Author Archives: Chris North

About Chris North

Dr Chris North is the Ogden Science Lecturer in Cardiff University's School of Physics and Astronomy. He also holds an STFC Public Engagement Fellowship entitled "The Dawn of Gravitational Wave Astronomy". Chris is also an astronomy researcher by training, focusing most recently on the Herschel Space Observatory.

Pythagorean Astronomy: Cassini’s Grand Finale

[Cross-posted from the Cardiff Physics Outreach blog]

Cassini at Saturn. Image credit: NASA

The 15th of September marked the Cassini spacecraft’s final plunge into Saturn’s gaseous atmosphere. This grand finale marked then end of a 20 year journey, 13 of which were spent orbiting Saturn, studying the ringed planet and its extended family of moons. Here in Cardiff, Dr Emily Drabek-Maunder has been closely following Cassini, and working with some of its data. This seemed like an ideal time to gather Emily’s thoughts on the remarkable mission. Continue reading

Pythagorean Astronomy: The Astronomer Royal and Potatoes on Mars

MartinRees

[Cross-posted from the Cardiff Physics Outreach blog]

April’s edition of our monthly astronomy podcast, presented by Chris North and Edward Gomez.

Earlier this month we were treated to a talk in Cardiff by Lord Martin Rees, the Astronomer Royal and Professor of Astrophysics at University of Cambridge. This afforded us the opportunity to speak to Professor Rees about the subject of his talk: “The World in 2015 – and beyond”. After discussing the challenges facing the long-term survival of humanity, and possible solutions, we also discussed Lord Rees’ role in the House of Lords, and recent developments in astronomy and cosmology. Continue reading

Pythagorean Astronomy: TRAPPIST-1 and other stories

TRAPPIST-1 artist impression

At the end of last month, there was a lot of interest in the discovery of seven roughly Earth-sized planets in the TRAPPIST-1 system. One month on, Chris North and Edward Gomez discuss the implications of this discovery. We also get an update from the Amaury Triaud, of the University of Cambridge, about TRAPPIST and its successor, SPECULOOS.

Here in our own Solar System, there’s the discovery of a cometary landslide from Rosetta, a milestone in wheel-wear on the Mars Curiosity Rover, and an update on some of Saturn’s darker rings from Japan. Further afield, a study of the rotation of galaxies in the distant Universe came under some scrutiny, shedding a bit of light on the process of scientific discovery.

An extended edition of the an original broadcast on 27th March 2017 as part of Pythagoras’ Trousers on Radio Cardiff.

For an archive of Pythagorean Astronomy, visit pythagastro.uk.

Pythagorean Astronomy: Backyard Worlds

Planet-9-Art-NEWS-WEB

Artist’s impression of the proposed Planet Nine. Image Credit: Caltech/R,. Hurt (IPAC)

[Cross-posted from pythagastro.uk]

February saw the first launch of SpaceX’s Falcon Rocket from Launchpad 39A – the same launchpad used by the Apollo missions and the Space Shuttle. In this month’s Pythagorean Astronomy, Edward Gomez and Chris North discuss these impressive structures along with the study of a supernova (the explosive death of a massive star) just hours after it exploded, providing crucial insights into the very early stages of these extreme events.

A new Zooniverse project, Backyard Worlds: Planet 9, was also announced designed to let “citizen scientists” (i.e. you!) help track down Planet Nine – whose existence was seriously proposed a year ago. Project leader Marc Kuchner told us about that project.

For those wondering, we recorded this before the announcement of both TRAPPIST-1 and the SpaceX announcement of their planned lunar missions – but they’re pretty safe bets for discussion next month!

An extended edition of the an original broadcast on 27th January 2017 as part of Pythagoras’ Trousers on Radio Cardiff.

For an archive of Pythagorean Astronomy, visit pythagastro.uk.

What’s really interesting about TRAPPIST-1?

TRAPPIST-1 planets

The planets around TRAPPIST-1. Image credit: NASA/R. Hurt/T. Pyle [Click for larger image]

Earlier this week there was an announcement that a team of astronomers had discovered seven planets around a nearby star. That star is a cool dwarf star called “TRAPPIST-1”, and gets its name from the project that started this all off – the TRAnsiting Planet and PlanetIsimals Small Telescope (TRAPPIST), with a small (0.6m) telescope in Chile. A few years ago the team running the telescope, led by Michaël Gillon and including many members from around the world (including the UK), spotted some unusual transits around a small, cool, red dwarf star that used to go by the name “2MASS J23062928-0502285” (the star was originally discovered by the 2MASS survey), but which is now commonly referred to as TRAPPIST-1.

