Archive for gravitational waves

Bernard Schutz FRS!

Posted in Cardiff, The Universe and Stuff with tags , , , , on May 6, 2021 by telescoper

I was idly wondering earlier this week when the annual list of new Fellows elected to the Royal Society would be published, as it is normally around this time of year. Today it finally emerged and can be found here.

I am particularly delighted to see that my erstwhile Cardiff colleague Bernard Schutz (with whom I worked in the Data Innovation Research Institute and the School of Physics & Astronomy) is now an FRS! In fact I have known Bernard for quite a long time – he chaired the Panel that awarded me an SERC Advanced Fellowship in the days before STFC, and even before PPARC, way back in 1993. It just goes to show that even the most eminent scientists do occasionally make mistakes…

Anyway, hearty congratulations to Bernard, whose elevation to the Royal Society follows the award, a couple of years ago, of the Eddington Medal of the Royal Astronomical Society about which I blogged here. The announcement from the Royal Society is rather brief:

Bernard Schutz is honoured for his work driving the field of gravitational wave searches, leading to their direct detection in 2015.

I thought I’d add a bit more detail by repeating what was included in the citation for Bernard’s Eddington Medal which focuses on his invention of a method of measuring the Hubble constant using coalescing binary neutron stars. The idea was first published in September 1986 in a Letter to Nature. Here is the first paragraph:

I report here how gravitational wave observations can be used to determine the Hubble constant, H 0. The nearly monochromatic gravitational waves emitted by the decaying orbit of an ultra–compact, two–neutron–star binary system just before the stars coalesce are very likely to be detected by the kilometre–sized interferometric gravitational wave antennas now being designed1–4. The signal is easily identified and contains enough information to determine the absolute distance to the binary, independently of any assumptions about the masses of the stars. Ten events out to 100 Mpc may suffice to measure the Hubble constant to 3% accuracy.

In this paper, Bernard points out that a binary coalescence — such as the merger of two neutron stars — is a self calibrating `standard candle’, which means that it is possible to infer directly the distance without using the cosmic distance ladder. The key insight is that the rate at which the binary’s frequency changes is directly related to the amplitude of the gravitational waves it produces, i.e. how `loud’ the GW signal is. Just as the observed brightness of a star depends on both its intrinsic luminosity and how far away it is, the strength of the gravitational waves received at LIGO depends on both the intrinsic loudness of the source and how far away it is. By observing the waves with detectors like LIGO and Virgo, we can determine both the intrinsic loudness of the gravitational waves as well as their loudness at the Earth. This allows us to directly determine distance to the source.

It may have taken 31 years to get a measurement, but hopefully it won’t be long before there are enough detections to provide greater precision – and hopefully accuracy! – than the current methods can manage!

Here is a short video of Bernard himself talking about his work:

Once again, congratulations to Bernard on a very well deserved election to a Fellowship of the Royal Society.

UPDATE: a more detailed biography of Bernard is now available on the Royal Society website.

The Hubble Constant from Gravitational Waves

Posted in The Universe and Stuff with tags , , , , on March 22, 2021 by telescoper

Some time ago I blogged about how one can use gravitational waves to estimate the Hubble Constant, H0. Well, about a month ago the LIGO people produced a user-friendly update on progress in that regard which you can find here.

The full paper (i.e. author list plus a small amount of text) can be found here. Here are two plots from that work.

The first shows the constraints from the six loudest gravitational wave events selected for the latest work, together with the two competing measurements from Planck and SH0ES:

As you can see the individual measurements do not constrain very much. The second plot shows the effect of combining all relevant data, including  a binary neutron star merger with an electromagnetic counterparts. The results are much stronger when the latter is included

Obviously this measurement isn’t yet able to resolve the alleged tension between “high” and “low” values described on this blog passim, but it’s early days. If LIGO reaches its planned sensitivity the next observing run should provide many more events. A few hundred should get the width of the posterior distribution shown in the second figure down to a few percent, which would be very interesting indeed!

