Asteroseismology: A New Keplerian Revolution



Professor Donald Kurtz

Jeremiah Horrocks Institute
University of Central Lancashire, UK

Thursday, 30 January, 2020

4pm-5pm, INB3305

In 1926 in the opening paragraph of his now-classic book, The Internal Constitution of the Stars, Sir Arthur Eddington lamented, “What appliance can pierce through the outer layers of a star and test the conditions within?” While he considered theory to be the proper answer to that question, there is now an observational answer: asteroseismology. We are in a time of a significant advance in our understanding of stellar astrophysics with data from the Kepler and TESS Space Missions. These have improved our ability to see pulsations and variability in stars by 100 to 1000 times compared with ground-based telescopes, allowing us to probe stars using asteroseismology. We are seeing as never before: heartbeat stars, the new tidally enhanced pulsators, novel eclipsing stars, spots, flares and magnetic cycles as in our own Sun. Astrophysics that used to be theoretical is now also observational: internal stellar rotation from core to surface; gravitational lensing in eclipsing binary stars; Doppler boosting; multiple pulsation axes; period doubling; tidal excitation in highly eccentric binary stars. Kepler and TESS data for solar-like stars are now comparable to data for the Sun seen as a star, giving us masses, radii and ages for thousands of single stars, allowing determination of their orbiting planets’ sizes, and giving new constraints on stellar evolution theory. It is now even possible to see into the cores of red giants and observe which stars are hydrogen shell-burning and which also are helium-core burning. This talk will introduce the concepts of asteroseismology and show a selection of exciting observational results from the Kepler and TESS missions.

Star Wars: Could we really live on moons?

In its opening scenes, the immortal line, “In a galaxy far, far away”, teased the idea of new, unseen worlds in what we would come to know as the Star Wars universe.

From the cold desert moon Jedha and the forest moon Endor, to the rebel headquarters on the jungle moon Yavin 4, moons have played an important part of the Star Wars landscape.

When the first film was released in 1977 these fantastical places really did seem ‘far, far, away’ and as the latest instalment of the Disney franchise is about to hit cinemas, it’s likely that astrophysicists (the ones who happen to be into Star Wars) have debated what the reality of those types of planets being able to sustain life is.

But without access to the Millennium Falcon, the Star Wars moons are outside our reach and we’re left with our own galaxy, which aren’t as far, far away – so could we really inhabit planets or moons away from earth?

While it might sound as unfathomable as Jabba the Hutt on a treadmill, in fact, many of the worlds depicted in Star Wars could exist in our universe – particularly if we colonised the older moons which have become tidally locked to the planet they orbit, and their orbits more circular. Dynamically young moons, despite looking habitable on paper with the right atmosphere and temperature, would likely have significant tides from the much larger planets they orbit; this would cause daily volcanic activity, even before discussing what might happen to any oceans on these moons

In our own galaxy, Kepler-16b is a Saturn sized gas giant orbiting two stars with a combined mass comparable to the sun at a distance close enough for liquid water to exist, known as the habitable zone. However, the planet itself is not habitable as it is too large, but it does have the potential to support a moon; recent research suggests that an earth-sized moon could orbit this binary planet and be habitable, proving that moons orbiting planets just like Tatooine can exist.

Two relatively nearby moons that are strong candidates that could support life are Enceladus and Europa which are moons orbiting Saturn and Jupiter respectively.

Both of these moons are a long way from the Sun and have frozen surfaces which are hostile to life, but the close proximity to their host planets can cause some internal heating, which is thought to maintain the liquid water oceans located under the deep-frozen surface. Enceladus, Saturn’s icy moon can be seen to have large cracks in its surface spewing out water ice from its liquid ocean beneath, powered, at least in part, by the large tides from Saturn.

Now, though, evidence is beginning to show that exomoons – a natural satellite that orbits a planet just like Earth’s own moon, but outside of our solar system – are viable targets for the search for life.

The more work that is done on exomoons and their link to those depicted in sci-fi suggests that it is difficult to form earth-like moons around large planets close enough to their stars that they have earth-like surface properties. For example, a recent study showed that Hot Jupiter’s – large gas giants that are close to their stars – cannot form earth-sized exomoons as they move inwards to their current location close to the star.

