Detection of gravitational waves, a gamma ray burst, and visible light, all from the same source, played a role in what has to be one of the most exciting and noteworthy events in modern day astronomy!
130 million years ago, in a galaxy far away… two closely orbiting neutron stars radiated gravitational-waves out across the cosmos as they spiraled-in ever closer towards each other. Finally coalescing together in a violent event knows as a kilonova, the merger released energy across the electromagnetic spectrum – right up into the gamma-ray range.
Fast-forward to August 17, 2017: a short gamma-ray burst (GRB) was observed by the Fermi Gamma-ray Space Telescope at 12:41:06 UTC; an automatic alert was issued 14 seconds later. About six minutes later, a gravitational wave (GW) candidate was registered by the LIGO-Hanford Gravitational-Wave Observatory – named GW170817, the timing of this GW was consistent with it being 1.74±0.05s before the GRB that Fermi detected.
The LIGO Scientific Collaboration and the Virgo Collaboration released a circular announcing the GW detection at 13:21:42 UTC.
Six teams of astronomers from the Swope Supernova Survey, DLT40, VISTA, Master, DECam, and the Las Cumbres Observatory (LCO) in Chile imaged the source independently; the first to detect optical light from the event was Swope at 23:33 UTC – 10 hours and 52 minutes after the GW detection.
Manual processing of data from the INTEGRAL Gamma-ray Space Telescope also detected the same GRB; the difference in arrival time between Fermi and INTEGRAL helped to improve the sky localization.
All gravitational wave detectors are L shaped, and have a blind spot along the diagonal through the vertex of the L; the Advanced Virgo Gravitational-wave Observatory in Italy was in a blind spot during the time of the observation, and did not initially make a detection – seeing only a weak signal (see pic). However, this information was crucial, as it helped astronomers to localize the source in the sky.
The IceCube South Pole Neutrino Observatory did not detect any neutrinos from the event.
Ultimately, about 70 observatories on the ground and in space observed the event at their representative wavelengths; this event provides the first direct evidence of a link between the merger of neutron stars and short gamma-ray bursts.
The source of the event is located in the galaxy NGC 4993, an elliptical galaxy 130 million light-years distant in the constellation Hydra.
This video shows the waveforms of the detected signals: (Source)
The paper that involves the Gravitational Wave detectors and the telescope observations – the multi-messenger observation has about 3500 authors names associated with it- that’s how big the LIGO/Virgo collaboration is!
Dr. Luca Matone, a part of the LIGO Scientific Collaboration, allowed me to interview him for this article; he had this to say about the event:
“This was an amazing event for many reasons. It was the first time that a gravitational event was discovered with with an optical counter-part. The previous detections dealt with black-hole mergers, no light should be emitted from these events. And no visible counterpart was observed. In the case of neutron star mergers, however, there should be a visible counter-part — and it was observed! Confirming expectations. And it is simply amazing how telescope and GW detectors were able to work together to understand more about this single event. Simply amazing. And refreshing.”
What’s in the near future for gravitational wave science?
“For the near future we are improving the GW detectors to design sensitivity. More GWs detectors will join the search (like Kagra). In the future we will have a space gravitational wave detector, NASA/ESA’s LISA.”
Are any courses are being offered in gravitational wave science?
“Caltech has courses specifically on this. It is relatively a new topic (well, the topic was always around since Einstein but now we have means to directly detect these waves). More courses will appear as we settle in this new way of observing the universe.
The GW detectors can be thought of as microphones — cosmic microphones. There is no sound in space but the detectors pick up a signal that could be sent to speakers to produce a sound (for example here). So now we can see and, if you will, hear the universe. But there is no sound in space. Almost as if we had silent movies before and now we have movies with sound. More information about the universe is given because of the detection of gravitational waves.”
I mentioned to Dr. Matone that I was discussing LIGO with my daughter – when I mentioned that LIGO “detects the bending of the space-time continuum due to the passage of gravitational waves,” she looked at me like I had lobsters crawling out of my ears… but HEY! This stuff was science fiction just a few years ago!
