You wait ages for a neutron star and black hole to collide, then two pairs come along at once
- Reference: 1625038144
- News link: https://www.theregister.co.uk/2021/06/30/gravitational_waves_neutron/
- Source link:
This is the first time scientists have been able to confirm the detection of the merger of a black hole and neutron star, too.
Although several gravitational wave events have been detected since America's Laser Interferometer Gravitational-Wave Observatory (LIGO) [1]made the first grav wave discovery in 2015, they have always involved collisions between objects of the same type, such as two black holes smashing into each other, or two neutron stars.
[2]
These latest discoveries, however, are the result of odd pairings: a black hole with nine times the mass of our Sun crashing into a 1.9-solar-mass neutron star, and a slightly smaller black hole measuring six solar masses impacting with a 1.5-solar-mass neutron star.
[3]
[4]
The cosmic prangs were announced on Tuesday by multiple teams working with the LIGO and Virgo detectors in Louisiana, USA, and Santo Stefano a Macerata, Italy, respectively.
As the LIGO and Virgo detectors become more and more finely tuned, the detection of these merger events are expected to crop up like buses: none for ages, and then many along at once. These latest collisions were detected ten days apart, on January 5, 2020, at 1624 UTC, and January 15 at 0423 UTC.
[5]
The first event, the more energetic of the two and involving the more massive bodies, was code-named GW200105, and took place about 900 million light-years from Earth. The second event, referred to as GW200115, was further away at about one billion light-years away.
We had long expected to see a merger between a black hole and neutron star, but there are many uncertainties that made it difficult to predict how many of this pairing there are in our universe
“We had long expected to see a merger between a black hole and neutron star, but there are many uncertainties that made it difficult to predict how many of this pairing there are in our universe,” Ryan Magee, co-author of a paper [6]published in The Astrophysical Journal and a postdoctoral scholar at the California Institute of Technology, told The Register .
“From these two detections, we can infer that, in a fixed volume of space, there are a few more neutron star-black hole mergers per year than black hole-black hole [ones], but not as many as there are neutron star-neutron star mergers.”
Previous attempts to confirm a black hole-neutron star collision were unfruitful. One signal detected in April 2019 may have been skewed by noise, and another from August of the same year is [7]still being debated .
Both black holes likely swallowed their neutron stars whole, leaving no trace of light for the team to follow. “These were not events where the black holes munched on the neutron stars like the cookie monster and flung bits and pieces about,” Patrick Brady, a professor at University of Wisconsin-Milwaukee and spokesperson of the LIGO Scientific Collaboration, [8]said in a statement. “That 'flinging about' is what would produce light, and we don't think that happened in these cases.”
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A merger between a galactic void and the densest type of star probably occurs within a billion light years of Earth about once a month, the team reckon.
"The detector groups at LIGO, Virgo, and [10]KAGRA are improving their detectors in preparation for the next observing run scheduled to begin in summer 2022," Prof Brady added.
"With the improved sensitivity, we hope to detect merger waves up to once per day and to better measure the properties of black holes and super-dense matter that makes up neutron stars." ®
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[1] https://www.theregister.com/2016/02/11/gravitational_wave_detected/
[2] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_offbeat/science&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=2&c=2YNxAwvrmrhSxafmXzoHIrQAAAIY&t=ct%3Dns%26unitnum%3D2%26raptor%3Dcondor%26pos%3Dtop%26test%3D0
[3] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_offbeat/science&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=4&c=44YNxAwvrmrhSxafmXzoHIrQAAAIY&t=ct%3Dns%26unitnum%3D4%26raptor%3Dfalcon%26pos%3Dmid%26test%3D0
[4] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_offbeat/science&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=3&c=33YNxAwvrmrhSxafmXzoHIrQAAAIY&t=ct%3Dns%26unitnum%3D3%26raptor%3Deagle%26pos%3Dmid%26test%3D0
[5] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_offbeat/science&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=4&c=44YNxAwvrmrhSxafmXzoHIrQAAAIY&t=ct%3Dns%26unitnum%3D4%26raptor%3Dfalcon%26pos%3Dmid%26test%3D0
[6] https://iopscience.iop.org/article/10.3847/2041-8213/ac082e
[7] https://www.theregister.com/2020/06/24/grav_wave_boffins/
[8] https://www.ligo.caltech.edu/news/ligo20210629
[9] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_offbeat/science&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=3&c=33YNxAwvrmrhSxafmXzoHIrQAAAIY&t=ct%3Dns%26unitnum%3D3%26raptor%3Deagle%26pos%3Dmid%26test%3D0
[10] https://gwcenter.icrr.u-tokyo.ac.jp/en/
[11] https://whitepapers.theregister.com/
Re: Lies, damned lies, and statistics...
As Einstein observed, the whole concept of time is relative to the observer. The "once a month" is relative to us observing the events on Earth.
Re: Lies, damned lies, and statistics...
As long as we see it once a month there's no reason to think the recent past (1Byo is relatively recent) was substantially different from the present. It should still be cranking on at about that rate even if we're only still seeing the old ones.
If you went back 13By it would be a different story, but not a 'mere' 1By.
Re: Lies, damned lies, and statistics...
I think you can claim thar, with only fairly mild assumptions.
First of all if the cosmological principle is true then isotropy and homogeneity will mean that any observer at the current cosmological time will observe about one NS-BH collision within a billion light years a month. It's not just us. So this rate should be approximately constant everywhere.
However those collisions will happen, generally, at earlier cosmological times. But not very much earlier. So you'd then need to model how the rate of such collisions goes with cosmological time to get an estimate of the number happening at the current cosmological time. I don't know the answer to that: I bet people at LIGO/VIRGO/KAGRA have good estimates because they needed to know how sensitive to make their machines so they needed to do modelling.
However with some handwaving I can convince myself that it likely won't be declining in the recent past and might even be increasing. Handwaving follows. (Almost) all of the objects that will eventually collide are in galaxies which are gravitationally bound and hence not affected by any expansion, so there's no effect from the expansion of the universe. The early stages of inspirals take a very long time and I would expect that the number of neutron stars and stellar BHs might go up over time as massive stars age and die, so it might even be that the rate of collisions rises over time in the recent past.
But the last paragraph is a very handwavy argument.
What about the buses?
> ..merger events are expected to crop up like buses: none for ages, and then many along at once.
There is no explanation for this part of the prediction, what am i missing?
Don't forget, people
Whatever the event, the black hole always wins.
Lies, damned lies, and statistics...
occurs within a billion light years of Earth about once a month
Given that the signal will take anything up to a billion years to reach us, they can't really claim the event itself 'occurs once a month', though.