Jocelyn Bell and the Breakthrough prize 2018

Pulsars were first detected in 1967 by a research student called Jocelyn Bell when she was taking observations for her PhD thesis. Her supervisor, Anthony Hewish, went on to win the Nobel prize in 1974 for the discovery, and her contribution was overlooked. Many at the time felt that Jocelyn Bell should have been given at least a share in the prize, since she was the person who had initially spotted the signal from the first pulsar.

Jocelyn Bell 

This was finally addressed this month when she was awarded the $2.3 million Physics Breakthrough Prize for the discovery. Previous recipients include Stephen Hawking, researchers at Cern who discovered the Higgs boson, and physicists on the Ligo experiment who detected gravitational waves.

According to the BBC website, Bell has decided to donate her entire winnings to set up a fund to help women, under-represented ethnic minority and refugee students to become physics researchers.

Bell who is now 75 years old told the BBC:

‘I don’t want or need the money myself and it seemed to me that this was perhaps the best use I could put it to.’

If you would like to know more, please see my post from last year on the discovery of pulsars below.

———–

In 1967 Jocelyn Bell, a 24-year-old student from Cambridge University, was doing the research for her PhD. She was using a radio telescope to study radio waves emitted from compact astronomical objects known as quasars, and when she analysed the data, she noticed a signal which appeared to pulse on and off every 1.3 seconds. After doing this continuously for about an hour, the pulsing signal would stop altogether, but it would start again precisely 23 hours 56 minutes later after it had first started. As Jocelyn Bell – and indeed all astronomers – knew, the Earth rotates on its axis once every 23 hours 56 minutes, a period of time called a ‘sidereal day’, and the fact that the pulsating signal was detected at the same time in each sidereal day meant that it must almost certainly be coming from space rather than being man-made as shown below.

 

Not only was the time interval between each pulse very short at only 1.3  seconds, but this time interval was completely constant and didn’t vary to any significant degree.  The fact that the pulses were very short in duration and so regular meant that whatever was emitting the pulses must be extremely small in astronomical terms.  A larger object – something, for example, the size of the Sun – would not be able to generate such precise pulses. For a while Bell and her PhD supervisor Antony Hewish considered the possibility that the mysterious signals were generated by a signaling beacon left by an alien civilisation. For this reason, they briefly nicknamed  the unknown object ‘Little Green Men-1’. However, this explanation was rejected when it became clear that the pulses contained no information and when they also discovered additional pulsing sources in other parts of the sky.

Pulsars

The origin of the mysterious signals turned out to be a hitherto unknown class of astronomical objects, known as neutron stars. Neutron stars are very small, typically around 20 km in diameter, but have an enormous mass – between 1.1 and 3 times the mass of the Sun.  Having such a large mass squeezed into a small volume means that their density is incredibly high.  A cubic centimetre of neutron star material would weigh about 500 million tons. They are called neutron stars because they consist mainly of neutrons, which are subatomic particles found in the nucleus of ordinary atoms. In a neutron star the neutrons are so tightly squeezed together that they are touching each other. Neutron stars also have very strong magnetic fields – around 1 trillion times stronger than the Earth’s.

Neutron stars which rotate extremely rapidly, around once a second, are known as pulsars, and these are the objects which Bell and Hewish had detected. This rotation causes electrically charged particles around the neutron star to move rapidly in the intense magnetic fields. This causes electromagnetic radiation (such as radio waves) to be emitted in two cone-shaped beams along the magnetic North and South poles of the pulsar, shown as B in the diagram below.

In the diagram above A is the axis around which the pulsar rotates and B is the magnetic axis.

As you can see, the magnetic poles are at an angle to the line through the North and South poles of the pulsar about which it rotates. This means that the cone-shaped beams will rotate around the axis of the pulsar and only when either of the beams is pointing directly at the Earth will it be detected. A pulsar behaves like a lighthouse – the light is on all the time but appears to a viewer to switch on when it is pointing towards them and switch off when it is pointing away.

Neutron stars are formed when a large massive star explodes at the end of its life in a violent event known as a supernova. Most of the outer parts of the star are blown out into space by the force of the explosion. The remaining material in the star’s core collapses, forming a neutron star.  In fact, if the remaining material from the star’s core is more than three times the mass of the Sun, a neutron star won’t be formed at all.  Instead, an even more compact object called a black hole will result.

Large stars with a diameter of tens of millions of kilometres rotate relative slowly, taking around one year to complete one rotation. As the star collapses into a small massive object, millions of times smaller in diameter, a law of physics called the conservation of angular momentum causes its rotation to speed up massively.  A  more familiar example of this is from the world of ice skating: ice skaters spin more rapidly when they pull in their arms.

Why this knowledge has been useful to astronomy

In the last 50 years more than 2000 pulsars have been detected. Understanding the properties of pulsars has led to further discoveries in various areas.  For example, it has led to greater understanding of the diffuse gas between stars known as the interstellar medium, and it has also been used to test Einstein’s theory of general relativity. I will discuss these advances in more detail in future posts.

Knowledge of pulsars was also used in a very interesting way in the 1970s.  Four spacecraft were launched, destined to the leave the Solar system and head out into interstellar space. The missions are described in more detail in my previous post Artefacts from Earth.  On each spacecraft there was a diagram devised by the American astronomer, Frank Drake (1930-), consisting of a circle with 15 lines coming out of it.