What kind of thing is GW190814?

Posted in The Universe and Stuff with tags , , , , , , , on June 24, 2020 by telescoper

There’s been a lot of interest in the past day or two over an event that occurred in the LIGO detectors last August, entitled GW190814. A paper has appeared declaring this to be “the observation of a compact binary coalescence involving a 22.2–24.3 M  black hole and a compact object with a mass of 2.50–2.67 M “. That would be interesting of course because the smaller object is smaller than the black holes involved in previous detections and its mass suggests the possibility that it may be a neutron star, although no electromagnetic counterpart has yet been detected.  It’s a mystery.

I was quite excited when I saw the announcement about this yesterday but my enthusiasm was dampened a bit when I saw the data from the two LIGO detectors at Hanford and Livingston in the USA and the Virgo detector in Italy.

Visually, the Livingston detection seems reasonably firm, but the paper notes that there were thunderstorms in the area at the time of  GW190814 which affected the low-frequency data. There doesn’t look like anything at all but noise in the Virgo channel. The Hanford data may show something but, according to the paper, the detector was “not in nominal observing mode at the time of GW190814” so the data from this detector require special treatment. What you see in the Hanford channel looks rather similar to the two (presumably noise) features seen to the left in the Livingston plot.

I know that – not for the first time – I’m probably going to incur the wrath of my colleagues in the gravitational waves community but I have to sound a note of caution. Before asking whether the event involves a black hole or a neutron star you have to be convinced that the event is an event at all.  Fortunately, at least some of the data relating to this have been released and will no doubt be subjected to independent scrutiny.

Now I’m going to retreat into my bunker and hide from the inevitable comments…

PhD Studentship in Gravitational Wave Astrophysics at Maynooth University!

Posted in Uncategorized with tags , , , , on February 11, 2020 by telescoper

With the arrival of Dr John Regan in the Department of Theoretical Physics at Maynooth University we are delighted to announce a fully-funded PhD studentship. In order to boost the circulation, here’s a copy of the advert you can find on John’s own website.

–o–

 

Project Description. Recent detections of gravitational waves from stellar mass sized black holes with the LIGO observatory has opened up a new window for black hole astrophysics as well as heralding the dawn of multimessenger astrophysics. LIGO is sensitive to the mergers of black holes in the range 10 solar masses up to approximately 100 solar masses out to a few Megaparsecs.

LISA is the planned, next generation, space-based gravitational wave observatory due for launch in 2034. LISA will be sensitive to gravitational waves at a much lower frequency compared to LIGO and as a result will be able to detect the mergers of both much larger and much more distant black holes. Planning for LISA is now well underway and the science base and objectives are being determined.

This PhD project will involve computing gravitational wave forms from mergers of massive black holes from the early Universe – which will be detectable by LISA. The origin of massive black holes is currently unknown and hence being able to detect their mergers from the early Universe is seen as a critical aspect in understanding their formation pathways. In this project the student will use the state-of-the-art Enzo-E code to model the mergers of black holes. In doing so the student will be able to accurately compute the gravitational wave signal from black holes which are merging in the distant Universe thus making predictions for LISA.

Student fees and a full stipend (€18k per annum) are available as part of this studentship.

Candidate Criteria. Applicants should have (or be about to complete) an undergraduate degree and/or taught postgraduate degree in (applied) mathematics, (theoretical) physics, computer science or a related discipline. Past experience shows that successful applicants usually have a very good first class degree (or equivalent). Applicants with computational experience are particularly encouraged to apply. In addition, the applicants must have excellent communication, planning and team working skills.

Application Procedure

Application Deadline: Friday May 1st 2020

Students who wish to apply for this studentship should apply in writing to john.regan@mu.ie. Please put “PhD Studentship Position” in the subject of the email. The application must comprise:

  • A full CV
  • A covering letter outlining why you wish to pursue this PhD program
  • Two references, preferably from your current academic institution, outlining your suitability for the position

Shortlisted candidates will be notified of the outcome of the selection process in early May with interviews in mid-late May. The start date for the PhD is expected to be September 2020.

