El experimento LIGO y el descubrimiento de Ondas Gravitacionales Dr. Carlos Javier Solano Salinas

1. El experimento LIGO y el descubrimiento de Ondas Gravitacionales Dr. Carlos Javier Solano Salinas Facultad de Ciencias Universidad Nacional de Ingeniería FC-UNI, 24 junio 2016 1

2. Electromagnetic vs Gravitational Waves 2

3. Outline The view with electromagnetic radiation Past revolutions in astronomy The view with gravitational radiation Similarities and differences Sources of gravitational radiation Tones, chirps, backgrounds, and bursts Gravitational-wave detectors Bars, interferometers, and space antennae 3

4. Electromagnetic waves Time-varying disturbance in electromagnetic field Arise as a direct consequence of relativity (causality) • Field of a stationary charge

5. Electromagnetic waves Time-varying disturbance in electromagnetic field Arise as a direct consequence of relativity (causality) • Field of a stationary charge • Field of a moving charge

6. Electromagnetic waves Time-varying disturbance in electromagnetic field Arise as a direct consequence of relativity (causality) • Field of a stationary charge • Field of a moving charge • Field of an accelerated charge

7. Electromagnetic waves Time-varying disturbance in electromagnetic field Arise as a direct consequence of relativity (causality) • Field of a stationary charge • Field of a moving charge • Field of an accelerated charge • Oscillating charges  waves with characteristic lengths • Different wavelengths make up electromagnetic spectrum

8. Electromagnetic astronomy Visible light: only form of astronomy until 1930s Powered by steady heat from ordinary stars Serene view of stars, planets, galaxies

9. Electromagnetic astronomy Radio: revolutionized our view of the Universe! Powered by electrons blasted to near-light speed Violent picture of active galaxies, Big Bang

10. Electromagnetic astronomy X and  rays: Further revealed our violent Universe Solar flares, stellar remnants (neutron stars, black holes), thermonuclear detonations on stars

11. If observing new wavelengths of light lead to such revolutions in astronomy, what might we expect when we observe an entirely new spectrum?

12. Gravitational waves Underlying field is the gravitational tidal field (g’) • Oscillations produce gravitational waves in exactly the same manner as electromagnetic waves

13. Gravitational waves Underlying field is the gravitational tidal field (g’) • Oscillations produce gravitational waves in exactly the same manner as electromagnetic waves • Strength is given by the strain amplitude (h) • Typically of order 10 -21 or less!

14. Gravitational waves: differences from EM A fundamentally different way of observing the Cosmos! Electromagnetism: Gravity: • A strong force, but with opposing charges (  and ) • A weak force, but with only one charge (mass) • Fields built up incoherently from microscopic charge separations • Fields built up coherently from bulk accumulation of matter • Wavelengths smaller than the source • Wavelengths larger than the source • Waves are easy to detect, but easily blocked • Waves are hard to detect, but pass undisturbed through anything • Show the surfaces of energetic bodies • Reveal the bulk motion of dense matter • Used to construct images of celestial objects • Can be though of as sounds emitted by those objects

15. Gravitational Waves (sources and detection) 15

16. Gravity Einstein’s General theory of relativity : Gravity is a manifestation of curvature of 4- dimensional (3 space + 1 time) space-time produced by matter (metric equation? gμν = ημν ) If the curvature is weak, it produces the familiar Newtonian gravity: F = G M1 M2/r2

17. Gravitational-waves When the curvature varies rapidly due to motion of the object(s), curvature ripples are produced. These ripples of the space-time are Gravitational-waves. Gravitational-waves propagate at the speed of light. Animation by William Folkner, LISA project, JPL

18. Electromagnetic vs Gravitational-waves EM waves are produced by accelerated charges, whereas GWs are produced by accelerated “masses”. EM waves propogate through space-time, GWs are oscillations of space-time itself. Typical frequencies of EM waves range from (107 Hz – 1020 Hz)... ...whereas GW frequencies range from ~ (10-9 Hz – 104 Hz). They are more like sound waves.

19. Quadrupole Field An oscillating dipole produces EM waves. A time varying mass-quadrupole produces GWs

20. Gravitational-waves GWs stretch and compress the space-time in two directions (polarizations): ‘+’ and ‘x’. h+ & hx are time-varying and their amplitude depend on the source that is emitting GWs.

21. Gravitational-waves h+ hx

22. Propagation h+ hx

23. Sources of GWs Inspiral sources: Binary black holes, Binary Neutron stars (pulsars), Binary white-dwarfs or combination of these. As two stars orbit around each other, they steadily lose energy and angular momentum in the form of GWs. This makes the orbital separation to shrink slowly and they merge after some time (this time depends on their masses and orbital separation that we observe)

24. Inspiraling binary stars

25. Sources of GWs Exploding stars: Core collapse Supernovae Pulsars (rotating Neutron stars) Stochastic sources: Jumble of signals from lot of sources

26. Sources of gravitational waves Supernova: Explosion caused by the collapse of an old, burnt-out star Produces a burst of gravitational radiation, if it is non-symmetric! • Exact “sound” is difficult to predict theoretically • Challenge is to identify suspicious-sounding bursts in a noisy background • Leftover core may be a . . .

