Table Of ContentAstrophysics and Space Science Library 457
Luciano Rezzolla
Pierre Pizzochero
David Ian Jones
Nanda Rea
Isaac Vidaña Editors
The Physics and
Astrophysics
of Neutron Stars
The Physics and Astrophysics of Neutron Stars
Astrophysics and Space Science Library
SeriesEditor:
STEVENN.SHORE,DipartimentodiFisica“EnricoFermi”,UniversitàdiPisa,
Pisa,Italy
AdvisoryBoard:
F.BERTOLA,UniversityofPadua,Italy
C.J.CESARSKY,CommissionforAtomicEnergy,Saclay,France
P.EHRENFREUND,LeidenUniversity,TheNetherlands
O.ENGVOLD,UniversityofOslo,Norway
E.P.J.VANDENHEUVEL,UniversityofAmsterdam,TheNetherlands
V.M.KASPI,McGillUniversity,Montreal,Canada
J.M.E.KUIJPERS,UniversityofNijmegen,TheNetherlands
H.VANDERLAAN,UniversityofUtrecht,TheNetherlands
P.G.MURDIN,InstituteofAstronomy,Cambridge,UK
B.V.SOMOV,AstronomicalInstitute,MoscowStateUniversity,Russia
R.A.SUNYAEV,MaxPlanckInstituteforAstrophysics,Garching,Germany
Moreinformationaboutthisseriesathttp://www.springer.com/series/5664
Luciano Rezzolla • Pierre Pizzochero (cid:129)
˜
David Ian Jones (cid:129) Nanda Rea (cid:129) Isaac Vidana
Editors
The Physics
and Astrophysics
of Neutron Stars
123
Editors
LucianoRezzolla PierrePizzochero
Institutfu¨rTheoretischePhysik Universita’degliStudidiMilano
GoetheUniversityFrankfurt DipartimentodiFisica
Frankfurt Milan,Italy
Hessen,Germany
DavidIanJones NandaRea
UniversityofSouthampton InstituteofSpaceSciences(ICE)
MathematicalSciences ConsejoSuperiordeInvestigaciones
Southampton,UnitedKingdom Científicas(CSIC)
Barcelona,Spain
IsaacVidan˜a
IstitutoNazionalediFisicaNucleare
(INFN)
DipartimentodiFisica,Universitàdi
Catania
Catania,Italy
ISSN0067-0057 ISSN2214-7985 (electronic)
AstrophysicsandSpaceScienceLibrary
ISBN978-3-319-97615-0 ISBN978-3-319-97616-7 (eBook)
https://doi.org/10.1007/978-3-319-97616-7
LibraryofCongressControlNumber:2018960864
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Coverillustration: Composite imageoftheCrabnebula withX-raysfromChandra (blue andwhite),
NASA’s Hubble Space Telescope (purple) and NASA’s Spitzer Space Telescope (pink). Also shown
withacartoonisthestructureofthecompactstaratthecenterofthenebulaandshowingthevarious
partsofaneutronstar:thecore,theoutercoreandthecrust.Credit:X-ray:NASA/CXC/SAO;Optical:
NASA/STScI;Infrared:NASA-JPL-Caltech;Cartoon:L.Rezzolla(GU)
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Foreword
Compact stars, such as neutron stars, strange stars, and hybrid stars, are unique
laboratories that allow us to probe the building blocks of matter and their inter-
actions at regimes complementary to terrestrial laboratories. These exceptionally
complex astrophysical sources have already led to breakthrough discoveries in
nuclear and subnuclear physics, QCD, general relativity, and high-energy astro-
physics.Themostrecentlandmarkwas thefirstgravitationalwavedetectionfrom
the merging of two neutron stars on August 17, 2017 (GW170817), 2 years after
the first ever direct detection of gravitational waves, which has closed a chapter
initiatedalmostonecenturyago,withthefirstpaperofAlbertEinsteinongeneral
relativity.With the observationof coalescing neutronstars, the gravitational-wave
detectors LIGO and Virgo have demonstrated their potential to directly probe
the properties of matter at the extreme conditions found in this scenario. Indeed,
constraints have been placed on the tidal effects of the coalescing stars, which in
turn constrain the neutron star radii and the equation of state of matter at twice
the nuclear saturation density. These observations also mark the beginning of the
multi-messenger astronomy era with the simultaneous detection of gravitational
waves, gamma-ray burst, and electromagnetic emission from the same source. In
thecomingyears,thepredictedlargenumberofneweventswillgreatlyimproveour
understandingofneutronstarmergersandofneutronstarinternalstructure.During
2019,theobservatoryNICER(NeutronStarInteriorCompositionExplorer)hosted
bytheInternationalSpaceStation(ISS)willreleaseitsfirstone-yearcampaignof
X-rayobservationsofafewneutronstarsaimingatdeterminingtheradiusofthese
starswithinlessthan10%accuracy.WeshallalsomentiontheGAIAsatellitewhich
ismeasuringthepositionofbillionsofobjectsinouruniversewithanunprecedented
accuracy.Weareconfidentthatthesemeasureswillconsiderablyhelpunderstanding
the multiplefaces ofneutronstarsand will providea better pictureof the neutron
starjigsawpuzzle.
