Neutron Star Collision Didn’t Create a Black Hole, It Birthed a Hypermassive Neutron Star Baby

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This artist’s conception portrays two neutron stars at the moment of collision [CfA/Dana Berry]

It has only been a couple of years since the first historic detection of gravitational waves, but now physicists are already dissecting a handful of signals that emanated hundreds of millions of light-years away to elucidate how some of the most violent events in our universe work.

Most of the gravitational wave signals detected so far involve the merger of black holes, but one signal, detected on Aug. 17, 2017, was special—it was caused by the smashup of two neutron stars. This merger also generated a powerful gamma-ray burst (GRB) that was detected at nearly the same time, linking GRBs with neutron star mergers and highlighting where heavy elements in our universe are forged. A new era of “multimessenger astronomy” had begun.

Now, the signal (designated GW170817) has been reanalyzed to understand what happened after the merger. Analysis that came before suggested that the collision of the two neutron stars would have tipped the mass balance to create a black hole. According to a new study, published in the journal Monthly Notices of the Royal Astronomical Society: Letters, two physicists suggest a contradictory scenario: GW170817 didn’t create a black hole, it produced a hypermassive neutron star, instead.

“We’re still very much in the pioneering era of gravitational wave astronomy. So it pays to look at data in detail,” said Maurice van Putten of Sejong University in South Korea. “For us this really paid off, and we’ve been able to confirm that two neutron stars merged to form a larger one.”

The “chirp” of GW170817’s colliding neutron stars as seen in the LIGO dataset. New research suggests that after the two neutron stars merged, they formed one hypermassive neutron star, not a black hole [LIGO / M.H.P.M van Putten & M. Della Valle]

The secret behind this finding focuses on the datasets recorded by the US-based Laser Interferometer Gravitational-wave Observatory (LIGO) and Italian Virgo observatory. When gravitational waves are recorded during a black hole or neutron star merger event, their frequency rapidly increases (as the objects orbit one another faster and faster as they get closer and closer) and then abruptly cuts off (when they collide). When turned into an audio file, mergers sound like “chirps.” Apart from sounding like an eerie bird call coming from deep space, physicists have been able to extract surprisingly detailed information from the conditions of the merging objects, such as their mass and rates of spin.

And this is where van Putten’s work comes in.

Working with Massimo della Valle of the Osservatorio Astronomico de Capodimonte in Italy, the duo applied a new analysis technique to these data and detected a 5-second descending “chirp” (as shown by the downward arrow in the graph above). This descending chirp happened immediately after the GRB was detected coming from the same location as the gravitational wave signal’s origin. According to their analysis, the spin-down—from 1 KHz to 49 Hz—was most likely representative of a very massive neutron star and not a black hole.

If corroborated, this discovery could have profound implications for astrophysics. How hypermassive neutron stars (like the one that was created by GW170817) can exist without collapsing into a black hole will likely keep theorists busy for some time and physicists will be hopeful for another gravitational wave event like GW170817.

Nancy Writes for Wired: “Giants of Earth and Space”

Gran Telescopio Canarias located on La Palma, Spain - one of the giant observatories looking at the stars (GTC)
Gran Telescopio Canarias located on La Palma, Spain - one of the giant observatories looking at the stars (GTC)

My Universe Today colleague and superb science writer Nancy Atkinson has written her first article for! This is obviously a huge step as her writing has instantly accessed potentially millions of readers. So, CONGRATULATIONS NANCY!

Nancy was approached by Wired to put together an article about some of the biggest and boldest observatories on Earth. Her writing is accompanied by some stunning photography of these giant structures that include the Hobby-Eberly Telescope (HET) on Mount Fowlkes, Texas (sporting 91 separate one-meter hexagonal mirrors); the W. M. Keck Observatory on Hawaii’s Mauna Kea volcano (with two 10-meter mirrors composed of 36 hexagonal segments); and my personal favourite, the Very Large Telescope Interferometer on the Andes mountaintop of Cerro Paranal, Chile (four 8.2-meter diameter telescopes working in tandem). There is a huge amount of information in Nancy’s excellent article, making it more than worthy of being included in this hugely popular science & technology magazine website.

Be sure to check out “Giants of Earth and Space,” by Nancy Atkinson over at