Dr. Matone commented: “The sentiment your daughter has is very common and it is difficult for everyone to digest this.” He went on to explain:
“Albert Einstein worked out the General Theory of Relativity: he stated that we don’t live in a three dimensional world but a four dimensional world where time is the fourth dimension. He worked out the theory not in a three dimensional grid but a four-dimensional one. That four-dimension world is referred to as space-time. If we stick to this formalism we arrive at an understanding of the universe that is confirmed by experiments all the time (even gravitational waves). For this reason then, it must be true that we indeed live in 4-dimensions and not three.
Now, this grid can be stretched and squeezed, and time is not an absolute quantity but a relative one. Mass distorts space-time. This four-dimensional grid can be warped by mass. We have a hard time picturing this.
Let me try explaining it a different way. Let’s imagine that space-time is represented by the surface of a trampoline. If you place a bowling ball in the middle of the trampoline, you distort the surface of the trampoline — just like mass would distort space-time around it (see link). Now, if you throw marbles on the trampoline, the marbles tend to approach the bowling ball because they sense that the surface of the trampoline is warped, not flat anymore.
Same thing happens with space-time. The core of Einstein’s general theory of relativity can be summarized by a simple quote from John Wheeler: “Mass tells space-time how to curve, and space-time tells mass how to move.” This means that as you approach a Black Hole, the Black Hole is able to distort space-time around it to a significant degree, and one of the many effects is that time would not flow normally as you approach this mass. Interstellar the movie that came out a few years ago, played with this notion.
So — if the bowling ball for some reason shakes, then it will generates ripples on the surface of the trampoline that propagate away from the source. These would be the gravitational waves. In space-time, if a massive system undergoes a cataclysmic event, this event would generate GWs that would propagate throughout the universe. The passage of a GW would then change the position of objects relative to each other and that’s what LIGO and Virgo measure.”
At the end of the interview, Dr. Matone mentioned:
“Just recently the Pope had a video conference with the crew of the International Space Station. The US astronaut and mission commander Randy Bresnik was quoted as saying: “What gives me the greatest joy is to look outside every day and see God’s creation – maybe a little bit from his perspective.” I feel the same way. To be aware that out there there are these bizarre objects such as Black Holes with the ability to manipulate the flow of time (among many other effects) and to fully realize that this is real and not science fiction. I find this jaw-dropping. I continue to marvel, I feel very small, I am humbled.”
About Dr. Luca Matone:
Dr. Luca Matone is part of the LIGO Scientific Collaboration – a group of more than 1000 scientists worldwide who have joined together in the search for gravitational waves. On February 11, 2016, the LIGO collaboration, in partnership with its European counterpart Virgo, announced their success in making the first direct gravitational wave observation on September 14, 2015. This observation consisted of a gravitational-wave signal produced by a cataclysmic event involving the merger of a pair of black holes more than a billion light-years away.
Dr Matone first began working on gravitational wave research as a student. He is a native of Rome, Italy, and began his research in Italy with the Virgo collaboration. He earned a master’s degree in physics at the University of Rome ‘Tor Vergata’ and continued with physics studies in France, also with the Virgo collaboration, earning a PhD in physics at the Universitè de Paris XI. This eventually led Dr. Matone to the California Institute of Technology (Caltech) where he joined the LIGO commissioning team.
Dr. Matone currently holds a research position at Columbia University; he has taught at Fordham University, and is teaching at Regis High School in New York City. He is the author of more than 100 scientific publications, and focuses on public outreach and mentoring students in their scientific research.
GW170817 Press Release – Laser Interferometer Gravitational-Wave Observatory (LIGO)
Multi-messenger Observations of a Binary Neutron Star Merger -The Astrophysical Journal Letters
GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral – Physical Review Letters
LIGO Detects Fierce Collision of Neutron Stars for the First Time – The New York Times
LIGO and Virgo make first detection of gravitational waves produced by colliding neutron stars – MIT News
MSU contributes to merging neutron star discovery – MSU College of Natural Science
INTEGRAL sees Blast Travelling with Gravitational Waves – ESA Science
I would also like to thank Dr. Brenda Frye for consulting with me on this article.