In the show this time, we talk to Dr Ettore Carretti about magnetised outflows from the Milky Way, Stuart rounds up the latest news and we hear what we can see in the February night sky from Ian Morison and John Field.
This month in the news: bubble trouble for the Milky Way, solar snapshots and synchronised dancing dwarves.
Something in the center of the Milky Way is making a bit of a stir, blowing out two bubbles of hot ionised gas which stretch out so far above and below the Galaxy that together they are almost as large as the Galactic diameter. The bubbles, known as the FERMI bubbles or Galactic haze, were first seen as a faint glow of x-rays in the direction of the Galactic center, but later were also seen in the gamma ray and radio parts of the spectrum. The current explanation for these bubbles comes from observations of other galaxies around which we also see large bubbles of hot gas being expelled. The driving force in the other galaxies originates from their central supermassive blackhole which feeds upon the dense environment of stars, gas and dust within some galaxies cores and then expelling the left overs into intergalactic space. The Milky Way also has a supermassive blackhole, however it long ago consumed most of the material near it and therefore sit's quiet and invisible in the direction of Sagittarius A. This means that the bubbles we see are not the product of a constantly fueled blackhole engine but the sputtering fumes from intermittent stars which strayed to close to the event horizon.
The latest set of observations of the Milky Way's bubbles comes from a team of researchers led by Ettore Carretti, who used the Parkes observatory in Australia to map the entire southern sky at a frequency of 2.3GHz. By observing at these low frequencies the team were able to map the light being emitted from spiraling electrons as they followed the multitude of magnetic field lines that permeate the Galaxy. Most of these magnetic field lines are produced by the Galaxy itself but others can generated by highly energetic events such supernovae or, importantly for Parkes researchers, by whatever is blowing out the bubbles from the Galactic center.The conclusions of the Parkes observatory research flies in the face of general consensus for what in the Galactic core is producing the Milky Way's bubbles. This is because they are able to trace the bubbles much more deeply into center of the Galaxy then any other previous observations and what they find is the bubbles do not appear to be closing to a point as would be expected if the Milky Way's supermassive blackhole is to blame. Instead the bubbles are still 700 light years wide at the Galactic center. This happens to coincide with a recently discovered ring of highly dense star forming gas. This is a region thought to form more stars on average than any other part of the Milky Way and therefore there will be lots of stars dying, which means lots of supernova events. So many supernova events in fact that Carretti and his team think it is more than enough to be the engine blowing the Milky Way's bubbles.
The Sun's corona is a spectacle that many have seen as the striking white filaments of light during an eclipses moment of totality. For solar physicists though the corona poses an unusual and long standing problem for our understanding of the Sun, it is far too hot. The temperature of the corona exceeds one million degrees Celsius which is more like the temperatures at the Sun's core than the much cooler photosphere, the layer we see daily in the sky, which is only a mere 5500 degrees Celsius. An explanation for why the corona is so much hotter comes from the theory of magnetic reconnection. The theory proposes that tremendous amounts of energy can be injected into the corona when magnetic fields from the Sun's surface stretch precariously out into space. Then if two magnetic field lines should get to close they snap together and in the process release the surge of energy that powers the corona. The problem with the theory is a case of scale, as to definitively prove magnetic reconnection is the cause of the heating of the solar corona requires observing the Sun's surface on scales of just 100 to 200Km.
The High Resolution Coronal Imager, known as Hi-C, is a pathfinder experiment to test if it is possible to build a space based telescope with a high enough resolution to observe the process of magnetic reconnection occurring on the Sun's surface. Hi-C was launched on a small rocket to reach a sub-orbital height so that it would be in space for only five minutes, but in that time it would take images of the Sun with unprecedented levels of detail. Previous experiments such as the Solar Dynamics Observatory saw only saw large scale structures in the corona, and some believed that smaller structures would not occur, but the Hi-C experiment sees tiny braids within these larger structures which is perhaps evidence of magnetic reconnection. However five minutes of observations of only a small part of the Sun only gives a tiny, if intriguing, insight into the finer structures of the corona. This is the real success of the Hi-C experiment since it has proved there is something there and that we can observe it then the next logical step can be taken which is to launch a satellite to orbit the Sun and allow for continuous observations over a much longer time frame.
And finally, large spiral galaxies like the Milky Way or Andromeda never form alone. They always come with a entourage of many smaller dwarf galaxies which slowly orbit their hosts over billions of years and in many cases are slowly pulled apart as the larger galaxy pulls long strings of stars into its fold. As well as being smaller, dwarf galaxies are also usually much fainter because they contain only the very oldest stars as after the first generation of stars began to die they violently expelled all the gas and dust required for new stars in a series of supernovae. The observational consequences for this mean our only real comprehensive example for how dwarf galaxies behave comes from our nearest neighbouring spiral galaxy, Andromeda.