The centre of the diagram, from which the lines radiate, represents the Sun.  The right-hand end of the longest line (at 3 o’clock) represents the centre of the galaxy. The end of each of the remaining line represents a pulsar and the length of the line between the Sun and the pulsar represents the distance to the pulsar.

The diagram relies on the fact that each pulsar has its own distinct period between pulses. So if, in the far distant future, an alien civilisation were to recover the spacecraft they would be able to identify the pulsars from their periods.  To enable this, each of the lines depicts the length of the pulsar’s period not in seconds (which as a man-made unit would be meaningless to an alien race) but in multiples of a ‘fundamental time unit’ that an alien might understand.  The alien civilisation could then have sufficient information to identify the fourteen pulsars and the distance of the Sun from each pulsar, and thus work out the location of our Solar system within the galaxy.

The Nobel prize controversy

Jocelyn Bell and Antony Hewish published their results in February 1968 (Hewish et al 1968). The discovery of this entirely new type of astronomical object was a major advance. Interestingly, it had been suggested as long ago as 1934 by the astronomers Baade and Zwicky that neutron stars would be the end result of supernova explosions. However, this prediction was ignored. Before 1967 most astronomers regarded neutron stars as hypothetical objects which might or might not actually exist in reality.

Such was the impact of the discovery that it led to the Nobel prize for physics in 1974. Two astronomers were awarded the prize – but Jocelyn Bell was not one of them. Antony Hewish and Martin Ryle were the recipients, the former for the discovery of pulsars and the latter for his work in radio astronomy.  Jocelyn Bell’s contribution was not recognised.

Antony Hewish (1924- ) 

Many at the time felt that Jocelyn Bell should have been given at least a share in the prize, since she was the person who had initially spotted the signal from the first pulsar. The British astronomer Fred Hoyle was particularly vocal on the issue and stated publicly  that Bell should have been given a major share of the prize to acknowledge her contribution. Bell herself said very little about the controversy in the years immediately afterwards. The few statements she made were, in general, supportive of the Nobel prize committee’s decision. In the 1960’s and 1970’s it was commonplace for the senior person leading a team of scientific researchers to get the credit for a major discovery on behalf of the entire team. This is largely still true today.

Bell went on to have a successful academic career and always has been a passionate advocate for getting women more involved in science. From 2002 to 2004 she served as the president of the Royal Astronomical Society, the organisation for British Astronomers. She was the first ever woman to hold that role.  She later served as the first ever female president of the Institute of Physics. In 2006, nearly 40 years after the discovery, she said in an  interview:

In those days, it was believed that science was done, driven by great men . . . And that these men had a fleet of minions under them who did their every bidding, and did not think. It also came at the stage where I had a small child and I was struggling with how to find proper childminding, combine a career, and before it was acceptable for women to work. And so I think at one level it said to me ‘Well men win prizes and young women look after babies.’

Postscript: a different kind of pulsar discovered in 2016

Stars such as the Sun do not end their lives in violent supernova explosions resulting in neutron stars. Instead, when they have used up all their nuclear fuel, the outer layers of the star are blown away into space and form a bright glowing shell of gas called a planetary nebula, shown below.

Planetary Nebula

The remnants of the star’s core collapse into a dense hot star called a white dwarf, an object which is roughly the same size as the Earth.  For the last 50 years astronomers have predicted that some white dwarfs might also form pulsars, although because white dwarfs are much larger and rotate more slowly than neutron stars, the radiation would be much weaker than neutrons star pulsars, making them harder to detect and the pulses would be much longer.  This prediction was finally confirmed in 2016 when a team led by Tom Marsh from Warwick University discovered that the white dwarf star AR Scorpii was a pulsar with a period of about 2 minutes.

References

Baade, W.and Zwicky, F. (1934) ‘Remarks on supernovae and cosmic rays’, Physical Review, 46(1), pp. 76-77.

Hewish, A., Bell. S. J., Pilkington, J. D. H, Scott P. F. and Collins, A (1968) ‘ Observation of a rapidly pulsating radio source’, Nature, 217(), pp. 709-713.

 

Jupiter at opposition 9 May 2018

On May 9 the planet Jupiter will be what is known as ‘at opposition’.  This event, which occurs every 399 days, happens when Jupiter is at its closest to the Earth and at its brightest.  To the naked eye it will be a brilliant white object, three times brighter than the brightest star. Features such as coloured bands and the famous great red spot can easily be seen with a small telescope.

Jupiter

Jupiter through a telescope – image from NASA

What is opposition? 

The series of diagrams below show Jupiter and Earth at different points in their orbits around the Sun. The Earth takes just over 365 days to complete an orbit. Jupiter, which is further away from the Sun and moves more slowly in its orbit, takes nearly 12 years.

In the first diagram, below, Jupiter is at its closest point to the Earth  As seen from Earth, Jupiter is in the opposite direction from the Sun. This is why it is called opposition. All night between sunset and sunrise, Jupiter is above the horizon and it reaches its highest point in the sky in the middle of the night. Jupiter is at its brightest at opposition because it is at its closest to Earth and the entire sunlit side is facing Earth.

