Archive for gravitational waves

Astronomical and Other Events this Week

Posted in Biographical, The Universe and Stuff with tags , , , , , on July 4, 2017 by telescoper

This week sees the 2017 National Astronomy Meeting which is taking place in Hull (which, for those of you unfamiliar with British geography, is in the Midlands). I usually try to attend this annual event but this year haven’t been able to make it owing to other commitments. I’m particularly sad about this because I’ll miss seeing two old friends (Nick Kaiser and Marek Kukula) being presented with their RAS medals. Moreover, one of the pieces of astronomical research announced at this meeting that has been making headlines features my office mate and fellow resident of Pontcanna, Dr Emily Drabek-Maunder.

Anyway, to keep up with what’s going on at NAM2017 you can follow announcements on twitter:

This week also sees a meeting in Cambridge on Gravity and Black Holes to celebrate the 75th birthday of Stephen Hawking, which goes on until tomorrow (Wednesday 5th). This conference also looks like a very good one, covering a much wider range of topics than its title perhaps suggests. Stephen’s birthday was actually in January, but I hope it’s not too late to wish him many happy returns!

Finally, though not a conference as such, there’s annual Royal Society Summer Science exhibition going on in London this week too. This is a showcase for a wealth of scientific research including, this year, an exhibit about gravitational waves called Listening to Einstein’s Universe. There’s even a promotional video featuring some of my colleagues at Cardiff University (along with many others):

Anyway, if you’re in London and at a loose end and interested in science and that, do pop into the Royal Society and have a look. The Summer Science Exhibition is always well worth a visit!

 

The ‘Danish Paper’ and How Science Works

Posted in The Universe and Stuff with tags , on June 27, 2017 by telescoper

I’m off work today but couldn’t resist posting a very quick update on the controversial claims of inconsistencies in the recent detection of gravitational waves by LIGO.

If you’re following the story you will know that it started with a paper on the arXiv by Cresswell et al.,  a group mainly based in Denmark, which is why the paper is now frequently referred to as ‘The Danish Paper’ although its authors actually come from all round the world.

Well the same group have now  written a rejoinder to the LIGO critique of their analysis. They’re clearly sticking to their guns, at least on their claim that the residuals left after removing the gravitational wave events from the two time series are correlated, which they should not be if they are simply noise.

Hopefully the public airing this controversy had received will lead to other independent groups downloading and analysing the data, which is all in the public domain, and we’ll eventually arrive at the truth.

Contrary to the opinion of one of my Cardiff colleagues I think this is how science works and, importantly, how it should be seen to work. Science  is a process of investigation, and it doesn’t come to an end when  results have been published in refereed journals. 

 The more the public see how science really works – warts and all – the better they will understand its strengths as well as its limitations.

Whatever the eventual outcome of this discussion I think we will find that the ‘Danish Paper’ has helped advance our understanding, and for that the authors deserve a great deal of credit.

 

LISA gets the go-ahead!

Posted in The Universe and Stuff with tags , , , , , on June 21, 2017 by telescoper

Just taking a short break from examining duties to pass on the news that the European Space Agency has selected the Laser Interferometric Space Experiment (LISA) – a gravitational wave experiment in space – for its large mission L3. This follows the detection of gravitational waves using the ground-based experiment Advanced LIGO and the success of a space-based technology demonstrator mission called Lisa Pathfinder.

LISA consists of a flotilla of three spacecraft in orbit around the Sun forming the arms of an interferometer with baselines of the order of 2.5 million kilometres, much longer than the ~1km arms of Advanced LIGO. These larger dimensions make LISA much more sensitive to long-period signals. Each of the LISA spacecraft contains two telescopes, two lasers and two test masses, arranged in two optical assemblies pointed at the other two spacecraft. This forms Michelson-like interferometers, each centred on one of the spacecraft, with the platinum-gold test masses defining the ends of the arms.

Here’s an artist’s impression of LISA:

This is excellent news for the gravitational waves community, especially since LISA was threatened with the chop when NASA pulled out a few years ago. Space experiments are huge projects – and LISA is more complicated than most – so it will take some time before it actually happens. At the moment, LISA is pencilled in for launch in 2034…

Questioning LIGO

Posted in The Universe and Stuff with tags , on June 17, 2017 by telescoper

Well. Cat, meet pigeons..

