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## The birth and death of stars

A few months ago this story caught my attention on the BBC news website. It is an image of part of the Large Magellanic Cloud (LMC), a satellite galaxy of our Milky Way galaxy, and shows both star birth and star death.

The circular looking “shell” of gas towards the left of the image is a supernova remnant, part of the gases which have been blown off by an exploding massive star. To the right of the image is an area called the Dragon Nebula, which is an area of current star formation.

The LMC is about 170,000 light years from our Milky Way, visible to the naked eye from the Southern Hemisphere. It is a small irregular galaxy which is actually in orbit about our much larger Milky Way, and is so named because the first European to note it was Ferdinand Magellan, who was also captain of the first expedition to circumnavigate the Earth. It is called the Large Magellanic Cloud because near to it (and also visible to the naked eye) is a smaller irregular galaxy, which is called the Small Magellanic Cloud (astronomers are nothing if not inventive in their naming 😉 ).

In 1987 a massive star exploded (a supernova) in the LMC, SN1987A, which was the first naked-eye supernova visible since Kepler’s supernova in 1604. However, it is not the SN1987A supernova which is shown in this image, the supernova here is older than that, something we can determine from the size of the remnant (the expanding shell of gases which the supernova blows off when it explodes).

It may seem to be quite a coincidence to capture a supernova remnant and a region of star formation in the same image, but in fact it is not so surprising. The shock waves caused by a supernova explosion are thought to often trigger the collapse of giant molecular clouds which lead to new star formation, so stellar death leads to stellar re-birth. Not only that, but the new generation of stars will contain heavier elements which have been created in the massive star and its supernova. Elements up to iron can be created in the massive star itself, but the many elements beyond iron in the periodic table are mostly created in the supernova explosion itself.

The wispy (mainly) red areas in the image are due to the gases fluorescing, just as I have described in previous blogs, for example here and here. The red colour is due to the dominant line-emission process, the h-alpha emission in hydrogen. You may also notice some dark areas (lanes) in the right hand part of the image where the star formation is going on. This is not the absence of stars, but is due to stars being hidden by dust, the same kind of dust I mentioned in my blog on BICEP2 last week. To see through the dust and to see the stars which are currently still forming, we need to look in the infrared and millimetre, where we can see through the dust and see the much cooler “proto-stars”, I will blog about this in the near future.

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## Dark Matter: Unseen, But Yet Again in the Limelight

A great heads-up on recent *possible* observational evidence for dark matter.

The past two weeks have been busy!  I was on the road, consulting with and learning from particle experimenters and theorists at Caltech and the University of California at Irvine. And I’ve been giving talks: at the University of California Santa Barbara (for the Joe Polchinski Fest conference), at the University of California at Irvine, and yesterday in Boston at M.I.T. The Santa Barbara talk was only semi-technical, and is on-line.  The latter two, much more technical, focused on the two big projects that I completed this fall (one on whether searches for supersymmetry have been comprehensive, one on looking for unusual things the Higgs particle might do.)

While this has all been going on, there have been two big stories developing in dark matter searches, and those of you who already have heard about them will have noticed I have not written much about them yet…

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## 50 Years of The Beatles

As anyone who reads my blog knows, I am huge fan of The Beatles, so I had to re-tweet this blog…..

8 pm, February 9th, 1964.  An astonishing 76 million Americans gathered around their black and white televisions.  60% of America tuned in to see the four young men from Liverpool, the most watched television program to that date.  While the show’s studio was full of screaming girls, children and adults alike watched the event that would soon go down in cultural history: The Beatles on the Ed Sullivan show.

50 years later, this band has not only stood the test of time, but has become such a part of our culture that it seems as though they never left.  The Beatles paved the road for every artist that followed them; without them, music would not be what it is today.

When they arrived in America, no one was ready for the storm they brought with them.  The British Invasion, in my opinion, began the moment when Ed Sullivan introduced the…

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## The 2014 Grammys: A Beatles Reunion and the Winners

The 2014 Grammys was a huge night for classic rock (and especially for Beatlemaniacs!).  A few days ago, I published an article about the upcoming event, so now its time to look back and reflect on music’s most extravagant night.

First things first – a Beatles reunion! (Or, the remaining half of the band performing together.)  As a huge Beatles fan who has seen Paul McCartney twice in concert, I saw this as a monumental event.  Paul and Ringo Starr took the stage for one of McCartney’s new songs Queenie Eye.  When the song finished, the pair hugged and bowed to a standing audience in the classic Beatles manner.  Ringo also performed one his own songs, Photograph.

Since the band’s split in 1970 (which I can’t say I recall), fans have been waiting for some sort of reconciliation between the band members.  Although all four members came to…

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## Can Nadal make history in Australia?