 

In the diagram below, 133 days later, the Earth has completed more than one-third of its journey around the Sun, whereas Jupiter has done less than 3%. Jupiter appears less bright because it is further away from Earth and not all the sunlit side of Jupiter is facing us.  In addition, Jupiter appears fairly close to the Sun and for most of the time is only above the horizon during the daytime, when it is very difficult to see against the brightness of the daytime sky.

199.5 days later the Earth has completed more than half its journey around the Sun, whereas Jupiter has done just over 4.6%. At this point, which is known as a conjunction of Jupiter and the Sun, Jupiter is only above the horizon in the daytime and is impossible for an amateur astronomer to see without specialist equipment, because it is so close to the Sun.

399 days later, the Earth has caught up with Jupiter, so the two are level again in their orbits. Jupiter is once again at opposition.

 

 

How bright is Jupiter at opposition?

When discussing the brightness of objects in the sky, astronomers use a scale called magnitude, where the lower the magnitude the brighter the object.

The scale was invented by the ancient Greek astronomers who classified all the stars visible to the naked eye into six magnitudes. The brightest stars were said to be of magnitude 1, whereas the faintest were of magnitude 6, which is the limit of human visual perception (without the aid of a telescope). Today, the magnitude scale is applied to all objects in the sky, not just stars, and the magnitude of the very brightest objects is less than zero. The brightest objects in the sky are (obviously) the Sun, which has a magnitude of -26.7, followed by the Moon, which has a magnitude of -12.7, at a typical full Moon.

The scale is defined so that a decrease in magnitude by 1 means an increase in brightness by a factor of 2.512. Therefore, a decrease in magnitude by 2 would mean an increase in brightness by 6.31, because 2.512 x 2.512 = 6.31. So, for example:

  • a star of magnitude 1 is 15.9 times brighter than a star of magnitude 4. This is because 2.512 x 2.512 x 2.512 = 15.9.
  • a star of magnitude 1 is 100 times brighter than a star of magnitude 6. This is because 2.512 x 2.512 x 2.512 x 2.512 x 2.512 = 100

Jupiter moves in an elliptical orbit around the Sun; this means that its closest distance to Earth is different at each opposition. Therefore, as shown below, the brightness at each opposition will vary as well.

The diagram above shows that if an opposition occurs where Jupiter is closest to the Sun (point A,) Jupiter will also be closest to the Earth and thus brighter than an opposition which occurs where Jupiter is furthest from the Sun (point B) . In the diagram the elongation of Jupiter’s orbit has been exaggerated. 

The closest Jupiter can get to Earth is 589 million km; when this happens it shines with a magnitude of -2.9. On the May 9 opposition, it will be 658 million km from Earth and will shine with a magnitude of -2.5, making it three  times more luminous than the brightest star Sirius, which has a magnitude of -1.4.  For comparison, the table below shows the average magnitude at opposition of the planets which lie outside the Earth’s orbit.

 

Data from https://nssdc.gsfc.nasa.gov/planetary/factsheet/

How Does the brightness of Jupiter compare to Venus? 

For the two inner planets Venus and Mercury, the situation is a little different. They can never be at opposition because they lie inside the Earth’s orbit. This is shown in the diagram below for Venus.

Venus Phases

As Venus orbits the Earth it goes through phases, similar to those of the Moon. However, because Venus is so small, they are only visible through a telescope. When Venus is closest to the Earth, the point known as its inferior conjunction – labelled A in the diagram – it is almost impossible to see because it is almost in a direct line of sight with the Sun and its sunlit side is facing away from Earth. Venus is actually at its brightest just before and just after inferior conjunction,  points B and F, when it has a magnitude of around -4.5.

Although Venus appears brighter than Jupiter, unlike Jupiter it is never above the horizon all night. At point B it is only clearly visible for few hours before sunrise where it is known as the Morning Star. At point F it is only visible for a few hours after sunset where it is known as the Evening Star.

Properties of Jupiter

As nearly all my readers will know, Jupiter is the largest planet in the Solar System. Its diameter is on average 140,000 km which is roughly 11 times that of the Earth, making its volume 1320 times larger (Williams 2017). It is its large size which causes Jupiter to appear brighter than Mars despite it being more than three times further from the Sun.

Unlike the smaller inner planets (Mercury, Venus, Earth and Mars) which have large iron cores surrounded by rocky materials, Jupiter is mainly composed of gas. It is not known if it has a solid core, but if one exists it will only make up a small proportion of the planet. Being made up of largely of gas means that its density is only 25% that of the Earth. Even so, its mass is still 320 times greater, making it more massive than all the other planets, moons, asteroids and comets in the Solar System put together.

Exploration of Jupiter

So far nine unmanned spacecraft have visited Jupiter. The first was Pioneer 10 in 1973 shown below.

Pioneer_10_at_Jupiter

Image from NASA

This was followed by Pioneer 11 (1974), Voyager 1 and Voyager 2 (both 1979), Ulysses (1992), Galileo – which went into orbit around Jupiter between 1995 and 2003, Cassini (2000) and New Horizons (2007). The latest mission Juno (shown below) arrived in 2016 and is currently orbiting the planet studying its atmosphere, magnetic and gravitational fields. For more details on the Juno mission see my post Mission Juno.

