High time resolution astrophysics

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High time resolution astrophysics

• J. Cortina, Thursday meeting, March 2008

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• Cuando contemplo el cielo?
• de innumerables luces adornado.
• Quien mira el gran concierto?
• de aquestos resplandores eternales,?
• su movimiento cierto?
• sus pasos desiguales?
• y en proporción concorde tan iguales
• --Fray Luis de León

When I behold upon the sky Decorated with
innumerable lights. Whoever watches this grand
concert Of eternal splendor, Its certain
pace, Its unequal steps Still so equal in its
harmonic proportions --Fray Luis de León
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The inmutable sky

• Eternal, long-lived, ever-lasting.
• The sky has always been a reference for mankind.
  Weve used for sailing, for harvesting
• Aristotle and the Catholic Church were
  essentially right to a first order
  approximation, the sky doesnt change.
• Supernovae, comets, etc are weirdos. Bright stars
  are there season after season for thousands of
  years, the phases of the moon repeat every month,
  the sun doesnt stop shining.

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The inmutable OPTICAL sky

• Our natural detectors (the human eyes) are tuned
  to the wrong frequency. The optical sky is
  definitely boring.

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The X-ray sky

• X-rays are absorbed in the atmosphere so we had
  to wait for satellites to see the X-ray sky.
• In fact the first detectors were mounted on
  balloons and rockets, and took data for only
  hours or days.
• What they first detected was hard to believe.

First X-ray detector White Sands Missile Range
in New Mexico with a V-2 rocket in 1949.
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The X-ray sky

• To start with, nobody expected to see anything in
  the sky in X-rays. Stars are black-body emitters
  and one can easily predict the flux at X-rays 0.
• Then the X-ray celestial sources came and go!
• They are so-called transient.

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The X-ray sky
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Similar in ?-rays or radio

• Apparently the sky is only inmutable in optical
  or near-optical frequencies.
• Well, its only natural, right? the evolution
  has equipped us with eyes which work on a stable
  and reliable source of light.
• The Sun is always there (at day) and optical
  photons can traverse the atmosphere.
• It would be stupid to evolve X-ray eyes.

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THE MUTABLE SKY
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NEOs

• Near-Earth Objects.
• The atmospheric, geological, and biological
  effects of cosmic impact have become apparent
  only since the early 1980s, when the likely cause
  of the Cretaceous-Tertiary extinction was first
  linked to the impact of a 10-km asteroid.
• NASA has supported a groundbased program to
  identify the NEOs larger than 1 km in diameter.
  This task is about 50 percent complete, with
  estimates for the date of completion ranging from
  2010 to 2020 and beyond.

Asteroid Mathilde 59 by 47 km (image by NEAR
spacecraft)
Asteroid 2004 FH Missed us by 43 000 km
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NEOs

• The high-altitude explosion of an 80-m-diameter
  body above Tunguska, Siberia, in 1908 flattened
  trees over a broad area. A differently aimed
  impact of this scale could flatten a modern city
• Bodies larger than about 300 m in size cause
  ground-level explosions in the gigaton range.
  Such impacts would devastate whole countries.
• There is about a 1 percent chance that a gt300 m
  impact will occur in the next century. A higher
  chance for gt80 m impacts.
• These bodies are too faint to have been detected
  by the current surveys, and almost all remain
  undetected.

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Extrasolar planets

• We look for extrasolar planets using 9 different
  techniques. Popular ones are
• ?Astrometry If the star has a planet, then the
  gravitational influence of the planet will cause
  the star itself to move in a tiny orbit about
  their common center of mass.
• ?Radial velocity or Doppler method Variations in
  the speed with which the star moves towards or
  away from Earth can be deduced from Doppler
  effect. This has been by far the most productive
  technique used.
• ?Transit method If a planet transits in front of
  its parent star's disk, then the observed
  brightness of the star drops by a small amount.
  The amount by which the star dims depends on its
  size and on the size of the planet.
• ?Gravitational microlensing Microlensing occurs
  when the gravitational field of a star acts like
  a lens, magnifying the light of a distant
  background star. Possible planets orbiting the
  foreground star can cause detectable anomalies in
  the lensing event light curve.