Unfortunately the galactic waltz between Andromeda and thirteen of its orbiting dwarf galaxies has been observed to be behaving in a way not expected by current galaxy formation theories. The astronomers, using a telescope atop the dormant volcano Mauna Kea on Hawa'ii, have noted that all thirteen dwarf galaxies are orbiting Andromeda in the same direction and are all confined to a thin plane which is only a fraction of thickness of Andromeda's disc. This is almost completely the opposite to the expected theory that dwarf galaxies have unique randomly orientated orbits and the probability of this alignment occurring by chance is incredibly small. What is even more concerning is this adds to the already confusing question as to why we see less dwarf galaxies than we expect, by adding unexpected coherent structures to this older problem it goes to show that something in our understanding of the story of dwarf galaxies is flawed. However it is usually times like this that researchers are most excited, as it shows there is still much left to discover.
Interview with Dr Ettore Carretti
In this episode, we caught up with Dr. Ettore Carretti, from CSIRO in Australia. Dr. Carretti and his team recently published a paper in Nature announcing the discovery of large, magnetized gas outflows from the centre of the Milky Way. They found these structures using polarization measurements taken using the Parkes radio telescope. Here, he sheds some light for us on the significance of the discovery - explaining why we'd never seen such large structures in the middle of our galaxy before, and what future observations could tell us about these outflows.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during February 2013.
Orion, Taurus and Gemini light up the southern evening sky. The three stars of Orion's Belt act as pointers. To their lower left is the bright star Sirius, and binoculars reveal the open cluster M41 a few degrees below it. Taurus is above Orion, hosting the planet Jupiter. Higher up still, along the plane of the Milky Way, is Auriga, containing the bright star Capella and the open clusters M36, M37 and M38. Gemini lies eastward of it, made up of the twins Castor and Pollux. Another open cluster, M35, lies near to Castor's legs. The bright star Procyon, in Canis Minor, is visible below Gemini. Further east still is Cancer, containing the broad cluster Praesepe, M44. Below it is M67. Leo rises later on, with Ursa Major above it. The middle of the three stars in the handle of the Plough, which is part of Ursa Major, is a sextuple star system, of which two stars can be made out with the naked eye and a third using binoculars.
- Jupiter is, again, bright and high in the south after sunset, with an elevation of over 60° as seen from the UK. It has a magnitude of -2.5 and is about 6° to the upper right of Aldebaran, the red star which marks the eye of Taurus. Jupiter has now ended its retrograde motion and will move eastward during the month, ending it at magnitude -2.3. Its angular size is around 40", so that a telescope can reveal surface detail such as its bands and Great Red Spot.
- Saturn is a morning object, rising in Libra at around 01:00 UT (Universal Time) at the beginning of the month and about 23:30 UT at the end. It reaches a maximum elevation of 25°, but its rings are now 19° from the line of sight and becoming ever more visible. Saturn is 90° from the Sun in the sky (quadrature) in early February, allowing you to see the shadow of the planet cast onto its own rings. It moves towards the wide double star Alpha Libri in the sky for the first half of the month, reaching a separation of 4.2° on the 15th. Then the planet begins retrograde motion and moves westward, back towards where it came from. A small telescope show Cassini's Division between Saturn's rings, as well as its brightest moon, Titan.
- Mercury reaches greatest eastern elongation this month, providing the best evening view of the planet this year. Its magnitude as February begins is -1.1, but the fading glow of the setting Sun makes it difficult to spot. The disc is 5.2" across and 95% illuminated, and by the end of the month the angular size reaches 9", but the brightness is lower.
- Mars remains low in the south-west after sunset, around 6° above the horizon at the start of the month. The Sun's glare washes it from the sky by month's end. With a brightness of +1.2 and an angular size of 4", surface detail is very difficult to spot.
- Venus is passing behind the Sun, but may just be discernible as the Sun sets, 3° above the horizon. It will reappear as an evening object towards the end of May.
- Jupiter's Great Red Spot is prominent in the planet's South Equatorial Belt this month.
- Mercury and Mars lie just 0.3° apart on the 8th, with Mercury to the upper right. You can spot the pair using binoculars low in the west just after sunset, but don't use them until the Sun has gone below the horizon.
- On the evening of the 16th, the near-Earth object NEO 2012 DA14 should be visible as it passes the Earth. Although just past its closest approach of about 30,000 km from the Earth, it has a magnitude of around +7 and will be visible in binoculars. At 21:40 UT, it will be near to the star Alioth in the handle of the Plough.