Juno at Jupiter

Image from NASA

Jupiter’s moons

Jupiter has its own mini “solar system” of over 60 moons in orbit around it. The four largest moons were discovered by Galileo in 1610 and one of them, Ganymede, the largest moon in the solar system, is bigger than the planet Mercury. The innermost moon Io is the most volcanically active object known to exist anywhere. Europa, the second innermost, is of particular interest because its surface is composed of ice underneath which are thought to lie oceans of liquid water, warmed by a process called tidal friction. Many scientists think that Europa is one of the most promising places in the Solar System to find extraterrestrial life.

NASA  and the European Space Agency (ESA) are developing missions to Jupiter’s moons, will tell us a lot more about them . The ESA mission is called  (JUICE)  which stands for JUpiter ICy moon Explorer and the NASA mission is called Europa Clipper. Both missions are scheduled for launch in 2022.

Jupiter Moons

The four large moons of Jupiter: Io, Europa, Ganymede and Callisto -Image from NASA

I hope you’ve enjoyed this post and that you will have a clear night on the daysaround 9 May to see this sight.

Notes

In the discussion of magnitudes all the values quoted are visual magnitudes. This is how bright the objects are in light of wavelength of 540 nanometres, which is in the green part of the spectrum. The values at other wavelengths will be different for different objects. For details on light and the way the eye sees different wavelength as different colours see https://thesciencegeek.org/2015/09/30/why-is-the-sky-blue/

Reference

Williams, D. R. (2017) Jupiter Fact Sheet, Available at:http://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html (Accessed: 28 April 2018).

A Christmas gift from The Science Geek 2017

 

Christmas is almost upon us. Once again I’m offering my e-books for free during the first five days of December!  Just call me Father Christmas :-).

Is Anyone Out There?” is about the likelihood of there being extraterrestrial intelligent life.  It is based on a number of posts from my blog.  For readers based in the UK the book is available to download from Amazon in Kindle format by clicking here and for readers in the US by clicking here. If you’re based outside the UK or US , see the notes at the end of the post.

Is Anyone Out There Cover

The Moon” is also based on a series of posts from my blog and you can guess what it is about.  UK readers download here, US readers here and anyone else please see the notes below.

Moon Cover

How to download the books if you’re based outside the UK or US.

There are threeways of doing this.

Option 1 if you go into the Amazon Kindle store and search for “The Science Geek” as the author you should find my books.

Option 2  I have created a page on my website where you will be able to download either of books for free.
https://thesciencegeek.org/e-books/

I’ll put them there until at least the end of the year.

Option 3  If your country is listed below, I have added some links  to allow you to download the books by just clicking on the link for your country.

Is There Anyone Out There?

Australia http://www.amazon.com.au/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Brazil http://www.amazon.com.br/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Canada http://www.amazon.ca/gp/product/B0131LVNW8?*Version*=1&*entries*=0

France http://www.amazon.fr/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Germany http://www.amazon.de/gp/product/B0131LVNW8?*Version*=1&*entries*=0

India http://www.amazon.in/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Italy http://www.amazon.it/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Japan http://www.amazon.co.jp/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Mexico http://www.amazon.com.mx/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Netherlands http://www.amazon.nl/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Spain http://www.amazon.es/gp/product/B0131LVNW8?*Version*=1&*entries*=0

USA http://www.amazon.com/gp/product/B0131LVNW8?*Version*=1&*entries*=0

The Moon

Australia http://www.amazon.com.au/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Brazil http://www.amazon.com.br/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Canada http://www.amazon.ca/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

France http://www.amazon.fr/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Germany http://www.amazon.de/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

India http://www.amazon.in/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Italy http://www.amazon.it/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Japan http://www.amazon.co.jp/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Mexico http://www.amazon.com.mx/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Netherlands http://www.amazon.nl/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Spain http://www.amazon.es/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

USA http://www.amazon.com/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

The discovery of pulsars 1967

In 1967 Jocelyn Bell, a 24-year-old student from Cambridge University, was doing the research for her PhD.

She was using a radio telescope to study radio waves emitted from compact astronomical objects known as quasars, and when she analysed the data she had collected, she noticed a signal which appeared to pulse on and off every 1.3 seconds. After doing this continuously for about an hour, the pulsing signal would stop altogether, but it would start again precisely 23 hours 56 minutes later after it had first started. As Jocelyn Bell – and indeed all astronomers – knew, the Earth rotates on its axis once every 23 hours 56 minutes, a period of time called a ‘sidereal day’, and the fact that the pulsating signal was detected at the same time in each sidereal day meant that it must almost certainly be coming from space rather than being man-made. The diagram below shows how the radio telescope can only pick up the signal when the pulsing object is in its field of vision.

 

Not only was the time interval between each pulse very short at only 1.3  seconds, but this time interval was completely constant and didn’t vary to any significant degree.  The fact that the pulses were very short in duration and so regular meant that whatever was emitting the pulses must be extremely small in astronomical terms.  A larger object – something, for example, the size of the Sun – would not be able to generate such precise pulses. For a while Bell and her PhD supervisor Antony Hewish considered the possibility that the mysterious signals were generated by a signaling beacon left by an alien civilisation. For this reason, they briefly nicknamed  the unknown object ‘Little Green Men-1’. However, this explanation was rejected when it became clear that the pulses contained no information and when they also discovered additional pulsing sources in other parts of the sky.

