LIGHT AND GRAVITY: Using multi-messenger astronomy to see the Cosmos

Transcription

1 LIGHT AND GRAVITY: Using multi-messenger astronomy to see the Cosmos Shane L. Larson Department of Physics Utah State University Gravity Seminar UW Milwaukee 11 May

2 Storyline The state of the field (LISA, NGO & US Study) Traditional multi-messenger astronomy Ultra-compact binaries The population of multi-messenger compact binaries (w/ Tyson Littenberg) 2

3 LISA, NASA & Europe For the last ~15-20 years, LISA has been a joint NASA/ESA endeavour Total cost estimates vary: ~$2.2 billion Current budget climates caused NASA & ESA to dissolve the partnership Europe completed a go-it-alone study for a descoped mission: NGO/eLISA L1 downselect: JUICE (Jupiter Icy Moons Explorer). GW Mission compete in the L2 downselect, middle of next decade NASA instigated a similar go-it-alone study, soliciting ideas for missions in 3 price buckets: $1B+, $600M-$1B, and less than $600M 3

4 NASA Physics of the Cosmos Studies X-Ray and Gravitational Wave studies Mission concepts solicited; Community Science Teams formed Two day workshops to select three missions for further study and uniform costing by TeamX at JPL Gravitational Wave Proposals 21 Total proposals Science Team completed an alpha analysis of science performance What sources can be seen? How many sources can be seen? TeamX study underway on 3 GW missions; report due in June 4

5 GW Science & the Future Europe is shooting for the next decade Outcome of NASA study is not known Prospects for future renewed collaboration seem likely, but are also unknown We will probably not fly before the next decade (post JWST) Post decadal survey PhysPAG Conference on the Future of GW in Space August, Washington DC 5

6 GW Science & the Future 6

7 Gravity as an Astronomical Tool LIGO: In upgrade, online in ~2-3 years Next Decade: spaceborne detectors Within the decade, ground-based detectors (LIGO/VIRGO) will be making regular detections of gravitational waves Space-based detectors will fly in the next decade, but possibly at lower performance than we have planned for the last decade How do you maximize the science returns from both? 7

8 Science Questions Right now the community is focused on making detections. Right now the community is focused on measuring parameters. After the first detection, these questions will not be the focus! What is the equation of state of a neutron star? Does the area theorem hold in the merger of black holes? What is the shape of the Hubble flow? What is the nature of accretion disks in compact white dwarf binaries? 8

9 Multi-messenger astronomy Using multiple independent sensing strategies to observe a source Best when the two sensor streams complement each other Multiwavelength astronomy has long been the traditional multimessenger technique M31 ANDROMEDA GALAXY 9

10 Multi-messenger astronomy Other strategies exist, using multiple spectra light + particles SOLAR NEUTRINOS Highest energy cosmic rays have been traced back to active galactic nuclei There were 24 detected neutrinos from SN 1987a, which resulted in ~800 papers (~33/ neutrino). Gravitational wave advantages: AGN Unimpeded by matter (no extinction) Independent distance measure Generated by bulk matter motion, not individual atoms SN 1987A 10

11 AM CVn Binaries White dwarf primary Secondary is a low mass helium star, expanded to fill its Roche lobe Gas flows through the inner Lagrange point, and accretes onto the white dwarf Light curve varies through a flashlight mechanism at the accretion impact point 11

12 Gravitational Wave Sources The ultra-compact binaries are guaranteed sources for any low-frequency observatory. There are so many, their signals will be confused 12

13 Signals About 30% of the light in the system is from the bright spot, and manifests itself at the peaks in the light curve BRIGHT SPOT IMPACT The light curve peaks when the bright spot from the accretion disk impact sweeps across the observer s view The gravitational wave signal peaks when the binary axis is perpendicular or parallel to the line of sight AM CVN 13

14 Accretion Disks Measure the phase offset between the peaks of the GW and the light curve Use the phase offset as a propagation text (bound mass of the graviton LARSON & HISCOCK 2000; CUTLER, HISCOCK & LARSON 2003) α The phase offset is a measure of the accretion disk radius! ADDISON, BREIVIK, JOHNSON & LARSON 2012 Requires simultaneous observations 14

15 Parameters Dual observations can help with parameter estimation. The color is the posterior distribution for the gravitational wave amplitude, used to constrain mass of the binary. The dashed lines show example priors from EM observations constrain the acceptable amplitudes 15

16 How many can we see? LITTENBERG & LARSON 2012 Some subset will be visible to both electromagnetic and gravitational wave telescopes For a LISA style instrument, WD+WD binaries are visible throughout the entire galaxy For EM telescopes, WD+WD binaries are visible to a distance limited by several factors (aperture, WD brightness, extinction in the galaxy) Use population synthesis to model the ultra-compact binary population in the galaxy 16

17 30S EXPOSURE 90S EXPOSURE Electromagnetic Sources Use the magnitude distribution of known white dwarfs (McCook-Sion Catalogue) Use distances from our synthesized galaxy, together with a dust model for extinction (Dehnen & Binney) EM detectability is a function of aperture and integration time CDK20 ~1 MILLION X FAINTER THAN NAKED EYE 17

18 Dual Population The dual detectable population is similar to the verification binaries Known binaries (~40) in advance of any flight (AM CVn) At even conservative limiting magnitudes there will be a large population of dual detectable binaries Full Catalogue L = 2 Gm L = 1 Gm ecliptic latitude ecliptic longitude 18

19 Last Thoughts Detections are coming soon! How do we maximize science returns? Gravitational waves are a completely separate spectrum for observations, with its own distinct advantages that complement traditional methods I am optimistic about the future of low-frequency GW observatories How can we not look for them? Especially after first detections from LIGO/pulsars! Limit your angst because you talk about/work on/mentioned LISA! 19