A paper appeared on the arXiv this week with the following abstract:

To date, the LIGO collaboration has detected three gravitational wave (GW) events appearing in both its Hanford and Livingston detectors. In this article we reexamine the LIGO data with regard to correlations between the two detectors. With special focus on GW150914, we report correlations in the detector noise which, at the time of the event, happen to be maximized for the same time lag as that found for the event itself. Specifically, we analyze correlations in the calibration lines in the vicinity of 35 Hz as well as the residual noise in the data after subtraction of the best-fit theoretical templates. The residual noise for the two more recent events, GW151226 and GW170104, exhibits equivalent behavior with respect to each of their time lags. A clear distinction between signal and noise therefore remains to be established in order to determine the contribution of gravitational waves to the detected signals.

I’m going to tread carefully here because (a) I have a number of colleagues at Cardiff who are directly involved in the analysis of LIGO data; (b) one of the authors of the new paper (Panel Naselsky) is a longstanding collaborator of mine; and (c) the new paper has not yet been refereed.

In fact I’m planning to visit Copenhagen in July/August and will catch up with Panel and the other authors then.

Whether or not the points raised in the new paper are correct – and I am firmly agnostic, having not done the analysis myself – I think it’s entirely reasonable of the authors to subject the LIGO data to independent analysis. That’s how science is supposed to work; the relevant data are in the public domain now. 

No doubt the LIGO consortium will respond officially in due course. Of course, if anyone would like to comment unofficially then they are free to do so through the box below.
Update: Here is a fairly detailed rebuttal post.

Simulation of the binary black-hole coalescence GW170104

Posted in The Universe and Stuff with tags , , , on June 2, 2017 by telescoper

Via the Cardiff University news website, I found this video of a computer simulation of the binary black-hole coalescence that gave rise to the gravitational wave event GW170104 whose detection was announced yesterday, so I thought I’d share it here.

Here’s the  blurb accompanying the video:

The video shows a numerical simulation of a binary black-hole coalescence with masses and spins consistent with the GW170104 observation. The strength of the gravitational wave is indicated by elevation as well as color, with blue indicating weak fields and yellow indicating strong fields. We rescale the amplitude of the gravitational wave during the simulation to show the signal during the entire animation not only close to merger, where it is strongest. The sizes of the black holes are increased by a factor of two to improve visibility. The bottom panel in the video shows the gravitational waveform starting at frequency of 25Hz. The fade in of the video corresponds to a frequency of about 30Hz.

© Numerical-relativistic simulation: S. Ossokine, A. Buonanno (Max Planck Institute for Gravitational Physics) and the Simulating eXtreme Spacetimes project; scientific visualization: T. Dietrich (Max Planck Institute for Gravitational Physics), R. Haas (NCSA).

The colour scheme gives me a headache, and there’s no sountrack, but it’s quite instructive nonetheless.

 

New Astronomy at the New Year (GW170104)

Posted in The Universe and Stuff with tags , on June 1, 2017 by telescoper

The inside story of the detection of gravitational wave event announced earlier today..

Write Science

by Shane L. Larson

Newton’s portrait.

January 4 holds a special place in the hearts of scientists — it is Isaac Newton’s birthday (*). Newton stood at the crossroads that led to modern science, and astronomy in particular. He was the first person to build a workable reflecting telescope, a design that now bears his name and for the past 4 centuries has been the dominant type of telescope used by amateurs and professionals alike. Newtonian telescopes have revealed much about the Cosmos to our wondering minds. Newton was also responsible for the first formulation of a physical law that describes the working of gravity, called the Universal Law of Gravitation. Today we use the Universal Law to launch satellites, send astronauts into orbit, convert the force of your feet on the bathroom scale into your “weight“, and a thousand other applications.  There is much to celebrate…

View original post 1,623 more words

Newsflash: another LIGO detection!

Posted in The Universe and Stuff with tags , , , on June 1, 2017 by telescoper

I’ve just heard the news that  LIGO has just announced the detection of another gravitational-wave signal, which has been given the identifier GW170104; it was detected on 4th January 2017.

The event was the merger of a black-hole binary system a redshift z=0.2, which is a proper distance of about 800 Mpc in the standard cosmological model, the most distant event yet detected. There are also tantalising hints that at least one of the black holes had spin opposite the orbital angular momentum, which implies it may have originated in a globular cluster. For more details please see the refereed paper.

If you’d rather just look at the plot here is the evidence for the event, in the form of coincident signals at the two components of LIGO:

 
LIGO

I reckon there’s a good chance of seeing members of the Cardiff University Gravitational Physics group celebrating in the pub later this evening!

It’s also a reasonable inference given the rate of detection of these events so far that we’re going to see many more in the very near future!