There were previously three planets known about (well, two for sure and another maybe). The new results have confirmed six, with another tentative seventh. All seven have been identified through the “transit method”, whereby the planets pass in front of the star from our point of view. This gives us an estimate of their size (relative to the star), but not their mass – at least that’s usually the case. The seven planets are labelled “b” to “h” (by convention, “a” is reserved for the star itself).

Finding Earth-mass planets isn’t new anymore. Finding lots of planets in one system isn’t new. Finding planets very close to Earth isn’t new. So what’s so interesting about TRAPPIST-1? I think it’s fair to say that the news was overhyped in much of the media coverage, I guess partially because of the embargo period which tends to get people wound up. Getting people talking about exoplanets is good – but the community needs to be careful that people don’t think that these results are all the same, and so stop paying attention. Having said that, while some aspects of this result are “incremental”, there are some really neat bits in there when you dig down.

A packed system

Environment of the planets in TRAPPIST-1 compared with our Solar System

Environment of the planets in TRAPPIST-1 compared with our Solar System. Original source & more info: Gillon et al. (2017) [Click for larger image]

The orbital periods of the planets (i.e. their years) are all less than a couple of weeks, putting them much, much closer to the star than any planets in our Solar System. However, the parent star is so faint (less than a thousandth the luminosity of than the Sun), that they could potentially all be of the right temperature to host water.

There have been many articles and commentaries about the possible conditions on the seven planets, three of which lie in what is normally called the “habitable zone” (i.e. where the surface temperature could allow liquid water) and all of which are classed as “temperate”, meaning that the right atmospheric density and composition could allow for liquid water.

There are a lot of “coulds” in there, and we simply have no idea about their atmospheres – though it’s very possible that future telescopes, such as the planned Extremely Large Telescope and the soon-to-be-launched James Webb Space Telescope, will be able to make progress on that front.

For now, all we know is how much starlight falls on the planets, and therefore what the temperature of a bare lump of rock would be. As shown in the image above, even though they are similar in that sense to Earth and Venus, that doesn’t tell us much. That’s perfectly illustrated by the fact that Earth (nice and temperate) and Venus (inhospitable hellhole) are so different. The Earth’s average surface temperature would be -15°C without the atmosphere, but is increased to about +15°C by the atmosphere. Venus, on the other hand, receives twice as much light from the Sun, but with its thick atmosphere has a surface temperature of about 500°C. Put simply, although the right atmosphere could lead to nice temperature planets, the wrong atmosphere could equally lead to a very inhospitable planet.

Multiple transits

Triple-transit of TRAPPIST-1 planets

Triple-transit of three TRAPPIST-1 planets observed in December 2015 by the VLT. A cartoon of the planets passing in front of the star is shown at the bottom. Original source & more info: Gillon et al. (2017) [Click for larger image]

There are lots of neat things here just in the discover itself. For example, the reason there was so much interest in this system was that the initial observations (by TRAPPIST and the Very Large Telescope) a few years ago caught a triple transit – where three planets passed in front of the star at about the same time (see left). That led the team to observe the system with a whole host of other telescopes – the Liverpool Telescope (in La Palma, despite its name), the William Herschel Telescope (also in La Palma), the UK Infrared Telescope (in Hawaii), the South African Astronomical Observatory 1m telescope (in, erm, South Africa), the Spitzer Space Telescope (in space, duh), and a northern-hemisphere twin of the original telescope, TRAPPIST-North (in Morocco) [TRAPPIST-1 is on the celestial equator so can, conveniently, be observed from the northern and southern hemispheres]. That’s a lot of telescopes, but having all these observations is key to uncovering the secrets of this unusual system.

Resonances

TRAPPIST-1_resonances

Orbital resonances of the TRAPPIST-1 planets. Image credit: C. North [Click for larger image]

For me the really interesting thing is quite how much has been learned from transits. I mentioned above that the transit method normally only gives us the size of the planet. To get a planet’s mass (and therefore its density), we normally need to use another method, usually the Radial Velocity method, to pick out the weak gravitational effect of the planet on the star, causing the star to wobble a little bit. However, the TRAPPIST-1 system has another feature that helps us out – the planets are so close together that we can measure their gravitational effects on each other.