Please direct any questions or queries on the above position to Dr. John Regan (john.regan@mu.ie)

 

 

New Publication at the Open Journal of Astrophysics!

Posted in Open Access, The Universe and Stuff with tags , , , , , , , , on September 24, 2019 by telescoper

Yesterday we published another new paper at The Open Journal of Astrophysics, but I didn’t get time to write a post about because of teaching and other start-of-term business so I’m correcting that omission now.

 

The authors are Selim Can Hotinli  of Imperial College London (UK), Marc Kamionkowski of Johns Hopkins University, Baltimore (USA) and Andrew Jaffe, also of Imperial College.

You can find the accepted version on the arXiv here. This version was accepted after modifications requested by the referee and editor. Because this is an overlay journal the authors have to submit the accepted version to the arXiv (which we then check against the copy submitted to us) before publishing; version 2 on the arXiv is the accepted version.

You will see that this is  one for the `Cosmology and Nongalactic Astrophysics’ folder. We would be happy to get more submissions from other areas, especially Stellar and Planetary astrophysics. Hint! Hint!

P.S. Just a reminder that we now have an Open Journal of Astrophysics Facebook page where you can follow updates from the Journal should you wish..

On the Fellowship of Roy Kerr

Posted in The Universe and Stuff with tags , , , , , , , on April 18, 2019 by telescoper

Among the new Fellows of the Royal Society announced this week, I was astonished to see the name of Roy Kerr, the man who gave his name to the Kerr Metric an exact solution of Einstein’s equations of general relativity which describes the geometry of space-time around a rotating black hole.

When I say “astonished” I don’t mean that Kerr does not deserve this recognition. Far from it. I’m astonished because it has taken so long:the Kerr solution was published way back in 1963.

Anyway, better late than never, and heartiest congratulations to him!

While I’m on about Roy Kerr I’ll also say that I now think there is a very strong case for him to be awarded a Nobel Prize. The reasons are twofold.

One is that all the black hole binary systems whose coalescences produced gravitational waves detected by LIGO have involved Kerr black holes. Without Kerr’s work it would not have been possible to construct the template waveforms needed to extract signals from the LIGO data.

Second, and even more topically, the black hole in M87 recently imaged (above) by the Event Horizon Telescope is also described by the Kerr geometry. Without Kerr’s work the modelling of light paths around this object would not have been possible either.

Gravitational Wave Flash!

Posted in The Universe and Stuff with tags , , , , on April 9, 2019 by telescoper

The third observing run for Advanced LIGO – O3 – started on April 1 2019, after 19 months upgrading the detectors. Last night, April 8, saw the first new detection of a candidate gravitational wave source, apparently another black hole binary, dubbed S190408an.

It is anticipated that sources like this will be discovered at a rate of roughly one per week for the (planned) year-long run. Given the likely rate of events the policy of LIGO is now to make data publicly available directly without writing papers first. You can find the data entry for this event here, including this map of its position.

Whether the LIGO Scientific Collaboration will release sufficient data for others to perform a full analysis of the signal remains to be seen, but if the predicted detection rate matches reality, the field is going to move very rapidly from studies of individual events to statistical analysis of large populations. Such is the way of science!

Bernard Schutz wins the 2019 Eddington Medal

Posted in Cardiff, The Universe and Stuff with tags , , , on January 14, 2019 by telescoper

I wasn’t able to get to the Ordinary Meeting of the Royal Astronomical Society on Friday 11th January as I was otherwise engaged. In case you didn’t know, these meetings happen on the second Friday of every month and consist of short talks, longer set-piece prize lectures and Society business. The January meeting is when the annual awards are announced, so I missed the 2019 crop of medals and other prizes. When I got to the Athenaeum for dinner I was delighted to be informed that one of these – the prestigious Eddington Medal – had been awarded to my erstwhile Cardiff colleague Bernard Schutz (with whom I worked in the Data Innovation Research Institute and the School of Physics & Astronomy).

