what will it mean to be a gravitational wave astronomer?

What will it mean to be a gravitational wave

astronomer?

Alberto Vecchio

Imaging the future: Gravitational wave astronomyPenn State 27th – 30th October, 2004

Outline

• Some general remarks• Three possible research projects• Conclusions

Imaging the future: GW astronomy A Vecchio

• Gravitational waves provide a new and unique view of the universe “orthogonal” to ordinary astronomy– Astronomy– Cosmology– Fundamental physics


Gravitational wave astronomy

• Astronomy in a new frequency band

• Tests of the behaviour of gravity in the strongly non-linear relativistic regime

• A new arena for fundamental physics and the exploration of fundamental fields at high energy and early cosmic times

Gravitational wave astronomy


Are GW astronomers “special”?

• Is there a fundamental difference between a GW astronomer and a radio/x-ray/optical/… astronomer?– No: then we should simple learn from what astronomers have done

in the past and act consequently– Yes: then may be our approach ought to be different from

“traditional astronomy”

• We have had a long time to prepare gravitational wave astronomy; this is surely not the case for the other frequency bands– Is it necessary good?– Is there the danger that “the unexpected” does not have a place in

our plan, so that we won’t be ready for it?

• We want to do all in one go: all-sky, all-frequency, all-sources surveys of the GW sky


Three possible research projects for a (GW)

astronomer

• Black hole demographics and channels of black hole formation

• EM radiation in GW bursts• Mapping the early universe


Instruments

• Several ground-based interferometers • (>) 3 in US• 2 in Europe• 1 in Japan• And possibly one in China and one in Australia

• A few very-high frequency resonant detectors• 2 in Europe• 1 in Brazil

• LISA• The band 0.1 mHz – 10 kHz is essentially completely

covered, although between a 0.1 Hz and a few Hz not in an optimal way


Black hole demographics – 1

• Study of the BH formation history and channels (let’s concentrate on the range 100 – 10,000 Msun).The goal:– dN/dMdz– Link between BHs and their environment

• Start from catalogue of detected sources covering ~ 10 yr, say 100 to 1000 sources– Late stage of coalescence detected with HF interferometers– Some low redshift IMBH+BH/NS detected with LISA (and

possibly by both LISA and HF)– High redshift IMBH binaries detected by LISA– MBH+IMBH (EMRI) detected by LISA



• Need most accurate determination of the source parameters: download the original time series around the events and re-do the analysis:– Use most accurate waveforms produced by GR community

– Use some fancy algorithm to do a multi-detector multi-parameter fit and generate the best estimate of the source parameters

– Of course this is likely to be computationally intensive and I’ll run everything on the grid

• At the end of this stage one can produce dN/dMdz and study some simple properties, such as correlations between e.g. M and spin

• This will also produce an update version of the catalogue



• I have the BH formation history (in the relevant mass range), now I need to find models that explain it

• I need to know where (i.e. environment) BH are:– Galaxy

– Field

– Globular cluster

– …

• I need to go on the archives of the major relevant surveys in a number of observational bands and check what’s in the GW error box

• If there are sure detections of other interesting objects (such as isolated BHs) I should probably include them as well



• Now I need to do some modelling, such as:– Initial mass function and stellar evolution– Dynamics of dense star clusters– Dynamics of galaxy cores with different density profiles– N-body simulation of galaxy mergers + gas to study star formation

rate– Evolution of structures in the high z universe (hierarchical clustering

for different models) – I need model for dark matter, black hole seeds and distribution, …

– …

• Only at the end of this I will be able to argue that we have physical models to explain different paths of BH formation

• Or we just can’t explain the observations which will require some serious work on the modelling side


EM/GW – 1

• The goal is to establish whether during violent GW bursts there is a “channel” though which part of the available energy can be converted into and radiated as EM waves: – During a supernova explosion there is all sorts of radiation (including

neutrinos)– What about NS-NS binaries? Are they the progenitors of (some class

of) gamma ray bursts? – And black hole binaries?

• “In vacuum”• With accretion disks

• This is a:– GW all sky on-line survey– Where I need to provide in real time pointing information (that could

even be early warning) for coordinated follow up observations with other telescopes


EM/GW – 2

• The GW survey requires:– Robust and reliable 24x7 on-line network analysis– Method and infrastructure for

• Accessing the data simultaneously• Processing the data• Broadcasting the results to other observatories (including other

GW instruments)

– Coordinated scheduling for data taking (a minimum number of detectors need always to be on-line)

• There is little to do with LISA• But for ground-based experiments this is necessary

• Agreements at project level: some telescope time needs to be dedicated to this effort


EM/GW – 3

• Whether or not GW-EM associations are found, the results of this survey require a “global” interpretation– Model fitting of observations in different frequency bands will

likely be carried out first, and will lead to “consistency checks”

– But then one model is required to explain consistently all the observations of the same source in the different frequency bands

• This requires a non negligible effort by the theoretical community– GR– Magneto-hydrodynamics– …


Mapping the GW early universe

• Assume LISA reaches a sensitivity ~ 10-12 in some portion of the spectrum: opportunity for quantum-gravity phenomenology– WMAP-like analysis– But to test radically new ideas and theories

• We need: – Sophisticated data analysis techniques (Markov Chain

Monte Carlo + large simulations) – we can gain a lot from CMB experience

– Models for GW signals (from “incomplete” theories)– Modelling and “subtraction” of foregrounds and individual

sources


Conclusions

• What will it mean to be a gravitational wave astronomer?


Conclusions

• What will it mean to be a gravitational wave astronomer?– As I said, I don’t really know.– However…


Conclusions (cont’)

• Gravitational wave astronomers can not work in “isolation”: they will provide data to, and closely collaborate with a number of communities:– Astronomers – from stars to super-clusters– Cosmologists– Relativists– Nuclear and particle physicists– Theoretical physicists

• It takes time to learn how to work together• The modus operandi of those communities is very

different


Conclusions (cont’)

• We need to pay attention to technical issues that could prove to be the actual major roadblocks:– Data formats, conversions, access– Software and computational resources

• Hopefully, presently ongoing efforts in our and other fields will make our life easier:– Grid computing– Virtual Observatory

• “Bidding for telescope time”: does it have any role in the life of a GW astronomer?


what will it mean to be a gravitational wave astronomer?

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