In the show this time, we talk to Professor Jim Drake about whether Voyager 1 has really left the Solar System, Ian Harrison rounds up the latest news and we find out what we can see in the November night sky from Ian Morison and Claire Bretherton.
In the news this month: simulated black holes and smelly comets.
Astronomers received help from an unexpected source this month, as it was revealed that the creation of visual effects for a new science fiction film has led to new insight into the physics of black holes.Interstellar, the new film from director Christopher Nolan (other sci-fi adventure films are of course available), has held significant attention amongst astronomers since the announcement that highly-regarded theorist Kip Thorne was collaborating with Nolan on the film, seeking to preserve as high a level of scientific accuracy as possible. And, it appears the project has exceeded expectations, actually leading to new discoveries he expects to be able to publish as research papers.
As part of the film, Thorne worked with the visual effects team to attempt to make an accurate visualisation of a spinning black hole, an object used as a plot device central to the film's story. Black holes themselves are, of course, almost by definition invisible, but they can be observed via two key effects. The first, a consequence of Einstein's thoery of General Relativity, is gravitational lensing -- the bending of light rays caused by the curving of space-time by massive objects. This lensing effect has many uses, with which regular Jodcast listeners are probably familiar, and in the case of ultra-massive, ultra-dense black holes is capable of distorting images of background stars and galaxies into spectacular arcs and rings. In addition, when a black hole feeds on external matter, be it gas, cosmic dust or an unlucky nearby star, this matter is expected to form an 'accretion disc' around the black hole. In these accretion disks, matter particles rub up against each other and becomes increasingly hot and dense and emitting light, making accretion disks some of the most luminous things in the Universe. Thorne and the visual effects team set out to calculate how such an accretion disk would appear to an oberver within viewing distance the black hole -- not a trivial task given the extreme mass densities involved. Fortunately, Kip Thorne is pre-eminent in matters of General Relativity, with a 50 year career (and significant cult following) within the field. Thorne worked out the form Einstein's equations describing the path taken by light rays around the highly spinning black hole required by the film's plot and gave the resulting equations to the visual effects team to code up onto their computers.This required the creation of a whole new suite of visual redering software, as previous codes relied on the assumption -- safe outside extreme astrophysical environments -- that light rays travelled in straight lines. The team then turned loose their significant computing power on Thorne's equations, generating nearly 800 terabyes (that's eight hundred thousand gigabytes) of data, with some individual frames of animation (typically displayed on screen for only around 1/24th of a second) taking up to 100 hours to produce.
The result is something spectacular.
In addition to the light coming directly from the accretion disk in one plane around the black hole, light is bent around and around the black hole, circling it four or five times before escaping to the virtual camera. This gives a beautiful visual effect, with 'rainbows of fire' appearing perpendicular to the original accretion disk and with a complex, finger-print like pattern at the very edge of the dark shadow created by the black hole itself. Both Thorne and director Christopher Nolan are understandably excited about this, having produced something both visually arresting and scientifically accurate. In addition to the film, it is expected that the work will produce technical scientific papers, relating both the discoveries about black hole physics and the new computing techniques which were required to produce the animation. The news met with highly positive reactions amongst prominent physicist on social media, although many also offered the caveat that much of the broad sense of the physics had already been worked out, particularly in pioneering work by Jean-Pierre Luminet and J.A. Marck in the 1970s and 1990s. These works also point out extra effects not present in the simulations for Interstellar, with relativistic doppler effects causing the accretion disk to appear brighter on one side than the other. Luminet is in contact with Kip Thorne however, and suitably reassured that such effects will be considered and due credit given when the technical papers are writtern up for publication.
In other news: the success of the Rosetta satellite's mission to comet 67P/Churyumov-Gerasimenko continued with the startling revelation of the comet's odour. Yes, that's right, it's odour.
As it turns out, the comet smells of cats' urine, rotten eggs and bitter almonds. Using it's ROSINA instrument, which stands for Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, the satellite collected and analysed molecules emanating from the comet's surface and found a mixture of hydrogen sulphide, ammonia and hydrogen cyanide, which combine to give a distinct and not exactly pleasant whiff. Astronomers are interested in detecting such complex molecules on comets as they provide a frozen record of their abundance in the early solar system, when planets were still being formed. Being able to view this record will potentially be able to provide us with clues as to how compounds crucial for life came to be here on Earth. The ability to sniff the comet so soon was a surprise however, with Rosetta scientists expecting to have to wait for the comet to warm up in the sun before the smell became powerful enough to detect, like a wet dog maturing next to a radiator. We shouldn't worry about 67P stinking out the solar system though, with the molecules not present in large enough quantities to be smelt by a human on the comet, Katherine Altwegg of the University of Bern in Switzerland pointing out that even stood on the surface "You would probably need a good dog to smell it."