Thenuclearandsubnuclearexperimentalfacilities,suchasFAIRandGANILin
Europe, offer a complementary approach to explore the phase diagram of dense
matter as well as reaction rates and transport properties. They have nurtured
innovativeand fundamentaldiscoveriesthanksto the synthesis ofnew radioactive
v
vi Foreword
elements, on one side, and to the productionof new states of matter in heavy ion
collisions, on the other side. Theoretical approaches in nuclear physics have also
been greatly renewed over the last decade, mainly thanks to the new chiral EFT
methodswhichhaveallowedtoestablishconstraintsonthepropertiesoflow-density
nuclear matter—up to 1−2 times the nuclear saturation density. The description
of the nuclear equation of state at zero and finite temperature,in uniformor non-
uniform matter, as well as reaction rates and transport properties has also made
a big step during the last decade. The more systematic use of nuclear physics
inputsin compactstar modelinghas contributedto reduce the uncertaintiesin the
modelpredictions.The variousconstraintscoming from both nuclear physicsand
astrophysics have been instrumental in improving our understandingof the dense
matterequationofstate.Detailedquestionsrelatedtophasetransitionsandtransport
propertiesarenowemerging,andfutureexperimentsandobservationswillprovide
evenbetterdatatokeepimprovingthemodels.
Theoutstandingvarietyofobservationalpropertiesofcompactstarschallenged
observers and requires quite dedicated instruments. NICER is an example, but
observations in the whole electromagnetic range, from radio to gamma rays, are
crucial to understand the properties of compact stars. Future instruments, e.g.,
FAST,LOFT,ATHENA,andSKA, willprovideanunprecedentedamountofdata
on compact stars. One particular issue that has received significant attention is
the astonishing large magnetic fields exhibited by neutron stars. From both the
microphysicsand the macrophysicssides, the relevance of strong magnetic fields
in different processes has been acknowledged. Understanding their impact, for
instance,incore-collapsesupernovae,thelong-termcoolingofstronglymagnetized
neutron stars, the bursting activity of magnetars, the merger of neutron stars
binaries,andthecrustalcoolingofquiescentlow-massX-raybinaries,amongother
scenarios,hasbeentheobjectofmanytheoreticalstudies,improvingourknowledge
ofthesefascinatingobjects.
The book is meant to address a large spectrum of readers, from first-year
PhD students up to senior researchers, who will find a thorough overview of the
variousfacetsof the physicsand astrophysicsofcompactstars. Theaim is thatof
summarizing the recent progress in the field and the many challenging questions
which still remainto be answered;most importantly,the bookaims at identifying
effective strategies to explore, both theoretically and observationally, the open
problems. To accomplish this goal, each of the 13 chapters of the book written
by internationally renowned experts includes a brief overview of the historical
context, a detailed review of the main theoreticalachievements, experimentaland
observationalresults,andfinallythepresentchallenges,futureprospects,andopen
questions.
The book is organized into three thematic blocks: the first part (Chaps.1–4)
covers the astrophysical context where neutron stars are formed (core-collapse
supernovae),discussestheimpactofstrongmagneticfieldsin neutronstars(mag-
netarsandtransientphenomena),reviewstestsofgravitywithcompactstarsandthe
detectionofgravitationalwaves,andstudiesthecomplexityofbinarysystems.
Foreword vii
The second part (Chaps.5–9) is dedicated to nuclear physics. Several decades
ago, it was suggested that the neutron star equation of state could be directly
determinedfromobservations.Asatransitionfromastrophysicstonuclearphysics,
a review is made of the constraints from electromagnetic observations. Then the
nuclearequationsofstateatbothzeroandfinitetemperaturearepresented,followed
by the connection with low-energy QCD and super-dense matter. Interestingly,
since the nuclear interaction is attractive at long range, a part of the volume of
neutron star core and crust could host superfluid neutrons, or charged particles
in superconducting state. Pairing is believed to be responsible for glitches and
can affect neutron star oscillations. Finally, the microphysics part of the book is
concludedbyaddressingthequestionsrelatedtotransportphenomenaandreaction
ratesinhadronicandquarkmatter.