Pulsars

The origin of the mysterious signals turned out to be a hitherto unknown class of astronomical objects, known as neutron stars. Neutron stars are very small, typically around 20 km in diameter, but have an enormous mass – between 1.1 and 3 times the mass of the Sun.  Having such a large mass squeezed into a small volume means that their density (mass divided by volume) is incredibly high.  A cubic centimetre of neutron star material would weigh about 500 million tons. They are called neutron stars because they consist mainly of neutrons, which are subatomic particles found in the nucleus of ordinary atoms. In a neutron star the neutrons are so tightly squeezed together that they are touching each other. Neutron stars also have very strong magnetic fields – around 1 trillion times stronger than the Earth’s.

Neutron stars which rotate extremely rapidly, around once a second, are known as pulsars, and these are the objects which Bell and Hewish had detected. This rotation causes electrically charged particles around the neutron star to move rapidly in the intense magnetic fields. This causes electromagnetic radiation (such as radio waves) to be emitted in two cone-shaped beams along the magnetic North and South poles of the pulsar, shown as B in the diagram below.

In the diagram above A is the axis around which the pulsar rotates and B is the magnetic axis.

As you can see, the magnetic poles are at an angle to the line through the North and South poles of the pulsar about which it rotates. This means that the cone-shaped beams will rotate around the axis of the pulsar and only when either of the beams is pointing directly at the Earth will it be detected. A pulsar behaves like a lighthouse – the light is on all the time but appears to a viewer to switch on when it is pointing towards them and switch off when it is pointing away.

Neutron stars are formed when a large massive star explodes at the end of its life in a violent event known as a supernova. Most of the outer parts of the star are blown out into space by the force of the explosion. The remaining material in the star’s core collapses, forming a neutron star.  In fact, if the remaining material from the star’s core is more than three times the mass of the Sun, a neutron star won’t be formed at all.  Instead, an even more compact object called a black hole will result.

Large stars with a diameter of tens of millions of kilometres rotate relative slowly, taking around one year to complete one rotation. As the star collapses into a small massive object, millions of times smaller in diameter, a law of physics called the conservation of angular momentum causes its rotation to speed up massively.  A much more familiar example of this is from the world of ice skating: ice skaters spin more rapidly when they pull in their arms.

Why this knowledge has been useful to astronomy

In the last 50 years more than 2000 pulsars have been detected. Understanding the properties of pulsars has led to further discoveries in various areas.  For example, it has led to greater understanding of the diffuse gas between stars known as the interstellar medium, and it has also been used to test Einstein’s theory of general relativity. I will discuss these advances in more detail in future posts.

Knowledge of pulsars was also used in a very interesting way in the 1970s.  Four spacecraft were launched, destined to the leave the Solar system and head out into interstellar space. The missions are described in more detail in my previous post Artefacts from Earth.  On each spacecraft there was a diagram devised by the American astronomer, Frank Drake (1930-), consisting of a circle with 15 lines coming out of it.

The centre of the diagram, from which the lines radiate, represents the Sun.  The right-hand end of the longest line (at 3 o’clock) represents the centre of the galaxy. The end of each of the remaining line represents a pulsar and the length of the line between the Sun and the pulsar represents the distance to the pulsar.

The diagram relies on the fact that each pulsar has its own distinct period between pulses. So if, in the far distant future, an alien civilisation were to recover the spacecraft they would be able to identify the pulsars from their periods.  To enable this, each of the lines depicts the length of the pulsar’s period not in seconds (which as a man-made unit would be meaningless to an alien race) but in multiples of a ‘fundamental time unit’ that an alien might understand.  The alien civilisation could then have sufficient information to identify the fourteen pulsars and the distance of the Sun from each pulsar, and thus work out the location of our Solar system within the galaxy.

The Nobel prize controversy

Jocelyn Bell and Antony Hewish published their results in February 1968 (Hewish et al 1968). The discovery of this entirely new type of astronomical object was a major advance. Interestingly, it had been suggested as long ago as 1934 by the astronomers Baade and Zwicky that neutron stars would be the end result of supernova explosions. However, this prediction was ignored. Before 1967 most astronomers regarded neutron stars as hypothetical objects which might or might not actually exist in reality.

Such was the impact of the discovery that it led to the Nobel prize for physics in 1974. Two astronomers were awarded the prize – but Jocelyn Bell was not one of them. Antony Hewish and Martin Ryle were the recipients, the former for the discovery of pulsars and the latter for his work in radio astronomy.  Jocelyn Bell’s contribution was not recognised.

Antony Hewish (1924- ) 

Many at the time felt that Jocelyn Bell should have been given at least a share in the prize, since she was the person who had initially spotted the signal from the first pulsar. The British astronomer Fred Hoyle (who readers of a previous post may recall was a founder of the steady state theory of the origin of the Universe) was particularly vocal on the issue and stated publicly many times that Bell should have been given a major share of the prize to acknowledge her contribution. Bell herself said very little about the controversy in the years immediately afterwards. The few statements she made were, in general, supportive of the Nobel prize committee’s decision. In the 1960’s and 1970’s it was commonplace for the senior person leading a team of scientific researchers to get the credit for a major discovery on behalf of the entire team. This is largely still true today.