Rafael Nadal stands on the verge of making tennis history should he win the men’s final of the Australian Open tomorrow (26th of January). Not only will victory give him his 14th Majors title, but also he will become the first player in the Open era to have won each one of the Majors at least twice. As of now, Nadal has won the French Open 8 times, Wimbledon 2 times, the US Open 2 times and the Australian Open once.

By beating Federer to reach the Australian Open final, Nadal could become the first man in the Open era to win at least 2 of each of the 4 tennis Majors.

There are two other players who have won at least 2 of the 4 tennis Majors, namely Roy Emerson and Rod Laver. But neither of them achieved this during the open era. When Emerson won most of his titles in the 1960s the majority of his major rivals (including Laver) were not competing as they had turned professional and were therefore barred from playing in the 4 Majors. Rod Laver won the Grand Slam (all 4 Majors in the same year) in 1961 and 1969, as well as some Majors in other years. But many of these titles were won before tennis went open.

As a big Federer fan I have often been reluctant to admit what an exceptional player Nadal is. When Nadal and Federer play each other I always want Federer to win. But should Nadal win in Australia tomorrow it will make him one of the truly great tennis players of all time.

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## Every 1’s a Winner – Hot Chocolate (song)

Today I thought I would share with you this song from the 1970s – “Every 1’s a Winner” by Hot Chocolate.

The song was a hit in 1978, reaching number 12 in the Disunited Kingdom charts, and number 6 in the US charts. It was co-written by band member Tony Wilson and lead singer Errol Brown. Enjoy!

Which is your favourite Hot Chocolate song?

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## Five Christmas Songs – “Fairy tale of New York” – The Pogues and Kirsty MacColl

The third Christmas song I thought I would share with you is “Fairy tale of New York” by The Pogues and Kirsty MacColl.

This song was released in 1987 and reached number 2 in the DUK charts. It is one of my favourite Christmas songs, and has consistently been in the top 5 in various “all time greatest Christmas songs” lists.

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## In My Life – The Beatles (song)

On this day in 1980 John Lennon was gunned down in front of his apartment in New York City.

John Lennon in 1965, the year “In My Life” was recorded.

Here is one of his more beautiful songs, “In My Life” from the 1965 album Rubber Soul.

(Words & music by Lennon & McCartney)

There are places I remember
All my life, though some have changed
Some forever not for better
Some have gone and some remain
All these places have their moments
With lovers and friends I still can recall
Some are dead and some are living
In my life I’ve loved them all

But of all these friends and lovers
There is no one compares with you
And these memories lose their meaning
When I think of love as something new
Though I know I’ll never lose affection
For people and things that went before
I know I’ll often stop and think about them
In my life I love you more

Though I know I’ll never lose affection
For people and things that went before
I know I’ll often stop and think about them
In my life I love you more
In my life I love you more

John – you’re missed 😦

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## Studying the Universe using gravitational waves

The European Space Agency announced last week (28th of November) that a space-based gravitational wave observatory will form one of its next two large science missions. This is exciting news for Cardiff University, as it has a very active gravitational waves research group headed up by Professor B S Sathyaprakash (known to everyone as “Sathya”). The Cardiff group, along with others in the Disunited Kingdom, played an important role in persuading ESA to make this observatory one of its next large science missions. Just over a year ago I blogged about some theoretical modelling of gravitational waves the Cardiff group had done.

The ESA plan is to launch a space-based gravitational wave observatory in 2034, which will have much more sensitivity than any current or even future ground-based gravitational wave observatory. Although NASA also had plans to launch a space-based gravitational wave observatory, there is currently none in existence, so this is really ground-breaking technology that ESA is announcing. From what I can understand, the current announcement by ESA is their commitment to the proposed LISA (Laser Interferometer Space Antenna) gravitational wave observatory. It would seem NASA has withdrawn their commitment to what was originally going to be a joint NASA/ESA mission.

ESA has chosen a space-based gravitational wave detector to be funded as one of its two key future missions. It should go into operation in 2034.

## What are gravitational waves?

Gravitational waves are ripples in the fabric of space. They were predicted by Einstein as part of his theory of general relativity, the best theory we currently have to describe gravity. In his theory, events which involve extreme gravitational forces (such as two neutron stars orbiting each other (or merging), or the creation of a black hole) will lead to the emission of these gravitational waves. As they spread out from the source at the speed of light, they literally deform space as they pass by, just as ripples deform the surface of a pond as they spread out from a dropped stone.

An artist’s impression of gravitational waves being produced as two black holes orbit each other.

## Current gravitational wave observatories

There are several current gravitational wave observatories, all ground-based. These include VIRGO (in Italy) and LIGO (Laser Interferometer Gravitational Wave Observatory) which is in the United States. LIGO is the most sensitive of the current generation of gravitational wave detectors. LIGO actually comprises three separate detectors; one in Livingston, Louisiana and two in Hanford, Washington State. Each of the three separate detectors consists of two long arms at right angles to each other, forming a letter “L”. The idea behind these detectors is that, if a gravitational wave were to pass the detector, each of the two arms would have its length changed differently by the deformation of space as the gravitational wave passes through. Thus the detectors work on the principle of an interferometer, looking for tiny changes in the relative length of the two arms. And, when I say tiny, I mean tiny. In a 4km arm they are looking for changes of the order of $10^{-18} \text{ m}$, or about one thousandth the size of a proton!