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Extrasolar planets ?-lensing

• In 1991 Mao and Paczynski (Princeton) first
  proposed using gravitational microlensing to look
  for exoplanets.
• In 2002 when astronomers from Warsaw and
  Paczynski (project OGLE, 1.3m telescope in Las
  Campanas) developed a workable technique.
• Since then, 8 (?) confirmed extrasolar planets
  have been detected using microlensing.
• Only method capable of detecting planets of
  Earth-like mass around ordinary stars.
• Problem microlensing events happen only once!

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Extrasolar planets transits

• So far 11 cases of planetary transits were
  discovered ?rst photometrically and con?rmed
  spectroscopically later.
• Most of them were detected with 10 cm (!)
  telescopes TrES-1 (Alonso et al. 2004), XO-lb
  (McCullough et al. 2006), TrES-2 (ODonovan et
  al. 2006), HAT-P-1b (Bakos et al. 2006), WASP-1b
  and WASP-2b (Collier et al. 2006).

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Extrasolar planets transits

• COROT First space mission targetted at planetary
  transits.
• 27 cm diameter telescope.
• Launched December 2006, reported first light
  January 2007.
• Detected its first extrasolar planet,
  COROT-Exo-1b, May 2007.
• Sensitivity allows to detect Earth-like planets.

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Extrasolar planetsDysonian SETI

• See my last Thursday meeting.
• Astrophys. J. 627 (2005) 534 look for structure
  in planetary transit lightcurves.
• Proposed Kepler mission expects to survey 105
  stars and detect hundreds of planets through
  transits. Sensitive to non-spherical object
  shapes.

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Gamma Ray Bursts

• The Vela satellites (May 1969 - June 1979) were a
  series of satellites launched by the US Air Force
  to monitor compliance with the Nuclear Test Ban
  Treaty.
• These satellites were sensitive to ?-radiation,
  since a nuclear blast in the Earth's atmosphere
  would produce a large amount of ?-rays.
• Surprisingly enough, they detected lots of ?-ray
  explosions! By 1979, they had detected 70.
• But they could triangulate their position and it
  was way out of our solar system Gamma Ray
  Bursts.

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Serendipity

• "It was once when I read a silly fairy tale,
  called The Three Princes of Serendip as their
  highnesses travelled, they were always making
  discoveries, by accidents and sagacity, of things
  which they were not in quest of for instance,
  one of them discovered that a mule blind of the
  right eye had travelled the same road lately,
  because the grass was eaten only on the left
  side. -Horace Walpole on 28 January 1754

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Serendipity

• The greatest act of serendipity in Human History
  took place in Spain 500 years ago when a stubborn
  Italian came with the idea of traveling West to
  make it to the Far East.

• First he was confronted with a Committee of
  Experts in the University of Salamanca.

• Quite rightfully, the experts argued that the
  Earth was round and its perimeter was about 40000
  km, so it was suicidal to sail through 20000 km
  of empty ocean.

• Columbus ignored the Committee of Experts and
  went directly to the Funding Agency a.k.a. as
  Queen of Castile.

• The Queen, out of political arguments, funded his
  project.

• Columbus never made it to the Far East. But,
  serendipitously, he found America on the way...

• Strictly speaking, he should have given the money
  back to the Funding Agency he never achieved his
  goals.

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Gamma Ray Bursts

• In the 80s and most of the 90s, GRB were one of
  the biggest misteries in Astronomy. We knew
  NOTHING.
• All kind of theories from objects in the comet
  cloud around the solar system to black holes in
  our galaxy or cosmological explosions.
• Observational breakthroughs
• CGRO/BATSE maps thousands of GRBs and they are
  isotropic.
• Beppo-Sax measures redshifts and they are at
  cosmological distances.

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Gamma Ray Bursts

• GRBs are the most luminous electromagnetic events
  occurring in the universe since the Big Bang.
• Propotypical transient typically a few
  seconds, although can range from a few
  milliseconds to minutes. Essentially two kinds
  short (lt 2s) and long.

• The origin is uncertain for both of them
• Short GRB may be neutron star and neutron
  star/black hole mergers. Or they may be
  magnetars.

• Long GRBs are associated to Supernovae. Probably
  come from some sort of super-supernova
  hypernova or collapsar.