A more likely scenario for a planet to have a sufficiently large moon that would be habitable, like those in Star Wars, is if they were smaller planets that came to close to the planet and were captured. We do know this can happen as Neptune captured a dwarf planet with an atmosphere which is now known as Triton.

Triton is in fact larger than Pluto, yet is classed as moon due to being captured by the gravitational field of Neptune. The difference here is that Neptune is a long way from the strong gravitational forces of the Sun. A Hot Jupiter would have to compete against a much closer star in order to capture a moon, making it harder to have an earth-like moon close enough to its star that we could live on the surface.

Despite the exhaustive efforts to detect exomoons none have been confirmed – recently, I was investigating the whether gaps formed in a large ring system around the exoplanet J1407b could have been formed by an unseen exomoon. I ran simulations to see if this would confirm the theory, but it actually showed the opposite.

Hopefully as we do more investigations into our vast universe, these elusive exomoons will become more common, similar to what has happened to the explosion in exoplanet discoveries in the last few decades, which now stands at just over 4,000 confirmed exoplanets.

This is an exciting possibility, and would be a genuine potential for living outside of our own Solar System, but right now we’re not at the level seen in Star Wars.

Talk at Lincoln Shortwave Club About Cassini’s Radio Science

Dr Phil Sutton

On 31st July I visited Lincoln shortwave club to talk about some of the important discoveries made by the Cassini spacecraft by utilising the radio part of the electromagnetic spectrum. We started by looking at some of the many radar images taken of Titan, Saturn’s largest moon, before discussing some of the least known science about the internal structures of Saturn and its moons by measure the doppler shift in radio transmissions sent back to Earth.

Below: Maps of the surface of Titan show large lakes and seas of methane. Due to the thick atmosphere, one of the only moons in the solar system to have such an atmosphere, radar was very important to gain detailed surface maps. Image credit: NASA / JPL


Below: The internal structure of Titan with Saturn and its rings in the background. by measure the doppler shift in the radio transmission sent back to earth…

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Field trip to La Palma for Lincoln physics students

On 23rd May the third year physics students in the School of Mathematics and Physics went on a week long field trip to La Palma in the Canary islands. The purpose was to visit Roque de Los Muchachos Observatory which houses one of the largest collection of professional telescopes in the world:

  • MAGIC (telescope) – 2 x 17 m gamma-ray imaging Cherenkov telescopes
  • Gran Telescopio Canarias – 10.4m reflecting telescope
  • William Herschel Telescope – 4.2m reflecting telescope
  • Telescopio Nazionale Galileo – 3.58m reflecting telescope
  • Nordic Optical Telescope – 2.56m reflecting telescope
  • Isaac Newton Telescope – 2.5m reflecting telescope
  • Liverpool Telescope – 2.0m robotic telescope
  • Mercator Telescope – 1.2m reflecting telescope
  • Swedish 1-m Solar Telescope – 1.0m solar telescope
  • Jacobus Kapteyn Telescope – 1.0m reflecting telescope
  • Dutch Open Telescope – 0.45m reflecting solar telescope
  • Carlsberg Meridian Telescope – 0.18m refracting telescope
  • SuperWASP – 5 wide angle cameras with 0.11m diameter lenses

Physics students in their third year take a module in the second semester titled “Physics of the Universe”. This introduces them to some of the key physics at all scales in the universe, from planets all the way to cosmological scales. The final assignment for this module was based on the trip where students had to use the same software used by professional astronomers at La Palma to plan their observations.

During the trip students got to visit the 10.4m GTC (Gran Telescopio Canarias) and the 2.5m Isaac Newton Telescope.

GTC (Below)

Isaac Newton Telescope (Below)

The Magic Telescopes (Below)

During their time on the island and at one of the best locations in the world for astronomical seeing students also got the chance to make their own observations up the mountain (Below).

There was also some free time during the week to enjoy the spectacular scenery on the island.  