Bell went on to have a successful academic career and always has been a passionate advocate for getting women more involved in science. From 2002 to 2004 she served as the president of the Royal Astronomical Society, the organisation for British Astronomers. She was the first ever woman to hold that role.  She later served as the first ever female president of the Institute of Physics. In 2006, nearly 40 years after the discovery, she said in an  interview:

In those days, it was believed that science was done, driven by great men . . . And that these men had a fleet of minions under them who did their every bidding, and did not think. It also came at the stage where I had a small child and I was struggling with how to find proper childminding, combine a career, and before it was acceptable for women to work. And so I think at one level it said to me ‘Well men win prizes and young women look after babies.’

Postscript: a different kind of pulsar discovered only last year

Stars such as the Sun do not end their lives in violent supernova explosions resulting in neutron stars. Instead, when they have used up all their nuclear fuel, the outer layers of the star are blown away into space and form a bright glowing shell of gas called a planetary nebula, shown below.

Planetary Nebula

The remnants of the star’s core collapse into a dense hot star called a white dwarf, an object which is roughly the same size as the Earth.  For the last 50 years astronomers have predicted that some white dwarfs might also form pulsars, although because white dwarfs are much larger and rotate more slowly than neutron stars, the radiation would be much weaker than neutrons star pulsars, making them harder to detect and the pulses would be much longer.  This prediction was finally confirmed in 2016 when a team led by Tom Marsh from Warwick University discovered that the white dwarf star AR Scorpii was a pulsar with a period of about 2 minutes.

References

Baade, W.and Zwicky, F. (1934) ‘Remarks on supernovae and cosmic rays’, Physical Review, 46(1), pp. 76-77.

Hewish, A., Bell. S. J., Pilkington, J. D. H, Scott P. F. and Collins, A (1968) ‘ Observation of a rapidly pulsating radio source’, Nature, 217(), pp. 709-713.

 

Voyager 40th anniversary

Nearly 40 years ago, on 20 August 1977, the Voyager 2 space probe was launched from Cape Canaveral, Florida, on a mission to study the Solar System’s four outermost planets. It was followed 15 days later by the launch of an identical spacecraft, Voyager 1.

The Voyager spacecraft -Image from NASA

Although Voyager 1 was launched after Voyager 2, it followed a different path which meant that it actually visited its first target, the planet Jupiter, four months earlier.

Image from Wikimedia Commons

The diagram above shows the trajectory of the Voyager spacecraft. The first targets, the giant planets Jupiter and Saturn, had previously been visited by NASA’s Pioneer 10 and 11 spacecraft, but the Voyagers had better instruments and were able to take more accurate observations. Among the discoveries made by Voyager was that Io, one of Jupiter’s moons, has a number of active volcanoes. This made Io the first place other than the Earth where volcanoes had been seen to erupt.

Jupiter’s moon Io – Image from NASA

Voyager 1 passed close to Saturn’s giant moon Titan. Titan is 5,150 km in diameter, nearly twice as large as the Moon, and is in fact slightly larger than the planet Mercury. It is the only moon in the Solar System with a thick atmosphere, which surrounds it with a dense haze hundreds of kilometres deep, making it impossible to see any surface details. At Titan’s surface the atmospheric density is roughly 5 times greater than the Earth’s at sea level.  Voyager 1 discovered that it consists mainly of nitrogen (98.4%) and methane (1.4%) with trace amounts of other gases such as ethane.

Saturn’s moon Titan – Image from NASA

These discoveries led to speculation that, like Earth, Titan has complex weather patterns. Being so far from the Sun, Titan’s surface is very cold, around minus 180 degrees.  This temperature is near the boiling point of hydrocarbons such as ethane and methane, which on Earth are found in natural gas. Voyager 1’s discoveries suggested that on Titan it rains liquid hydrocarbons in a similar way to how it rains water on Earth and that there were lakes of liquid hydrocarbons on Titan’s surface. A later mission by the spacecraft Cassini to Saturn and its moons did indeed detect many lakes of liquid methane on Titan (NASA 2016).

After passing Saturn, Voyager 2 visited the two outermost planets Uranus and Neptune (shown below).

Neptune – image from NASA

Uranus and Neptune are of similar size and are both much smaller than the gas giants Jupiter and Saturn. They are mainly composed of frozen water, ammonia and methane and are sometimes called the “ice giants”  So far Voyager 2 is the only mission to have visited the ice giants and most of what we know about Uranus and Neptune came from this spacecraft. No further missions to Uranus or Neptune are planned. Although it is possible that a mission to the ice giants could be launched by NASA in the the 2030s (Clark 2015), this is very much at the proposal stage. I think that this won’t happen, given the high cost of space missions and other higher priority targets such as exploring Mars.

After completing their primary mission to study the outer planets, the Voyagers left the Solar System. They are still in contact with Earth and are now sending back data about interstellar space. For more details on this part of the Voyagers’ mission click here.

The golden record

Each Voyager contained a golden record, the cover of which is shown below.

Voyager Record Cover

Image from NASA

The purpose of the golden record was twofold. If either of the Voyager spacecraft were ever found by an alien intelligence in the far future then, as I’ll explain later, from the golden record cover they would be able to work out the location of the Sun within the galaxy and, by playing the record, get some information about the sounds and sights of Earth in the 1970s.

If you look at the bottom left hand corner of the golden record cover there is a small circle with 15 lines coming out of it. This is shown in more detail in the diagram below.

