February 11, 2020


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First Papers on The Black Hole-Neutron Star Merger Are In. Here’s What We Didn’t See

Very last yr, the LIGO and Virgo gravitational wave detectors pinged with an solely new type of collision: not two neutron stars, not two black holes, but a neutron star and a black gap together. Experts ended up thrilled: this could be the 1st time we’ve at any time witnessed this kind of a binary system.


Now, following poring about the corner of house in which the collision took spot, an worldwide crew of astronomers has viewed the aftermath – or rather, the lack of a single.

Employing some of the world’s most strong astronomical devices, the ElectromagNetic counterparts of GRAvitational wave sources at the Incredibly Huge Telescope (ENGRAVE) collaboration located not even a short flash of light connected with the collision. Their exploration awaits peer review, and has been printed on pre-print server arXiv.

Now, this doesn’t signify that the party, identified as S190814bv, failed to acquire spot. It doesn’t even signify there was certainly no flash of electromagnetic radiation – what is identified as the “electromagnetic counterpart” to a gravitational wave detection.

What it does signify is that astronomers have a tiny far more details – the beginnings of a databases that will help us to understand far more about these elusive mergers in the upcoming. And it may perhaps let scientists to spot some tentative constraints on the aftermath of a black gap devouring a neutron star – if that’s what the party really was.


“We don’t obviously discover a counterpart,” physicist Morgan Fraser of University College Dublin in Ireland explained to ScienceAlert.

“This could signify that either: there was no counterpart (potentially the black gap swallowed the neutron star complete) there was a counterpart but it was much too faint for us to detect [or] there was a counterpart that we missed (potentially a single of the transients that we see in the industry and ruled out was in point what we ended up hunting for).”

It can be nevertheless not solely obvious what the party was – analysis is nevertheless staying executed on the gravitational wave knowledge. But all those knowledge counsel the collision was between an item below a few periods the mass of the Sunshine, and a further about 5 periods the mass of the Sunshine.

Both of those neutron stars and black holes are the ultradense stays of useless stars, but we’ve in no way viewed a black gap scaled-down than 5 photo voltaic masses, or a neutron star bigger than all-around two.5 photo voltaic masses.

So S190814bv – which had an really minimal bogus alarm price – could quite effectively be that elusive neutron star-black gap binary collision. An electromagnetic counterpart as the black gap pulls aside the neutron star could have revealed us some thing we know fairly tiny about – what is actually truly inside a neutron star.


Alas, it wasn’t to eventuate. Even although the S190814bv gravitational wave signal was strong, finding this hypothetical flash of light from so significantly absent – all-around 800 million light-years – was not this kind of a straightforward undertaking.

Not only did the ENGRAVE crew return a null detection, so much too did the Australian Square Kilometre Array Pathfinder, looking the radio spectrum the Development collaboration, looking optical and in close proximity to-infrared and the Observatorio Astronómico Nacional in Mexico, searching for gamma radiation.

“[S190814bv is] really at the higher limit of the distant vary where we can hope to detect emission,” Fraser explained.

And that’s not the only problem – even with far more strong tools that could detect fainter flashes, we’d require to uncover a way to distinguish the electromagnetic counterpart from all the other transients in the similar corner of house.

“It can be not just a matter of detecting the counterpart, it really is how to pull this needle out of a huge haystack of supernovae from exploding stars, flares from the nuclei of galaxies, eruptions on the surface of stars and far more,” Fraser explained to ScienceAlert.

The crew did that as totally as they could – but there’s nevertheless a probability that the party was just much too faint, and nevertheless a probability that a single of the transient gatherings they discarded was truly from the merger.

It can be also feasible that the neutron star wasn’t shredded right until following it was already inside the black hole’s party horizon – avoiding any light from escaping out of the black gap.

And even if S190814bv wasn’t a neutron star and a black gap, there is nevertheless some thing to understand. Astronomers are also avidly looking for what is identified as a “mass-hole” party, where a single or both of those of the colliding bodies is in-between the higher mass limit of neutron stars (two.5 photo voltaic masses) and the reduce limit of black holes (5 photo voltaic masses).

We may perhaps not be able to understand if what sits in this hole is a tiny black gap or a chunky neutron star from the knowledge gathered on S190814bv. But the crew has demonstrated that their collaboration is effective, and they are prepared and waiting to obtain the future spherical of observations, and the future, and the future following that.

“What we have demonstrated listed here is that we can make a look for of a major fraction of the location connected with a gravitational wave at this distance, and that we can set some valuable limitations on any opportunity counterpart,” Fraser reported. 

“Getting the counterparts of gravitational waves is an huge problem, and in this case we failed to see everything. But with what we’ve uncovered, we are even far more geared up for the future a single the Universe presents us!”

The exploration has been submitted to Astronomy & Astrophysics, and is out there on arXiv.