Upgraded LIGO Reactivated: Resumes Unraveling Universe’s Secrets With Enhanced Gravitational Wave Detection

Astrophysics Gravitational Waves Concept

When two massive objects – like black holes or neutron stars – merge, they warp space and time. These distortions in distortions in spacetime are known as gravitational waves.

Scientists have reactivated the upgraded Laser Interferometric Gravitational-Wave Observatory (LIGO) after a three-year break, improving its ability to measure gravitational waves. These waves offer new opportunities for multi-messenger astronomy and deepen our understanding of astrophysical phenomena. The upgraded LIGO began its fourth observation run in May 2023, focusing on real-time detection and localization of gravitational waves, which are generated by the merging of massive objects like black holes and neutron stars.

After a three-year hiatus, scientists in the U.S. have just turned on detectors capable of measuring gravitational waves — tiny ripples in space itself that travel through the universe.

Unlike light waves, gravitational waves are nearly unimpeded by the galaxies, stars, gas, and dust that fill the universe. This means that by measuring gravitational waves, astrophysicists like me can peek directly into the heart of some of these most spectacular phenomena in the universe.

Since 2020, the Laser Interferometric Gravitational-Wave Observatory – commonly known as LIGO – has been sitting dormant while it underwent some exciting upgrades. These improvements will significantly boost the sensitivity of LIGO and should allow the facility to observe more-distant objects that produce smaller ripples in spacetime.

By detecting more events that create gravitational waves, there will be more opportunities for astronomers to also observe the light produced by those same events. Seeing an event through multiple channels of information, an approach called multi-messenger astronomy, provides astronomers rare and coveted opportunities to learn about physics far beyond the realm of any laboratory testing.

Sun Earth Gravity General Relativity

According to Einstein’s theory of general relativity, massive objects warp space around them.

Ripples in spacetime

According to Einstein’s theory of general relativity, mass and energy warp the shape of space and time. The bending of spacetime determines how objects move in relation to one another – what people experience as gravity.

Gravitational waves are created when massive objects like black holes or neutron stars merge with one another, producing sudden, large changes in space. The process of space warping and flexing sends ripples across the universe like a wave across a still pond. These waves travel out in all directions from a disturbance, minutely bending space as they do so and ever so slightly changing the distance between objects in their way.

When two massive objects – like a black hole or a neutron star – get close together, they rapidly spin around each other and produce gravitational waves. The sound in this NASA visualization represents the frequency of the gravitational waves.

Even though the astronomical events that produce gravitational waves involve some of the most massive objects in the universe, the stretching and contracting of space is infinitesimally small. A strong gravitational wave passing through the Milky Way may only change the diameter of the entire galaxy by three feet (one meter).

The first gravitational wave observations

Though first predicted by Einstein in 1916, scientists of that era had little hope of measuring the tiny changes in distance postulated by the theory of gravitational waves.

Around the year 2000, scientists at Caltech, the Massachusetts Institute of Technology, and other universities around the world finished constructing what is essentially the most precise ruler ever built – the LIGO observatory.

LIGO Hanford Observatory

The LIGO detector in Hanford, Washington, uses lasers to measure the minuscule stretching of space caused by a gravitational wave. Credit: LIGO Laboratory

LIGO is comprised of two separate observatories, with one located in Hanford, Washington, and the other in Livingston, Louisiana. Each observatory is shaped like a giant L with two, 2.5-mile-long (four-kilometer-long) arms extending out from the center of the facility at 90 degrees to each other.

To measure gravitational waves, researchers shine a laser from the center of the facility to the base of the L. There, the laser is split so that a beam travels down each arm, reflects off a mirror and returns to the base. If a gravitational wave passes through the arms while the laser is shining, the two beams will return to the center at ever so slightly different times. By measuring this difference, physicists can discern that a gravitational wave passed through the facility.

LIGO began operating in the early 2000s, but it was not sensitive enough to detect gravitational waves. So, in 2010, the LIGO team temporarily shut down the facility to perform upgrades to boost sensitivity. The upgraded version of LIGO started collecting data in 2015 and almost immediately detected gravitational waves produced from the merger of two black holes.

Since 2015, LIGO has completed three observation runs. The first, run O1, lasted about four months; the second, O2, about nine months; and the third, O3, ran for 11 months before the COVID-19 pandemic forced the facilities to close. Starting with run O2, LIGO has been jointly observing with an Italian observatory called Virgo.

Between each run, scientists improved the physical components of the detectors and data analysis methods. By the end of run O3 in March 2020, researchers in the LIGO and Virgo collaboration had detected about 90 gravitational waves from the merging of black holes and neutron stars.

The observatories have still not yet achieved their maximum design sensitivity. So, in 2020, both observatories shut down for upgrades yet again.