Interview with Prof. Jim Drake
Professor Jim Drake works at the University of Maryland, studying magnetic fields in plasmas. In particular, he is interested in the phenomenon of magnetic reconnection around the Sun and elsewhere in space, which suddenly releases the energy trapped within magnetic fields. In this interview, Prof. Drake talks about recent measurements made by humanity's most distant explorers, the iconic Voyager space probes, which indicate that Voyager 1 has passed the heliopause. The heliopause marks the boundary between the flow of particles from the Sun known as the solar wind and the denser gas of the interstellar medium (ISM), and, as Prof. Drake explains, we now have a more detailed understanding of it. He discusses Voyager 1's measurements of plasma density, cosmic ray count, magnetic field strength and magnetic field direction, showing that the increase in density and the change in cosmic ray type seem to indicate that Voyager 1 crossed the boundary in 2012, even though the expected change in magnetic field direction did not occur. He is involved in producing complex simulations that suggest that the direction of the magnetic field should indeed change more slowly from that of the Sun to that of the ISM, and that the boundary is more porous to cosmic rays than previously thought. He talks about the cultural, as well as scientific, significance, of the Voyager missions, and sounds a warning to potential Mars astronauts about the dangers of energetic particles in interplanetary space.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during November 2014.
The four stars of the Square of Pegasus are in the south after dark, with the Horse's head and mane to their lower right. Just beyond the head is the globular cluster M15, visible in binoculars or a telescope. Starting at Alpheratz, the top-left star of the Square, you can find M13, the Andromeda Galaxy. The W-shaped constellation of Cassiopeia is almost overhead, and the V of the upper-right stars also points towards M31. Pisces is to the lower-left of Pegasus, with Aries further left still. Orion and Taurus rise higher in the sky as the night wears on, with the Pleiades Cluster climbing in the south-east and the Hyades Cluster to its lower-left. The red-orange star Aldebaran appears to be part of the Hyades, but is actually around halfway between us and the cluster. Orion is below Taurus, the three stars of his Belt pointing up towards Aldebaran and the brightest night-time star, Sirius. The lower-right star of Orion is the blue giant Rigel, while the upper-left is the red giant Betelgeuse. Coming down from Cassiopeia, along the plane of the Milky Way, you reach Perseus. It contains the Perseus Double Cluster, between Cassiopeia and the star Mirfak, and also hosts Algol, known as the Demon Star due to a periodic dip in brightness that results from the eclipse of one star by another in a binary system. Descending from Perseus, you get to the yellow star Capella in Auriga, with the three open star clusters of M38, M36 and M37 nearby. Further down is Gemini, rising in the east after nightfall, with the stars of Castor and Pollux representing the Twins and the open cluster M35 near to the feet of the figure of Castor.
- Jupiter is beginning its apparition, shining at magnitude -2.1 and rising around 23:30 UT (Universal Time) at the start of the month. It is about 10° up and right of the star Regulus in Leo. By the end of November, it rises around 21:40 and has a magnitude of -2.3, reaching an elevation of 53° by 05:30. Its angular has increased from 37 to 39" by this point, allowing surface details and larger moons to be seen with binoculars or a telescope.
- Saturn reaches conjunction (passing behind the Sun) on the 18th, and is only just visible at the end of the month, rising an hour before the Sun.
- Mercury has a good apparition in the pre-dawn sky this month, reaching greatest western elongation (its greatest separation from the Sun in our sky) at 18° from the Sun on the 1st. It is then 15° above the east-south-eastern horizon at sunrise, with a magnitude of -0.5, an angular diameter of 7" and a phase of around 50%. By the 15th, Mercury measures 5" across and is sliding back towards the horizon.
- Mars is moving eastwards in Sagittarius, appearing low in the south-west after sunset. It dims from magnitude +0.9 to +1 and shrinks from 5.5 to 5.2" during the month, preventing surface details from being seen easily. It passes the globular clusters M28 on the 2nd and M22 on the 6th, and approaches M75 towards the end of the month.
- Venus reached superior conjunction (behind the Sun in the sky) on the 26th of October, and it will be December before it truly appears as an evening object, but it may just be visible after sunset during the last week of November.
- Mercury lies above the star Spica in Virgo from the 1st to the 8th, passing within 5° on the 1st. You may need binoculars to spot them, low in the east-south-east, but don't use them after the Sun has risen.
- The Moon passes just above the planet Uranus in our sky from 17:00-18:00 UT on the 4th. They are just 2' apart at 17:00 for observers in north-west England, but Uranus may be hard to spot against the twilight sky. The separation is 6' at 17:30, but the growing darkness makes for easier viewing using binoculars or a telescope. The Moon is 19' from Uranus at 18:00. It should be possible to spot the planet's turquoise colour, but making out its tiny disc, at 3.3" across, may be harder.
- Jupiter is close to a third-quarter Moon 1 hour before sunrise on the 14th.
- Mars lies just above the Teapot asterism in Sagittarius 1 hour after sunset on the 14th.
- The Leonid meteor shower is at its best after midnight UT on the 17th and 18th, and is not spoiled by moonlight this year. Originating from Comet Tempel-Tuttle, the dust that enters the atmosphere to produce the Leonids has its radiant in the constellation of Leo, and around 12 meteors per hour may be visible at the shower's peak.
- Mars is close to a thin crescent Moon an hour after sunset on the 25th and 26th, near to the Teapot of Sagittarius.
Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during November 2014.
As Scorpius sets in the west after dark, Orion, Taurus and Canis Major rise in the east. The red star Antares, in Scorpius, is just above the south-western horizon at 23:00 NZDT. Known to Māori as Rehua, it marks one of the four Pou, or pillars, holding up the Sky Father, Ranginui. The other Pou are Matariki (the Pleiades), Tautoru (Orion's Belt) and Takurua (Sirius), and line the eastern horizon in the late evening. Their rising positions are close to those of the Sun at the winter solstice, the equinoctes and the summer solstice respectively. Stretching between Orion and Scorpius is Te Waka o Tama-rereti, a canoe represented by the tail of Scorpius (also known as Te Waka o Mairerangi) at its front and Orion's Belt (Tautoru) at its stern, with Crux (Te Punga) and the Pointer Stars (Te Taura) as its anchor and anchor line. Tama-rereti was said to have been a man who sailed across the sky in his canoe, placing the stars from his Kete (basket) into the heavens to allow navigation on Earth. He then capsized the canoe and spilled the remaining stars to form the Milky Way, or Te Ikaroa. The Māori new year is celebrated at the summer solstice, when the bright star Atutahi (Canopus), the Ariki (high chief) of the heavens, pulls up the anchor and sets the canoe in motion across the sky. Canopus is midway up the south-eastern sky in the evening in November.
A little higher and further south are two fuzzy patches of light called the Large and Small Magellanic Clouds (LMC and SMC), a pair of dwarf galaxies neighbouring the Milky Way and each containing several billion stars. The LMC is the lower of the two, and young star clusters within it may be seen as small patches of light through binoculars or a telescope. Prominent among these is the Tarantula Nebula (also called 30 Doradus or NGC 2070), an active starburst region containing over 800,000 stars and protostars. It was here that the most recent supernova visible to the naked eye on Earth, SN 1987A, occurred. The SMC appears close to the globular cluster 47 Tucanae, but is actually over ten times further away from the Earth than is the cluster. 47 Tucanae is the second-brightest globular cluster in our sky at magnitude +4.9, and is visible to the naked eye when the sky is dark. A telescope reveals a dense core of over a million stars, surrounded by a sparser sprinkling of many more.
- Mars remains visible in the western evening sky, moving through the constellation of Sagittarius and setting around midnight NZDT (New Zealand Daylight Time, 13 hours ahead of Universal Time). It is moving away from the Earth and becoming smaller in our telescopes.
- Venus is just visible at the end of the month, setting 50 minutes after the Sun in the west-south-west.
- Jupiter rises around 03:00 NZDT at the beginning of November, and around 01:00 by the end. Its four largest moons are visible in binoculars, orbiting around the giant planet.
- The Leonid meteor shower peaks around the 17th, with meteors appearing to radiate from the constellation of Leo, which rises about two hours before the Sun.
Odds and Ends
A short film has been produced as part of promotional material for ESA's Rosetta mission; a probe that started its journey to Comet 67P/Churyumov-Gerasimenko 10 years ago in order to study the composition and chemistry of the comet, testing theories for how water made its way onto planets. Titled 'Ambition', the sci-fi short is seven minutes set in a future world, where Rosetta is seen as one of the first stepping stones to finding out more about the origins of life. The aim is to reach a wider audience who may not otherwise know much about the purpose of the mission, and has been timed to generate additional interest before its robot lander Philae touches down on the comet this month. It can be found on ESA's website.
Astronomers working on the Frontier Fields programme have discovered one of the most distant objects ever seen: an object estimated to be 13 billion light-years away with a redshift of around 10. The object is thought to be a galaxy 500 times smaller than the Milky Way. It has been discovered due to gravitational lensing by a foreground galaxy cluster, which has magnified it to appear 10 times brighter. Astronomers believe the galaxy offers insight into the evolution of the early universe, which they hope will help them answer some of the fundamental questions of cosmology such as structure formation and evolution.
A Hasselblad 500C camera that flew on at least one of the Mercury missions is set to be autioned in November 2014. The estimated sale price is 50,000-100,000 in US dollars. The camera was originally bought, modified, and used by Wally Schirra on Mercury-Atlas 8, as confirmed by RR Auction of Massachusetts. It has also been stated that this camera was also used by Gordon Cooper on Mercury-Atlas 9, although that claim is in doubt. While it is now common for astronauts to now use cameras in space, it was not something that either space agencies or many astronauts thought about doing at the start of the space race. As one of the first cameras to be used by astronauts in space, it is a small piece of space history. More information can be found in the space.com article about the camera.
|Interview:||Prof. Jim Drake, Mark Purver and George Bendo|
|Night sky:||Ian Morison and Claire Bretherton|
|Presenters:||George Bendo, Josie Peters and Hannah Stacey|
|Editors:||Ben Shaw, Monique Henson and Mark Purver|
|Segment Voice:||Tess Jaffe|
|Website:||Sally Cooper and Stuart Lowe|
|Cover art:||Cartoon depiction of the Voyager and Pioneer spacecraft heading towards the heliopause CREDIT: NASA/JPL|