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GRB060614 a new type of GRB

• But the show goes on
• GRB 060614 is neither short nor long.
• It was long (102s), but had no associated
  supernova.
• It also resided in a galaxy that appears to be
  atypical when compared to hosts of previously
  studied long GRBs.
• This GRB may well require a new process to
  explain it
• a massive star that is very different from those
  that make either long GRBs (and which does not
  end up as a supernova),
• a compact binary merger that can produce
  long-lived radiation
• something totally new.

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Easter Egg GRB080319B

• The show goes on (even on holidays). I found out
  about GRB080319B one week ago in El País.
• The most luminous GRB ever recorded.
• It reached lt6m, i.e. visible with naked eye.
• Redshift z0.9. Could have been detected in
  ?-rays by GLAST out to z5 and in X-rays by EXIST
  out to z12.
• GRBs probes of first stars in the universe...

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Orphan GRBs

• Can we see all GRBs?
• Some GRBs may not emit ?-rays (!).
• Off-axis or otherwise. Very likely, given current
  understanding of jets, in GRBs.
• Their detection and identification would allow
  the full understanding of GRB jets and source
  populations, which in turn may prove necessary
  for using GRBs as tracers of star formation rates
  out to large z.
• Nakar et al have estimated that these will be
  optimally detected (at highest rates) at V,R
  20-22.

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The Crab Pulsar
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Radio and optical pulsars

• A. Hewish built a funny array of radio antennas
  to study interstellar scintillation.
• In 1967, one of his PhD students, Jocelyn Bell,
  found a suspicious pulsation in the data.

• She had discovered the first radio pulsar
  Years later Hewish, not her, would get the Nobel
  Prize. (Students beware your advisors.)

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Radio and optical pulsars

• Bells discovery got the astronomers crazy. A
  race set in to find more pulsars.
• In a month Australians found a second one close
  to a Supernova Remnant. And then a pulsar at the
  Crab Nebula with 33 ms period.
• Problem radiotelescope had a poor angular
  resolution. You couldnt tell where the source
  really was.
• Optical telescopes did better,
• A device to very fast fold light with a period
  (like a stroboscope) was installed at an optical
  telescope at Kitt Peak.
• Pointed at the so-called Baades star in the
  center of the Crab Nebula and there it was! A
  star blinking with 33 ms period!

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Radio Pulsars

• There are now more than 1000 radio pulsars and
  more every day.
• The phenomenology is wild each pulse in a pulsar
  is different, there are giant pulses, sometimes
  the period jumps (glitch).
• There are extremely magnetized pulsars
  (magnetars), pulsars with extremely fast
  periods in binary systems (ms pulsars) and
  pulsars which pulse only every now and then
  (RRATs)..
• Pulsars are used to measured distance, and have
  been used to detect Earth-like planets, to prove
  the existence of gravitational waves,and recently
  also as gravitational wave detectors.

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Radio Pulsars

• New phenomena are frequent Nature 422 (2003) 141.

Equipped radiotelescope in Arecibo with faster
digitizer data storage to allow ns
sampling. Crab discovered giant radio pulses
lasting for 2 ns! The plasma structures
responsible for these emissions lt1m in size, the
smallest objects ever detected outside the Solar
System. They are also the brightest transient
radio sources in the sky.
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Radio transients in general a zoo

• Nature 434, 50-52 (3 March 2005)
• Trasient near the Galactic
• Center GCRT J1745-3009.
• Repeated bursts with 77 min period
• Nature 439, 817-820 (16 February 2006)
• Eleven objects characterized by single, dispersed
  bursts having durations between 2 and 30 ms.
• The average time intervals between bursts range
  from 4 min to 3 h with radio emission typically
  detectable for lt1 s per day.
• Periodicities in the range 0.4-7 s for ten of the
  eleven sources, suggesting origins in rotating
  neutron stars.

