Dany Page

RESEARCH INTERESTS


My work is mostly focused on the theoretical study of neutron stars. I started from deep inside and am now digging up my way to the surface. Hopefully some day in a not to remote future I will be studying neutron star magnetosphere.

I can divide my interests in several areas:

Thermal Evolution of Isolated Neutron Stars

My first steps in the field were in the study of neutron stars with a kaon condensate, for my Ph.D. dissertation in the Nuclear Theory Group of the Physics Department at Stony Brook. I had somewhat originally started my Ph.D. on Superstring at the ITP but couldn't accept to spend the rest of my life in this hole (= superstrings, not the ITP which is a great place) and finally decided to switch to astrophysics after the supernova SN 1987A. Kaon condensation had been proposed recently and the people in the Nuclear Theory Group were (and are still) very excited about it: SN 1987A opened the possibility to see a kaon condensate developing there. So, with K. Kubodera, P. Pizzochero and G. E. Brown, we calculated the neutrino emissivity of a kaon condensate [2] showing that it indeed would lead to rapid cooling of the neutron star but we also argued that, unfortunately, it will take several decade till the fast cooling of the core shows up at the surface: no hope to see the effect of the kaon condensate in the near future ! The next obvious step was to study in detail the cooling of a neutron star with a kaon condensate: the results demonstrated that the cooling is fast and takes a few decades to show at the surface [3]. That was it: I was launched into neutron star cooling for the good and the bad of it.

As a posdoc in the Columbia University Astronomy Department I went on studying the cooling of neutron stars in their various flavors. A bitter one is the strange star which is a "neuton star" without neutrons: made entirely of quark matter except, possibly, for a thin outer layer of normal matter. These strange stars also cool very fast, like neutron stars with a kaon condensate, but the fast cooling of the core affects the surface much sooner than in the case of a neutron star: a few years instead of a few decades because its crust is very thin [a]. Detection of thermal emission from the neutron that has been formed by SN 1987A may, or may not, give us a definite evidence for the existence of strange stars (but there may be no neutron star left there, i.e., it may have collapsed into a black hole).
In 1991 I heard from M. Prakash the big new that `One can fool all the people all the time': the most efficient neutrino emission process possible in neutron stars, the direct Urca Process, which was considered to be forbidden by momentum non-conservation, can occur in many cases. This is the most obvious process but because it had been stated in the early 60's that it is forbidden nobody had checked this again for 25 years (except Boguta but apparently nobody cared about his paper). The occurrence of the direct Urca process has a dramatic effect on the cooling [4] and I also took advantage of this opportunity to emphasize the importance of nucleon pairing which reduces strongly the neutrino emission (something that I had shown in my Ph.d. dissertation but people didn't notice it because kaons looked too `exotic').
After Halpern & Holt demonstrated the Geminga is a neutron star, I applied my cooling models to this new one ([b] & [5]) showing that extensive pairing in its core is necessary to obtain temperatures in agreement with the observed one. That was the best, maybe even the only, evidence for the presence of extensive pairing in the core of neutron star.

As things are, it turns out that this `evidence' for baryon pairing is now gone: I had ingeniously assumed (as everybody else) that the surface, and the envelope, of a neutron star is made of iron. This is fine for a textbook neutron star, but real ones may be dirtier. The late post-supernova accretion may deposit light elements at the surface and this strongly affects the transport of heat, i.e., it change dramatically the relationship between the interior temperature and the surface temperature, as shown recently by Potekhin Chabrier and Yakovlev. When applying this to the cooling it turns out that you can `explain everything' without requiring pairing [13]. So, neutron star cooling is presently (early 1997) in a state of total confusion [A].

Thermal Evolution of Neutron Stars in Binary Systems

Neutron Star Envelope and Surface: Thermal Emission Properties

Neutron Star Magnetic Field Evolution


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Dany P. Page (page@astro.unam.mx)
(Created: 3-VI-1994. Last modified: 10-VIII-2021)