This diagram was also put on a plaque on the earlier Pioneer probes and was devised by Frank Drake (1930-), who has been heavily involved in the search for extraterrestrial intelligence (SETI). The centre of the diagram, from which the lines radiate, represents the Sun.  The right-hand end of the longest line (at 3 o’clock) represents the centre of the galaxy.  The end of each of the remaining lines represents an object called a pulsar and the length of the line between the Sun and the pulsar represents the distance to the pulsar.

Pulsars are rapidly rotating objects which emit radio waves in regular pulses a few seconds or fractions of a second apart. Each pulsar has its own distinct interval or period between pulses and the marks drawn on the lines depict the length of the pulsar period not in seconds but in multiples of a fundamental time unit that an alien might understand (see note below).  The alien civilisation could then have sufficient information to identify the fourteen pulsars and the distance of the Sun from each pulsar, and thus work out the location of our Solar system.

On the upper part of the golden record cover is a picture of the record itself plus instructions for playing it.

Voyager Record

Image from NASA

The content of the record was agreed by a committee chaired by Carl Sagan (1934-1996) itself, and includes:

  • greetings in 55 different languages,
  • natural sounds and some music from Earth
  • 116 pictures of a variety of objects such as the planets in the solar system, human anatomy, groups of children, important landmarks, interesting places, and man-made structures such as airports, large telescopes, the Golden Gate Bridge in San Francisco, and an American highway in the rush-hour.
  • a printed message from the then United States president Jimmy Carter, part of which is given below:

“…This is a present from a small different world, a token of our sounds, our science, our images, our music, our thoughts, and our feelings.  We are attempting to survive in our time so that we we may live into yours. We hope someday, having solved the problems we face, to join a community of galactic civilisations. This record represents our hope and our determination and our goodwill in a vast and awesome universe.”

Where are the space probes now?

As well as the two Voyagers, three other spacecraft have been launched on a trajectory to take them out of the Solar System. They are New Horizons, which passed the dwarf planet Pluto in 2015 and Pioneer 10 and 11, which were the first spacecraft launched to leave the solar system. As you can see from the table, the Pioneer spacecraft  are no longer in contact with Earth.  There are two possible reasons for this: either their power supply has run out, or the radio transmitter is no longer lined up with the Earth and is beaming out signals in a completely different direction. The Voyager spacecraft are still in contact and should have enough power to continue transmitting messages back to the Earth until the mid 2020s.

 

In the table, the distance of the probes is given both in kilometers and astronomical units (AU). 1 AU is the average distance from the Earth to the Sun and is equal to just under 150,000,000 km. The outermost planet Neptune is about 30 AU from the Sun and the nearest star about 250,000 AU away. The speed column shows how fast the spacecraft is moving away from the Sun in AU per year.

Will the Voyagers ever be found?

Even astronomers who think that alien life is widespread within our galaxy think that it is very unlikely, given the vastness of space, that the Voyager spacecraft will ever be found.  The spacecraft are small and their power sources will have long died, thus making them unable to transmit a signal which could be picked up. However if they were ever to be intercepted by an alien civilisation it is fascinating to think what they would make of them.

Note about the pulsar diagram

Clearly units of time such as hours, minutes and seconds, which have been invented by humans, would be meaningless to an alien. Atomic hydrogen is the most common element in the Universe and Drake used the transition of a hydrogen atom, shown on the bottom right hand corner of the record cover, to create a “fundamental time unit” which he hoped an extraterrestrial race would understand.  When a hydrogen atom flips from one state to another it emits radio waves at a frequency of 1,420,406,000 waves per second, a fact that any advanced civilisation would be well aware of. So each individual wave corresponds to a time interval of 0.000 000 000 704 seconds. All the pulsar periods are expressed in multiples of this fundamental time interval.

References

Clark, S (2015) Uranus, Neptune in NASA’s sights for new robotic mission, Available at: https://spaceflightnow.com/2015/08/25/uranus-neptune-in-nasas-sights-for-new-robotic-mission/ (Accessed: 15 June 2017).

NASA (2016) Cassini explores a methane sea on Titan, Available at: https://www.nasa.gov/feature/jpl/cassini-explores-a-methane-sea-on-titan (Accessed: 15 June 2017).

 

Happy New Year from The Science Geek

Happy New Year to all my readers and followers. I hope that you all will continue to read and enjoy my blog 🙂

For many people living in the USA the most memorable event of the coming year will not be the inauguration of the new president but the total solar eclipse, which I’ll talk about briefly at the end of this post. 2017 also marks the anniversaries of a number of major advancements in the fields of astronomy and space science.

Start of the space age 1957

On 4 October it will be 60 years since an event which marked the beginning of the space age – the launch in 1957 of Sputnik 1, the first ever artificial satellite, into orbit around the Earth by the Soviet Union.  As I’m sure you will know, this was the time of the Cold War between the Soviet Union and the West, and Sputnik’s success caught the US by surprise – most commentators expected the Americans to be first to do this. Not only did the Soviets beat them to it, but shortly afterwards, in December 1957, the first attempt by the Americans to put a satellite in orbit failed when the launcher exploded just after take off.  Many in the West were fearful that Soviet technology was more advanced than they had realised.

sputnik-stamppng

A USSR stamp showing Sputnik 1 orbiting the Earth – image from Wikimedia Commons

In the years following Sputnik there was a space race between the US and the Soviet Union, which the Americans won when they put the first man on the Moon in 1969.

