Hooray, this is the 500th blog post for Palmia Observatory! LISA Canada 2021 Workshop; LISA might see our cosmic dawn when the very first stars formed

 Greetings from Palmia Observatory

Well, here we are and I am not quite sure how it happened, but this is the 500th blog post from Palmia Observatory, which started seven years ago.

Regardless of how you got to this particular page, you can always go the website home page for a bigger picture view of all of the topics covered in this blog.  This is what the web page looks like if you just go to the website reference at: http://www.palmiaobservatory.com/

The Palmia Observatory start page with 499th post  (Source: Palmia Observatory)

You can search around by looking at the titles of pages by date or you can search for word or topic by using the search box.   You can search for the particular aspect of astronomy or cosmology or physics that might have come up in this journey over the past seven years.  These 500 posts, written over 7 years, means over 70 posts per year on average, which is above 1.5 posts per week.  Writing the posts helps me formalize and firm up some of my own understanding, and hopefully of interest to many others, of the meetings, seminars, colloquia, star parties, observational outings and travels as well as lessons learned.  It has been a fun journey and I hope you can also find some parts of it useful!

Anyway, now back to our main blog post topic for this time which the ongoing online LISA Canada 2021 Workshop.  LISA, which means Laser Interferometric Space Antenna, is the airborne version of LIGO for detecting gravitational waves.  The workshop was sponsored by Canadian scientists but was open to scientists around the world including physicist wannabes, like myself.  The workshop is held online from April 27 to April 29.

Waiting for the LISA Canada 2021 Workshop  (Source: Canada 2021 Workshop)

One of the purposes of the workshop was to introduce the LISA mission to all attendees and to give attendees the opportunity to join the LISA collaboration.  One of the sessions that I enjoyed the most is this one by Kelly Holley-Bockelmann on: "How Gravitational Wave Astronomy will be a Game Changer."

LISA will be a game changer for studying the universe  (Source: Kelly, LISA Canada 2021 Workshop)

The LIGO discoveries have brought us to a new era of multi-messenger astronomy.  With multiple binary black hole mergers and one binary neutron star merger, LIGO has led to many new discoveries and theories about the history of the universe.  Looking at the universe with photons is great but photons coming to us are distorted by intervening fields and matter.  Gravity waves on the other hand come to directly and mostly not effected by anything in their path.

Observing the universe with photons is ok, but distorted  (Source: Kelly, LISA Canada 2021 Workshop)

Kelly reminded us of the gravitational wave spectrum and how it compares with other wavelengths used to explore the universe.  You can see that LISA covers a much lower frequency range than does LIGO.  The lower frequency range is accessible only with interferometer path lengths much longer than could be installed on Earth.

The Gravitational Wave Spectrum (Source: Kelly, LISA Canada 2021 Workshop)

LISA can detect gravitational waves with much longer wavelength than LIGO, what does that mean in terms of the astrophysical objects that we are interested in?  This next screenshot of LISA Discovery Space explains how the inspiral of massive black hole binary systems can now be identified weeks and months longer than possible with LIGO.  Smaller binary systems of say neutron stars and white dwarfs will be observed as sort of a constant hum of background noise.  The signal received by LISA is the sum total of all of the astrophysical sources that are located all over the sky.  Being able to detect and identify one particular source and it location on the sky will be require a large software and signal processing effort.

LISA Discovery Space covers millions of sources (Source: Kelly, LISA Canada 2021 Workshop)

Black hole mergers can be used as standard sirens.  The measurement of the received gravitational wave gives directly the mass and distance to the source.  No need for distance ladders as used in the optical measurements.

What we can find with LISA (Source: Kelly, LISA Canada 2021 Workshop)

The merger history as detected with LISA will trace the formation of galaxies out to about redshift 20.  With the distances provided by gravitational waves, the structure and astrophysics of those sources can be studied with more precision with electromagnetic surveys.

Some of the things that LISA hopes to measure (Source: Kelly, LISA Canada 2021 Workshop)

One of the more significant capabilities for me was how LISA will be able to get back to the "Cosmic Dawn", back at redshift 10-20.  This period goes as far back as something like 50 million years after the big bang and comes forward about 1 billion years.  This period covers the major part of the history of the universe when the very first stars and galaxies were just being formed.   This is a part of history that is not easily accessible with optical telescopes.

LISA might see back in time to cosmic dawn (Source: Kelly, LISA Canada 2021 Workshop)

Another presentation discussed the design of the LISA satellites and instruments.  This technical session went into all of the noise sources of a space based interferometer.  This session by William Weber went into a lot of the details including how all of the noise sources and laser power and the wavelength of the desired gravitational waves entered into setting the arm length of the interferometer, which means the distance between the three LISA satellites.  The design arm length is 2.5 million km.

In the upper right corner of this slide you see the three satellites arranged as an equilateral triangle that is shown following behind the Earth in its orbit around the sun.  The satellites carry an isolated, floating test mass that moves only in accordance with the gravity of the solar system and the distance between each satellite can be measured precisely enough to detect gravitational waves.  The test masses doe not rely on suspension by tiny flexures, as is done with LIGO, and are not susceptible to ground motion.  The satellites are subject to solar wind and solar radiation, which the test masses are not, so the satellites are controlled to minimize the effects of solar radiation while letting the test masses just float along only under the influence of gravity.

If you are interested in more of the LISA details, schedule (with possible launch in 2035), and the science, a good web reference where you can start is at: https://www.elisascience.org/articles/lisa-consortium

GW event spectrum and orbit of LISA about the sun (Source: W. Weber, LISA Canada 2021 Workshop)

Until next time, here from our burrow, stay safe, as we recover more of our freedom,

Resident Astronomer George

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