Gravitational Waves: Opening a New Window on the Universe€¦ · EFCOG Nuclear Facility Safety Conference Luncheon PNNL, Keita KAWABE, Aug/14/2018 Gravitational Waves: Opening a

EFCOG Nuclear Facility Safety Conference Luncheon PNNL, Keita KAWABE, Aug/14/2018

Gravitational Waves:Opening a New Window on the Universe

Picture: “We will never stop listening”, N. Kijbunchoo

Keita KawabeLHO Detection Lead Scient


About the speaker.

河邊径太 (Kawabe, Keita) PhD, LHO Detection Lead and this.


This is a REALLY short condensed introduction of the following:

• Why we’re doing what we’re doing.• What is GW anyway.• How we detect it. (But not much time for

details.)• What kind of phenomena we observe.• Hopefully there’s time for questions at the end

of the talk, you can also ask me questions during the LIGO tour.


Why GW?

• This is a new sensory ability for mankind!• We want to observe the universe using it!


Observation of electro magnetic waves.

20th century

Radio, microwave, IR, UV etc.




Technology explodes, opening many new windows through which we can observe the universe

20th century



Just one example of one example: Radio and CMB

20th century


9 year microwave surveyCredit: NASA/WMAP Science Team


Or Neutrinos

20th century



And we want to open yet another window!

20th century


We opened a new window!!

2015


But wait a sec, let’s ask this.

• What are the gravitational waves anyway?• How do we detect them?


• 1915: Einstein found that space is not just a void.

What is the space anyway? Is it just a void, an empty container for “things”?


What is the space anyway?Is it just a void, nothing, in which “things” move?

• 1915: Einstein found that space is not just a void. • Space and time (space-time) are not totally unlike stretchy fabric

interacting with heavy objects.• Think of marbles on a taut table cloth.

• Matter “bends” the fabric, and the bending (or curvature) of the fabric tells the matter how to move.


OK, now we can discuss the gravitational waves.

• When heavy masses move rapidly, the fabric of space-time is stretched and shrunk back violently.

• 1917: Einstein found that this stretching/shrinking can propagate as a wave, i.e. gravitational wave!

Credit: NASA


So how do we detect it? What happens to matter when GW passes by?


It stretches the space in one direction and shrinks in the other and vice versa, repeatedly.

But this is a tiny tiny effect, like 1/1000th of a proton diameter (that’s a bit smaller than one trillion-th of 1/16 of an inch) or less over kilometers.


And this is how LIGO instruments work by measuring distances accurately.

• We measure the distance between mirrors that are 4km apart very, very, very precisely.


LIGO instrument is a more complex machine with some optical enhancements,

1E-9 torr vacuum


with big 40kg fused silica mirror with state-of-the-art coating and seismic isolation,


and can detect very small displacement.


(Noise budget, L1, O2)


So what can we observe using GW?Collision of binary black holes, for example.

• Imagine: Two black holes, away from the Earth by about 1.3 billion light years, running around with each other.• about 90 trillion times the distance

between the Sun and the Earth.• Each as 30 times heavy as our Sun.

Pixabay.com CC0 License


• Imagine: Two black holes, away from the Earth by about 1.3 billion light years, running around with each other.• about 90 trillion times the distance

between the Sun and the Earth• Each as 30 times heavy as our Sun.• About 1.3 billion years ago, after rapid

inspiral motion they collided with each other and formed one big black hole.

• That shook the universe and created something called gravitational wave.Pixabay.com CC0 License


• Imagine: Two black holes, away from the Earth by about 1.3 billion light years, running around with each other.• That’s about 90 trillion times the

distance between the Sun and the Earth• Each as 30 times heavy as our Sun.• About 1.3 billion years ago, after rapid

inspiral motion they collided with each other and formed one big black hole.

• That shook the universe and created something called gravitational wave.

• And shook LIGO detectors’ 4km arms by ~1000 times smaller than proton, and we detected it!

Pixabay.com CC0 License


Twin black holes merged.


Awesome!

• Nobody knew that twin black holes existed.• Black holes don’t emit EM

• And that they could collide within the age of the universe.

• And they are heavy! 30 solar mass each!• (And three LIGO founders won Nobel Prize for

Physics in 2017!)


So far, 2 observing runs, 5 such BBH collisions (and one “candidate”)


GW170817: Binary neutron star collision, another ground-breaking discovery!

• Neutron stars: The smallest, densest stars known, ~Msun in O(10km) diameter, but not as heavy as BH.

