;:ems probable that systems of plant photosynthesis, the photo­ phyll a and 10 carotenoid molecules, giv­ the observed spin-up (P= -2 x to- " s s-') system I reaction centre. Ingrid Witt and ing the crystals an intense green colour. is only apparent. It is likely to be the result her collaborators have now succeeded' in The overall form of the cyanobacterial of the acceleration of the pulsar towards showing that crystals of this reaction centre complex is known from electron micro­ the Earth in a gravitational field, either can diffract X-rays to 4 A. Moreover, the scopy (see figure) . Witt et at. present a that of its nearest neighbour or that of the hexagonal crystals are relatively stable in model for the organization of the com­ collapsed core of the cluster: the ch ain of the X-ray beam, which will reduce the plexes within the crystals in which the regular pulses from the object becomes problems for data collection. It seems repeating unit of dimensions 285 x 285 x increasingly compressed from our point of likely that the atomic structure of this big 167 A is composed of two pairs of trimeric view. The implied acceleration of about but beautiful protein will soon be obtained. complexes.