Aldrin_Apollo_11

Image from NASA

Launch of the Voyager spacecraft 1977

On 20 August it will be the fortieth anniversary of the launch of Voyager 2, the first of the two Voyager spacecraft (Voyager 1 was actually launched two weeks later on September 5). It conducted a grand tour of the Solar System, visiting all four of the outer planets: Jupiter, Saturn, Uranus and Neptune.

voyager-trajectory

The Voyager spacecraft made many exciting discoveries. Indeed most of what we know about the two outermost planets, Uranus and Neptune, was uncovered by Voyager 2. One of their most interesting findings was that Jupiter’s moon Io (shown below) had active volcanoes.

io

Image from NASA

Discovery of the first pulsar 1967

28 November 2017 marks the fiftieth anniversary of the discovery of the first pulsar by radio astronomers based at Cambridge University in England. Pulsars are objects which emit regular pulses of radiation a fixed period of time apart. The time interval between each pulse is very small, typically around one second.  When the signals were first observed the small interval between the pulses led the team to consider briefly that they were beacons left by an extraterrestrial civilisation.  In fact, the team in Cambridge code-named their mysterious signal LGM-1, an abbreviation for Little Green Men 1.

However, pulsars  turned out to be rapidly rotating small objects called neutron stars. A neutron star is an object where a mass similar to that of the Sun is compressed into a sphere about 10 km in diameter. Neutron stars are so dense that a cubic centimetre of neutron star material would have a mass of around 500 million tonnes.

Invention of the Transistor 1947

2017 is also the seventieth anniversary of the transistor which was invented in 1947 in the Bell laboratories, New Jersey.  The transistor forms the basis of all modern electronic devices. Initially the first transistors were quite large. However over the decades transistors have got smaller and smaller and integrated circuits have been developed containing more and more transistors.

In the early 1970s simple integrated circuits used in computers contained a few thousand transistors. Today’s modern electronic devices,such as the laptop I am writing this post on, have integrated circuits containing billions of transistors. The invention of the transistor and the ability to make circuits containing a vast number of transistors, which in turn led to advances in computing, ranks as one of the greatest scientific advances of the last 70 years.

transistor-count

 

Image from Wikimedia commons.

The solar eclipse

As I mentioned at the start of this post, the most significant astronomical event of the year for many of my readers in the US will be the total solar eclipse on 21 August.

Solar_eclipse_1999

Image from NASA

Although partial eclipses occur every few years, total eclipses where the Moon completely covers the Sun and the sky becomes dark are relatively rare. This will be first total eclipse visible in the continental US for nearly 40 years. The last one was in 1979. The path of the eclipse is shown in the diagram below, people located in the band marked will see a total eclipse. Areas either side of the side of this band will see a partial eclipse

 

eclipse-us

Image from NASA

 

On that note I’ll sign off for now and I hope that, wherever you live, 2017 will be a great year for you.

 

The Science Geek

A Christmas present from The Science Geek

 

Now that we are into December, Christmas is almost upon us. So, as I did last year, I’d like to give my readers an early Christmas present, by letting you download my short e-books for free during the first five days of December!

Is Anyone Out There?” is about the likelihood of there being extraterrestrial intelligent life.  It is based on a number of posts from my blog.  For readers based in the UK the book is available to download from Amazon in Kindle format by clicking here and for readers in the US by clicking here. If you’re based outside the UK or US , see the notes at the end of the post.

Is Anyone Out There Cover

The Moon” is also based on a series of posts from my blog and you can guess what it is about.  UK readers download here, US readers here and anyone else please see the notes below.

Moon Cover

How to download the books if you’re based outside the UK or US.

There are two ways of doing this.

Firstly, if you go into the Amazon Kindle store and search for “The Science Geek” as the author you should find my books.

Secondly, I have added some links below to allow you to download the book by just clicking on the link for your country.

Is There Anyone Out There?

Australia http://www.amazon.com.au/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Brazil http://www.amazon.com.br/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Canada http://www.amazon.ca/gp/product/B0131LVNW8?*Version*=1&*entries*=0

France http://www.amazon.fr/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Germany http://www.amazon.de/gp/product/B0131LVNW8?*Version*=1&*entries*=0

India http://www.amazon.in/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Italy http://www.amazon.it/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Japan http://www.amazon.co.jp/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Mexico http://www.amazon.com.mx/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Netherlands http://www.amazon.nl/gp/product/B0131LVNW8?*Version*=1&*entries*=0

Spain http://www.amazon.es/gp/product/B0131LVNW8?*Version*=1&*entries*=0

USA http://www.amazon.com/gp/product/B0131LVNW8?*Version*=1&*entries*=0

The Moon

Australia http://www.amazon.com.au/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Brazil http://www.amazon.com.br/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Canada http://www.amazon.ca/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

France http://www.amazon.fr/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Germany http://www.amazon.de/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

India http://www.amazon.in/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Italy http://www.amazon.it/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Japan http://www.amazon.co.jp/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Mexico http://www.amazon.com.mx/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Netherlands http://www.amazon.nl/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

Spain http://www.amazon.es/gp/product/B00WRPR2S4?*Version*=1&*entries*=0

USA http://www.amazon.com/gp/product/B00WRPR2S4?*Version*=1&*entries*=0