• Twin neutron stars collided with each other ~130million light years away (they’re “close by”).


(artist depiction, not a simulation)

Credit NASA, Dana Berry)


• Twin neutron stars collided with each other ~130million light years away, emitting GW and electro-magnetic waves. It reached earth on 2018/Aug/17.

• GW detected by a network of LIGO and Virgo(our French/Italian counterpart), info released ~40 min later to select partners.

• Short gamma ray burst was detected by Fermi first, released ~15 sec later.

• Seeing GW (and GRB) sky map, everybody started pointing their telescope frantically to see something!

GW170817: Binary neutron star collision, another ground-breaking discovery!


And they saw it!


BTW there are ~4000 authors on this paper, I’ve heard that this is ~1/3 of astronomer population out there.


Cool pictures from Hubble

Credit NASA/ESA


Exciting things!

• Mystery of sources of short GRB solved, it’s BNS!• Mystery of synthesis of ~half of heavy things in the

universe like gold solved, EM signature seen in EM!• General relativity test, e.g. speed of GW VS light.• Cosmology, e.g. Hubble constant.• First hint of how squishy neutron matter is. • List goes on and on, we don’t understand everything

and new mysteries emerge, but we’ll deepen our understanding as we detect many more.


This is the start of new exciting era because

• LIGO/Virgo will start distributing GW event alerts to public automatically in the upcoming observation run O3 (starting 2019).

• Everybody can point their instruments in the direction of GW. Multi-messenger astronomy for all!


More GW detectors are to be made, and not only on the Earth, and with different

techniques!


LIGO won’t stop either!

• Reduce noise of our instruments.• Can see further away for the same signal. (Number of

sources proportional to volume ~ distance^3.)• Can see smaller events at the same distance.

• Upgrade-observation-upgrade cycle.• O1 (Sep 2015 – Jan 2016), 2 BBH and 1 “candidate”.• O2 (Nov 2016 – Aug 2017), 3 BBH, 1 BNS.• We’re installing upgrade (almost done)• O3 expected to start early next year!• O4 planned after O3.• Large upgrade beyond advanced LIGO called A+ was

approved by NSF recently.


Thank you very much for listening!


O3 laser: Smaller power, but we cannot use 150W for now anyway.

From 200W monstrosity to 70W laser, but with a help of squeezing.

Old New


O3 Upgrade for Shot Noise: Squeezing

• Smaller shot noise without using high power! • Already demonstrated in GEO and iLIGO.

• aLIGO design in place, aiming for 3dB improvement.


More power and squeezing


O3: New mirrors

• Coating in the installed ETMs shows ripple.• Increased scattering.

• Later batch from LMA shows no ripple.


O3: End Reaction MassReplacement

• Electrodes on a glass substrate (ERM) behind a test mass• Used for controlling test masses

• Narrow gap (5mm) -> “squeezed film” residual gas damping non-negligible


O3: End Reaction MassReplacement

• Electrodes on a glass substrate (ERM) behind a test mass• Used for controlling test masses

• Narrow gap (5mm) -> “squeezed film” residual gas damping non-negligible

• New, donut-shaped ERM


A+: Current facility, bigger mirror, frequency dependent squeezing

• Mirror twice as heavy• 300m “filter cavity” to rotate the phase of the

squeezed vacuum so the radiation pressure is not harmful while we can enjoy good high frequency performance

• … and other improvements.• NSF Oked it recently!


To put the size of things in perspective: 500~600miles apart at the start of the

recorded signal

Richland

Yakima

SF


And in 0.17 sec they merged to form a bigblack hole with about 120 mi radius.


Recorded Waveform

• This is what was recorded.


Recorded Waveform

• (LLO 7/1000 sec earlier)


• Each instrument cannot tell where the source is located.

• Oh no, what do we do?

Awesome, but where’s that big black hole in the sky?


That’s why we have more than one instrument (for now only two).

LHO LLO


Mode detectors.

Approved


• GW150914 410Mpc, z~0.09• GW151226 440 Mpc, z~0.09• GW170104 880 Mpc, z~0.18• GW170608 340 Mpc, z~0.07• GW170814 540 Mpc, z~0.11• GW170817, 40 Mpc, z~0.01

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Gravitational Waves: Opening a New Window on the Universe€¦ · EFCOG Nuclear Facility Safety Conference Luncheon PNNL, Keita KAWABE, Aug/14/2018 Gravitational Waves: Opening a