The last part (Chaps.10–13) is mainly focused on gravitational physics and
kilonovaephenomena;the gravitationalwave emission from mergingneutronstar
binariesaswellasthepost-mergingdynamicsisdiscussed,andtheelectromagnetic
emissionofkilonovaeanditsengine—thenucleosynthesis—isdescribed.Gravita-
tional waves emitted by a single neutron star due to its quadrupolar “mountain”
deformation are also discussed, as these could be the next new signals to look
for in advanced terrestrial interferometers. Finally, this section is concluded with
a presentation of universal relations arising in general relativity—the so-called
I-Love-Q relations—and of alternative theories of gravity and their universal
relations.
Thisbook,theNewCompStarWhiteBook,isthefinaldeliverableoftheMP1304
COST Action, which ran from 2013 to 2017and was the naturalextension of the
ESF-fundedRPN “CompStar”(2008–2013),which coordinatedvariousinitiatives
at the national level such as EMMI in Germany and TeonGrav in Italy (still
continuing),SN2NS continuingas MODE in France,and manymore. After more
than 10 years of continued networking at the highest European level, research on
compact stars is more active than ever before and has reached maturity. The near
future activities are also guaranteed by the new COST Action PHAROS which
will operate until 2021. But NewCompStar did not end in Europe. It was also
connectedtoresearchgroupsinnon-EUcountries,suchasArmenia,Australia,the
Russian Federation, and the USA. Many of the world leading experts in the field
have participatedin our internationalconferencesand schools.NewCompStar has
therefore been an important nexus acting as a global reference for compact star
physics.
At thispoint,the NewCompStarWhite Book providesa timely summaryof the
enormous progress in our field during the last decade. As illustrated through the
chapters of this book, progress has been possible thanks to the multidisciplinary
interaction among astrophysicists, nuclear and particle physicists, and experts in
gravitational physics. NewCompStar was the framework which allowed leading
experts in these fields to work together and jointly address fascinating and chal-
lengingproblems.Thedeepandrichinterconnectivitybetweenareaswas stressed
andexploitedsincethebeginningofourEuropeannetworkingefforts,beingoneof
thekeystonesofourproject.Inadditiontothepureresearchagenda,Compstarand
viii Foreword
NewCompStar also provided a dedicated training program for a new generation
of scientists, which grew with a broader view and better skills than previous
generations. This book also represents a synthesis of the many ideas transmitted
toyoungresearchersduringtheinternationalschools.
To conclude, it is worth stressing again that, although this white book is a
collection of contributionsfrom NewCompStar community members, most of the
discussed results have been obtained by large international, worldwide collabo-
rations trying to understand the physics of compact stars. Given its pedagogical
purposes and the very broad range of topics covered, we have no doubt that this
volume will find its place among the few general books on neutron stars, and
we hope it will further stimulate research on these fascinating celestial objects,
accompanyinganewgenerationofphysicists.
Roma,Italy ValeriaFerrari
Seattle,WA,USA JeromeMargueron
Alicante,Spain JoseA.Pons
June2018
Preface
Astrophysical objects have always inspired in us a deep sense of wonder, awe
andinspiration.Astrophysicalcompactobjects—suchasneutronstars—obviously
belong to this class and are, arguably,among the most exquisite exampleof what
driveshumanfascination.
This sense of fascination has pervaded “NewCompStar”, a network that
between 2013 and 2017 has collected scientists across Europewith very different
backgrounds—astrophysicsandgravitationalandnuclearphysics—inthecommon
quest for a better understanding of neutron stars and of the fundamental physics
behindthem.
Numerousaretheachievementsofthesescientists,whohavemetinanumberof
meetings—smallandlarge—andwhohavecollectivelywrittenhundredsofpapers
over 4 years only. More importantly, a legacy of collaborations, synergies and
friendshipshasbeenpassedoverto“PHAROS”,thenewandimprovedincarnation
ofthisspirit.
As a way to cast on paper a small part of what NewCompStar has ultimately
achieved, we have organised this collection of chapters that aim at providing the
excitingportraitofourpresentunderstandingofneutronstars.
Theauthorsofthesechaptershavebeenchosenfortheirextraordinaryexpertise
and to reflect NewCompStar’s natural geographic and gender balance. More
importantly, these authors are not only very active in their corresponding fields,
buttheywillprobablyshapetheminapermanentmanner.
Wetrustthatthisbookwillbeusefulbothasareferenceforresearchersworking
in the field and as a first introduction to the subject for the generation of young
scientistswillingtojointheexcitingadventureofunderstandingcompactstars.
Frankfurt,Germany LucianoRezzolla
Milan,Italy PierrePizzochero
Southampton,UK DavidIanJones
Barcelona,Spain NandaRea
Catania,Italy IsaacVidaña
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