LIGO Upgrades

Upgrades to the mechanical equipment and data processing algorithms should allow LIGO to detect fainter gravitational waves than in the past. Credit: LIGO/Caltech/MIT/Jeff Kissel

Making some upgrades

Scientists have been working on many technological improvements.

One particularly promising upgrade involved adding a 1,000-foot (300-meter) optical cavity to improve a technique called squeezing. Squeezing allows scientists to reduce detector noise using the quantum properties of light. With this upgrade, the LIGO team should be able to detect much weaker gravitational waves than before.

My teammates and I are data scientists in the LIGO collaboration, and we have been working on a number of different upgrades to software used to process LIGO data and the algorithms that recognize signs of gravitational waves in that data. These algorithms function by searching for patterns that match theoretical models of millions of possible black hole and neutron star merger events. The improved algorithm should be able to more easily pick out the faint signs of gravitational waves from background noise in the data than the previous versions of the algorithms.

LIGO Gravitational Waves Neutron Star Collision Galaxy NGC 4993

Astronomers have captured both the gravitational waves and light produced by a single event, the merger of two neutron stars. The change in light can be seen over the course of a few days in the top right inset. Credit: NASA and ESA

A hi-def era of astronomy

In early May 2023, LIGO began a short test run – called an engineering run – to make sure everything was working. On May 18, LIGO detected gravitational waves likely produced from a neutron star merging into a black hole.

LIGO’s 20-month observation run 04 will officially start on May 24, and it will later be joined by Virgo and a new Japanese observatory – the Kamioka Gravitational Wave Detector, or KAGRA.

While there are many scientific goals for this run, there is a particular focus on detecting and localizing gravitational waves in real time. If the team can identify a gravitational wave event, figure out where the waves came from and alert other astronomers to these discoveries quickly, it would enable astronomers to point other telescopes that collect visible light, radio waves or other types of data at the source of the gravitational wave. Collecting multiple channels of information on a single event – multi-messenger astrophysics – is like adding color and sound to a black-and-white silent film and can provide a much deeper understanding of astrophysical phenomena.

Astronomers have only observed a single event in both gravitational waves and visible light to date – the merger of two neutron stars seen in 2017. But from this single event, physicists were able to study the expansion of the universe and confirm the origin of some of the universe’s most energetic events known as gamma-ray bursts.

With run O4, astronomers will have access to the most sensitive gravitational wave observatories in history and hopefully will collect more data than ever before. My colleagues and I are hopeful that the coming months will result in one – or perhaps many – multi-messenger observations that will push the boundaries of modern astrophysics.

Written by Chad Hanna, Professor of Physics, Penn State.

Adapted from an article originally published in The Conversation.The Conversation

6 Comments on "Upgraded LIGO Reactivated: Resumes Unraveling Universe’s Secrets With Enhanced Gravitational Wave Detection"

  1. Excited! I visited LIGO a few years ago and they were talking about this. I saw a presentation on the squeezed light hardware, and it was super interesting. For the uninitiated, you can basically pin down one side of the uncertainty principle very well as long as you let the other side get very large.

  2. Xinhang Shen | May 25, 2023 at 6:24 pm | Reply

    There is no such thing called spacetime in nature, not to mention the ripples of spacetime because our physical time is absolute and independent of the reference frame and Einstein’s relativity is wrong as shown below:

    We know that a variable can only be defined once. Any double definition of a variable will either generate contradictions or become redundant. Time had been defined by physical clocks, but Einstein used Lorentz Transformation to have redefined the space and time, which leads to a fatal contradiction:

    According to Lorentz Transformation, the time of the moving frame t’ is shorter than the time of the stationary frame t:

    t’ = t/γ < t

    which is so called "time dilation", from which mainstream physicists including Einstein jump to a conclusion that the frequency of the moving clock becomes lower than that of the stationary clock. They even believe that the traveling twin would be younger than the twin stayed on the earth when they reunited on the earth after a space travel.

    But the period of the moving clock p' as an interval of the time of the moving frame should also be shorter than the period of the stationary clock p:

    p' = p/γ f.

    That means, the effect of “time dilation” will make the moving clock tick faster than the stationary clock, a fatal contradiction to the claim of special relativity that the moving clock ticks more slowly than the stationary clock. This contradiction disproves special relativity.

