Transcript Alberto Vecchio, University of Birmingham

What will it mean to be a
gravitational wave
astronomer?
Alberto Vecchio
Imaging the future: Gravitational wave astronomy
Penn State 27th – 30th October, 2004
Outline
• Some general remarks
• Three possible research projects
• Conclusions
Imaging the future: GW astronomy
A Vecchio
Gravitational wave astronomy
• Gravitational waves
provide a new and unique
view of the universe
“orthogonal” to ordinary
astronomy
– Astronomy
– Cosmology
– Fundamental physics
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Gravitational wave astronomy
• Astronomy in a new
frequency band
• Tests of the behaviour of
gravity in the strongly nonlinear relativistic regime
• A new arena for
fundamental physics and
the exploration of
fundamental fields at high
energy and early cosmic
times
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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
Imaging the future: GW astronomy
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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
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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
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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
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Black hole demographics – 2
• 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
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Black hole demographics – 3
• 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
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Black hole demographics – 4
• 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
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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
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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
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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
– …
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Mapping the GW early
universe
• Assume LISA reaches a sensitivity W~ 10-12 in some
portion of the spectrum: opportunity for quantumgravity 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
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Conclusions
• What will it mean to be a gravitational wave
astronomer?
Imaging the future: GW astronomy
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Conclusions
• What will it mean to be a gravitational wave
astronomer?
– As I said, I don’t really know.
– However…
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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
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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?
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