The principle of a gravitational wave detector. They are essentially “interferometers”, with two arms at right angles to each other. As the gravitational waves pass the detector, space will be deformed and alter the relative lengths of the two arms.

## LIGO (Laser Interferometer Gravitational Wave Detector)

Currently the most sensitive gravitational wave detector is LIGO. LIGO consists of three separate detectors, one in Livingston, Louisiana and two in Hanford, Washington State. The detector in Louisiana is shown below.

The LIGO detector in Livingstone, Louisiana. Each arm is 4km in length, and can detect changes in the relative length of the two arms of less than the size of a proton.

The detector in Louisiana, and one of the two detectors in Washington State, consist of two 4km long arms at right angles to each other. An event like the collapse of a 10 solar-mass star into a black hole is expected to produce a change in length in a 4km arm of about $10^{-18} \text{ m}$, which is about one thousandth the size of a proton. This is just at the limit of the detection capabilities of LIGO, which is why astrophysicists are wanting more sensitive detectors to be placed into space. The other detector in Washington State has arms which are 2km in length, but just as sensitive as the detector with 4km arms at frequencies above 200 Hz, due to a different design.

## LISA – Laser Interferometer Space Antenna

The ESA plans just announced will be based on the NASA/ESA plans for LISA, which have been on the drawing board for most of the last 10 years. ESA’s plan is to build two space-based interferometers, which will be in the form of equilateral triangles as this artist’s description shows.

An artist’s impression of LISA, the “Laser Interferometer Space Antenna”. Each interferometer will consist of an equilateral triangle, with each side 5 million km in length.

The plan for LISA is to have arms which are 5 million km long! Compare this to the 4km long arms of LIGO. The changes in the length of a 5 million km long arm would be roughly one million times more than for LIGO, so rather than $10^{-18} \text{ m it would be } 10^{-12} \text{ m}$, which should be well within the capabilities of the detectors. This means that less energetic events than the collapse of a 10-solar mass star into a black hole would be detectable by LISA. All kinds of astrophysical events which involve large changes in gravitational fields should be detectable by LISA, including the afore-mentioned creation of black holes, but also the merging of neutron stars, and even the merging of less massive stars.

But, possibly most exciting is the opportunity that gravitational waves provide to probe the very earliest moments after the Big Bang. With normal electromagnetic radiation (light, x-rays, infrared light etc.), we can only see as far back as about 300,000 years after the Big Bang. This is when the Cosmic Microwave Background Radiation was produced. Prior to this time, the Universe was opaque to EM radiation of any wavelength, because it was full of unbound electrons, and the photons would just scatter off of them and not get anywhere (see my blog here about the CMB). But, it was not opaque to gravitational waves, so they provide a way for us to see back beyond the CMB, and a unique way to learn about the conditions of the Universe in its earliest moments.

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## The 500 greatest albums – no. 6 – “What’s Going On” (Marvin Gaye)

At number 6 in Rolling Stone Magazine’s 500 greatest albums is “What’s Going On” by Marvin Gaye.

At no. 6 in Rolling Stone Magazine’s 500 greatest albums is “What’s Going On” by Marvin Gaye.

This is the only other album in the top 10 (along with “London Calling” by The Clash) which I did not own prior to seeing this list. So, I bought it about 18 months ago, and since then I have listened to it about two dozen times. The only songs on the album I knew before buying the album were “Mercy Mercy Me” and “What’s Going On”, both songs I like a lot.

I must say I am not sure what to make of this album, I find it very dated. I can appreciate that in the early 1970s it was very groundbreaking, and is possibly one of the first environmentally aware albums. Certainly Marvin Gaye has a message to get across. But I cannot imagine an album sounding like this being made now, it sounds as if it comes from the early 1970s and does not sound timeless. To be controversial, is this album the token album by a black artist in the top ten? Is it in the top ten just so there is a “black/soul album” in the top ten? Or does it deserve to be in the top ten on its own merits? I don’t know, I am just raising these questions as a talking point.

I am a big fan of Motown music in general, and have quite a number of Motown compilation albums. And, to my years, much of Motown’s music sounds timeless, but of all the stuff Marvin Gaye has done with which I am familiar, this album has the most songs which I cannot imagine being recorded at any other time but the early 1970s. What do you think?

Here is a live performance from 1980 of “Mercy Mercy Me” and “What’s Going On”. Enjoy!

Is this album Marvin Gaye’s greatest work? Does it deserve to be in the top ten of the 500 greatest albums of all time?

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