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Kilonovas and multi-messenger astrophysics

So many media headlines today regarding the observation of both light (EM spectrum, not just visible/optical light) and gravitational waves from colliding neutron stars. Lots of visualizations. Big science in action.

Here’s a sampling of headlines:

  • Gravitational waves from kilonova collision of neutron stars discovered – The Washington Post
  • Gravitational waves: So many new toys to unwrap – BBC News
  • How LIGO-Virgo scientists tracked down a kilonova, 2017’s biggest discovery – Quartz
  • First Glimpse of Colliding Neutron Stars Yields Stunning Pics –
  • 2 Neutron Stars Collided, So Are They a Black Hole Now? –
  • Scientists witnessed the most spectacular event in the universe, and now we know where gold comes from – Gears Of Biz
  • A cosmic first! Gravitational waves and telescopes reveal the clash and flash of neutron stars – Gears Of Biz
  • Vast amounts of gold, platinum and uranium forged in titanic collision between two dead stars – Coventry Telegraph
  • Neutron stars collide, solve major astronomical mysteries – Ars Technica UK
  • What cosmic crash confirmed: Einstein was as good as gold – The Recorder
  • Neutron Stars Collide, and Astrophysics Feels the Ripple – WIRED
  • Gravitational Wave Astronomers Hit Mother Lode – Scientific American

Washington Post’s article (containing many ads) provides a good summary of the discovery and includes video (from Caltech’s YouTube channel), animation, and photos.

The distant collision created a “kilonova,” an astronomical marvel that scientists have never seen before. It was the first cosmic event in history to be witnessed via both traditional telescopes, which can observe electromagnetic radiation like gamma rays, and gravitational wave detectors, which sense the wrinkles in space-time produced by distant cataclysms. The detection, which involved thousands of researchers working at more than 70 laboratories and telescopes on every continent, heralds a new era in space research known as “multimessenger astrophysics.”

The collaboration’s capstone paper in Astrophysical Journal Letters lists roughly 3,500 authors, approaching the record set in 2015 by 5,154 Large Hadron Collider physicists who estimated the mass of the Higgs boson. If gravitational wave research had already weakened the stereotype of a lone astronomer genius, the dawn of multi-messenger astrophysics dealt it a fatal blow.

A more technical (and ad free) summary may be viewed on NASA Goddard Space Flight Center’s Goddard Media Studios page or their YouTube channel’s animation.

The best video overview of the discovery is on Caltech’s YouTube channel: “Ripples of Gravity, Flashes of Light” (published on October 16, 2017).

On Aug. 17, 2017, the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo detected, for the first time, gravitational waves from the collision of two neutron stars. The event was not only “heard” in gravitational waves but also seen in light by dozens of telescopes on the ground and in space. Learn more about what this rare astronomy event taught us in a new video from LIGO and Virgo.

What’s multi-messenger astrophysics/astronomy?


Multi-messenger astronomy is astronomy based on the coordinated observation and interpretation of disparate “messenger” signals. Electromagnetic radiation, gravitational waves, neutrinos, and cosmic rays are created by different astrophysical processes, and thus reveal different information about their sources.

The main sources are expected to be compact binary pairs (black holes and neutron stars), supernovae, irregular neutron stars, gamma-ray bursts, active galactic nuclei, and relativistic jets.

Detection from one messenger and non-detection from a different messenger can also be informative.

arXiv: “The Dawn of Multi-Messenger Astronomy” (submitted on 30 Jun 2016).1

The recent discoveries of high-energy astrophysical neutrinos and gravitational waves have opened new windows of exploration to the Universe. Combining neutrino observations with measurements of electromagnetic radiation and cosmic rays promises to unveil the sources responsible for the neutrino emission and to help solve long-standing problems in astrophysics such as the origin of cosmic rays. Neutrino observations may also help localize gravitational-wave sources, and enable the study of their astrophysical progenitors. In this work we review the current status and future plans for multi-messenger searches of neutrino sources.

The Max Planck Institute for Gravitational Physics (Albert Einstein Institute):

In view of future gravitational wave detections, a new and exciting field of astrophysics is opening, namely multi-messenger astronomy incorporating gravitational radiation. This will deepen and challenge our understanding of the universe. The numerical modelling of astrophysical sources plays a central role in studying candidates for multi-messenger astronomy. We use the Einstein theory of General Relativity coupled with the Maxwell equations in order to compute the gravitational and electromagnetic signals. We investigate full general relativistic modeling of astrophysical sources, ranging from black holes in magnetized environments to magnetized neutron stars, with the purpose of extracting information about the physical system and possible correlations between the gravitational wave and electromagnetic signature.

[1] About arXiv: Started in August 1991, … is a highly-automated electronic archive and distribution server for research articles. Covered areas include physics, mathematics, computer science, nonlinear sciences, quantitative biology, quantitative finance, statistics, electrical engineering and systems science, and economics. arXiv is maintained and operated by the Cornell University Library with guidance from the arXiv Scientific Advisory Board and the arXiv Member Advisory Board, and with the help of numerous subject moderators.


5 thoughts on “Kilonovas and multi-messenger astrophysics

  1. The Caltech Alumni Association sent out an email on October 13, 2017: On Monday, new details will be revealed about the latest advance in gravitational-wave astronomy. Live stream the press conference on Monday, October 16 at 7:00am PDT.

    Monday, October 16, at 7:00 am PDT representatives from the National Science Foundation, LIGO, and nearly 70 other observatories will gather at the National Press Club in Washington to reveal new details about the latest advance in gravitational-wave astronomy.

