Astronomers detect neutron star merger in both light and gravitational waves


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Big news! Astronomers from dozens of telescopes on the ground and in space have observed for the first time the light burst caused by the merger of two neutron stars because earlier observations of the merger’s gravitational wave and gamma ray burst told them where to look in the sky.

On 17 August 2017 the NSF’s Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States, working with the Virgo Interferometer in Italy, detected gravitational waves passing the Earth. This event, the fifth ever detected, was named GW170817. About two seconds later, two space observatories, NASA’s Fermi Gamma-ray Space Telescope and ESA’s INTErnational Gamma Ray Astrophysics Laboratory (INTEGRAL), detected a short gamma-ray burst from the same area of the sky.

The LIGO–Virgo observatory network positioned the source within a large region of the southern sky, the size of several hundred full Moons and containing millions of stars. As night fell in Chile many telescopes peered at this patch of sky, searching for new sources. These included ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA) and VLT Survey Telescope (VST) at the Paranal Observatory, the Italian Rapid Eye Mount (REM) telescope at ESO’s La Silla Observatory, the LCO 0.4-meter telescope at Las Cumbres Observatory, and the American DECam at Cerro Tololo Inter-American Observatory. The Swope 1-metre telescope was the first to announce a new point of light. It appeared very close to NGC 4993, a lenticular galaxy in the constellation of Hydra, and VISTA observations pinpointed this source at infrared wavelengths almost at the same time. As night marched west across the globe, the Hawaiian island telescopes Pan-STARRS and Subaru also picked it up and watched it evolve rapidly.

Press releases today from numerous other observatories are too numerous to link here, and most essentially say the same thing. The key facts so far gleaned however are intriguing:

Distance estimates from both the gravitational wave data and other observations agree that GW170817 was at the same distance as NGC 4993, about 130 million light-years from Earth. This makes the source both the closest gravitational wave event detected so far and also one of the closest gamma-ray burst sources ever seen

This event also highlights the advantages of observing the universe in as many ways as possible. Some phenomenon get to us sooner, and thus provide us clues on where to look with other tools. Without the gravitational wave and gamma ray burst detectors, on Earth and in space, the other optical and infrared telescopes would have almost certainly not have recorded this merger.

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16 comments

  • wayne

    Very interesting!

    on a more fanciful (art bell-esque) note: What if it’s actually a beacon?
    Star Trek Discovery
    “T’kuvma’s Speech”
    https://youtu.be/-XTce38ef98
    1:34

  • wodun

    First they detected the gravitational wave, then the gamma ray burst, but they didn’t see the light until later. Its too bad there wasn’t a scope looking in real time.

  • Joe

    Fascinating science, that the scientists were able to detect where to look is great, this is why the telescopes are so important, ligo is a pretty cool instrument that helps add to the knowledge of interstellar space.

  • Wayne:

    Anyone who can send a beacon 130 MLY is not someone I want to notice me.

  • Bill

    Wait, “Some phenomenon get to us sooner…”. This wording seems to hint that the speed of light can be exceeded by a gravitational wave?

  • Bill: I think the explanation is that the visible light fireball simply takes longer to get bright enough for us to see. The gravitational wave and gamma ray burst are immediately “visible.”

  • wayne

    Bill & Mr. Z;
    (I’m just a total amateur and forgive my verbiage.)

    As Bill touches upon- the initial merger touches off a high energy cascade, as it were, so we get the gravity waves, high energy x-rays, gamma-rays, etc., first. (All the high energy stuff, which is “invisible.”) Everything is travelling at the speed of light but nothing is yet decayed sufficiently, to morph into the optical spectrum. Frequency & Energy are also equivalent terms, when you hold the speed of light constant.
    As Mr. Z touches upon– the photons in the optical spectrum only become visible as higher energy stuff is radiated outward and cools down to the visible spectrum. As well, the photons can bounce all over being absorbed/emitted many times before they head toward us.

    Tangentially– I believe for that one Hubble deep-field picture, they were only receiving 1 photon per second, over the entire exposure.

    This is all fascinating stuff and I’ll try to follow it going forward.

  • LocalFluff

    Gravity waves lose power linearly as they propagate. That is, in proportion to the radius of the propagation, not to the sphere it describes all around. Any sensible description of that in a few sentences, would be nice. Anyone? Is it because of the entangled time waves? Or simply because space does as it pleases with itself, not caring about whatever matterenergy there happens to be in its emptiness.