27. Sources of gravitational waves Neutron star: A city-sized atomic nucleus! Can spin at up to 600 cycles per second Emits continuous gravitational radiation (again, if it is non-symmetric) • Signal is very weak, but can be built up through long observation • This is a computationally-intensive process! • Plan to recruit computers from the general public: Einstein@home • A pair of these could lead to a . . .

28. Sources of gravitational waves Merging compact binary: Collision of two stellar remnants (neutron stars or black holes) Produce a sweeping “chirp” as they spiral together • Already the first indirect evidence of gravitational waves • Our most promising source: strong and easy to model • However, event rate is highly uncertain!

29. Sources of gravitational waves Primordial background: Leftover radiation from the beginning of the Universe Tells us about the state of the Universe at or before the Big Bang! Sounds like “noise” with a characteristic spectrum • Difficult to distinguish from instrumental noise • Correlate the data from several independent detectors

30. Sources of gravitational waves Things that go bump in the night: Sources that are highly speculative, or not predicted at all! Could sound like anything E.g. a possible signal from a folded cosmic string: • Probably the most exciting of all the sources, but we don’t know what to listen for! • Again, would need to hear it in several detectors

31. How do we know GWs exist?Indirect proof. Hulse-Taylor binary pulsar (Nobel prize 1993) Steady decrease in orbital separation due to loss of energy through GWs.

32. Detecting gravitational waves Strongest sources induce strains less than h = 10-21 Exceedingly hard to measure! Attempts since 1960s, but nothing so far Newer instruments are approaching these sensitivities Some examples . . .

33. Detecting gravitational waves Resonant bars: selectively amplify distortions that are “tuned” to their natural frequency • First detectors built in the 1960s • Respond only to a narrow frequency range 2.3 tonne aluminum bars: Explorer (Geneva) Nautilus, Auriga (Italy) Allegro (Louisiana) 1.5 tonne niobium bar: Niobe (Australia)

34. Detecting gravitational waves Laser interferometers: measure relative motions of separate, freely-hanging masses • Masses can be spaced arbitrarily far apart • Respond to all frequencies between 40 and 2000 Hz

35. Detecting gravitational waves LIGO: 2 detectors (4km & 2km) in WA 1 detector (4km) in Louisiana VIRGO: 3km detector in Italy GEO: 600m detector in Germany TAMA: 300m detector in Japan • Chinese Academy of Sciences is also supporting a proposal to build an underground instrument • Less affected by ground motion

36. Detecting gravitational waves Laser Interferometer Space Antenna (LISA): like ground-based interferometers, but masses are three freely-orbiting spacecraft • Use onboard lasers to amplify and reflect beams • 5 million km arms  respond to very low frequencies (0.0001 to 0.1 Hz) • Sensitive to supermassive black holes • Joint NASA/ESA mission, proposed 2013-2014 launch

37. Detecting gravitational waves Laser Interferometer Space Antenna (LISA):

38. Space-based GW detection LISA (Laser Interferometer Space Antenna)

39. Sources for LISA Double White Dwarfs White-dwarf black hole Supermassive and Intermediate mass black holes

40. Livingston, Louisiana Hanford, Washington Livi

41. Laser Interferometer Gravitational wave Observatory - LIGO Length of each arm, L = 4 km, frequency range , f = 10 Hz – 104 Hz ΔL ~ 10-18 meters, size of proton ~ 10-15 meters

42. LIGO Measuring GWs

43. LIGO Current range for an inspiralling binary NS averaged over all orientations and locations is ~ 15 Mpc ( near Virgo cluster of galaxies)

44. Signal and Noise No noise With Noise

45. What type of sources can LIGO detect? Last stages of inspiral of Binary NS Mergers of stellar and supermassive black holes Core-collapse supernovae Pulsars

46. What’s the big deal ? GWs bring info about objects that can not be seen with EM observations and vice-versa. This is a radically different field than EM observations. Measuring a length smaller than proton size is no longer a science fiction !! Observations have already been taken with the first version of LIGO (and VIRGO, GEO). We talked about signals and sources that we *know* about. Any new field has it’s own surprises (radio, gamma-ray). “….there are known knowns, there are known unknowns, But there are also unknown unknowns….” ---- Don Rumsfeld

47. The future Enhanced LIGO ~ 2010, Advanced LIGO ~ 2013 , Can see black hole binaries upto 4 Gpc (12 billion light years, z ~ 1) Advanced LIGO can detect hundreds of merger events in one year of observations because it can observe to larger distances !!