    On behalf of the Division of Physics, Mathematics and Astronomy I would like to invite you to watch a live stream of the press conference at from 7:00am-8:00am PDT. In addition, there will be a discussion with Caltech faculty about the meaning and impact of these new details and discoveries. That discussion will be streamed live at 9:00am PDT at

  2. Caltech News posted these two fine articles on October 16, 2017. Important highlights are the use of computer models and global collaboration.

    1. Caltech-Led Teams Strike Cosmic Gold

    With the August 17 event, dubbed GW170817, this alert was somewhat delayed when, due to a glitch, the gravitational-wave signal first noted by the Hanford detector was not immediately evident in Livingston data, but the Hanford signal triggered a deeper analysis of the data that quickly located the signature in the second detector. “Fermi’s observation of a gamma-ray burst at nearly the same time added to the excitement and urgency of the moment,” Weinstein says. At around 7 a.m. PDT, a little more than an hour after the gravitational wave arrived at the LIGO observatories, astronomers were notified about the event.

    The LIGO gravitational-wave data—combined with information obtained by the Virgo detector in Europe—and Fermi’s observations indicated that the source of GW170817 was within a fairly small patch of sky in the Southern Hemisphere. David Cook, a Caltech postdoctoral scholar in astrophysics, quickly compiled a prioritized list of around 50 possible galaxies that could potentially be the home of the neutron star merger, and then the multiwavelength searches began.

    A week after it was first detected, GW170817 was arguably the best-studied cosmic transient event in history.

    2. LIGO and Virgo Make First Detection of Gravitational Waves Produced by Colliding Neutron Stars

    The discovery was made using the U.S.-based Laser Interferometer Gravitational-wave Observatory (LIGO), funded by the National Science Foundation (NSF); the Europe-based Virgo detector; and some 70 ground- and space-based observatories.

    While binary black holes produce “chirps” lasting a fraction of a second in the LIGO detector’s sensitive band, the August 17 chirp lasted approximately 100 seconds and was seen through the entire frequency range of LIGO—about the same range as common musical instruments. Scientists could identify the chirp source as objects that were much less massive than the black holes seen to date.

    But while one mystery appears to be solved, new mysteries have emerged. The observed short gamma-ray burst was one of the closest to Earth seen so far, yet it was surprisingly weak for its distance. Scientists are beginning to propose models for why this might be, McEnery says, adding that new insights are likely to arise for years to come.

    “This detection opens the window of a long-awaited ‘multi-messenger’ astronomy,” says Caltech’s David H. Reitze, executive director of the LIGO Laboratory. “It’s the first time that we’ve observed a cataclysmic astrophysical event in both gravitational waves and electromagnetic waves—our cosmic messengers. Gravitational-wave astronomy offers new opportunities to understand the properties of neutron stars in ways that just can’t be achieved with electromagnetic astronomy alone.”

  3. An astronomical detective story, this article talks about how scientists revisited old data based on insights from LIGO‘s 2017 observation of two neutron stars merging to identify a 2016 kilonova: “When Neutron Stars Collide: Scientists Spot Kilonova Explosion from Epic 2016 Crash” by Elizabeth Howell (August 31, 2019).

    Scientists recently spotted a gold-and-platinum factory in space, the remains of a massive collision of stellar corpses.

    The precious elements were formed in a “kilonova,” or an epic explosion that likely happened when two very dense stars (called neutron stars) slammed into each other. (A kilonova is an even stronger type of explosion than the typical supernova that happens when large stars blow up.)

  4. Forbes > “This Is Why ‘Multi-Messenger Astronomy’ Is The Future Of Astrophysics” by Ethan Siegel (November 15, 2019)

    Today, we take advantage of all the different forms of light [the messenger of electromagnetic quanta] that there are to study the objects present in the Universe.

    Gamma-rays and X-rays reveal high-energy objects like pulsars, black holes, and transient “burst” events,

    ultraviolet, visible, and near-infrared light reveal stars and star-forming material,

    mid-infrared and far-infrared light shows the presence of cooler gas and dust,

    while microwave and radio light reveals jets of particles, diffuse background emissions, and details in individual protoplanetary disks.

    Whenever we look at an object in a different wavelength of light, we have the potential to reveal an entirely new class of information about it.

    Numerous classes of objects don’t merely emit light, but also [messenger] particles. From all over the sky, including from the Sun, we detect a wide variety of cosmic ray particles, including:

    positrons (the antimatter counterpart of electrons),
    neutrinos and anti-neutrinos,
    and even heavier, complex atomic nuclei, from helium all the way up to iron.

    But the 2010s brought us something even more remarkable: a third type of fundamental messenger. On September 14, 2015, the first new signal arrived: in the form of gravitational waves.

    With multi-messenger astronomy still in its infancy, we can expect a deluge of new events and new discoveries as this science progresses throughout the 21st century.

  5. • Universe Today > “Some Quasars Shine With the Light of Over a Trillion Stars” by Evan Gough (Oct 16, 2019) – Quasars are some of the brightest objects in the Universe. The brightest ones are so luminous they outshine a trillion stars. But why? And what does their brightness tell us about the galaxies that host them?

    There are sub-classes of AGNs [active galactic nuclei], and a new study focused on one of those sub-classes called quasars. A quasar is the most powerful type of AGN, and they can shine with the light of a trillion Suns. But some of these quasars are hidden behind their own torus, which blocks our line of sight. In studies of quasars, these ones are ignored or omitted, because they’re difficult to see.

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