- Jupiter lies near an eight-day-old Moon in the east, between the Hyades and Pleiades Clusters, on the evening of the 18th.
- The Moon occults the open star cluster M67 from around 19:50 to 21:40 UT on the evening of the 23rd. It also occults the star 50 Cancri before this and 60 Cancri afterwards.
- Saturn's rings occult a star of magnitude +11.5 very early on the morning of the 25th. You will need a telescope to see this, and may spot the star peeping through Cassini's Divison at about 01:30 UT. It will emerge at around 02:45 UT.
John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during February 2013.
The planet Jupiter dominates the evening sky, along with the constellations of Orion, Canis Major and Taurus in the north. Jupiter continues to pass in front of the stars of Taurus the Bull - one of the constellations of the zodiac through which the Sun and planets move. The Bulls's head appears as a V of stars, with two horn tips stretching towards the northern horizon, and contains the Hyades Cluster and the red stars Alderbaran. The Pleiades Cluster, marking the Bull's back, lie to the west of his head. A compact cluster with at least six stars visible to the naked eye, the Pleiades make a fine sight in binoculars. Jupiter and the Moon will be close together in the evening sky on the 18th, with the Moon occulting (covering) the Jovian system as seen from southern Australia and making a stunning sight for binoculars or a telescope. Gemini and Cancer are two of the other zodiacal constellations in the summer sky. The bright stars Castor and Pollux mark the heads of the Gemini twins, and are found in the north after sunset. Gemini is on the eastern edge of the Milky Way, and there are five faint galaxies to be found within 1° of Castor using a large telescope. The open cluster M35 is near to the star Eta Geminorum, and can be seen with the naked eye under a dark sky, while binoculars or a wide-field telescope will provide a better view. Cancer consists of five stars with the beautiful Beehive Cluster, or Praesepe, visible at the centre. Orion, standing tall in the summer sky, hangs upside-down and contains a number of bright stars and other objects. The Orion Nebula appears as a fuzzy star in the middle of Orion's Sword, but binoculars or a small telescope reveal a bat-shaped cloud, and a larger telescope show a tight group of four stars called the Trapezium. To the east are Orion's hunting dogs, Canis Major and Canis Minor. Canis Major, also upside-down, hosts Sirius, the brightest night-time star, while Canis Minor contains the bright star Procyon. Just over a third of the way between these two stars is the cluster M50, visible in binoculars. Halfway from Procyon to Betelgeuse, the red star in Orion, is a rectangular cluster of stars embedded in the Rosette Nebula. Canopus, the second-brightest star in the night sky, is almost overhead in the early evening. The planet Saturn rises in the east from around midnight, and will become an evening object as it moves through the constellation of Libra during the southern hemisphere winter of 2013. At the same time, Saturn's rings will continue to tilt towards us, giving a better view of them.
- Comet PANSTARRS should, according to predictions, become visible in the morning sky in mid-to-late February.
Odds and Ends
AuroraLive is a website that monitors the aurora borealis and tells you when and where the Aurora Borealis is meant to happen. It gives you the most up-to-date times and latitude where you can see it, along with some background information. Also there are links to telescopes monitoring the Sun, so you can see the solar activity.
Deep Space Industries have released a very optimistic plan to mine asteroids by 2023! The plan could entail refining the astroid in-situe instead of retrieving the asteroids and bringing them back to earth. The business aims include retrieving rare metals from space, as well as reducing the cost of other space exploration.
NASA have been officially announced as joining ESA's Euclid mission. AN ESA led mission, Euclid, is a future space telescope set for launch in 2020. Euclid hopes to detect the shape, brightness of distribution over two billion galaxies throughout out the Universe. The aim of these observations is to constrain the roles of dark energy and dark matter in the evolution of Universe. NASA will be providing 20 detectors to Eculid and adding 40 US scientist to the already 1000 strong European Euclid Consortium.
We were also sent a link to some free outreach and teaching materials, "A Kid's Guide to Astronomy".
|Interview:||Dr Ettore Carretti and Indy Leclercq|
|Night sky:||Ian Morison and John Field|
|Presenters:||Adam Avison, Liz Guzman and Chris Wallis|
|Editors:||Adam Avison, Claire Bretherton, Sally Cooper, Mark Purver and Christina Smith.|
|Segment Voice:||Cormac Purcell|
|Website:||Christina Smith and Stuart Lowe|
|Cover art:||Milky Way Panorama CREDIT: ESO/S Brunier|