  • wayne

    LocalFluff-
    correct me if I’m mistaken; spherically radiated, drops off as the cube of the distance. (?)

  • LocalFluff

    Radiation (of “normal matter” such as light) falls with the square (root) of the distance. The photons don’t do anything until they hit something. They expand like a surface. Timespace itself seems to disagree, though, as I’ve heard Nobel laureates say publicly popularly anyway. I don’t get it. And I think that even if I read and understood a bookshelf of math, I would still sit here and not understand it, although I then might calculate it.

  • wayne

    lots-o-good images & graphs….

    Colliding Neutron Stars, Gravity Waves & Gamma Ray Bursts
    Scott Manley 10-16-17
    https://youtu.be/j6-rd8e9oLw
    7:27

  • Edward

    wayne wrote/asked: “correct me if I’m mistaken; spherically radiated, drops off as the cube of the distance. (?)

    It decreases with the inverse of the square of the distance:

    Force = (surface force)/(distance^2)

    The same is true for light:

    Brightness = (surface brightness)/(distance^2)

    This is why solar arrays at Mars get only about half the power for the same area of array.

    In the 1980s, I worked on a gamma ray detector that was used as a telescope to see the gamma rays from a supernova that was visible in the southern hemisphere. We packed it up and sent it to Australia to fly on a balloon. The gamma rays were not expected for a while after the nova was first observed, and the detector saw some.

    Other phenomena that would come later are any particles that have been ejected close to, but not at, the speed of light. Of course, this far away we may not be able to detect any, because their distribution also is an inverse square relation.

  • wayne

    Edward-
    [are you getting wildfire effects, where you are?]

    Thanks for the clarification. Too lazy to look it up & too old to remember for certain today.
    Hey– very cool with the gamma-ray detector!

  • Edward

    wayne asked: “are you getting wildfire effects, where you are?

    Yes. I am not near any evacuation zones, but the upper air gets smokey most days. Usually we don’t “see” the air, but last week and this week we can, but not as bad as how Los Angeles used to be. Early on I smelled the smoke, too, but maybe I am used to it, now.

    very cool with the gamma-ray detector!

    Thanks. I am starting to realize that I have worked on some interesting stuff. At the time it seemed more challenging than interesting.

  • wayne

    Edward-
    Thanks for the update. Stay safe.
    We are pretty dry in Michigan this year, and have been at “moderate-high” risk for forest-fire all Summer. Fortunately, we rarely get the wildfire type of disaster.
    (Totally tangential- we have some Pine tree variety that only propagates if the cones are subjected to heat from fire. They try to manage that carefully.)

    -Do you mean to say… the air-quality in the LA Basin, is greatly improved since 1970?

    You have great Adventure Story’s! Never forget– for people who can’t do, what you have already done, it’s all magical stuff!

    This man for example: what an amazing life he had!
    https://behindtheblack.com/behind-the-black/points-of-information/the-man-who-suited-up-astronauts-during-the-1960s-passes-away-at-101/

    -You ever play around with any Heathkit electronics?

  • Edward

    wayne,
    Much of California has two seasons: the rainy season and the dry season. Some parts, the deserts (e.g. Mojave and the LA basin) have only one season: the dry season.

    I have relatives in the LA area, so I get there every so often. Not only do they have blue skies but you can even see the mountains from the beaches. Who knew?

    Never forget– for people who can’t do, what you have already done, it’s all magical stuff!

    All that magical stuff is one of the reasons that I identify as a major deity. Also, I often performed miracles beyond the usual magic, such as getting things done in time for a deadline. This usually meant getting everything prepared in advance and nothing going seriously wrong. Sort of like SpaceX is doing getting pad 39A ready for Falcon Heavy; some miracle worker there has pared down the conversion time from 60 days after the last Falcon 9 launch to only 45, by doing as much work in advance as possible. That is good leadership and management.
    https://behindtheblack.com/behind-the-black/points-of-information/mysterious-spacex-launch-scheduled-for-november-10/#comment-1017245

    My father was the electrical engineer, so I got to see several Heathkit electronics projects. Unfortunately, I am terrible at soldering.

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