There’s also a sort of synchronicity between the orbits. Take the 4th and 5th planets, called “e” and “f”, for example: for every two times planet “f” orbits the star, planet “e” orbits three times. That means that every other time “f” gets to a particular point in its orbit, planet “e” is in the same place. Having that repeatable pattern is something called a “mean motion resonance”, and there are links between all the planets. The image on the right shows the orbital periods and the “resonances” relative to the inner-most planet.

We see this in our own Solar System. Three of Jupiter’s largest moons (Io, Europa and Ganymede) have orbital periods in the ratio of 1:2:4 (for Io:Europa:Ganymede) – so for every once Ganymede goes round, Europa goes round twice and Io four times. This keeps their orbits locked, means Europa’s orbit is slightly elliptical, and ultimately helps generate the heat that create Europa’s subsurface ocean. There are also resonances between the orbits of asteroids and Jupiter, as well as between Kuiper Belt objects and Neptune (with Pluto and Neptune having periods in a 3:2 ratio).

Transit Timing Variations of TRAPPIST-1

Transit Timing Variations of TRAPPIST-1, comparing the simulations (red) with the observations (black datapoints). Original source & more info: Gillon et al. (2017) [Click for larger image]

These relationships mean that the planets have small, regular tugs on each other, effectively either slowing them down or speeding them up a bit. That changes the precise time that they pass in front of the star, which is something we can measure very accurately. By predicting what the effect would be of different masses, and comparing that to the observed “transit time variations” (sometimes called TTV) it is possible to estimate the masses of the planets. Since such resonant systems have a habit of being unstable, and this one presumably has been there for a long time (unless we got really lucky!), it may even be possible to even better constrain the masses of the planets.

Masses and radii of the TRAPPIST-1 planets, compared with models.

Masses and radii of the TRAPPIST-1 planets, compared with models. Original source & more info: Gillon et al. (2017) [Click for larger image]

At the moment, those masses aren’t know very well, but it does start to give a handle on the density of the planets. The graph below shows the masses and densities along with some predictions of various compositions. Although two of the planets look like they could be “water worlds” (made largely of water), the uncertainties are large enough that they could also be your common or garden rocky planets.

To get the masses better we need radial velocity measurements, but that could be tricky. I had a play with the Radial Velocity Simulator from the Nebraska Astronomy Applet Project, and put in the values for the closest planet (star mass = 0.08 Msun, planet mass=0.003 Mjup, semi-major axis=0.01au, inclination=90deg, ecentricity=0) to see the size of the effect. The planet’s mass are so small that it would only cause the star to wobble by about 2m/s, which is, in principle, within reach of the best instruments on the largest telescope, but the issue may well be that the star is too faint to get a strong enough signal. I’m not an expert on the intricacies of radial velocity measurements, though, and would be delighted to be proved wrong!

Gravitational Waves: One year on

It’s a year since the LIGO Scientific Collaboration, including the Gravitational Physics group here in Cardiff, announced the very first detection of gravitational waves. I’ve been working with the teams in Cardiff and internationally for a little over a year, and it’s been a rollercoaster.

The announcement day itself was, quite frankly, crazy – but a good kind of crazy (radio interviews, live TV interviews on the roof, videos, podcasts, press conferences etc.). Since then I’ve given a number of interviews, public talks and school workshops about the detection and it’s all still as amazing as it was a year ago.

A lot of that is because the numbers are so earth-shattering, for example:

It says something that to express the power you need not one but two non-standard expressions of magnitude (septillion and yotta) – though since “yotta” and septillion both mean 1024, I can’t help thinking that it might sounds better as a “yotta-yotta-Watt”!

I also took this opportunity to update the Gravitational Wave Catalogue I made a while ago (fullscreen version here). You can change the axes on the graph, and show more information about the detections.

As for the future, LIGO is currently in Observing Run 2 (“O2” for short). Nothing much to say at the moment, but an official announcement by the LIGO Scientific Collaboration on 28th January read:

The second Advanced LIGO run began on November 30, 2016 and is currently in progress. As of January 23 approximately 12 days of Hanford-Livingston coincident science data have been collected, with a scheduled break between December 22, 2016 and January 4, 2017. Average reach of the LIGO network for binary merger events have been around 70 Mpc for 1.4+1.4 Msun, 300 Mpc for 10+10 Msun and 700 Mpc for 30+30 Msun mergers, with relative variations in time of the order of 10%.

So far, 2 event candidates, identified by online analysis using a loose false-alarm-rate threshold of one per month, have been identified and shared with astronomers who have signed memoranda of understanding with LIGO and Virgo for observational followup. A thorough investigation of the data and offline analysis are in progress; results will be shared when available.

