# Black Hole and Neutron Star Collisions Detected Twice in Ten Days

Two instances of black hole-neutron star collision events have been detected using the Advanced LIGO and Virgo gravitational wave detectors, details of which have been published today in Astrophysical Journal Letters.

Previous gravitational wave detections have spotted black holes colliding, and neutron stars merging, this is the first time that scientists have detected a collision from one of each.

Dr Vivien Raymond, from Cardiff University’s Gravity Exploration Institute, said: “After the detections of black holes merging together, and neutron stars merging together, we finally have the final piece of the puzzle: black holes swallowing neutron stars whole. This observation really completes our picture of the densest objects in the universe and their diet.”

Gravitational waves are produced when celestial objects collide and the ensuing energy creates ripples in the fabric of space-time which travel all the way to the detectors we have here on Earth.

On 5 January 2020, the Advanced LIGO (ALIGO) detector in Louisiana in the US and the Advanced Virgo detector in Italy observed gravitational waves from this entirely new type of astronomical system.

The detectors picked up the final throes of the death spiral between a neutron star and a black hole as they circled ever closer and merged together.

On 15 January, a second signal was picked up by Virgo and both ALIGO detectors – in Louisiana and Washington state – again coming from the final orbits and smashing together of another neutron star and black hole pair.

Researchers from Cardiff University, who form part of the LIGO Scientific Collaboration, played a crucial role in the data analysis of both events, unpicking the gravitational wave signals and painting a picture of how the extreme collisions played out.

This involved generating millions of possible gravitational waves and matching them to the observed data to determine the properties of the objects that produced the signals in the first place, such as their masses and their location in the sky.

From the data they were able to infer that the first signal, dubbed GW200105, was caused by a 9-solar mass black hole colliding with a 1.9-solar mass neutron star.

Analysis of the second event, GW200115, which was detected just 10 days later, showed that it came from the merger of a 6-solar mass black hole with a 1.5-solar mass neutron star, and that it took place at a slightly larger distance of around 1 billion light-years from Earth.

During its third observing run, the LIGO–Virgo GW detector network observed GW200105 and GW200115, two GW events consistent with NSBH coalescences. Event GW200105 is effectively a single-detector event observed in LIGO Livingston with an S/N of 13.9. It clearly stands apart from all recorded noise transients, but its statistical confidence is difficult to establish.

Astrophysical Journal Letters – Observation of Gravitational Waves from Two Neutron Star–Black Hole Coalescences

Abstract
We report the observation of gravitational waves from two compact binary coalescences in LIGO’s and Virgo’s third observing run with properties consistent with neutron star–black hole (NSBH) binaries. The two events are named GW200105_162426 and GW200115_042309, abbreviated as GW200105 and GW200115; the first was observed by LIGO Livingston and Virgo and the second by all three LIGO–Virgo detectors. The source of GW200105 has component masses $8.{9}_{-1.5}^{+1.2}$ and $1.{9}_{-0.2}^{+0.3}\,{M}_{\odot }$, whereas the source of GW200115 has component masses $5.{7}_{-2.1}^{+1.8}$ and $1.{5}_{-0.3}^{+0.7}\,{M}_{\odot }$ (all measurements quoted at the 90% credible level). The probability that the secondary’s mass is below the maximal mass of a neutron star is 89%–96% and 87%–98%, respectively, for GW200105 and GW200115, with the ranges arising from different astrophysical assumptions. The source luminosity distances are ${280}_{-110}^{+110}$ and ${300}_{-100}^{+150}\,\mathrm{Mpc}$, respectively. The magnitude of the primary spin of GW200105 is less than 0.23 at the 90% credible level, and its orientation is unconstrained. For GW200115, the primary spin has a negative spin projection onto the orbital angular momentum at 88% probability. We are unable to constrain the spin or tidal deformation of the secondary component for either event. We infer an NSBH merger rate density of ${45}_{-33}^{+75}\,{\mathrm{Gpc}}^{-3}\,{\mathrm{yr}}^{-1}$ when assuming that GW200105 and GW200115 are representative of the NSBH population or ${130}_{-69}^{+112}\,{\mathrm{Gpc}}^{-3}\,{\mathrm{yr}}^{-1}$ under the assumption of a broader distribution of component masses.