    People claim that there are numerous experiments that have proved special relativistic effects, but we can use special relativity itself to prove that all relativistic effects can never be shown on any physical process in the universe because in real experiments, all we can observe is the change of a physical process and the change is always the product of time and the changing rate, as the time of the moving frame becomes shorter than that of the stationary frame, the changing rate on the moving frame, just like the frequency of the moving clock, becomes faster than that of the stationary frame to make the change i.e. the product of time and the changing rate the same as that of the stationary frame, i.e., the relativistic effects of the time and the changing rate always cancel each other to make the change of the process Lorentz invariant. Therefore, we can never see relativistic effects in any experiments, and all so-called experimental proofs are misinterpretations of other effects such as the effects of aether – the medium of light, the existence of which is a direct conclusion of the disproof of special relativity.

    The absoluteness of the physical time measured with physical clocks can also be seen in the following reasoning:

    Let a series of vertically standing candles as clocks with the same initial height and burning rate move at different constant horizontal velocities relative to an inertial reference frame of (x, y, z, t) where x, y, z, t are relativistic positions and relativistic time. Thus, at any moment t of the relativistic time of the reference frame (x, y, z, t), all candles have the same height H relative to the reference frame of (x, y, z, t) and the height H represents the physical time of the clocks. Therefore, we have the simultaneous events in both relativistic time t and physical time H relative to the frame of (x, y, z, t):

    (Candle1, x1, y1, H, t), (candle2, x2, y2, H, t), …, (CandleN, xN, yN, H, t)

    When these events are observed on anther horizontally moving inertial reference frame (x’, y’, z’, t’), according to special relativity, these events in the reference frame of (x’, y’, z’, t’) can be obtained through Lorentz Transformation:

    (Candle1, x’1, y’1, H, t’1), (Candle2, x’2, y’2, H, t’2), … , (CandleN, x’N, y’N, H, t’N),

    where t’1, t’2, …, and t’N are relativistic times of the events in the frame of (x’, y’, z’, t’). It is seen that after Lorentz Transformation, these events have different relativistic times:

    t’1 ≠ t’2 ≠ … ≠ t’N

    That is they are no longer simultaneous in terms of the relativistic time of the frame of (x’, y’, z’, t’). But the heights of the candles remain the same H because the vertical heights here do not experience any Lorentz contraction. As the heights of the candles represent the physical time, these events still have the same physical time, i.e., they are still simultaneous in terms of the physical time H. Therefore, the physical time is Lorentz invariant, absolute and independent of inertial reference frames, which is different from relativistic time. Thus relativistic time is no longer the physical time measured with physical clocks, but an artificial time without physical meaning.

    Some people may argue that atomic clocks won’t behave like that. Please note that all clocks including atomic clocks can always use the height of a stick to represent their accurate time which will behave exactly the same as the candle clock.

    • Torbjörn Larsson | May 27, 2023 at 4:56 am | Reply

      General relativity is a well tested theory that underlies the merger observations which you somehow pretend do not exist. (Or even worse, the enormously well testing that goes into it forming the basis of modern cosmology with its vast data sets it usefully explains.)

      Special relativity can’t be “disproved” or tested wrong today since we now know it underlies magnetism – a low velocity relativistic effect of the electric field – and more generally electromagnetism that underlies the workings of computers and so the web. Ironically the very comment you wrote to give your personal opinion on the topic test that relativity is working!

      • Torbjörn Larsson | May 27, 2023 at 4:58 am | Reply

        More specifically, if you are interested in the topic, you need special relativity to understand semiconductors and transistor function. If you study these topics in engineering you (or physics) you will be introduced to relativistic theory throughout, from its mechanics (physics) to electronics (engineering).

  3. Torbjörn Larsson | May 27, 2023 at 4:47 am | Reply

    The reason Virgo will be delayed – and so quick source triangulation is on hold – seems to be that commissioning uncovered a problem: “Damage delays restart of Italy’s giant gravitational wave detector
    Hunt for cosmic collisions resumes without Virgo detector, limiting research 16 MAY 20235:05 PM BYADRIAN CHO” [Science]”

    From that article:
    “Later this month, physicists will resume their hunt for astrophysical monsters: black holes and neutron stars going bump in the dark and emitting ripples in space called gravitational waves. But one of the three detectors that have spotted such waves—Virgo, near Pisa, Italy—has run into technical problems that will delay its restart, 3 years after all the facilities shut down for maintenance and upgrades. For the next few months, just the two detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO), in Louisiana and Washington state, will take data, making it harder to pinpoint sources on the sky.

    The problem appears to originate not in the upgrades, but in older parts that are creating noise that would drown out many signals, says Fiodor Sorrentino, a physicist with Italy’s National Institute for Nuclear Physics (INFN) and Virgo’s commissioning coordinator. “But we cannot be 100% sure” before opening the detector, he says. Daniel Holz, an astrophysicist at the University of Chicago, says such hiccups are normal, although LIGO and Virgo had dodged them. “We’re owed this kind of bad luck because our excessive good luck had to run out.””

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