Dr Phil Sutton gives scientific guidance for new children’s book”Halo Moon”

A new children’s book recently published Sharon Cohen titled “Halo Moon” follows 12 year old Halo Moon who is a keen stargazer. As with films many authors often seek the guidance of scientific advisors to make sure that elements of the story are factually and scientifically correct. Dr Phil Sutton offered advice on how Halo Moon might use the skywatcher telescope she had in the story and what sort of objects she might be able to observe during the summer. Some of the objects Halo was able to see with her telescope was M13 (below), a globular cluster of stars and Jupiter’s four largest moons.


During the story the characters observe a meteor as it falls to Earth and Dr Sutton also advised how this might be seen, heard and maybe even felt. A short synopsis is given below:

“Bravery, friendship and the magic of an unknowable universe combine in this extraordinary adventure from the heart. Great for fans of Frank Cottrell Boyce and David Almond.

In Ethiopia, Ageze has unearthed an ancient device that can make predictions. It tells him: there is a date, there is a place, there is a moment when it will happen. A disaster that will change everything.

Halo Moon loves stars, and the night sky is full of them in her remote Yorkshire village. It’s a place where nothing interesting ever happens, let alone a catastrophe.

So when a stranger appears at the end of a near-impossible journey and tells her lives are at risk, she can barely believe it. But if she doesn’t help Ageze, everything and everyone she knows might disappear for ever …

As Halo says: there’s a hundred ways to start this story, a hundred ways to tell it. Each one is impossible. Each one, unbelievable. But it did all happen and I promise it’s all true.”

More information about the book can be found here.


New paper accepted on the ringed exoplanet J1407b

A new paper has been accepted for publication in MNRAS (Monthly Notices of the Astronomical Society) by Dr Phil Sutton titled “Mean Motion Resonances With Nearby Moons: An Unlikely Origin For The Gaps Observed In The Ring Around The Exoplanet J1407b”.

J1407b is a large exoplanet (more than 20 times the mass of Jupiter) orbiting its star over 400 lightyears away from Earth. Like many exoplanets before, it was discovered by the transit method which detects a dip in a star’s brightness as a planet passes in front it. However, the star J1407 showed a prolonged and irregular dip in brightness that was attributed to a ring orbiting the planet 200 times larger than Saturn’s ring system. Modelling of this transit showed it was not uniform and instead had gaps. In Saturn’s rings gaps are caused by nearby moons outside the rings or smaller moons inside the rings that gravitationally clear a gap.


Figure 1 | A gap between the B and A ring, which can be seen from Earth, is caused by an orbital resonance with the nearby moon Mimas. Ring particles orbit twice for every orbit of the moon causing a resonance effect (2:1).


Figure 2 | Daphnis, one of Saturn’s many moons, carves out a gap from within the A ring.

In the paper computer simulations we carried out to investigate if nearby moons could create a gap at the locations predicted by the transit. Similar to how Mimas creates the Cassini Division. It was discovered that it was not possible to form gaps in the ring due to moons orbiting outside the ring. In order to create the expected gaps in the ring a moon would need to be too close to outer edge of the ring system, which would cause significant distortion of the ring.

Figure 2

Figure 3 | The radial and angular position of ring particles taken at a time of a) 10 orbital periods and b) 50 orbital periods for ring particles located at 0.4AU (Astronomical Units). The moon is located at the 3:1 MMR (Mean Motion Resonance) with ring particles at 0.4AU. In this scenario we find that the moon is far enough away that there is no significant distortion or scattering of the ring edge with a moon mass 0.3 Earth masses. No obvious perturbation of particles located at 0.4AU is observed during the same time period with only one gap formed at the 2:1 MMR (0.523 AU).

Figure 11

Figure 4 | The eccentricity and radial position of ring particles is shown at a time of 50 orbital periods of particles located at . This is the same time and model as in Fig 2b. The nearby moon is placed at a 3:1 MMR with ring particles at . There is only evidence of the 2:1 MMR located at  in this plot. The eccentricity shows where ring particles are being perturbed by the moon with the location of resonances more clearly identified.

Further details on other models using different locations of the moon can be found here.

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