Archive for Neutron Stars

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!

 

Determining the Hubble Constant the Bernard Schutz way

Posted in The Universe and Stuff with tags , , , , , on October 19, 2017 by telescoper

In my short post about Monday’s announcement of the detection of a pair of coalescing neutron stars (GW170817), I mentioned that one of the results that caught my eye in particular was the paper about using such objects to determine the Hubble constant.

Here is the key result from that paper, i.e. the posterior distribution of the Hubble constant H0 given the data from GW170817:

You can also see latest determinations from other methods, which appear to be in (slight) tension; you can read more about this here. Clearly the new result from GW170817 yields a fairly broad range for H0 but, as I said in my earlier post, it’s very impressive to be straddling the target with the first salvo.

Anyway, I just thought I’d mention here that the method of measuring the Hubble constant using coalescing binary neutron stars was invented by none other than Bernard Schutz of Cardiff University, who works in the Data Innovation Institute (as I do). 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 in the 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!

Above all, congratulations to Bernard for inventing a method which has now been shown to work very well!

Gravitational Waves Flash!

Posted in The Universe and Stuff with tags , , , , on October 13, 2017 by telescoper

I got up early this morning to hitch a ride in a car to Mumbai so that I can give a talk this afternoon. We left Pune about 6am and got here about 8.30 so the trip was a quite a bit quicker than coming here! I’ll post about that and include some pictures when I get a moment, but first I’ll post a quick announcement.

There will be an announcement on Monday 16th October at 10am EDT (3pm BST; 7.30pm in Pune) by `the National Science Foundation (NSF) as it brings together scientists from the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo collaborations, as well as representatives for some 70 observatories’. Further details can be found here. The European Southern Observatory has also announced that it will be holding a press conference on Monday about an `unprecedented discovery’.

The fact that it involves LIGO, Virgo and representatives of other observatories strongly suggests that this announcement will address the subject of the rumours that were flying around in August. In other words, it’s likely that on Monday we will hear about the first detecting of a coalescing binary neutron star system with an optical counterpart. Exciting times!

I’ll be back in Pune by Monday and will probably be able to watch the announcement and will update if and when I can.

What’s with the Wang Particle?

Posted in Astrohype, The Universe and Stuff with tags , , , , , , on September 11, 2012 by telescoper

Not long ago a colleague ran into my office all of a flutter and asked me about this new discovery called the “Wang particle” that had been in the media. I’m the one around here who’s supposed to know about particle astrophysics stuff, so I was quite embarrassed that I’d never heard of the Wang particle, although I’ll be delighted if it becomes famous as the name has a great deal of comedy potential.

Anyway, I vowed to find out a little bit about it and finally got around this lunchtime to doing so. It turns out that the story was sparked by press release from the British Science Association which, out of the goodness of my heart, I reproduce below (link added by me).

 A new particle, similar to the Higgs Boson, could provide a clue to one of the greatest mysteries of the Universe.

Dr Charles Wang from the University of Aberdeen believes that a new scalar particle is behind the intense supernova explosions that occur when a star implodes. He presented his work to the British Science Association on Tuesday.

Supernova explosions are the most powerful forces in the universe, second only to the Big Bang.

Once frequent, the energy produced in these explosions is responsible for combining particles to produce all the recognisable elements on earth, providing all the known building blocks of life on earth.

There are still many gaps in our understanding of physics and one of the major blanks is how the implosion of a star subsequently produces an intense explosion.

It is known that as elements are created at the centre of a star, a huge amount of energy is released.  However, it is believed that the conversion of known elements would never produce enough energy to result in an explosion.

Dr Wang’s theory states that “a scalar particle – one of the most elementary types of particles in the universe and similar to the Higgs Boson – is at work within these stars and responsible for the additional energy which causes the explosion to take place.”

The scalar particle would effectively enable the high transfer of energy during a supernova, allowing shockwaves from the implosion of a star to become re-energised and cause an explosion.

A new collaboration between Dr Wang and CERN could provide the equipment to make this theory a reality and demonstrate the existence of the ‘Wang particle’ – or as Dr Wang himself refers to it the ‘scalar gravitational particle’. It is hoped that using the ISOLDE facility at CERN it may be possible assimilate a nuclear reaction that would determine the process of a starburst.

If demonstrated, the existence of the ‘Wang particle’, like the Higgs Boson, would hold major implications for physics, shedding new light on the theory of everything and affecting our understanding of how different physical phenomena interact.

There’s no link to an academic paper with it, which is a bit disappointing, but an older piece in the CERN Courier does provide a reference to the paper, which is

C H-T Wang et al. 2011 Parametric instability induced scalar gravitational waves from a model pulsating neutron star, Phys. Letts. B 705 148

If you’re prepared to shake hands with the Devil that is Elsevier you can find the paper here.

I have to confess that this is a new one on me. I haven’t gone through the paper in detail yet but, at a quick skim, it seems to be based on a variation of the  Brans-Dicke scalar-tensor theory of gravity. It’s probably an interesting paper, and I look forward to reading it in detail on a long flight I’m about to take, but I am a bit mystified as to why it created such a stir in the media. Looks more a result of hype than real significance to me. It certainly isn’t the “new Higgs boson” anyway. Nor is it likely to be relevant in explaining Climate Change. Or am I missing something? Perhaps hot air generated by press releases is responsible for global warming?

Anyone out there an expert on Wang’s work? Care to comment?