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Parkes radio transient

• Science 318/2 (2007) 777
• Analyzed archival Parkes radio survey data and
  found a 30-jansky burst, less than 5 ms in
  duration, 3º from the Small Magellanic Cloud.
• So bright it overloaded the detector!
• Models for the free electron content in the
  universe imply that the burst is less than 1 Gpc
  away.
• Expect hundreds of such events occur throughout
  the sky every day.
• New method to measure baryon component of the
  universe?
• Origin?? Came out of the blue

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WATCH THE UNIVERSE
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Limited instrumentation (1)

• Optical telescopes look at the most boring window
  to the Universe.
• By definition. Stars, life

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Limited instrumentation (2)

• One century ago we moved to photographic plates
  and then to CCDs.
• These devices improve on sensitivity by
  integrating for minutes or hours, so by
  definition they are not sensitive to faster
  events.

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Limited instrumentation (3)

• We have increased the sensitivity at the cost of
  the Field of View the more we zoom, the smaller
  the FOV.
• Optical FOVgt5º are hard to accomplish optics and
  size of instrumentation (huge expensive CCDs).
• Radio multibeam receivers are just starting.
  Small FOV.
• X-rays, ?-rays expensive cameras, problems with
  optics.

Hubble Ultra Deep Field 800 exposures, 36.7
square arcminutes, 1/13 000 000 of the sky
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Optical CONCAM

• A CONCAM is a CONtinuous CAMera that is placed
  somewhere in the world with a fisheye lenses to
  watch the entire sky every night.
• Each camera takes a 180-second exposure every 4
  minutes, then relays the data back to
  nightskylive.net.

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CONCAM Night sky live

• Collectively, these physical CONCAM devices are
  part of the Night Sky Live project that also
  includes people, data, web pages, etc.
• The Night Sky Live project aims to make these
  images and data available to those who are
  interested.

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Optical ASAS

• The All Sky Automated Survey
• Final goal is photometric monitoring of approx.
  107 stars brighter than 14 magnitude all over the
  sky.
• The initial idea for the project is due to Bohdan
  Paczynski (Princeton)
• The prototype instrument, located at the Las
  Campanas Observatory (operated by the Carnegie
  Institution of Washington), and the data pipeline
  were developed at the Warsaw University.
• Recently developed ASAS-N at Faulkes North site
  at the Haleakala on Maui (Hawaii) to cover all
  sky.
• Papers using ASAS data in ADS Database 192
  entries.

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ASAS

• It uses telescopes with the aperture of 7 cm, the
  focal length of 20 cm, 2K x 2K CCD cameras 3 with
  15?m pixels from Apogee.
• Standard V-band and I-band ?lters.
• The I-band data are still being processed but all
  V-band data have already been converted to
  catalogs of variable stars.
• ASAS reaches 14-mag stars in 2 minute exposures
  over a ?eld of view of (9º)2 degrees.

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Sloan Digital Sky Survey

• The SDSS uses a dedicated, 2.5-meter telescope on
  Apache Point, New Mexico.
• A pair of spectrographs can measure spectra of
  (and hence distances to) more than 600 galaxies
  and quasars in a single observation.
• However the 120-megapixel camera can image 1.5
  square degrees of sky at a time.
• This means that it took SDSS five years to scan
  8,000 square degrees (20) of the sky.

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Optical LSST

• The Large Synoptic Survey Telescope (LSST) is a
  proposed 8.4-m, 10 square-degree-field telescope.
• In a relentless campaign of 15 second exposures,
  LSST will cover the available sky every three
  nights.
• Will also be used to trace billions of remote
  galaxies and measure gravitational lensing
  produced by Dark Matter.

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LSST

• Funny funding for the time being
• Jan 2008 LSST Receives 30M from Charles Simonyi
  and Bill Gates
• July 2007 LSST Receives 3 Million from Keck and
  TABASGO Foundations
• Jan 2007 Google joins Large Synoptic Survey
  Telescope Project
• Sept 2005 LSST receives 14.2 Million from NSF.
• Now they only need 400 million more from NSF

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LSST a data challenge

• CCD pixel count 3.2 Gpixels
• Readout time 2 sec
• Dynamic range 16 bits
• Nominal exposure time 15 seconds
• Nightly data generation rate 15 Tbytes.
• Yearly data generation rate (average) 6.8 Pbytes

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Radio Allen Telescope Array

• Joint project between the SETI Institute and the
  UC Berkeley.
• 90 miles northeast of San Francisco.
• Concept many small (6m ?) cheap antennas. When
  completed 350. First phase with 42 antennas
  operational since 2007.
• Field of View 2.5º at ? 21 cm (17x VLA),
  complete instantaneous frequency coverage from
  0.5 to 11.2 GHz
• Donation of 12 million by Paul Allen, co-founder
  of Microsoft.