SOURCES- Cardiff, Astrophysical Journal Letters
Written By Brian Wang, Nextbigfuture.com

### 17 thoughts on “Black Hole and Neutron Star Collisions Detected Twice in Ten Days”

1. hard to envision an actual 'campus' as a meaningful way to research, house, and teach(?) … though McMurdo station, as an example, appears to contain most College campus amenities in recognizable, though primitive, layouts…

2. Easier to put the U of E on the Moon, maybe a pole to facilitate communication/ observation with dark side observatories. Frosh week would be a blast.

3. More luck with the Aerospace Programs at MIT, Stanford, and Texas A&M for getting your projects designed and built.

4. Well.
France appears to be getting us there.
https://www.isunet.edu
Though not sure on validity of programs for the purely techno-logistical parts of 'getting us up there'…

5. Yes. yes. Could feature audience-attracting dramatic episodes based on Star Trek Lower Decks or Big-Bang-Theory-in-Space or Real Genius (loosely based on Cal Tech, as I understand it)

6. Mission planning and approval -not to mention financing/ budgeting- is excessively slow.
Large-part-of-a-decade+ concept to launch timelines are backlogged, increasing tech obsolesence, and bottlenecking the gathering of research data. Doesn't appear to be effective entity to advocate for increased project roll-out quantities outside of NASA and ESA — Musk needs to offer an Education-discount on his launches and part of grand learning objectives — must be some programs that align with his values – NEO assessments, Exoplanet info gathering, inner solar system manned-launch pre-logistical assessment — c'mon I want to see The University of Earth – CisLunar campus (aligned with U of A, methinks) taking applications by the end of the decade.

7. Everything you say…

8. The tidal gradients use up kinetic energy until the bodies are tidally locked to each other, not so much after that. And two black holes will have a joint accretion disc which will also tend to eat away at it. But gravitational radiation eats angular momentum, at an increasing rate as they get close together, and dominates towards the end.

9. Binary systems almost certainly. Conservation of angular momentum dictates that most star will form in pairs, and most of them stay in pairs.

10. Yep, even we happened. Although who can say yet as to how many universes had to appear for us to be in one of them?

11. From memory, I think the 1a type supernova is *always* the same because the double star as it forms slings off excess mass to *always* form a system of a same maximum mass. When they eventually run together as in your last para, the amount of energy produced is the same, so we can tell how far away they are from that alone.

edit: "two compact binary coalescences" means they are binary now, but black holes will suck anything down eventually, so they were probably not always close, as you say. When our big black hole in the galaxy center grabs something, it is not really what we would call binary. This post 1970s astronomy stuff is over my head.

12. Sure, but for these purposes, you'll want to deploy them out in the Kuiper belt. Things are too gravitationally active down here near the Sun, the pieces of your 'bench' would be continuously jostled.

I really think the next major space telescope should consist of free flying segments that use ultra-precision station keeping to form a huge mirror. That way it could start out with a small area, and be continuously upgraded by adding mirror segments, and swapping instruments in and out. A good candidate to put at one of the Earth-Sun Lagrange points.

I should add that, for really large structures, the pieces are for all practical purposes 'free flying' anyway, on a time scale shorter than the transit time for sound waves through the structure. Any frame is just something to push against when station keeping.

13. You've got that backwards. With all that space, almost anything can happen. And when you can detect this sort of thing from an enormous distance, you're going to detect those almost anythings fairly frequently.

Just think about how much space is within a one billion lightyear radius of Earth. An event can be seriously rare, and still happen frequently within such a volume.

14. Wild speculation by someone who hasn't looked through a telescope since 2000.

We are looking at binary systems maybe? Where the two stars start off in orbit around eachother, and they both end up going supernova and end up black holes/neutron stars.
I guess they need to be a distant orbit, or the supernova from one would destroy the other.
And then the orbits decay over time until "Gulp" the big one swallows the little one.

And I wouldn't be too suprised if there's probably some gravitational effect where the intense tidal gradients result in chewing up kinetic energy and so causes the orbits to decay faster or something.

15. With all that space, why are things colliding so often?