Here is a short video of the man himself talking about the work that led to this award:

The citation for Bernard’s award focuses on his invention of a method of measuring the Hubble constant using coalescing binary neutron stars. The idea was first published in September 1986 in a Letter to Nature. Here is the first paragraph:

I report here how gravitational wave observations can be used to determine the Hubble constant, H 0. The nearly monochromatic gravitational waves emitted by the decaying orbit of an ultra–compact, two–neutron–star binary system just before the stars coalesce are very likely to be detected by the kilometre–sized interferometric gravitational wave antennas now being designed1–4. The signal is easily identified and contains enough information to determine the absolute distance to the binary, independently of any assumptions about the masses of the stars. Ten events out to 100 Mpc may suffice to measure the Hubble constant to 3% accuracy.

In this paper, Bernard points out that a binary coalescence — such as the merger of two neutron stars — is a self calibrating `standard candle’, which means that it is possible to infer directly the distance without using the cosmic distance ladder. The key insight is that the rate at which the binary’s frequency changes is directly related to the amplitude of the gravitational waves it produces, i.e. how `loud’ the GW signal is. Just as the observed brightness of a star depends on both its intrinsic luminosity and how far away it is, the strength of the gravitational waves received at LIGO depends on both the intrinsic loudness of the source and how far away it is. By observing the waves with detectors like LIGO and Virgo, we can determine both the intrinsic loudness of the gravitational waves as well as their loudness at the Earth. This allows us to directly determine distance to the source.

It may have taken 31 years to get a measurement, but hopefully it won’t be long before there are enough detections to provide greater precision – and hopefully accuracy! – than the current methods can manage!

Congratulations to Bernard on his thoroughly well-deserved Eddington Medal!

 

A LIGO Orrery

Posted in The Universe and Stuff with tags , , , , on December 5, 2018 by telescoper

Following yesterday’s post here is a nice video visualization of all the black hole binary mergers so far claimed to have been detected by Advanced LIGO. They’re computer simulations, of course, not actual black holes (which you wouldn’t be able to see). I always thought an Orrery was a clockwork device, rather than a digital computer, but there you go. Poetic license!

I can’t say I’m very keen on the music.

The New Wave of Gravitational Waves

Posted in The Universe and Stuff with tags , , , , on December 4, 2018 by telescoper

I think it’s very sneaky of the LIGO Scientific Collaboration and the Virgo Collaboration to have released two new gravitational wave papers while I was out of circulation fora  couple of days, so I’m a bit late on this, but here are links to the new results on the arXiv.

You can click on all the excerpts below to make them bigger.

First there is GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs with this abstract:

Here is a summary of the properties of the binary systems involved in the events listed in the above paper:

There are several (four) events in this catalogue that have not previously been announced (or, for that matter, subjected to peer review) despite having been seen in the data some time ago (as far back as 2015). I’m also intrigued by the footnote on the first page which contains the following:

…all candidate events with an estimated false alarm rate (FAR) less than 1 per 30 days
and probability > 0.5 of being of astrophysical origin (see Eq. (10) for the definition) are henceforth denoted with the GW prefix.

The use of false discovery rates is discussed at length here as a corrective to relying on p-values for detections. The criteria adopted here don’t seem all that strong to me.

The second paper is Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo which has this abstract:

I’ve been teaching and/or preparing lectures all day today, so I haven’t yet had time to read these papers in detail. I will try to read them over the next few days. In the meantime I would welcome comments through the box about these new results. I wonder if there’ll be any opinions from the direction of Copenhagen?

UPDATE: Here’s a montage of all 10 binary black hole mergers `detected’ so far…

I think it’s safe to say that if GW151266 had been the first to be announced, the news would have been greeted with considerable skepticism!