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Radio LOFAR

• LOw Frequency ARray array for detection lt250
  MHz.
• Half of it funded and under construction in the
  Netherlands.
• LOFAR uses an array of simple omni-directional
  antennas instead of mechanical signal processing
  with a dish antenna. It looks at the whole sky!

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Radio LOFAR

• The electronic signals from the antennas are
  digitised, transported to a central digital
  processor, and combined in software to emulate a
  conventional antenna.
• In the core of CEP is IBMs latest supercomputer,
  the BlueGene/L system.
• Data transport requirements are in the range of
  many Tera-bits/sec and the processing power
  needed is tens of Tera-FLOPS.
• The cost is dominated by the cost of electronics
  and follows Moore's law.
• LOFAR is an IT-telescope.

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• The antennas are simple enough but there are a
  lot of them - 25000 in the full LOFAR design.
• To make radio pictures of the sky with adequate
  sharpness, the antennas are spread out over an
  area of ultimately 350 km in diameter.

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X-ray SWIFT

• The state of the art X-ray survey instrument is
  the US/UK/Italian satellite detector SWIFT.
• Main goal look for GRB with a 1.4 sr FOV (1/6th
  of the sky), inmediate alert sent worldwide.
• Will fly until 2011.
• Very succesful
• 330 GRBs.
• 65 Supernovae.
• Catalogue of AGNs.
• Constant monitoring of 514 variable sources.

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X-rays Black Hole Finder Probes EXIST

• No instrument foreseen for the next future. Only
  advanced proposals by NASA, so-called BHFPs.
• The best candidate right now, EXIST, could be
  launched in 2015.

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X-rays Black Hole Finder Probes EXIST

• Energy range 4-300 keV
• Field of View 160º x 70º 3 sr (25 of the sky).
• Much better sensitivity over SWIFT or INTEGRAL.

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• The long-awaited sucessor to EGRET which detected
  250 ?-ray sources in the 90s.
• To be launched next May 16.
• Energy range 20 MeV- 100 GeV.
• 20x better sensitivity than EGRET expect
  thousands of sources.
• Field of View 2 sr (1/6th of the sky).
• First goal of GLAST all sky survey and permanent
  monitoring. Will cover the whole sky every 3
  hours.

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Its the data, stupid!

• Both extragalactic radio burst and RRATs were
  discovered through a reanalysis of data obtained
  for a large-scale pulsar survey (serendipity
  public data). The keyword is Data Mining.

Virtual Observatory make all astronomical data
available online and develop tools to crosslink
all wavelengths.
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CONCLUSIONS

• The sky is ephemeral. New astronomical windows
  have revealed a zoo of transient phenomena. Many
  are not even repeatable! The Big Bang is not
  repeatable, right?
• Essential to keep constant watch in all
  wavelengths and all directions. Armada of all-sky
  instruments coming online.
• Keep your eyes and minds open discoveries may
  come at unexpected time scales or using
  innovative techniques!

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BACKUP
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V838 Mon

• The Galactic transient V838 Mon, discovered by
  Brown (2002), had a peak outburst amplitude of
  10 mag, reaching V of 6.7 mag during its
  multi-peaked, two month-long eruption.
• Soon after the eruption, spectacular expanding
  light echoes were detected, the evolution of
  which has been imaged with the Hubble Space
  Telescope.
• Possible scenarios include a binary merger or a
  star swallowing a planet

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Dormant massive black holes

• Open question is there a supermassive black hole
  at the center of each galaxy?
• Hard to tell because most of them have no matter
  to swallow, so they do not emit radiation. They
  are dormant.
• But every now and then, a star gets too close to
  the black hole and is disrupted through tidal
  forces follows an episode of strong X-ray
  emission.
• Should be detectable by next generation X-ray
  surveys at rate 10-30/year (out to 200 Mpc).

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• We have been exploring the static universe.
• Variable objects are a terra incognita.
• You, anybody, can find new phenomena while
  looking at the data. We dont know the time
  scale!

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SKA

• Not only about music Square Kilometer Array.