The “reach” of the LIGO is defined by its sensitivity – because more distant events are fainter and so harder to detect (meaning that a more sensitive detector network can detect more distant events. The reason for giving three distances for different mass pairings is because more massive binaries produce stronger signals so can be “seen” further away – historically the range of gravitational wave detectors has been stated as the 1.4+1.4 Msun mergers (i.e. two neutron stars).

In terms of scale a Mpc is a “megaparsec” (one million parsecs), which is about 3.26 million light years. The Andromeda Galaxy (our nearest large neighbour) is about 2.5 million light years (0.75 Mpc) away. The Virgo cluster of galaxies, the closest large galaxy cluster, is about 50 million light years (15 Mpc) away, so well within range of LIGO. Though do remember that the previous detections were much further away than that – at around 1 billion light years.

Pythagorean Astronomy: Star Attractions

Star Attractions. Image courtesy of National Museum, Cardiff

Image courtesy of National Museum Cardiff

Join Chris North and Edward Gomez as they discuss the month’s astronomy news. Not only were there two new NASA missions announced this month, but Space-X successfully returned to flight with their Falcon 9 rocket. Further afield, there are predictions of a pair of stars that are set to explode in a few years.

Being January, the National Museum in Cardiff hosted its annual public event celebrating all things space. With exhibits, demonstrations and shows for all ages, several thousand people attended “Star Attractions” and get to learn a bit more about astronomy and space. While we were there with a stand from the School of Physics and Astronomy, Chris spoke to a few people who were there to find out what they got out of it.

Originally broadcast on 30th January 2017 as part of Pythagoras’ Trousers on Radio Cardiff.

Pythagorean Astronomy: Assassin Supernova

artist's impression

Close-up of star near a supermassive black hole (artist’s impression) Image credit: ESO, ESA/Hubble, M. Kornmesser

When is a supernova not a supernova? The brightest supernova on record was discovered in 2015 by the All Sky Automated Survey for Supernovae (ASAS-SN). Named ASASSN-15lh, this remarkable event – what looked like a huge brightening of a star in a distant galaxy – was observed by many other telescopes, including the Hubble Space Telescope and the Las Cumbres Observatory network. With careful study, it became apparent that ASASSN-15lh was not quite what it seemed. Rather than being the explosion of a massive star, it is now thought that it was the final flash as a star was swallowed by a supermassive black hole.

This month, Morgan Fraser, from University College Dublin, and Las Cumbres Observatory’s Edward Gomez explain the story of this discovery – and rediscovery! We finish with a brief recap of 2016, and a look forward to 2017.

Originally broadcast on 19th December 2016 as part of Pythagoras’ Trousers on Radio Cardiff.

Pythagorean Astronomy: the GLEAM Survey

gleam-survey

The GLEAM Survey

We’ve got a lot of news items to discuss this month. In the outer Solar System, Edward Gomez and I discuss the Cassini spacecraft, which has made its final major orbital manoeuvre, and the Juno spacecraft, which has had a few issues getting into its main science orbit. Further from home, we’ve got the first “official” star names from the International Astronomical Union, and the discovery of the roundest known star.

Our main guest this month is Dr Natasha Hurley-Walker, based at the International Centre for Radio Astronomy Research (ICRAR) at Curtin University. Natasha works on the Murchison Widefield Array, and has produced GLEAM: an all-sky image of the sky at radio wavelengths at very high resolution and in a wide range of radio “colours”, or wavelengths. This gives us a better understanding of some of the most energetic processed taking place in the centres of nearby galaxies, but the end goal is somewhat further afield. Natasha tells me all about the MWA, the GLEAM project, and even how you can view it – on the interactive GLEAMoscope site (or using the GLEAM Android app)

Originally broadcast on 28th November 2016 as part of Pythagoras’ Trousers on Radio Cardiff.

Pythagorean-Astronomy: ExoMars and Galaxies

A lot has happened this month – ESA got a spacecraft into orbit around Mars, but sadly lost the Schiaparelli lander, China launched two new taikonauts to their space station, and the Swarm mission uncovered details from Earth depths. Edward Gomez and I discussed these, and more, this month (though before the full nature of the status of the Schiaparelli lander were available).

In other astronomy news, a scientific paper hit the headlines claiming to have worked out how many galaxies there are in the observable Universe. Cardiff colleague Professor Steve Eales told me quite what he thought of this latest result…

Originally broadcast on 24th October 2016 as part of Pythagoras’ Trousers on Radio Cardiff.